Article
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The role of functionalized multiwalled carbon nanotubes (MWNTs) decorated with platinum nanoparticles (Pt/f-MWNTs) and platinum–cobalt alloy nanoparticles (Pt3Co/f-MWNTs) has been investigated for oxygen reduction reaction (ORR) in a proton exchange membrane fuel cell. The electrocatalysts are synthesized by a conventional sodium borohydride reduction method and modified polyol reduction method. The modified polyol reduction method yields better uniform dispersion, higher loading and optimum particle size of Pt and Pt3Co alloy nanoparticles over the MWNTs compared to the conventional sodium borohydride reduction method. The electrochemical surface area of the electrocatalysts is calculated using cyclic voltammetry. Pt3Co/f-MWNTs synthesized via modified polyol reduction method yield the highest performance with a maximum power density of 798 mW cm−2 at 60 °C without any back pressure. The enhanced catalytic activity of Pt3Co/f-MWNTs toward ORR is attributed to uniform dispersion and optimum particle size of Pt3Co alloy nanoparticles over the surface of f-MWNTs.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Researchers and manufacturers of fuel cells with proton exchange membranes (PEMFC) are especially interested in issues related to electrocatalytic activity [1][2][3][4][5][6]. ...
... The trend of recent years is a wide use of modified carbon materials to increase the electrocatalytic activity of the metal catalyst in the ORR. In this case, synergism in the catalysis involving functional groups of carbon and metal catalysts (Pt, Pd, and various alloys with other metals) is used [2][3][4][5][6]. Vinayan et al. [2] studied the role of functionalized multi-walled carbon nanotubes (MWCNTs) decorated with platinum nanoparticles (Pt/f -MWCNT) and platinum-cobalt alloy nanoparticles (Pt 3 Co/f -MWCNT) in ORR PEMFC. ...
... In this case, synergism in the catalysis involving functional groups of carbon and metal catalysts (Pt, Pd, and various alloys with other metals) is used [2][3][4][5][6]. Vinayan et al. [2] studied the role of functionalized multi-walled carbon nanotubes (MWCNTs) decorated with platinum nanoparticles (Pt/f -MWCNT) and platinum-cobalt alloy nanoparticles (Pt 3 Co/f -MWCNT) in ORR PEMFC. The electrocatalysts were synthesized using two methods: the traditional sodium borohydride reduction method and the modified polyols reduction method. ...
Article
Full-text available
This paper presents a study of the platinum activity in the ORR in a hydrogen polymer electrolyte membrane fuel cell with electrodes containing multi-walled CNTs in a wide range of compositions and conditions. The data of the comparative analysis of the platinum activity on a fraction of Nafion in the electrode, the composition of the oxidizing agent (oxygen, air), pressure, and temperature are provided. The reasons for the dependence of the platinum surface activity on the component composition of the electrode are considered. Specific mass activity and surface activity of platinum in the ORR in MEA with the electrodes with CNTs depend on the ionomer/platinum ratio. Both dependences have a maximum at the level of the 25% Nafion fraction. The maximum appears as a result of an optimal structure formation, which ensures the fullest use of the platinum surface and minimal concentration overvoltages. Specific mass activity and surface activity of platinum for the sample with 34% CNTs at T = 60 °C and excessive pressure of p = 2 atm amount to 0.46 A/mg and 0.72 mA/cm2, respectively.
... Yu et al. [36,37] comprehensively discussed the catalyst activity and durability of Pt/C catalysts for PEMFC cathodes. Moreover, many researchers [38][39][40][41][42] [117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132][133][134] suggested that CO poisoning at the anode involves three stages; adsorption / diffusion, the degree of charge transfer and proton hydration. CO covers the active sites of the catalyst, adsorbs onto the carbon matrix and then reduces the speed of hydrogen adsorption on the electrode surface. ...
... Renewable and Sustainable Energy Reviews 89 (2018) [117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132][133][134] sulfonated polymer (Nafion) [79], polybenzimidazole (PBI), fluorinated ethylene propylene (FEP), and polybenzimidazole-blended polyvinylidene difluoride (PBI/PVDF) [80][81][82]. Nafion is the conventional polymer binder for low-temperature PEMFCs. ...
... Renewable and Sustainable Energy Reviews 89 (2018) [117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132][133][134] author found that the PTFE content influenced the in-plane conductivity of the GDL. GDLs with in-plane conductivity along different perpendicular directions exhibited double conductivity. ...
... 12,13 Other bimetallic CoPt NPs represent excellent fuel cell catalysts. 14,15,16,17,18 Similarly, Co-Ru NPs find applications as a catalyst for many reactions such as the Fischer-Tropsch CO hydrogenation reaction, 19 nitroarene reduction reactions 20 and as an electrocatalyst for oxygen reduction in fuel cells. 21 For all these examples, mixing Ru with Co significantly improved the catalyst performance. ...
... Numerous researchers have reported that Pt-Co (typical Pt 3 Co, PtCo, and PtCo 3 ) alloy nanoparticles were chemically disordered, and most of them were coated by Pt-skin surface layer due to the thermally activated preferential surface segregation of Pt or preferential dissolution of the non-noble component during catalyst processing and operation of the fuel cell. 14,15,16,17,18 These nanoparticles all possess face-centered cubic (fcc) crystal phases with a concomitant lattice contraction for Pt due to the incorporation of Co atoms. ...
... One important notice for all these structurally controlled bimetallic NPs is that they were prepared either physically, 12,13,117,118,122 or chemically, applying either a polyol reduction technique, 15, 17, 119, 120 transmetalation reaction, 14,125 or through the reduction of the corresponding metal salts with a strong reducing agent like NaBH 4 . 16,123,124 Physical methods give an accurate access to the ordered intermetallic structures together with possible localization arrangement of the NPs on a solid support if it is combined with lithography techniques (which is required for memory storage applications). 130 On the other hand, the advantages of these techniques are always limited by the high costs and the needs of sophisticated equipments. ...
Thesis
Full-text available
Metallic nanoparticles (NPs) exhibit unique physical and chemical properties. However, their use is conditioned by the ability to control their size and structure. The decomposition of organometallic (OM) precursors under H2 is efficient to generate metallic NPs in organic solvents, but also in ionic liquids (ILs). We have shown that in the latter media, the size can be finely tuned without adding stabilizing agents. Moreover, the resulting “naked” metallic NPs are suitable for catalysis or further reaction with a second OM precursor to form bimetallic NPs.In this work, we applied this knowledge to the synthesis of mono- and bimetallic NPs in imidazolium-based ILs C1CaImNTf2. CoNPs with a diameter of ca. 4 nm were successfully synthesized by decomposition of [Co(?3-C8H13)(?4-C8H12)] under H2. Structural analysis and magnetic characterizations demonstrated that these NPs are metallic and, as expected for this size, superparamagnetic. This approach was extended to the synthesis of bimetallic CoPt and CoRu NPs. It turned out that the best strategy is probably to simultaneously decompose the Co and Pt (or Ru) precursors. This reaction provides monodisperse suspensions of NPs, a good indication that they are bimetallic. Further structural characterizations, in particular using anomalous SAXS, are also considered to elucidate their structure
... Some research has shown that the polyol method is the optimal method for saturating and depositing metal alloys on carbon. According to Yang et al. [44] and Vinayan et al. [45], the polyol method is superior in generating a higher dispersion of metal nanoparticles (Pt, Fe, and Co) and achieving optimal metal particle sizes on the carbonaceous support, as well as exhibiting better catalytic performance [46][47][48]. Fig. 1 illustrates the structure and morphology of the synthesized NG and ZrO 2 -NG through FESEM images. ...
... [46]. In comparison to the sodium borohydride reduction method [45], this method not only reduces the particle size of metal nanoparticles but also improves their distribution, resulting in a more effective approach for achieving a uniform nanoparticle size distribution. Fig. 3 shows the oxidation state and surface composition of Fe-Co/ ZrO 2 -NG using the XPS analysis. ...
... Nanomaterials offer different properties as compared to their bulk counterparts, have very high surface areas for a given volume and predominantly exhibit quantum effects. Nanoparticles have shown great promise in terms of their performance in various fields [18][19][20][21][22][23][24]. The general factors which can affect the performance of nanomaterials can be classified as (1) size, (2) shape, (3) composition (4) synthesis methodology, and (5) postsynthesis treatments. ...
... One of the main challenges being faced by fuel cells is to minimize the precious Pt catalyst at the electrodes. Some success has been met in reducing the Pt content by PtM (M = Fe, Co, Ni, Cu, Au, etc.) alloy catalysts or non Pt catalysts, while maintaining high electrochemical activity as shown in Fig. 5.8 [21,23,24,36,37]. CS structures help in minimizing the Pt content while maintaining the high level of performance (catalytic activity and stability). ...
Chapter
Full-text available
Metal Semiconductor Core-Shell Nanostructures for Energy and Environmental Applications provides a concise, scholarly overview of current research into the characterization of metal semiconductor core-shell nanostructures; the book shows how their properties can be best used in energy and environmental applications, particularly for solar cell and catalysis application. Coverage is also given to the effect of metal nanoparticle for charge generation or charge separation. The book is a valuable resource for academic researchers working in the areas of nanotechnology, sustainable energy and chemical engineering, and is also of great use to engineers working in photovoltaic and pollution industries.
... The successful removal of metallic Co after acid treatment was initially confirmed with XRD spectra, as all the peaks corresponding to cobalt were absent in fNCNT leaving behind a broad peak at 26.6 º and a less intense peak at 43.6 º which signify the (002) and (100) planes of the graphitic carbon, respectively [19]. The peaks corresponding to graphitic carbon (002) along with (111), (200), (220) and (311) peaks corresponding to crystalline Pt (JCPDS-ICDD, Card No. 04-802) in Pt/ fNCNT confirms the successful dispersion of Pt nanoparticles on fNCNT using microwave-assisted polyol method, [20] and the particle size estimated using Debyee-Scherrer method is found to be 3.6 nm and for commercial Pt/C it is calculated to be 3.2 nm [21]. The structural defectiveness in the material is further analyzed using Raman spectra quantitatively. ...
Article
Full-text available
A cost-effective thermal pyrolysis route was adopted to synthesize N-doped carbon nanotube (NCNT) in a single step with the aid of melamine (carbon and nitrogen source) and cobalt catalyzed growth for the formation of N-doped carbon nanotubes. The NCNT was acid treated (fNCNT) to remove the metallic Co from the CNT which was elucidated using X-ray diffraction. Even though these noble metal-free materials are explored as Oxygen reduction reaction (ORR) electrocatalyst, for it to be employed in actual fuel cell the cathode requires noble metals such as Platinum (Pt) nanoparticles to improve its sluggish kinetics. Thus, this study is mainly focused on employing fNCNT as catalyst support in PEMFC, wherein the electrocatalyst was synthesized using microwave-assisted polyol method to decorate Pt nanoparticles on fNCNT, demonstrating its excellent durability of 32% electrochemical active surface area (ECSA) loss when subjected to standard protocols, and full cell performance of hybrid ((Pt/fNCNT) + CB) 412 mW cm⁻² (better than commercial Pt/C) when deployed as electrocatalyst for ORR in Polymer electrolyte membrane (PEM) fuel cell, thus our findings open new avenues to explore, design and develop N-doped carbon nanotubes as durable catalyst for fuel cells. Graphical abstract
... Carbon Black (C) is the most widely used support to support the metal alloys of the electrocatalyst. Nonetheless, carbon allotropes as nanotubes (CNT), graphene (G), and reduced graphene oxide (rGO) have been used as alternative support [20][21][22][23]. These allotropes present a high surface area, electrical conductivity, porosity, adsorption resistance to some chemical species, and other superior properties to carbon black [21,[24][25][26]. ...
Article
Full-text available
Direct ethanol fuel cell (DEFC) is promising source for mobile and portable applications, but the electrocatalysts are based on metal noble alloys or doping elements to minimize the incomplete ethanol oxidation and poisoning effect. While the main problem persists, this study describes the enhancement of ethanol oxidation reaction by adding graphene (G) to Vulcan XC-72R carbon black (C) metal support, with different C/G ratios. The Graphene was prepared from exfoliated graphite following by dried at ambient temperature. The 60 wt% graphene hybrid support enhances the current density at 5% cyclic voltammetry (CV) and 127% chronoamperometry (CA) higher than carbon pure support in acid electrolyte, whereas in alkaline, graphene (60 wt%) showed the highest electrochemical activity with an increase of current 82% (CV) and 130% (CA). Therefore, we demonstrated the enhancement of the catalyst electrochemical activity in both electrolytes through a simple synthesis method. The 40 wt% carbon and 60 wt% graphene hybrid support achieving higher performance in ethanol oxidation, evidencing a potential application in DEFC. Graphical abstract
... Carbon Black (C) is the most widely used support to support the metal alloys of the electrocatalyst. Nonetheless, carbon allotropes as nanotubes (CNT), graphene (G), and reduced graphene oxide (rGO) have been used as alternative support [20]- [23]. These allotropes present a high surface area, electrical conductivity, porosity, adsorption resistance to some chemical species, and other superior properties to carbon black [21], [24]- [26]. ...
Preprint
Full-text available
Direct ethanol fuel cell (DEFC) is promising source for mobile and portable applications, but the electrocatalysts are based on metal noble alloys or doping elements to minimize the incomplete ethanol oxidation and poisoning effect. While the main problem persists, this study describes the enhancement of ethanol oxidation reaction by adding graphene (G) to Vulcan XC-72R carbon black (C) metal support, with different C/G ratios. The Graphene were prepared from exfoliated graphite following dry in cool plasma under vacuum. The 60 wt% graphene hybrid support enhances the current density at 5% cyclic voltammetry (CV) and 127% chronoamperometry (CA) higher than carbon pure support in acid electrolyte. Whereas in alkaline, graphene (60 wt%) showed the highest electrochemical activity with an increase of current 82% (CV) and 130% (CA). Therefore, we demonstrated the enhancement of the catalyst electrochemical activity in both electrolytes through a simple synthesis method. The 40 wt% carbon and 60 wt% graphene hybrid support achieving higher performance in ethanol oxidation, evidencing a potential application in DEFC.
... During start/stop conditions, the Pt on carbon catalyst deteriorates mostly on the cathode side. 3,4 Carbon support corrosion is one of the causes of fuel cell performance degradation. 5 The corrosion speeds up the agglomeration of Pt metal particles and decreases the effective Pt content resulting in the cell degradation. ...
Article
Proton exchange membrane (PEM) fuel cells demonstrated to be feasible energy converters that convert chemical energy of fuels to electrical energy. The technology has proven to be competitive with conventional energy converters such as batteries and internal combustion engines. However; several challenges influence the commercialization of this technology which includes high costs, durability, and stability, which are contributed by the PEM fuel cell catalysts. Currently, the carbon-supported platinum electro-catalyst is being used. Unfortunately, carbon supports are not stable enough for fuel cell durability due to carbon corrosion on the cathode. Therefore it is necessary to replace carbon support materials to improve the durability of PEM fuel cells. In this study, antimony doped tin oxide (ATO) metal oxides are synthesized as alternative platinum catalyst support via co-precipitation with different antimony doping levels of 5, 7, and 10 %. The preliminary results of the acid resistance test show that the support is relatively acid-resistant with minor loss of dopant in acidic conditions. Surface area measurements, XRD, TEM, ICP characterization will be performed on the ATO before and after the addition of 40 wt. % of Pt particles. The mass and specific activity measurements for oxygen reduction reaction (ORR) and durability via ex-situ thin-fil rotating disc electrode (RDE) of Pt/ATO catalyst and the traditionally used Pt/C catalyst will be compared.
... In addition, DBFC anodes need to exhibit chemical stability in a basic solution. Common anodic catalysts for DBFCs include noble metal catalysts such as Au [12][13][14][15][16], Pt [17][18][19][20], and their corresponding alloy materials [21][22][23][24], as well as some nonprecious metal catalysts, e.g., Ni [25,26], Zn [27], and Co [28][29][30]. In particular, Au has been extensively studied, as it was originally thought to be capable of inhibiting borohydride hydrolysis; however, it exhibits rather slow kinetics for borohydride oxidation [31,32]. ...
Article
Full-text available
The synthesis of palladium-based trimetallic catalysts via a facile and scalable synthesis procedure was shown to yield highly promising materials for borohydride-based fuel cells, which are attractive for use in compact environments. This, thereby, provides a route to more environmentally friendly energy storage and generation systems. Carbon-supported trimetallic catalysts were herein prepared by three different routes: using a NaBH4-ethylene glycol complex (PdAuNi/CSBEG), a NaBH4-2-propanol complex (PdAuNi/CSBIPA), and a three-step route (PdAuNi/C3-step). Notably, PdAuNi/CSBIPA yielded highly dispersed trimetallic alloy particles, as determined by XRD, EDX, ICP-OES, XPS, and TEM. The activity of the catalysts for borohydride oxidation reaction was assessed by cyclic voltammetry and RDE-based procedures, with results referenced to a Pd/C catalyst. A number of exchanged electrons close to eight was obtained for PdAuNi/C3-step and PdAuNi/CSBIPA (7.4 and 7.1, respectively), while the others, PdAuNi/CSBEG and Pd/CSBIPA, presented lower values, 2.8 and 1.2, respectively. A direct borohydride-peroxide fuel cell employing PdAuNi/CSBIPA catalyst in the anode attained a power density of 47.5 mW cm−2 at room temperature, while the elevation of temperature to 75 °C led to an approximately four-fold increase in power density to 175 mW cm−2. Trimetallic catalysts prepared via this synthesis route have significant potential for future development.
... As shown in Fig. 5 b, similar spectra are obtained for the three types of investigated carbon supports. The broad peak at 3440 cm −1 is attributed to the stretching vibration of -OH in carboxyl group [43] , while the peak at 1384 cm −1 results from the C-O stretching vibration of carboxyl group [44] . Additionally, The peaks at 2920 cm −1 , 2850 cm −1 , 1640 cm −1 , 1590 cm −1 and 1069 cm −1 are, respectively, attributed to the asymmetric and symmetric stretching of -CH 2 -bond [45] , the stretching vibration of -OH in the absorbed water [43] , C = C stretching vibration of the aromatic ring structure [46] as well as C-O-C stretching vibration [45] . ...
Article
Carbon support not only promises to dispersedly anchor Pt-based metal nanoparticles but also functions as the critical component of catalyst layers (CLs) in polymer electrolyte membrane fuel cells (PEMFCs). Thus, the geometrical and surface properties of carbon support are believed to impact the mass transport greatly, especially the local oxygen transport in ultra-low Pt PEMFCs. Herein, we explore influences of carbon support on oxygen transport resistance in cathode catalyst layers (CCLs) through combining the limiting current method with a dual-layer CCL design. Results demonstrate that the properties of carbon support have a more significant effect on the local oxygen transport resistance relative to the bulk one. Based on various advanced physicochemical characterizations, it is analyzed that the geometrical morphology of carbon support influences the bulk oxygen transport resistance via featuring the pore structure in the electrode, while the surface functional groups of carbon support influence the local oxygen transport resistance via determining the distribution of ultra-thin ionomer films on the catalyst surface. It is believed that the findings on the interaction between carbon support and cathode mass transport behavior give a critical enlightenment on the design of high performance ultra-low Pt membrane electrode assemblies (MEAs).
... The suitable particle size distribution of all samples can be attributed to the use of polyol reduction method in the catalysts synthesis process [45]. It was reported that this method leads to a better distribution and smaller particle size of the metal nanoparticles on the support material compared to the conventional sodium borohydride reduction method [46,47]. ...
... As to anodic catalyst for DBFCs, it is necessary to have a high catalytic activity to BOR and inhibit the BH 4 − hydrolysis, and have a good chemical stability in a strongly basic solution. Common anodic catalysts for DBFCs include noble metal catalysts as Au [5][6][7][8][9][10], Pd [11][12][13][14], Pt [15][16][17][18], and their corresponding alloy materials, as well as some non-precious metal catalysts Ni [19], Zn [20], and Co [21][22][23][24][25]. Pt-based catalysts are the better choice for BOR because of the faster electrode kinetics [26][27][28], but the limited storage and high cost limit its application in DBFC anodic catalyst. ...
Article
Full-text available
Pd/C and Pd-Co/C nanocatalysts are prepared via a simple and environmentally friendly method and are used as anodic catalyst for direct borohydride–hydrogen peroxide fuel cells. X-ray diffraction and transmission electron microscopy results indicate that Pd and Pd-Co nanoparticles adhere on carbon with the mean diameter of about 4 nm. The cyclic voltammetry, chronoamperometry, chronopotentiometry, and rotating disc electrode voltammetry results show that the electrocatalytic activity of Pd-Co/C is higher than that of Pd/C, especially Pd67Co33/C which shows the highest electrocatalytic activity for BH4⁻ electro-oxidation with the electron-transfer number of 4.9 related to BH4⁻ electro-oxidation reaction. The single direct borohydride–hydrogen peroxide fuel cell with Pd67Co33/C anode obtains the maximum power density as high as 66.84 mW cm⁻² at 25 °C.
... The peaks of the D band at 1343 cm À1 and 2D band at 2680 cm À1 are due to the defects in the pristine MWCNTs. The increased intensity of the D and 2D bands after the acidic functionalization of f-MWCNTs confirms the successful attachment of the functional groups on the surface of pristine MWCNTs [45]. ...
Article
A nanocomposite from a green nanomaterial (nanocellulose) and f-MWCNTs was modified onto glassy carbon (GC) electrode for the detection of diclofenac sodium (DCF), a non-steroidal anti-inflammatory drug (NSAID) and widely used electroactive painkiller. The presence of OH groups in the nanocellulose provides more binding sites for different analytes. This ensures an axial modulus rearrangement and the incorporation of f-MWCNTs which provides larger surface area, high mechanical strength and improved electrical conductivity. On the other hand, the synergy between both compounds enhances the electrochemical detection of DCF in human blood and urine. Under optimum conditions, the modified electrode exhibited a remarkable improvement in the anodic peak current (41.6 μA) for 50 μM DCF at 0.677 V peak potential. The newly fabricated electrode showed two linear dynamic ranges from 0.05 to 1.00 μM and 2–250 μM DCF with low detection limit of 0.012 μM. In addition, differential pulse voltammetry (DPV) and cyclic voltammetry (CV) showed good sensitivity and selectivity for the determination of DCF. With this technique, the modified electrode was very effective and suitable for DCF determination from commercial tablets, ampoules (pharmaceutical preparations) and also from clinical preparations (human blood serum and urine sample) with good recoveries.
... As an alternative to overcome these problems, other procedures such as reduction of Pt and the second metal at low temperature (Xiong et al., 2002), micro emulsion methods (Xiong and Manthiram, 2005) or polyol methods (Jang et al., 2011) are aimed to synthesize bimetallic nanoparticles under milder conditions. However, these methods offer low alloying degree (Zignani et al., 2008;Jang et al., 2011;Vinayan et al., 2012;Lopez et al., 2016), mainly because the formation of alloyed intermetallic phases generally needs high temperatures (Furukawa and Komatsu, 2017). In addition, these processes require longer synthesis time (including cleaning protocols) and deployment on supports. ...
Article
Full-text available
C-encapsulated highly pure PtxCoy alloy nanoparticles have been synthesized by an innovative one-step in-situ laser pyrolysis. The obtained X-ray diffraction pattern and transmission electron microscopy images correspond to PtxCoy alloy nanoparticles with average diameters of 2.4 nm and well-established crystalline structure. The synthesized PtxCoy/C catalyst containing 1.5 wt% of PtxCoy nanoparticles can achieve complete CO conversion in the temperature range 125–175°C working at weight hourly space velocities (WHSV) of 30 L h⁻¹g⁻¹. This study shows the first example of bimetallic nanoalloys synthesized by laser pyrolysis and paves the way for a wide variety of potential applications and metal combinations.
... Among these, carbon corrosion would lead to serious Pt loss and cell performance decay, which must be addressed. In order to have better ORR activity, the size of the Pt nanoparticles and their uniform distribution, are critical [8,9]. Carbon corrosion usually occurs at high potentials in cathode catalyst layer after unprotected startup and shutdown: ...
Article
The performance and durability of PEMFCs highly depend on the catalyst support material. Traditionally, carbon is being used as support but its susceptibility to corrosion makes it less favorable for fuel cell applications. The weak interaction between Ptsingle bondC leads to the non-uniform distribution of platinum nanoparticles over the surface of support and poor durability, which in turn lowers the overall performance of PEMFCs. In order to introduce a robust support, which is more stable and durable as compared to the carbon, tantalum doped titania nanoparticles are synthesized via modified sol-gel method and investigated as a catalyst support for Pt electrocatalysts. The optimum calcination temperature for doped titania preparation is found to be 800 °C. The support is characterized through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICPOES) and transmission electron microscopy (TEM). Electrochemical performance shows that tantalum doped titania has much improved electrical conductivity than that of pure titania. Furthermore, Pt/Tasingle bondTiO2 exhibits higher ECSA retention and comparable ORR activity as compared to the Pt/C, indicating the desired durability.
... The metalated porphyrins were found to generate H 2 that could be enhanced by using platinum [27]. Note that the addition of Pt aids in easier hydrogen dissociation and has been investigated in detail [28][29][30]. The role of porphyrin-modified TiO 2 in the degradation of 4-nitrophenol using visible ultraviolet light was investigated by Duan et al., who found that the photoactivities of porphyrin-based TiO 2 structures were greater than that of pristine TiO 2 [31]. ...
Book
Full-text available
1. Covers all aspects of recent developments in multifunctional photocatalytic materials 2. Provides fundamental understanding of the structure, properties and energy applications of these materials 3. Contains contributions from leading international experts in the field working in multidisciplinary subject areas 4. Focuses on advanced applications and future research advancements, such as graphene-based nanomaterials and multi-hybrid nanocomposites 5. Presents a valuable reference for researchers and students that stimulates interest in designing advanced materials for renewable energy resources
... Note that Pt and Co atoms in the Pt−Co alloyed nanoparticles are distributed randomly in the fcc lattice (see Figures 1a,b), consistent with the experimental characterizations. 5,9,11,[13][14][15][16]23,26 Considering that core−shell structures have been synthesized experimentally in Pt−Co nanoparticles, 7,17,28,29 here we have also modeled Co−Pt core−shell (denoted as Co@Pt) nanoparticles, as illustrated in Figure 1e. Note that in Co@Pt nanoparticle Co atoms are arranged in hexagonal close packing (hcp) lattice and Pt ones are arranged in fcc lattice, in agreement with experimental results. ...
Article
Pt-Co bimetallic nanoparticles are promising candidates for Pt-based nanocatalysts and magnetic-storage materials. By using molecular dynamics simulations, we here present a detailed examination on the thermal stabilities of Pt-Co bimetallic nanoparticles with three configurations including chemically disordered alloy, ordered intermetallics, and core-shell structures. It has been revealed that ordered intermetallic nanoparticles possess better structural and thermal stability than disordered alloyed ones for both Pt3Co and PtCo systems, and Pt3Co-Pt core-shell nanoparticles exhibit the highest melting points and the best thermal stability among Pt-Co bimetallic nanoparticles, although their meltings all initiate at the surface and evolve inward with increasing temperatures. In contrast, Co-Pt core-shell nanoparticles display the worst thermal stability compared with the aforementioned nanoparticles. Furthermore, their melting initiates in the core and extends outward surface, showing a typical two-stage melting mode. The solid-solid phase transition is discovered in Co core before its melting. This work demonstrates the importance of composition distribution to tuning the properties of binary nanoparticles.
... Alloying Pt with 3d transition metals (TM), especially Co, Fe, Ni, and Cr, has been demonstrated to increase the ORR activity [23]. In particular, Pt-Co alloys have been found to exhibit enhanced catalytic activity toward the ORR [23][24][25][26][27]. The modified electronic structure of the Pt-TM alloy composite affects the Pt-Pt bond distance resulting in strong adsorption of the oxygen molecules and weak adsorption of ORR blocking OH − radicals over these alloy catalyst nanoparticles [23,28]. ...
Chapter
Full-text available
Energy is becoming a big issue in the present world due to the depletion of current fossil fuels and also due to environmental problems such as global warming and rising pollution levels. Hence, highly efficient and renewable energy materials are required to produce clean electricity. The utilization of different energy sources such as solar energy and wind energy is hampered by their fluctuation in time and non-uniform geographical distribution which are still under nascent stage. In this regard, hydrogen-based renewable energy is very promising due to higher chemical energy per mass of hydrogen (142 MJ kg⁻¹) as compared to liquid hydrocarbons (47 MJ kg⁻¹), zero emission, and its large abundancy on earth. Therefore, electrochemical conversion of hydrogen to electric energy using fuel cells would be the key technology in future. In hydrogen fuel cells, the development of highly efficient electrocatalysts mainly for sluggish cathodic oxygen reduction reaction, with inexpensive and easily available materials, is a major issue. Recent investigations suggest that chemically modified graphene support materials such as nitrogen-doped graphene can generate strong, beneficial catalyst support interactions which considerably enhance the catalyst activity and stability in fuel cells. This chapter describes the fundamental aspects of electrochemical conversion of hydrogen to electric energy using fuel cells. The chapter further explains the role of nitrogen-doped graphene nanomaterials and their hybrids with transition metal and their alloy nanoparticles in fuel cell catalysis. (iii) Ultrasonic cleavage method: Here, graphite is initially suspended in particular organic solvents or surfactants (N-methyl-2-pyrroldinone,N,N-dimethylformamide, sodium dodecyl benzene sulfonate, etc.) and then gives an ultrasonic agitation to supply the energy to cleave the graphite [8]. The yield of getting single layer graphene at the first stages of this method is very low (~1 wt. %) and it can be increased by repeated sediment recycling. The success of ultrasonic cleavage depends on the right selection of solvents and surfactants as well as the sonication frequency, amplitude, and time.
Article
Full-text available
We report a unique approach to fabricate lithium ion battery anodes based on multiwalled carbon nanotubes (MWCNTs) grown directly on copper foils via chemical vapor deposition. This process eliminates the use of binders for lithium ion battery anodes. The intermediate conductive Ti and alumina blocking layers have been optimized to seamlessly connect the CNTs with the Cu substrate, providing robust structural integrity that facilitates charge transfer. This anode material showed a high capacity of 448 mA h g⁻¹ at 50 mA g⁻¹, superior rate capability and no capacity degradation up to 70 cycles at different current densities (100 mA g⁻¹ to 500 mA g⁻¹). Within a small voltage window of 0.8 V vs. Li/Li⁺, this anode offers the usable capacity of 300 mA h g⁻¹. The observed electrochemical performance of this anode can be attributed to the high theoretical capacity of carbon nanotubes, faster Li-ion insertion into the walls of CNTs and better conductivity at the point of contact between the substrate and the CNTs enhanced by the inclusion of Ti at the substrate–CNT interface.
Chapter
In recent years, many fuel cell devices are produced due to their property of conversing chemical to electrical energy through reactions. From all the kinds of fuel cells, carbon nanotube (CNT)–based proton exchange membrane (PEM) fuel cells are the best in their stability, process at little temperature, maximum efficiency, and medium power generation. The Cu‐CNFs/PBI/IrO 2 membrane is developed to convert CO 2 to important products. In this membrane, low current density allowed the transformation of carbon dioxide into organic products with 85% selectivity and high current density increased catalytic activity and produce lighter saturated products. Nowadays, replacement of high‐cost catalysts with low‐cost, high‐efficient catalysts are a major challenge for the scientist. For this purpose, CNT‐based PEM fuel cells are the most interesting material. In this chapter overview of the application‐based approach, CNT‐based PEM fuel cells are explained due to their auspicious properties, for example, huge surface area, maximum conductivity, and resist to corrosion.
Article
Designing highly active and durable electrocatalysts towards oxygen reduction reaction (ORR) plays a paramount importance for proton exchange membrane fuel cells. Pt-based binary alloys Pt-M (M = 3d-transition metals) possessing excellent electronic and geometric properties have received increasing interests as highly active electrocatalysts. Herein, we report a series of PtxCo/C (x = 1, 2, 3) catalysts by a facile one-pot soft-chemistry method. In the acidic conditions, the mass activities of PtCo/C, Pt2Co/C and Pt3Co/C are 0.526, 0.462 and 0.441 A·mgPt−1, which are 2.60, 2.31 and 2.22 times higher than that of Pt/C (0.200 A·mgPt−1), respectively. The specific activities of PtCo/C, Pt2Co/C and Pt3Co/C are 706.59, 679.41 and 801.83 μA·cm−2, which are accordingly 2.89, 2.76 and 3.28 times higher than that of Pt/C (244.75 μA·cm−2). Notably, Pt3Co/C shows a remarkable durability. After 5000 cycles of the accelerated durability testing, the mass activity and specific activity of Pt3Co/C catalyst are 2.47 and 3.80 times higher than that of the commercial Pt/C, respectively. The improved ORR activity and durability can be ascribed to the synergistic interaction between Pt and Co.
Article
Full-text available
The lack of efficient and durable proton exchange membrane fuel cell electrocatalysts for the oxygen reduction reaction is still restraining the present hydrogen technology. Graphene-based carbon materials have emerged as a potential solution to replace the existing carbon black (CB) supports; however, their potential was never fully exploited as a commercial solution because of their more demanding properties. Here, a unique and industrially scalable synthesis of platinum-based electrocatalysts on graphene derivative (GD) supports is presented. With an innovative approach, highly homogeneous as well as high metal loaded platinum-alloy (up to 60 wt %) intermetallic catalysts on GDs are achieved. Accelerated degradation tests show enhanced durability when compared to the CB-supported analogues including the commercial benchmark. Additionally, in combination with X-ray photoelectron spectroscopy Auger characterization and Raman spectroscopy, a clear connection between the sp 2 content and structural defects in carbon materials with the catalyst durability is observed. Advanced gas diffusion electrode results show that the GD-supported catalysts exhibit excellent mass activities and possess the properties necessary to reach high currents if utilized correctly. We show record-high peak power densities in comparison to the prior best literature on platinum-based GD-supported materials which is promising information for future application.
Article
A simple design of electroactive and cost-effective electrocatalysts for oxygen reduction reaction (ORR) activity is crucial towards energy conversion in the commercialization of proton exchange membrane fuel cells (PEMFCs). Herein, we synthesized a stable electroactive bimetallic catalyst of Ni anchored with low loading of Pt nanoparticles, and graphene used as a supportive material for catalyst integration (Pt3-Ni/G). It exhibited maximum electrochemical surface area (ECSA, 108.56 m²/gPt), mass activity (2.2 A mgPt) and specific activity (3.47 mA cm⁻²), signifying an excellent ORR activity. In addition, a scalable PEMFC fabrication through 0.2 mgPtcm⁻² Pt3-Ni/G as cathode with an active area of 25 cm² and stainless steel-314L (SS-314L) used as a serpentine flow field. This strategy provides a maximum power output of 71.25 W mgPt⁻¹ at current density 1.59 A cm⁻². In addition, Pt3-Ni/C//Pt/C, based PEMFC system delivered a constant power output (68.75 W mgPt⁻¹) even after 4 h of continuous cycling.
Article
Platinum (Pt) nanoparticles with different sizes of 2nm and 5nm supported on functionalized high surface area carbon (HSC) have been successfully synthesized with a one-pot synthesis technique in large scale. Of the interest for the proton exchange membrane fuel cell applications, the synthesized supported catalysts are evaluated by physical characterizations, half-cell and scaled up single cell tests to study the impact of the catalyst sizes on cell performance and durability. Physical characterizations clearly demonstrate the sizes, shapes, crystallinity phases, and the total loading of the Pt nanoparticles on HSC. Half cell characterizations demonstrate higher electrochemical surface area, higher mass activity, and less durability for the working electrode prepared by the smaller Pt nanoparticle sizes (2nm) than the larger Pt nanoparticles (5nm). Scaled up single cell tests using air and hydrogen as the cathode and anode reactants demonstrate the membrane electrode assembly (MEA) prepared by smaller Pt nanoparticle sizes (2nm) shows the maximum power density of 1.1 W/cm², which is 7% higher than the maximum power density of MEA prepared by larger Pt nanoparticles (5nm) under similar operational conditions. The 30,000 cycles of accelerated stress test on the membrane electrode assembly prepared by larger Pt nanoparticles (5nm) demonstrates 13% drop at maximum power density, illustrating the excellent performance against degradation (ageing).
Article
Full-text available
Polymer electrolyte fuel cells (PEFCs) are a promising replacement for the fossil fuel–dependent automotive and energy sectors. They have become increasingly commercialized in the last decade; however, significant limitations on durability and performance limit their commercial uptake. Catalyst layer (CL) design is commonly reported to impact device power density and durability; although, a consensus is rarely reached due to differences in testing conditions, experimental design, and types of data reported. This is further exacerbated by aspects of CL design such as catalyst support, proton conduction, catalyst, fabrication, and morphology, being significantly interdependent; hence, a wider appreciation is required in order to optimize performance, improve durability, and reduce costs. Here, the cutting‐edge research within the field of PEFCs is reviewed, investigating the effect of different manufacturing techniques, electrolyte distribution, support materials, surface chemistries, and total porosity on power density and durability. These are critically appraised from an applied perspective to inform the most relevant and promising pathways to make and test commercially viable cells. This holistic view of the competing aspects of CL design and preparation will facilitate the development of optimized CLs, especially the incorporation of novel catalyst support materials.
Article
Two porous carbon supports as N-doped carbon (NC) and Fe/N-co-doped carbon (Fe-NC), are obtained from ZIF-8 (zeolitic imidazolate framework) and [email protected], respectively, through the pyrolysis process. They are then decorated with transition metals using a modified polyol method to precipitate Fe, Co, and Fe–Co nanoparticles. The as-prepared catalysts are characterized by different physicochemical, morphological, and electrochemical characterization methods. Field emission scanning electron microscopy images show well-defined preserved polyhedron morphology for all prepared catalysts. Transmission electron microscopy images confirm a uniform distribution of metal nanoparticles through the surface of the supports. X-ray photoelectron spectroscopy results illustrate the existence of high content of graphitic and pyridinic nitrogen. Oxygen reduction reaction (ORR) results show the prepared support, which is in-situ doped with iron (Fe-NC), has better ORR performance than NC support. The results also display Co and Fe nanoparticles' coincident precipitation on the supports can improve ORR. This finding indicates both in-situ and ex-situ metal doping can be beneficial for good ORR performance. The optimum catalyst (Fe–Co/Fe-NC) illustrates enhanced ORR activity and stability with onset potential ~0.9VRHE in 0.1 M HClO4. Superior performance is associated with a synergistic effect between small and uniform dispersion of Co and Fe nanoparticles and appropriate nitrogen content.
Article
Recently, the development of bimetallic nanoparticles with functional properties has been attempted extensively but with limited control over their morphological and structural properties. The reason was the inability to control the kinetics of the reduction reaction in most liquid-phase syntheses. However, the alcohol reduction technique has demonstrated the possibility of controlling the reduction reaction and facilitating the incorporation of other phenomena such as diffusion, etching, and galvanic replacement during nanostructure synthesis. In this study, the reduction potential of straight-chain alcohols has been investigated using molecular orbital calculations and experimentally verified by reducing transition metals. The alcohols with a longer chain exhibited higher reduction potential, and 1-octanol was found to be the strongest among alcohols considered. Furthermore, the experimental evaluation carried out via the synthesis of metallic Cu, Ni, and Co particles was consistent with the theoretical predictions. The reaction mechanism of metallic particle formation was also studied in detail in the Ni-1-octanol system, and the metal ions were confirmed to be reduced via the formation of nickel alkoxide. The results of this investigation were successfully implemented to synthesize Cu-Ni bimetallic nanostructures (core-shell, wire, and tube) via the incorporation of diffusion and etching besides the reduction reaction. These results suggest that the designed synthesis of a wide range of bimetallic nanostructures with more refined control has become possible.
Article
Recent researches have proven that incorporation of machine learning could significantly shorten development cycle of energy materials. However, this rising multidisciplinary field still needs a standard research paradigm instructing how potentialities of algorithms could be exploited comprehensively to optimize performance. Hence, we set up a standard workflow consisted of four processing modules started with feature selection followed by decision modelling, regression modelling and extremum optimization. Optimization of membrane electrode assembly (MEA) in proton exchange membrane fuel cells (PEMFCs) was taken as demonstration. By applying 35 different algorithms on the largest database so far, 27 key factors out of 66 complex parameters were screened out to provide decision aids and build prediction models with error less than 15%. Without trial-and-error processes, final optimization immediately inferred 13 optimal parameters based on existing conditions provided by users. A glimpse into the future energy material research has therefore been brought by this great precedent.
Article
The electrode is the key component of the membrane electrode assembly (MEA) of proton exchange membrane fuel cells (PEMFCs). The electrochemical reaction of hydrogen (fuel) and oxygen that transform into water and electrical energy occurs at the catalyst site. Attempts to improve the performance and durability of electrodes have sought to overcome the challenges arising from utilizing PEMFCs as an efficient and competitive energy source. To accomplish this goal and to solve the problems related to using PEMFC electrodes, the structure and function of each component and the manufacturing method must be comprehensively understood, and the electrode performance and durability of the cell must be characterized. Therefore, in this paper, we discuss the components, preparation, functions and performance of the electrodes used in PEMFCs. This review aims to provide comprehensive information regarding PEMFC electrodes.
Article
Proton Exchange Membrane Fuel Cells (PEMFCs) are considered to be one of the most promising clean technologies to mitigate climate change, air pollution, and the energy crisis. Although PEMFCs have been intensively investigated over the past five decades, the relatively low current density, high cost, and poor durability remain as obstacles to full commercialization. In this study, we present the development and the application of a porosity tunable carbon aerogel (CA) as an alternative to the carbon support in PEMFC to overcome its technical barriers. CA demonstrates highly tunable mesopore volume and surface area. The N2 isotherm with non-localized density functional theory (NLDFT) analysis shows the optimized CA had extremely high mesopore volume, which was 4.26 times larger than traditional carbon support (i.e., Vulcan XC-72R). The transmission electron microscopy (TEM) shows a better catalyst (i.e., platinum nanoparticles) distribution on the CA support. This even distribution of platinum nanoparticles significantly enhances the catalyst utilization of the electrodes in our cyclic voltammetry (CV) analysis. It also contributes up to a 713% higher specific power density in our fuel cell testing. The standard accelerated stress tests (AST) exhibit that CA has excellent durability compared to conventional carbon support. Thus, the mesoporous CA provides an efficient and durable alternative to existing carbon material as a catalyst support in PEMFCs.
Article
Here, the electronic structure and adsorption properties for O and OH of a series of Pt-Co alloys with different Pt/Co ratio (5:1, 2:1, 1:1, 1:2, and 1:5) were systematically studied using density functional theory calculations. Our computational results demonstrated that the introduced Co atoms have multiple effects on the surface electronic structure in different atomic layers of alloy, leading to the discrepancies in the electronic structure between Pt-skin structure and non-Pt-skin structure. Moreover, the influence of the surface electronic structure on the adsorption of O and OH slightly differs. Indeed, the adsorption of O is more remarkably affected by the Pt/Co ratio than the OH adsorption and better follows the d-band center theory. Due to the difference of the alloy structure and the effect of different layer Co atom, the adsorption of O and OH on the alloy configurations with the same Pt/Co ratio has different outcomes. Our results suggested that oxygen reduction reaction (ORR) activity is not only related to Pt/Co ratio of alloy surfaces but also the specific surface structure. Our research can provide theoretical insights into the development of ORR catalysts.
Article
Full-text available
Common carbon-blacks have shown insufficient stability as cathodic catalyst supports for proton exchange membrane fuel cells (PEMFCs). In this regard, alternative supports have been proposed and, specifically graphene or reduced graphene oxide (rGO), have attracted special attention. Herein, a set of electrocatalysts using reduced graphene oxide (rGO) as support is synthetized by a modified polyol method. The influence of Pt loading on the support is studied and compared with conventional supports, considering Pt particle morphologies and oxygen reduction reaction (ORR) performance in rotating disk electrode (RDE). Despite Pt average particle size typically increases with the Pt loading, 30 wt% of Pt on rGO is the optimal Pt loading, yielding the highest ORR activity among the rGO-supported electrocatalysts. These results show that both Pt loading and type of support greatly impact on the morphology and electrochemical performance of Pt nanoparticles.
Article
Full-text available
Sulfur- (S-CNT) and nitrogen-doped (N-CNT) carbon nanotubes have been produced by catalytic chemical vapor deposition (c-CVD) and were subject to an annealing treatment. These CNTs were used as supports for small (≈2 nm) Pt3M (M = Co or Ni) alloyed nanoparticles that have a very homogeneous size distribution (in spite of the high metal loading of ≈40 wt % Pt), using an ionic liquid as a stabilizer. The electrochemical surface area, the activity for the oxygen reduction reaction and the amount of H2O2 generated during the oxygen reduction reaction (ORR) have been evaluated in a rotating ring disk electrode experiment. The Pt3M/N-CNT catalysts revealed excellent electrochemical properties compared to a commercial Pt3Co/Vulcan XC-72 catalyst. The nature of the carbon support plays a key role in determining the properties of the metal nanoparticles, on the preparation of the catalytic layer, and on the electrocatalytic performance in the ORR. On N-CNT supports, the specific activity followed the expected order Pt3Co > Pt3Ni, whereas on the annealed N-CNT support, the order was reversed.
Article
This communication demonstrates the effect of electrostatically adsorbed alkali cations at electrochemical interface towards methanol oxidation reaction (MOR) in acidic medium. The well-known electrostatic interaction between adsorbed OH/(OHad) species of catalyst surface and hydrated metal cations (M⁺(H2O)x) at the interface could be accountable for the observed different electrocatalytic activity of Pt/C and f-MWCNT/Pt-Co alloy NPs towards MOR. This cation effect has been found predominantly in weekly adsorbed ClO4⁻ ion at Pt/C and f-MWCNT/Pt-Co alloy NPs surface than that of strongly adsorbed SO4²⁻ ion. Cyclic voltammetry results reveal that the strongly adsorbed cation at the interface shifts the oxidation potential more positively than that of weekly adsorbed cation.
Article
A facile synthesis at room temperature and at solid-state directly on the support yielded small, homogeneous and well-dispersed Pt nanoparticles (NPs) on CB-carbon black, GNP-graphene nanoplatelets, and CB-GNP-50:50 hybrid support. Synthesized Pt/CB, Pt/GNP and Pt/CB:GNP NPs were used as electrocatalysts for polymer electrolyte membrane fuel cell (PEMFC) reactions. HRTEM results displayed very small, homogeneous and well-dispersed NPs with 1.7, 2.0 and 4.2 nm mean-diameters for the Pt/CB-GNP, Pt/GNP and Pt/CB electrocatalysts, respectively. Electrocatalysts were also characterized by RAMAN, XRD, BET and CV techniques. ECSA values indicated better activity for graphene-based supports with 19 m² g⁻¹Pt for Pt/GNP and 55 m² g⁻¹Pt for Pt/CB-GNP compared to 10 m² g⁻¹Pt for Pt/CB. Oxygen reduction reaction (ORR) studies and fuel cell tests were in parallel with these results where highest maximum power density of 377 mW cm⁻² was achieved with Pt/CB-GNP hybrid electrocatalyst. Both fuel cell and ORR studies for Pt/CB-GNP indicated better dispersion of NPs on the support and efficient fuel cell performance that is believed to be due to the prevention of restacking of GNP by CB. To the best of our knowledge, Pt/GNP and Pt/CB-GNP electrocatalysts are the first in literature to be synthesized with the organometallic mild synthesis method using Pt(dba)3 precursor for the PEMFC applications.
Article
Tungsten (W), as one of the refractory 5d transition high-valency metals with unique physical and chemical properties, may substantially improve Pt-based alloys, providing superior electro-catalytic performance for the oxygen reduction reaction (ORR) that has been considered as the key cathode process in fuel cell automotives or portable devices. In this paper, we developed the graphene-supported Pt-Co-W ternary alloy, by using a facile one-pot polyol co-reduction of the above three metal. In the 0.1M HClO4 solution, the obtained Pt-Co-W ternary alloy exhibits a surprisingly high specific activity of 3.41 mA·cm-2, which is 4.3 times higher than that of the well-known Pt-Co binary alloy (0.80 mA·cm-2) and 13 times over that obtained by the state-of-the-art Pt/C (0.27 mA·cm-2). The mass activity of the alloy is 2.25 A·mg-1Pt, which is 4.2 times higher than that of the Pt-Co binary alloy (0.53 A·mg-1Pt) and 12 times over that obtained by the state-of-the-art Pt/C (0.19 A·mg-1Pt), at 0.9 V versus a reversible hydrogen electrode (RHE). The remarkably enhanced ORR activity can be attributed to the incorporating of small amount W into the Pt-Co alloy system at atomic level. The added W atoms can not only strengthen the chemical adsorption of oxygen molecules but also significantly facilitate the desorption of the oxygenated species on the active Pt sites in this ternary alloy, because W has stronger electronegativity, higher unsaturated 5d orbitals, and higher valency coordinated with these oxygenated groups. Therefore, introducing the cheap refractory transition metals like W into Pt-based binary alloys may open a door to fabricate the efficient next-generation ternary catalysts for the ORR.
Article
Carbon-supported Pt-Co (Pt-Co/C) nanoparticles of varying composition were synthesized by sonochemical technique in presence of PVP as a stabilizing agent. X-ray diffraction (XRD) analysis revealed that all compositions of as-synthesized Pt-Co/C nanoparticles exhibited the face centered cubic (fcc) structure. Transmission electron microscopy (TEM) images showed the narrow size distribution and the uniform dispersion of Pt and Co on carbon support. Electrochemical properties of Pt-Co/C electrocatalysts were analysed using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Electrochemical properties of Pt83-Co17/C composition exhibited the best catalytic activity and the highest stability for the oxygen reduction reaction (ORR) among all composition synthesized in this study. ORR performance is reported in terms of electrochemical active surface area (EASA) and current density. The current density decreased with increase in Co content and followed the trend as Pt83-Co17/C > Pt75-Co25/C > Pt50-Co50/C. The fabricated PEM fuel cell (PEMFC) presented power of 0.176 W/cm2 at 0.436 V using Pt83-Co17/C cathode and 40% Pt/C anode and followed the same trend as current density.
Article
Rather than their use as new energy sources, microbial fuel cells (MFCs) are promising for wastewater treatment as they allow for a significant energy saving and a high treatment efficiency if they are integrated with MBR (membrane bioreactor), where the electricity can be in-situ used over the cathode membrane, in spite of the insignificant power generation, the small current and low voltage output. The performance and cost of MFCs are largely influenced by the electrode materials. Nanocarbon materials with superior physical and chemical properties that conventional materials cannot match, are crucial for the development of MFCs. In this review, recent research progresses and applications of carbon nanotubes, graphene, g-C3N4 and their composites as MFC anode/cathode are highlighted, for insights into the characteristics, the modification /preparation methods and the performance of such MFCs. Different composit catalytic cathode membranes in integrated MFC-MBR systems are also reviewed. Because integrating MBR with catalytic cathode membrane in MFC improves the effluent quality and overcome the deficiencies of MFC, while using the recovered bio-energy to offset the energy consumption for aeration and filtration.
Chapter
Technological advances have led to higher energy demands across the world, which are largely met by fossil fuels. Many countries have resolved to bring down their carbon footprint by implementing newer, greener, and renewable sources of energy. Efforts to design materials with different physicochemical properties have led to engineering core–shell (CS) nanomaterials. The choice of shell and core is driven by the end-use for which nanoparticles are synthesized. CS nanomaterials have been successfully employed in energy conversion and storage applications like solar cells, fuel cells, rechargeable batteries, supercapacitors, and so on. This chapter discusses the role of CS nanomaterials for energy conversion and energy storage, especially by fuel cells, supercapacitors, and lithium-ion batteries and their structure-property relationship.
Article
We report novel method for synthesis of carbon aerogel as platinum support for PEM fuel cells applications. The sol gel polymerization has been carried out using resorcinol and furfuraldehyde in non-aqueous medium followed by gelation at high pressure. This resulted in highly conducting and mesoporous carbon aerogel under ambient drying conditions. Platinum nano-particles are impregnated in the mesoporous carbon aerogel using microwave assisted polyol process. The support material and the catalyst are characterized by different analytical techniques like surface area analyzer, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry and linear sweep voltammetry are used to evaluate the electro–catalytic activity of the Pt/carbon aerogel catalyst using rotating disk electrode technique. Well dispersed Pt nano-particles of size ∼3 nm on carbon aerogel showed good catalytic activity with onset potential of 964 mV and half wave potential of 814 mV towards oxygen reduction reaction kinetics. A membrane electrode assembly fabricated with the prepared Pt/carbon aerogel catalyst as a cathode and anode is tested in PEMFCs (H2O2) single cell, the power density of 536 mW cm⁻² at 0.6 V is obtained at 60 °C under atmospheric pressure.
Article
The present study aims at developing a high performing Pt/CNT catalyst for ORR in PEM fuel cell adopting modified chemical reduction route using a mixture of NaBH4 and ethylene glycol (EG) as reducing agent. In order to select the most suitable reduction conditions to realize high performing catalyst, heating of the reaction mixture is done following two methods, conventional heating (CH) or microwave (MW) irradiation. The synthesized Pt/CNT catalysts were extensively characterized and evaluated in-situ as ORR catalyst in PEM fuel cell. A comparison of their performance with the standard, commercial Pt/C catalyst was also made. The results showed deposition of smaller Pt nanoparticles with uniform distribution and higher SSA for Pt/CNT-MWH compared to Pt/CNT-CH. In-situ electrochemical characterization studies revealed higher ESA, lower charge transfer resistance, lower activation over-potential loss and higher peak power density compared to the cathode with Pt/CNT-CH and Pt/C. This study suggests the viability of MW assisted, metal particle deposition as a simple, yet effective method to prepare high performing Pt/CNT catalyst for ORR in PEM fuel cell.
Article
We have synthesized carbon-supported Pt and PtM (Au, Pd) nanoparticles (NPs) by using an aluminum (Al) metal foil as a reducing agent and conducted post heat treatments to investigate the relationship between oxygen reduction reaction (ORR) activity and surface crystalline/electronic structures of electrocatalysts. The as-prepared Pt and PtM (Au, Pd) NPs received the post heat treatment to induce structural modifications to improve ORR activity. From structural characterizations, well-synthesized carbon-supported Pt and PtM (Au, Pd) NPs were confirmed and the post heat treatment has the effect of inducing the alteration of surface crystalline structure and results in higher ORR activity. Furthermore, based on electrochemical characterizations, it is proved that after the heat treatment, the surface reconstruction brought about the increased fraction of Pt (111) and electrochemical active surface area of PtAu/C CO sample. And, the downshift of Pt d-band center of PtPd/C CO sample, which decreases the affinity of Pt to oxygen species, occurred resulting in more favorable kinetics of ORR.
Article
Full-text available
The electrocatalysis of the oxygen reduction reaction (ORR) on five binary Pt alloys (PtCr/C, PtMn/C, PtFe/C, PtCo/C, and PtNi/C) supported on high surface area carbon in a proton exchange membrane fuel cell was investigated. All electrocatalysts exhibited a high degree of crystallinity with the primary phase of the type PtâM (LIâ structure with fcc type lattice) and a secondary phase being of the type PtM (LI{sub o} structure with tetragonal lattice) as evidenced from XRD analysis. The electrode kinetic studies on the Pt alloys at 95 C and 5 atm pressure showed a two- to threefold increase in the exchange current densities and the current density at 900 mV as well as a decrease in the overvoltage at 10 mA/cm² relative to Pt/C electrocatalyst. The PtCr/C alloy exhibited the best performance. In situ EXAFS and XANES analysis at potentials in the double-layer region [0.54 V vs. reversible hydrogen electrode (RHE)] revealed (1) all the alloys possess higher Pt d-band vacancies per atom (with the exception of PtMn/C alloy) relative to Pt/C electrocatalyst and (2) contractions in the Pt-Pt bond distances which confirmed the results from ex situ XRD analysis. A potential excursion to 0.84 V vs. RHE showed that, in contrast to the Pt alloys, the Pt/C electrocatalyst exhibits a significant increase in the Pt d-band vacancies per atom. This increase, in Pt/C has been rationalized as being due to adsorption of OH species from the electrolyte following a Temkin isotherm behavior, which does not occur on the Pt alloys. Correlation of the electronic and geometric with the electrochemical performance characteristics exhibits a volcano type behavior with the PtCr/C alloy being at the top of the curve. The enhanced electrocatalysis by the alloys therefore can be rationalized on the basis of the interplay between the electronic and geometric factors on one hand and their effect on the chemisorption behavior of OH species from the electrolyte.
Article
Full-text available
Pt and Pt-Fe catalysts supported on multiwalled carbon nanotubes (MWCNTs) were prepared by impregnation and reduction at intermediate temperature (400°C). The MWCNTs with diameters ranging from 20 to 100 nm were synthesized by a spray pyrolysis technique. PtMWCNTs and Pt-Fe /MWCNT catalysts were characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscope-energy dispersive X-ray analysis, and transmission electron microscopy techniques. The electrocatalytic behavior for the oxygen reduction reaction was investigated in rotating disk electrode configuration in an acidic medium, also in the presence of various methanol concentrations (0.01, 0.1, and 1 M). An anodic shift of the peak potential for methanol oxidation of ∼150 mV was observed in the presence of 1 M methanol concentration for the Pt-Fe catalyst compared to the Pt catalyst. Both materials were used as cathodes in a direct methanol fuel cell at 30 and 60°C. A better performance was obtained for the cell based on Pt-Fe /MCWNTs as cathode catalyst. Although slight iron dissolution was observed after two weeks of discontinuous operation, the performance of the Pt-Fe catalyst was larger than the Pt catalyst.
Article
Full-text available
The electrocatalysis of the oxygen reduction reaction (ORR) on five binary Pt alloys (, , , , and ) supported on high surface area carbon in a proton exchange membrane fuel cell was investigated. All the alloy electrocatalysts exhibited a high degree of crystallinity with the primary phase of the type ( structure with fcc type lattice) and a secondary phase (only minor contribution from this phase) being of the type ( structure with tetragonal lattice) as evidenced from x‐ray powder diffraction (XRD) analysis. The electrode kinetic studies on the Pt alloys at 95°C and 5 atm pressure showed a two‐ to threefold increase in the exchange current densities and the current density at 900 mV as well as a decrease in the overvoltage at 10 mA cm⁻² relative to Pt/C electrocatalyst. The alloy exhibited the best performance. In situ EXAFS and XANES analysis at potentials in the double‐layer region [0.54 V vs.reversible hydrogen electrode (RHE)] revealed (i) all the alloys possess higher Pt d‐band vacancies per atom (with the exception of alloy) relative to Pt/C electrocatalyst and (ii) contractions in the Pt‐Pt bond distances which confirmed the results from ex situ XRD analysis. A potential excursion to 0.84 V vs. RHE showed that, in contrast to the Pt alloys, the Pt/C electrocatalyst exhibits a significant increase in the Pt d‐band vacancies per atom. This increase, in Pt/C has been rationalized as being due to adsorption of OH species from the electrolyte following a Temkin isotherm behavior, which does not occur on the Pt alloys. Correlation of the electronic (Pt d‐band vacancies) and geometric (Pt‐Pt bond distance) with the electrochemical performance characteristics exhibits a volcano type behavior with the alloy being at the top of the curve. The enhanced electrocatalysis by the alloys therefore can be rationalized on the basis of the interplay between the electronic and geometric factors on one hand and their effect on the chemisorption behavior of OH species from the electrolyte.
Article
Full-text available
Pt-loaded multiwalled carbon nanotubes (Pt/MWCNTs) have been prepared by chemical reduction method using functionalized MWCNT synthesized by pyrolysis of acetylene over MmNi2 (Mm denotes misch metal) hydride catalyst. Composites of Pt/MWCNT and commercial Pt-loaded carbon black (Pt/C) have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC). Cathode catalyst with 50% Pt/MWCNT and 50% Pt/C showed best performance due to better dispersion and good accessibility of MWCNT support and Pt electrocatalysts for oxygen reduction reaction in PEMFC. A maximum performance of 540 mV at a current density of around 535 mA cm−2 has been obtained.
Article
Full-text available
A detailed procedure for comparing high surface Pt/C catalysts was pointed out. Platinum dispersed carbon was prepared from carbonaceous material and chloroplatinic acid solution using sodium formiate. The real platinum metal surface area was evaluated by cyclic voltammetry on a thin porous coated disk electrode. The performance of catalysts prepared in our laboratory were similar to those of a well-known commercial one. The results show that electrochemical active surface (EAS) measurement is strongly influenced by the gas diffusion electrode (GDE) preparative method. It is only by means of a well-defined preparative procedure and data analysis that it is possible to use this technique to compare different carbon supported platinum catalysts.
Article
Full-text available
Carbon supported Pt and Pt–Co electrocatalysts for the oxygen reduction reaction in low temperature fuel cells were prepared by the reduction of the metal salts with sodium borohydride and sodium formate. The effect of surface treatment with nitric acid on the carbon surface and Co on the surface of carbon prior to the deposition of Pt was studied. The catalysts where Pt was deposited on treated carbon the ORR reaction preceded more through the two electron pathway and favored peroxide production, while the fresh carbon catalysts proceeded more through the four electron pathway to complete the oxygen reduction reaction. NaCOOH reduced Pt/C catalysts showed higher activity that NaBH4 reduced Pt/C catalysts. It was determined that the Co addition has a higher impact on catalyst activity and active surface area when used with NaBH4 as reducing agent as compared to NaCOOH.
Article
Carbon supported platinum metal alloy catalysts (Pt–M/C) are widely used in low temperature fuel cells. Pt alloyed with first-row transition elements is used as improved cathode material for low temperature fuel cells. A major challenge for the application of Pt–transition metal alloys in phosphoric acid (PAFC) and polymer electrolyte membrane (PEMFC) fuel cells is to improve the stability of these binary catalysts. Dissolution of the non-precious metal in the acid environment can give rise to a decrease of the activity of the catalysts and to a worsening of cell performance. The purpose of this paper is to provide a better insight into the stability of these Pt–M alloy catalysts in the PAFC and PEMFC environments and the effect of the dissolution of the non-precious metal on the electrocatalytic activity of these materials, in the light of the latest advances on this field. Additionally, the durability of a PtCo/C cathode catalyst was evaluated by a short test in a single PEM fuel cell.
Article
Polarization curves of membrane electrode assemblies (MEAs) containing carbon-supported platinum (Pt/C) and platinum–nickel alloy (Pt1Ni1/C) as cathode catalysts were obtained for durability test as a function of time over 1100 h at constant current. Charge transfer resistance was measured using electrochemical impedance spectroscopy and postmortem analysis such as X-ray diffraction and high-resolution transmission electron microscopy was conducted in order to elucidate the degradation factors of each MEA. Our results demonstrate that the reduced performance of MEAs containing Pt1Ni1/C as a cathode catalyst was due to decreased oxygen reduction reaction caused by the corrosion of Ni, whereas that of MEAs containing Pt/C was because of reduced electrochemical surface area induced by increased Pt particle size.
Article
The oxygen reduction reaction (ORR) was studied on carbon dispersed Pt and Pt-Co alloyed nanocatalysts with high contents of Co in H2SO4 and H2SO4/CH3OH solutions. The characterization techniques considered were transmission electron microscopy (TEM), X-ray diffraction (XRD) and in situ X-ray absorption near edge structure (XANES). The electrochemical activity for the ORR was evaluated from steady state polarization measurements, which were carried out in an ultra thin layer rotating disk electrode. The results showed that with the increase of Co content, the nanoparticle size distributions become sharper and the mean particle diameters become smaller. XRD indicated low degree of alloy formation but significant phase segregation of Co was observed only for Pt-Co/C 1:3 and 1:5 (Pt:Co atomic ratios). The electrochemical measurements indicated that the four-electrons mechanism is mainly followed for the ORR on all materials and the electrocatalytic activities per gram of Pt is higher for the catalysts with higher Co contents. This was explained based on the XANES results which evidenced a decrease of the coverage of oxygenated Pt adsorbates due to the presence of Co. In the methanol-containing electrolyte, the Pt-Co/C 1:5 catalyst showed the highest performance. This was attributed to its low activity for the methanol oxidation due to the smaller probability for presenting three Pt neighboring Pt active sites.
Article
To investigate the effect of carbon support adding sequence on Pt particle sizes and Pt utilizations during the polyol process of the electrocatalyst preparation, a series of Pt/C electrocatalysts (different Pt loadings, two kinds of carbon supports−Vulcan XC and Black Pearls 2000) were prepared, namely, Pt/C-a (first reduced Pt ions to form Pt nanoparticles, which subsequently deposited on carbon supports) and Pt/C-b (Pt precursors were first impregnated with carbon supports, then reduced to Pt nanoparticles). The physical properties of the electrocatalysts were characterized by X-ray diffraction, transmission electron microscopy and nitrogen adsorption. The catalytic activities of the electrocatalysts toward the oxygen reduction reaction and the methanol oxidation reaction were characterized by potentiodynamic measurements. The results show that the carbon support adding sequence has significant effects on the Pt particle sizes, especially for the carbon supports with large amount of micropores, as a result, leading to different catalytic activities.
Article
Non-precious metal catalysts for the oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells (PEMFCs) were obtained by pyrolysis of iron citrate and polyacrylonitrile on mesoporous xerogel carbon support. Chemical-physical characterizations, electrochemical studies by the rotating disc electrode, and electrochemical tests in a PEMFC configuration demonstrated that the porosity of the pristine carbon promotes the formation of graphene and carbon nanotube structures featuring ORR catalytic activity.
Article
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Article
Carbon-supported Pt–Co alloy catalysts with Co contents of 10–50 wt% have been synthesized by reducing aqueous Co2+ ions with borohydride or precipitating as hydroxide in the presence of a commercially available carbon-supported Pt catalyst followed by heat treatment in a 90% Ar–10% H2 mixture at 900 °C for 1 h. X-Ray diffraction indicates the Pt–Co alloys thus obtained to have the ordered Pt3Co or PtCo type structures or the disordered Pt type structure depending on the Co content. High resolution transmission electron microscopy (HRTEM) studies also confirm the formation of ordered structures. Structural analysis of the products after annealing at various temperatures 500 ≤ T ≤ 900 °C for 1 h suggests the ordering to be maximized for an annealing temperature of around 650 °C. Evaluation of the Pt–Co/C alloy catalysts for oxygen reduction in half cells employing KOH as the electrolyte and in proton exchange membrane fuel cells indicates that the alloys with the ordered Pt3Co or PtCo type structures have higher catalytic activity with lower polarization losses and higher power densities than Pt or disordered Pt–Co alloys. With the ordered phases, the activity increases with the extent of ordering. The enhanced catalytic activity is explained based on optimal structural and electronic features consisting of optimum number of Pt and Co nearest neighbors, Pt–Pt distance, and d-electron density in Pt.
Article
A straight forward method for immobilizing Pt-Co alloyed nanoparticles onto nitrogen-doped CNx nanotubes is presented. The as-prepared electrocatalysts exhibit good performance for oxygen reduction reaction in acidic medium arising from the high-dispersion and alloying effect of the Pt-Co nanoparticles and the intrinsic catalytic capacity of the CNx nanotubes.
Article
Publisher Summary This chapter reviews the group frequencies in terms of the spectral regions in which they occur. The first part of the chapter outlines an orderly procedure for the initial interpretation of an unknown infrared radiation (IR) spectrum by regions. Then, spectra-structure correlations are shown in a chart form where one can look for the groups that absorb in a given region or the regions where a given group absorbs. One of the useful features of infrared spectroscopy is its ability to give information about mixtures. When more than one component is present, the spectra tend to be additive but not completely so because of possible mutual interaction, such as hydrogen bonding for example. If the main component in the spectrum has been identified, a comparison with a reference spectrum may reveal some extra bands in the sample spectrum not in the reference. The chapter also presents some selected Infrared spectra and Raman spectra and illustrates their functional group frequencies.
Article
Multi walled carbon nanotubes (MWNTs) have been synthesized by chemical vapour deposition technique using AB3 alloy hydride catalyst. Platinum supported MWNTs (Pt/MWNTs) and platinum-tin supported MWNTs (Pt–Sn/MWNTs) electrocatalysts have been prepared by chemical reduction method. MWNTs and electrocatalysts have been characterized by powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), high resolution TEM (HRTEM) and Energy dispersive X-ray analysis (EDAX). The anode and cathode electrodes for DEFC have been fabricated using Pt–Sn/MWNTs and 1:1 Pt/MWNTs + Pt/C electrocatalyst respectively. Performances of Direct Ethanol Fuel Cell (DEFC) with these electrodes have been studied at different temperatures of the membrane electrode assembly at ambient fuel conditions and the results have been discussed. A maximum power density of 38.6 mW/cm2 at a current density of 130mA/cm2 is obtained. A six cell planar Micro Direct Ethanol Fuel Cell (μ-DEFC) stack was also constructed using these electrocatalysts and etched printed circuit boards as anode and cathode current collectors. A maximum power density of 2 mW/cm2 was achieved when the μ-DEFC was operated in air breathing mode at room temperature. This enhancement of the performance may be attributed to dispersion and accessibility of MWNTs support and Pt–Sn in the electrocatalyst mixture for ethanol oxidation reaction.
Article
Nano-sized Pt–Pd/C and Pt–Co/C electrocatalysts have been synthesized and characterized by an alcohol-reduction process using ethylene glycol as the solvent and Vulcan XC-72R as the supporting material. While the Pt–Pd/C electrodes were compared with Pt/C (20wt.% E-TEK) in terms of electrocatalytic activity towards oxidation of H2, CO and H2–CO mixtures, the Pt–Co/C electrodes were evaluated towards oxygen reduction reaction (ORR) and compared with Pt/C (20wt.% E-TEK) and Pt–Co/C (20wt.% E-TEK) and Pt/C (46wt.% TKK) in a single cell. In addition, the Pt–Pd/C and Pt–Co/C electrocatalyst samples were characterized by XRD, XPS, TEM and electroanalytical methods. The TEM images of the carbon supported platinum alloy electrocatalysts show homogenous catalyst distribution with a particle size of about 3–4nm. It was found that while the Pt–Pd/C electrocatalyst has superior CO tolerance compared to commercial catalyst, Pt–Co/C synthesized by polyol method has shown better activity and stability up to 60°C compared to commercial catalysts. Single cell tests using the alloy catalysts coated on Nafion-212 membranes with H2 and O2 gases showed that the fuel cell performance in the activation and the ohmic regions are almost similar comparing conventional electrodes to Pt–Pd anode electrodes. However, conventional electrodes give a better performance in the ohmic region comparing to Pt–Co cathode. It is worth mentioning that these catalysts are less expensive compared to the commercial catalysts if only the platinum contents were considered.
Article
Platinum nanocatalyst on multiwalled carbon nanotubes (MWCNTs) functionalized with citric acid (CA) was synthesized by a two-phase approach to transfer PtCl(6)(2)- from aqueous to organic phase. Pt-thiol ligand-based Pt/MWCNTs were fabricated with the presence of dodecanethiol (DDT). A homogeneous distribution as well as a uniform particle size of Pt particle was achieved by optimizing the CA and DDT contents. Pt/MWCNTs were examined by a high resolution transmission electron microscope for particle size and distribution. The Pt/MWCNT-based electrodes were characterized by electrochemical impedance spectroscopy for cell resistance and cyclic voltammetry (CV) for durability evaluation using humidified H(2) and N(2) gases at 80 degrees C. The single-cell fuel cell performance with 0.2 (anode) and 0.4 mg (cathode) Pt cm(-2) evaluated using Nafion 212 electrolyte showed a power density of about 1520 mW cm(-2) with H(2) and O(2) gases. The electrochemically active surface area, as measured by CV between 0.1 and 1.2 V, showed no degradation up to 1500 cycles for Pt/MWCNTs, showing exceptional durability.
Article
The design of high performance cathode electrocatalysts is essential for polymer–electrolyte fuel cells, which are now attracting enormous interest as a primary power source for zero-emission electric vehicles. We have discovered a significant enhancement of electrocatalytic activity of Pt by alloying with Fe, and found a maximum activity at ca. 50% Fe content, which results in 25 times higher activity than pure Pt activity. It was confirmed experimentally at Pt–Fe bulk alloys that the alloy catalyst surface consists of a pure Pt skin-layer (
Article
Monodispersed, uniformly alloyed Pt3Co alloy nanoparticle electrocatalysts were synthesized via reduction of metallic precursors by sodium borohydride in heptane/polyethylene glycol dodecylether (Brij)/water reverse micelles. These particles were further adsorbed on XC-72R carbon powder, separated from micelles, and characterized using X-ray diffraction (XRD), transmission electronic microscopy (TEM). The electrochemical activity for the oxygen reduction reaction (ORR) was characterized using a Rotating Disk Electrode (RDE) technique. Even though residual surfactants on the metallic nanoparticle reduced the active surface area of the electrocatalytic particles, the catalytic activity of the prepared Pt3Co nanoparticles exhibited higher Pt mass and Pt surface area specific activities compared to pure Pt. The impact of heat treatment on the mean particle size, the electrochemical surface area (ESA), and on the activity was investigated and correlated to the residual surfactant coverage. Intermediate annealing temperatures resulted in larger ESA, despite particle growth pointing to lower surfactant coverage. Higher annealing temperatures caused large particle growth and reduced ESA, yet significant activity gains. A surface segregation mechanism resulting in a catalytically active Pt skin structure is hypothesized.
Article
Multiwalled carbon nanotubes (MWNTs) have been synthesized by the pyrolysis of acetylene using hydrogen decrepitated Mischmetal based AB(3) alloy hydride catalyst. Structural, morphological, and vibrational characterizations have been carried out using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) spectroscopy. Pt-supported MWNTs (Pt/MWNTs) have been prepared by chemical reduction method using functionalized MWNTs. Composites of Pt/MWNTs and Pt/C in different weight proportions have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC) and the performance on the accessibility of Pt electrocatalysts for the oxygen reduction reaction in PEMFC has been systematically studied. The cyclic voltammetric studies of the electrodes have been performed in order to understand the factors influencing the elecetrocatalytic activity and fuel cell performance and the results have been discussed. [DOI: 10.1115/1.3176215]
Article
Electrocatalysts of Pt, PtCo and PtNi powders for the oxygen reduction reaction (ORR) were processed by Mechanical Alloying. Physical characterization was made by X-ray diffraction, scanning electron microscopy and scanning transmission electron microscopy. It was found that milled powders formed agglomerates in the range of 0.2–20μm formed by nanometric size crystallites. The synthesized powders were alloys of PtFe, PtCoFe and PtNiFe due to iron incorporation during the milling process. The binding energies of Pt in the alloys were determined by XPS. Polarization curves were obtained by Rotating Disk Electrode technique in 0.5M H2SO4 to determine the electrocatalytic activity of the mechanically alloyed powders. Tafel curves were plotted and kinetic parameters for the ORR were calculated. The PtFe alloy showed the highest electrocatalytic activity for the ORR. However, the lowest overpotential was found for the PtCoFe alloy and it also showed a higher current exchange density. A linear relationship was found between the Pt-binding energy in the alloys and the overpotential at the same current density independent of the Pt alloy composition.
Article
A highly dispersed platinum catalyst (platinum crystallite size less than 15A) on a conductive carbon support was prepared. These doped carbons were made into Teflon-bonded fuel cell electrodes and the platinum surface area and the dispersed platinum specific activity (i. e. , the activity per unit area of platinum) for oxygen electroreduction in acid electrolyte was determined. The specific activity of the dispersed platinum was found to be approximately twenty times less than that of crystalline platinum black. The lower activity of this catalyst compared with that of platinum black may be due either to the difference in the platinum crystallite sizes, or to the influence of the support on the platinum activity, or to a combination of both these factors.
Article
Monodisperse Pt3Co nanoparticles with size controlled from 3 to 9 nm have been synthesized through an organic solvothermal approach and applied as electrocatalysts for the oxygen reduction reaction. Electrochemical study shows that the Pt3Co nanoparticles are highly active for the oxygen reduction reaction and the activity is size-dependent. The optimal size for maximal mass activity was established to be around 4.5 nm by balancing the electrochemically active surface area and specific activity.
Article
Carbon nanotubes (CNTs) were prepared by ethylene decomposition on an Fe/Al2O3 catalyst in a fluidized bed reactor. Their gross defects at different growth periods are evaluated by using a combination of SEM, TGA and Raman spectroscopy. The initially grown CNTs have a much lower thermal stability and more defects as compared to the fully-grown ones. The difference in the defects of CNTs at different reaction times is attributed to the lift up of CNTs with the gradually crashing texture of catalyst and the increasing volume of CNTs in a limited reactor space.
Article
The activity for the oxygen reduction reaction (ORR) on carbon supported Pt–Ni electrocatalysts prepared by reduction of Pt and Ni precursors with NaHB4 was investigated in sulphuric acid both in the absence and in the presence of methanol and compared with that of a commercial Pt/C electrocatalyst. In methanol-free sulphuric acid solution the Pt70Ni30/C alloy electrocatalyst showed a lower specific activity towards oxygen reduction compared to Pt/C. In O2-free H2SO4 the onset potential for methanol oxidation on Pt70Ni30/C was shifted to more positive potentials, which indicates a lower activity for methanol oxidation than platinum. In the methanol containing electrolyte the higher methanol tolerance of the Pt70Ni30/C electrocatalyst for the ORR was ascribed to the lower activity of the binary electrocatalyst for methanol oxidation, arising from a composition effect.
Article
Pt3Cox/C electrocatalysts for use as cathodes in proton exchange membrane fuel cells are fabricated using various stabilizers to control the different reduction speeds between Pt and Co ions. Four different types of stabilizers—sodium acetate, oleylamine, tetraoctylammonium bromide (TOAB), and hexadecyltrimethylammonium bromide (CTAB)—differing in molecular structures and ionic states are tested. Primarily, Pt3Cox/C alloy nanoparticles are synthesized with 0.6 < x < 0.8 after heat treatment to remove the residual stabilizers. A significant improvement in the activity for oxygen reduction reaction is observed in the case of TOAB- and CTAB-mediated Pt3Cox/C catalysts. In particular, CTAB-mediated catalysts exhibit the best activity, which is about 2-times higher mass activity than commercial Pt/C catalyst. The higher mass activity is believed to result from not only the alloying effects with small atomic size Co but also better dispersion and smaller particle size after heat treatment at relatively low temperature.Highlights► Pt3Cox/C as an oxygen reduction catalyst for proton exchange membrane fuel cell. ► Stabilizer CTAB enables Pt3Co0.76/C alloy synthesis with very uniform size of 2.8 nm. ► Pt3Co0.76/C catalyst has superior oxygen reduction mass activity than commercial one by 2-times.
Article
A series of Platinum–Cobalt bimetallic catalyst supported on carbon (Vulcan XC-72R) were prepared by sequential deposition using an organic salt of cobalt for use as cathode in Phosphoric Acid Fuel Cell (PAFC). The atomic percent of non noble metal with respect to Pt in the alloy was varied from 5 to 100 and the composition of alloy catalyst was confirmed by chemical analysis and SEM – EDS spectra. Electrochemical performance of the catalyst was studied in half cell and unit cells. The exchange current densities for oxygen reduction reaction (ORR), for alloys with different concentration of non noble metal was evaluated from current-potential curves, which showed values close to 10−5 A/cm2 and the mass activity and specific activity, for the (ORR), were found to be higher for Pt–Co/C compared to that of 10% Pt/C catalysts. The catalyst was tested for its stability in unit cell for a period of 500 h using air as an oxidant which showed higher performance for Pt–Co/C containing 0.5 at% Co. The nature of hydrogen adsorption and dominant crystal plane was also evaluated from cyclic voltammetry. XPS analysis was carried out to determine the surface species present. Results show significant enhancement of electro catalytic activity of Pt by alloying with Co, with maximum activity at ca 0.5 at% Co.
Article
Recently one-dimensonal (1-D) Pt nanostructures have shown greatly enhanced intrinsic oxygen reduction reaction (ORR) activity (ORR kinetic current normalized to Pt surface area) and/or improved durability relative to conventional supported Pt catalysts. In this study, we report a simple synthetic route to create Pt-covered multiwall carbon nanotubes (Pt NPs/MWNTs) as promising 1-D Pt nanostructured catalysts for ORR in proton exchange membrane fuel cells (PEMFCs). The average ORR intrinsic activity of Pt NPs/MWNTs is 0.95 mA/cm2 Pt at 0.9 ViR-corrected versus reversible hydrogen electrode (RHE), 3-fold higher than a commercial catalyst −46 wt % Pt/C (Tanaka Kikinzoku Kogyo) in 0.1 M HClO4 at room temperature. More significantly, the mass activity of Pt NPs/MWNTs measured (0.48 A/mgPt at 0.9 ViR-corrected vs RHE) is higher than other 1-D nanostructured catalysts and TKK catalysts. The enhanced intrinsic activity of 1-D Pt NPs/MWNTs could be attributed to the weak chemical adsorption energy of OHads-species on the surface Pt NPs covering MWNTs.Keywords: platinum; functionalized multiwall carbon nanotubes; electrocatalysis; oxygen reduction reaction; fuel cells; nanostructure
Article
A sonochemical process was developed to treat carbon nanotubes in nitric and sulfuric acids to create surface functional groups for metal nanoparticle deposition. Carbon nanotubes treated in the sonochemical process are shown to lead to the deposition of uniformly dispersed high loading Pt nanoparticles, which have not been achieved with carbon nanotubes treated in reflux processes. Pt nanoparticles of a size less than 5 nm and loading up to 30 wt % with little aggregation were synthesized on the sonochemically treated carbon nanotubes. Cyclic voltammetry measurements in 1.0 M H2SO4 showed that the Pt nanoparticles on carbon nanotubes are more than 100% active in the electrochemical adsorption and desorption of hydrogen than the Pt nanoparticles supported on carbon black. This enhancement of electrochemical activity is attributed to the unique structures of carbon nanotubes and the interactions between the Pt nanoparticles and the carbon nanotube support. The ability to synthesize high loading Pt on carbon nanotubes using the sonochemical technique makes it possible to prepare high loading catalysts for the cathode of polymer electrolyte membrane (PEM) fuel cells.
Article
Multiwalled carbon nanotube-supported Pt (Pt/MWNT) nanocomposites were prepared by both the aqueous solution reduction of a Pt salt (HCHO reduction) and the reduction of a Pt ion salt in ethylene glycol solution. For comparison, a Pt/XC-72 nanocomposite was also prepared by the EG method. The Pt/MWNT catalyst prepared by the EG method has a high and homogeneous dispersion of spherical Pt metal particles with a narrow particle-size distribution. TEM images show that the Pt particle size is in the range of 2−5 nm with a peak at 2.6 nm, which is consistent with 2.5 nm obtained from the XRD broadening calculation. Surface chemical modifications of MWNTs and water content in EG solvent are found to be the key factors in depositing Pt particles on MWNTs. In the case of the direct methanol fuel cell (DMFC) test, the Pt/MWNT catalyst prepared by EG reduction is slightly superior to the catalyst prepared by aqueous reduction and displays significantly higher performance than the Pt/XC-72 catalyst. These differences in catalytic performance between the MWNT-supported or the carbon black XC-72-supported catalysts are attributed to a greater dispersion of the supported Pt particles when the EG method is used, in contrast to aqueous HCHO reduction and to possible unique structural and higher electrical properties when contrasting MWNTs to carbon black XC-72 as a support.
Article
We describe a comparative study of the oxygen reduction reaction on two carbon-supported Pt-based alloy catalysts in aqueous acidic electrolyte at low temperature. Both alloys have the bulk compositions of 50 and 75 at. % Pt, with the alloying elements being Ni and Co. Comparison is made to a pure Pt catalyst on the same carbon support, Vulcan XC-72, having the same metal loading (20 wt %) and nominally the same particle size (4 ± 2 nm). High-resolution electron microscopy was used to determine the size and shape of the particles as well as the particle size distribution on all catalysts. Electrochemical measurements were performed using the thin-film rotating ring−disk electrode method in 0.1 M HClO4 at 20−60 °C. Hydrogen adsorption pseudocapacitance was used to determine the number of Pt surface atoms and to estimate the surface composition of the alloy catalysts. Kinetic analysis in comparison to pure Pt revealed a small activity enhancement (per Pt surface atom) of ca. 1.5 for the 25 at. % Ni and Co catalysts, and a more significant enhancement of a factor of 2−3 for the 50 at. % Co. The 50 at. % Ni catalyst was less active than the Pt standard and unstable at oxygen electrode potentials. Ring-current collection measurements for peroxide indicated no significant differences between the Pt−Co catalysts or the 25 at. % Ni catalyst and pure Pt, while the 50 at. % Ni catalyst had a higher peroxide yield. Together with the observed Tafel slopes and activation energies, it was concluded that the kinetic enhancement is contained in the preexponential factor of the conventional transition state theory rate expression. It is, however, not clear why the alloying with Ni or Co produces this change in the preexponential factor.
Article
This paper presents a novel, cost-effective and single-step technique for the synthesis of single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs) and magnetic metal-filled MWNTs using a fixed bed reaction thermal chemical vapour deposition (CVD) using alloy hydride catalyst. The single-step method involves the pyrolysis of methane at suitable temperatures over fine powders of certain Mischmetal-based AB3 alloy hydride catalysts, prepared through the hydrogen decrepitation technique. These carbon nanostructures have been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray analysis (EDAX), thermo-gravimetric analysis (TGA) and Raman spectroscopy. The magnetic properties of these metal-filled MWNTs have been studied by vibrating sample magnetometry, and the results are discussed.
Article
Graphene-supported Pt and Pt3M (M = Co and Cr) alloy nanoparticles are prepared by ethylene glycol reduction method and characterized with X-ray diffraction and transmission electron microscopy. X-ray diffraction depicted the face-centered cubic structure of Pt in the prepared materials. Electron microscopic images show the high dispersion of metallic nanoparticles on graphene sheets. Electrocatalytic activity and stability of the materials is investigated by rotating-disk electrode voltammetry. Oxygen reduction activity of the Pt3M/graphene is found to be 3–4 times higher than that of Pt/graphene. In addition, Pt3M/graphene electrodes exhibited overpotential 45–70 mV lower than that of Pt/graphene. The high catalytic performance of Pt3M alloys is ascribed to the inhibition of formation of (hydr) oxy species on Pt surface by the alloying elements. The fuel cell performance of the catalysts is tested at 353 K and 1 atm. Maximum power densities of 790, 875, and 985 mW/cm2 are observed with graphene-supported Pt, Pt3Co, and Pt3Cr cathodes, respectively. The enhanced electrocatalytic performance of the Pt3M/graphene (M = Co and Cr) compared to that of Pt/graphene makes them a viable alternative to the extant cathodes for energy conversion device applications.Graphical abstractResearch highlights► Fabrication of layered graphene sheets decorated Pt and Pt3 M (M = Co and Cr) nanoparticles by a simple chemical reduction technique. ► Enhanced activity for oxygen reduction reaction on graphene-supported Pt3Co and Pt3Cr alloy nanoparticles. ► High durability of graphene-supported Pt3Co and Pt3Cr alloy nanoparticles. ► Graphene-supported Pt3Co and Pt3Cr electrodes are expected to deliver high power density in energy conversion devices.
Article
Using a combination of density functional theory calculations and X-ray emission and absorption spectroscopy for nitrogen on Cu and Ni surfaces, a detailed picture is given of the chemisorption bond. It is suggested that the adsorption bond strength and hence the activity of transition metal surfaces as catalysts for chemical reactions can be related to certain characteristics of the surface electronic structure.