Article

Fabrication of nanoporous palladium by dealloying and its thermal coarsening

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  • Graduate School of Energy Science, Kyoto University
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Abstract

Nanoporous Pd with an average ligament size of 5–20 nm was fabricated by dealloying Pd0.2Co0.8 alloy. An electrochemical potential of +0.5 V (vs saturated calomel electrode) on the initial alloy led to Co dissolution in H2SO4 aqueous solution. However, unlike nanoporous Au fabrication from Au–Ag alloy, the free corrosion of Pd0.2Co0.8 alloy in H2SO4 did not result in a nanoporous structure; the electrochemical potential must have been applied to generate a nanoporous structure from the Pd–Co alloy. Thermal coarsening of nanoporous Pd is also investigated. Heating nanoporous Pd increased the ligament size up to 650 nm. It is suggested that a solid state process like recrystallization, rather than melting, is responsible for the thermal coarsening of nanoporous Pd.

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... To date, a vast experimental material has been accumulated on the production of np-Pd by this method in aqueous solutions. 4,9,12,15,[21][22][23][24][25][26][27][28] As "sacrificial" metals in alloys with palladium Co, Al, Ni, Cu were used. The concentration of these metals in the alloy varied from 70 to 88 mol%. ...
... In that range it was possible to achieve almost complete removal of the electroactive component of the alloy without destroying the sample. Phase composition was represented by homogeneous solid solutions of palladium with cobalt 12,15,21,24,25,28 and copper, 22,23 single-and multiphase alloys with aluminum, 27 intermetallic Ni 80 Pd 20 . In addition, electrochemical dealloying was applied to the quasi-crystalline alloy Al 70 Pd 17 Fe 13 4 and metallic glasses Pd 30 Ni 50 P 20 9 and Co 75 Pd 20 Si 5 . ...
... Electrochemical dealloying was carried out in aqueous solutions of sulfuric acid 9,12,15,[21][22][23][24][25][26]28 and sodium chloride. 4,27 As a result of selective anodic dissolution of cobalt an almost pure palladium was obtained 24,25 or Pd containing less than 2 mol% of sacrificial metal. ...
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The electrochemical dealloying of Ag40Pd60 alloy in (LiCl)57(CsCl)26(KCl)17 melt with the addition of 3 mol% silver chloride has been studied. Selective anodic dissolution of the alloy was carried out both in the potentiostatic and in galvanostatic regimes at temperatures ranging from 300 to 500 °C. The obtained voltammetry characteristics of the initial alloy, chronoamperograms and chronopotentiogram during the dealloying are presented and discussed. At a temperature near 500 °C, the second maximum was observed in the chronoamperograms at two different values of the set potential. The unusual shape of the current curves is due to the superposition of several diffusion processes, which intensities in this case are greater than at lower temperatures. Bi-continuous structures of practically pure palladium with pores and ligaments of sizes ranging from a few to tens of micrometers were obtained in the potentiostatic regime. As the dealloying temperature increased, the sizes of pores and ligaments increased naturally. The same effect was also caused by the increase in applied potential. In the galvanostatic mode similar metallic structures were obtained, but the residual silver content reached 5%, and, in addition, the effects of samples sintering appeared.
... Moreover, it is worth noting Ligament size (nm) Figure 6: Relationship between annealing temperature and ligament size of annealed BHPPd materials. Results of nanoporous Pd (annealed at Ar atmosphere) [17], nanoporous Au (annealed at air atmosphere) [18], and nanoporous Ag (annealed at Ar atmosphere and vacuum) [19] were also shown for comparison. that ligament/pore of BHPPd slightly coarsens even after being annealed at 1073 K for 30 min, suggesting high stability property. ...
... Hakamada and Mabuchi reported that both pore size and ligament size of nanoporous Pd, prepared by electrochemical dealloying PdCo alloy, were significantly increased after annealing treatment. The average ligament size of nanoporous Pd after being annealed at 773 K is 180 nm [17]. These phenomena were often called thermal coarsening, as observed in nanoporous materials such as Au [22]. ...
... Relationship between annealing temperature and ligament size of annealed BHPPd materials is shown in Figure 6. Results of other reports were also shown for comparison [17][18][19]. Nanoporous Pd (annealed at Ar atmosphere) [17] and nanoporous Au (annealed at air atmosphere) [18] were unstable at high temperature, whose ligaments coarsen remarkably as increment of annealing temperature. As a contrast, nanoporous Ag (annealed at Ar atmosphere and vacuum, resp.) ...
Article
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We present a facile strategy to synthesize bulk hierarchical porous Pd materials (BHPPd) with pores ranging from a few nanometers to tens of micrometers through chemical dealloying of porous PdAl intermetallics. Owing to the small surface diffusivities of Pd atoms, the pore/ligament size of BHPPd did not coarsen remarkably as the concentration of HCl aqueous solution increases. Thermal stability properties of BHPPd materials at different temperature ranging from 673 to 1073 K were evaluated. BHPPd materials show superior thermal stability, whose bicontinuous interpenetrating ligament-channel structure can be maintained even after being annealed at 1073 K for 30 min. Such properties can be attributed to less defects and less-noble metal residues. Moreover, compression properties of BHPPd materials were also investigated.
... The investigation of nanoporous Pd were mainly focused on the dealloying of different Pd-containing materials such as single phase solid solution [12,13], metallic glass [14,15], intermetallics [3,16,17]. Considering the rich supply of Al, PdAl alloy was usually chosen as precursor for porous Pd [3,16,17]. ...
... Nanoporous Pd have been extensively studied due to their potential applications in the field of hydrogen isotopes storage [1,2], fuel cell [3][4][5] and sensor [6,7], etc. Considerable efforts have been made to develop the methods to the dealloying behavior of PdAl is indistinct, and the activation energy and diffusion constant of Pd atoms in the dealloying process are poorly known. Moreover, the high temperature utility of nanoporous metal can be degraded by its tendency to coarsen [12,21]. For high-temperature application, thermal coarsening is undesirable. ...
... As shown in Fig. 11, average ligament diameters of BHNPP heated at 1073 K was ~30 nm, which gave a very small change in ligament size. Thermal coarsening of nanoporous Pd was firstly report by Masataka et al. [12]. The pore and ligament sizes of nanoporous Pd were significantly increased by heating at 773 and 973 K. ...
Article
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In the present study, bulk hierarchical nanoporous Pd materials (BHNPP) were successfully prepared. Results show that the microstructure of nanoporous materials can be facile tailored by optimizing the dealloying temperature and the concentration of HCl solutions. The formation mechanisms of BHNPP materials were discussed, which reveal that the nucleation and growth of Pd crystalline is essential to form nanoporous Pd. Surface diffusivities, activation energies and diffusion constants at the bimodal porous structure and the monolithic porous structure of Pd atoms were also evaluated. Furthermore, BHNPP show favorable thermal stability, ligament diameters of which is ~30 nm even after heated at 1073 K for 1 h.
... Electrochemical dealloying was performed according to the procedure proposed by Hakamada et al. [28]. The Co 75 Pd 25 samples, which were contacted with a Au-wire, acted as working electrode. ...
... The typical effect of thermal annealing on nanoporous materials prepared by electrochemical dealloying is the coarsening of the structure. For example an increase of the ligament size was reported for np Au [30][31][32][33][34], np Pt [35], np Pd [28,[36][37][38] and np Ni [39,40]. The decrease of the specific surface area with (see Table 1) confirms that such an increase of the ligament size occurs for the investigated np Pd(Co) samples as well. ...
Article
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Nanoporous palladium samples containing superparamagnetic Co-rich clusters were prepared by electrochemical dealloying and the magnetic properties were subsequently varied by thermal annealing at different temperatures. It is shown that in this way porous magnetic nanomaterials exhibiting various magnetic characteristics can be obtained. The as-dealloyed, unannealed sample is ferromagnetic at 4.2 K and superparamagnetic at 300 K, with a blocking temperature TB of 100 K. The observed general decrease of the magnetization with increased annealing temperature is explained by the redistribution of Co from the Co-rich superparamagnetic clusters into the Pd matrix, leading to a shrinkage of the clusters and the formation of a diluted Co-Pd alloy phase. As a consequence of the smaller magnetic cluster size a down-shift of TB occurs for annealing temperatures of 373 K and 573 K. After annealing at 773 K the stronger dissolution of Co from the clusters into the Pd-matrix reduces TB further down to 35 K. Additionally, a second blocked magnetic phase with much higher TB emerges, which leads to ferromagnetic behavior at room temperature. The occurrence of this phase is attributed to the formation of larger magnetic entities consisting of Co-rich clusters lying close together and a Co-Pd alloy phase with relatively high Co concentration in between these clusters. After high temperature annealing at 973 K a weakly ferromagnetic phase is obtained at 4.2 K and at 300 K, which can be explained by the nearly completed dissolution of the Co in the Pd matrix.
... 5 The selective anodic dissolution in molten salts is a promising method for obtaining a variety of nanoporous materials which can be in demand in hot fields such as biochemistry, medicine, nuclear energy, etc. 6-10 Palladium alloys with industrial metals such as Fe, Ni, Co, Cu, Al and Zn have been used to fabricate nanoporous palladium within aqueous electro-chemical dealloying processes. [11][12][13][14][15] It has been shown that the morphology of nanoporous palladium is sensitive to the subsequent heat treatment regime. Enlargement of pores, coalescence of ligaments and scaling of the porous material have been observed. ...
... This is closely related to the temperature at the onset of palladium recrystallization, which is approximately 450°C. 12 It is certainly of interest to expand this line of investigation on the high-temperature electrochemical dealloying of the palladium containing metallic phases. The use of molten salts as electrolytes in high temperature EDL can provide simultaneous heat treatment of the alloy. ...
Article
A study of the high-temperature electrochemical selective dissolution of PdIn intermetallics in molten mixtures of alkali chlorides with the formation of nanoporous structures has been carried out to obtain a coherent structure consisting of Pd2In and Pd3In intermetallics. The smallest pore size (approximately 100 nanometers) with a bi-continuous structure of Pd2In-Pd3In is obtained from the PdIn intermetallic phase at a temperature of 450 °C and a current density of 50 mA cm-2 in a molten LiCl-KCl eutectic. It has been shown that the temperature of the anodic dissolution process is the most important factor in controlling the pore size and structural morphology. The morphology of pores and ligaments in the sample at 600 °C is a 3D hierarchy with pore sizes from several hundred nanometers to a micron-scale but with the same Pd2In-Pd3In (2 : 1) composition.
... Stable microstructures will be achieved if the dissolution rate and the diffusion rate are well balanced [12,32]. On the other hand, a post-fabrication heat treatment can lead to coarsening of the microstructures to obtain the desired ligament and pore sizes [33][34][35]. However, the underlying coarsening mechanisms are still under debated [30,32,[36][37][38][39][40][41]51]. ...
... Below 300 • C, no apparent coarsening of the nanoporous structure happens, while above 300 • C, d l rapidly increases as T ann increases. The observed coarsening behavior of nanoporous Pd is similar to that reported for nanoporous Au where a significant coarsening of ligaments occurs at T ann > 200 • C [34,44]. To further investigate kinetics of microstructure coarsening, the nanoporous Pd samples were respectively annealed at 200 • C, 400 • C and 600 • C for various time durations. ...
Article
Microstructures of nanoporous Pd are essentially important for its physical and chemical properties. In this work, we show that the microstructures of nanoporous Pd can be tuned by adjusting compositions of the precursor alloys, and dealloying and heat treatment parameters. Both the ligament and pore sizes decrease with increasing the electrochemical potential upon dealloying and the concentration of noble component in the precursor alloys. Heat treatment causes coarsening of the nanoporous structure. Above a critical temperature, the nanoporous structures are subjected to significant coarsening. Below the critical temperature, surface diffusion is believed to dominate the coarsening process. Above the critical temperature, the nanoporous structure coarsens remarkably at a rather high rate, which is ascribed to a multiple-mechanism controlled process.
... Lately, dealloyed nanoporous palladium (npPd) structures [16] have received attention in the literature as electrochemical actuator materials [17][18][19][20]. Due to the ability of palladium to host hydrogen atoms in its crystal lattice, such actuators show exceptionally strong, reversible expansion. ...
... KCl) electrode (Metrohm) served as counter and reference electrode, respectively. Electrochemical dealloying was conducted in 0.1 M sulfuric acid solution at a potential of +0.55 V (vs Ag/AgCl), a method that is commonly used to achieve homogeneous nanoporous palladium structures [16,17]. Dealloying was stopped at currents below 0.1 mA. ...
Article
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The mechanical strain response of nanoporous palladium (npPd) upon electrochemical hydrogenation using an in situ dilatometric technique is investigated. NpPd with an average ligament diameter of approximately 20 nm is produced via electrochemical dealloying. A hydrogen-induced phase transition from PdHβ to PdHα is found to enable internal-stress plasticity (or transformationmismatch plasticity) in nanoporous palladium, which leads to exceptionally high strains without fracture as a result of external forces. The high surface stress in the nanoporous structure in combination with the internal-stress plasticity mechanism leads to a peculiar strain response upon hydrogen sorption and desorption. Critical potentials for the formation of PdHα and PdHβ in npPd are determined. The theoretical concepts to assess the plastic strain response of nanoporous samples are elucidated, taking into account characteristics of structure and deformation mechanism.
... Hence, Pd-based alloys are interesting model systems to study and compare with the other systems. They have however received much less attention [20][21][22][23][24][25][26][27] even though palladium is a technically important element. Palladium is for example used for gas sensing applications, hydrogen storage, or for catalysis. ...
Article
Nanoporous metallic structures formed from dealloying have recently attracted considerable interest due to a wide range of potential applications in areas such as catalysis, actuators, biomedical sensors and fuel cell electrodes. The Cu-Pd system is interesting as a model system for corrosion as well as a potential catalyst material. We report a combined in-situ X-ray diffraction (XRD) and ex-situ atomic force microscopy (AFM) study of the initial structural evolution during the selective dissolution of Cu from Cu 3 Pd (111) and Cu 3 Pd (100). The experiments were performed under potential control in 0.1 M H 2 SO 4 solution. Below the critical potential, no distinct diffraction signal is evidenced by in-situ XRD but AFM reveals the existence of islands on the surfaces. At the critical potential, on both single crystal surfaces the formation of an epitaxial Pd layer exhibiting substrate orientation is evidenced by XRD. Ex-situ AFM imaging clearly showed at comparable stages the formation of larger nanoscale islands. We further compare and contrast the behavior of the dealloyed Cu-Pd surfaces with that of Cu-Au alloys. Dealloying is a common corrosion process during which one or more of the most reactive components of an alloy are selectively dissolved into the electrolyte. This selective dissolution can be realized electrochemically under applied voltage or at open circuit potential by chemical dissolution in an oxidizing corrosive environment. The less noble component is thus leached out of the system. The more noble component is accumulated on the surface and undergoes a self-organization process to form a passive-like protective layer below the so-called critical potential E c and nanoporous structures above E c. In general, the noble metal alloys exhibit a low current region below, and a steep current rise beyond E c where bulk dissolution takes place. This behavior is similar to passivity 1 but with a purely metallic surface state. Both stages are essentially controlled through surface diffusion and diffusion in the surface-near region of the topmost atomic layers. Binary noble metal alloys, including the Cu-Au, Ag-Au, Cu-Pt and Cu-Pd systems, serve as the most widely used model systems for investigating dealloying in the context of corrosion studies. 2-8 Deal-loying has also attracted considerable interest as a nano-machining tool to produce three-dimensional nanoporous structures with potential applications as sensors, 9 actuators, 10 supercapacitors, 11 electro-catalysis 12-15 or for catalysis of CO or methanol oxidation. 16-19 In particular Au-alloys have been widely addressed but also an increasing number of studies on different alloy systems has been performed recently. The elements in the Cu-Pd system possess a difference in lattice parameter of 0.028 nm which is similar to Cu-Pt (with a lattice parameter difference of 0.031 nm) and in between Cu-Au (with a lattice parameter difference of 0.047 nm) and Ag-Au (with a lattice parameter difference of 0.001 nm). Hence, Cu and Au possess a large difference in their respective lattice parameters of about 13%, while Ag and Au do not significantly differ. The surface mobility of Au in electrolytes is also higher than for Pd. Hence, Pd-based alloys are interesting model systems to study and compare with the other systems. They have however received much less attention 20-27 even though palladium is a technically important element. Palladium is for example used for gas sensing applications, hydrogen storage, or for catalysis. Palladium-based catalysts, including some reports on Raney-type Pd, 28-31 have been extensively used in several technologically important areas including petroleum refining and in automotive emission control. Their excellent performance in the combustion of hydrocarbons, thermal stability and the low volatility of Palladium particles make them the most widely reported reference catalyst for methane combustion. 32 Dealloying of Pd-alloys has thus also technical implications beyond fundamental corrosion research. Moreover, further alloying offers more options for structural and morphology control 33 and for target chemical reactivity in future. 34
... ΔHmix, A-C > 0, then by temperature control, only B elements dissolve out of the precursor A-B alloy into C melt. Therefore, A elements are removed out of C melt and self-organizes into a porous structure due to surface diffusion as for electrochemical dealloying method [20]. The LMD scheme with triangle relationship of the mixing enthalpies among A, B, and C elements is schematically shown in Figure 1. ...
Article
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The paper provides a short review of liquid metal dealloying (LMD) combined with subsequent polymer impregnation as promising technology to synthesize low modulus metal-polymer composites for biomedical applications. The introduction presents the key problems and relevance of the development and synthesis of such materials. The “Theoretical basis” chapter defines the LMD method and the main steps required to activate this process. The fundamental principles of thermodynamics, kinetics and morphology evolution of LMD process are presented here. Due to their favorable mechanical characteristics in the context of biomedical applications, the so-called biocompatible high-entropy alloys (bioHEAs) are proposed as promising candidates for LMD treatment combined with polymer impregnation and, accordingly, the synthesis of novel metal-polymer bioHEA materials.
... Most of the work on dealloying has been done on a bi-component, single-phase, solid solution alloys, among which the most common are the Cu-Au [3], Au-Ag [4,5], Cu-Mn [6], and more, in general, the Al x M 100− x alloys, where M=(Au, Pd, Pt, Ag and Cu) [7]. In this perspective, several binary systems have been considered for the production of porous palladium, such as AlPd [7], PdCu [8,9], NiPd [10], PdCo [11][12][13]. When it comes to the production of nanoporous binary alloys, the choice often falls on ternary alloy as starting material, such as FeAlPd [14], AlPdNi [15], AuPdMg [16], PdAuZn [17] and PdAuNi [18]. ...
Article
Nanoporous materials represent a unique class of materials, given to their unforeseen magnetic, mechanical, optical and catalytic properties arising from their network of pores and ligaments. Here a polycrystalline thin film of FePd is considered as a starting system, in which the porosity is induced via dealloying. This process determines the removal of iron from the alloy and the diffusion of palladium on the surface, which in turn influences the evolution of the material’s composition, magnetic properties and optical properties. In addition, from the magnetic point of view, the material acquires a more isotropic behaviour while the magnetic moment decreases due to the removal of iron. In the same way, there is an improvement of the surface enhanced Raman scattering as the dealloying proceeds, due to the formation of clusters of palladium on the surface. This mixture of optical and magnetic properties, combined with its high corriosn resistance and biocompatibility, gives the system a strong multifunctional connotation, paving the way for new applications, ranging from magnetic trapping to detection of low concentration of molecules.
... It is well-known that the freshly dealloyed samples own nonequilibrium structures containing lots of lattice defects, and the ligament size of nanoporous metal will increase after undergoing the high temperature annealing because of the surface diffusion [51]. The atoms rearrange and recrystallize through a solid state process to form new structures during the annealing process [52]. There are nearly all surfaces of the fresh dealloyed NP-Pd RT sample because of the very thin ligament size at ca. 5 nm. ...
Article
Herein, we present hydrogen isotope storage properties of the free-standing monolithic nanoporous palladium (NP–Pd) with different microstructure feature sizes. The NP-Pd samples fabricated by dealloying from Pd–Al alloy and the samples possess high surface area with all of the open pores and ligaments both at nanoscale, which provide the large quantities of reaction sites. The NP-Pd exhibits efficient hydrogen (H2) separation property from deuterium (D2) with distinguishable absorbing and desorbing plateau pressures. The samples own high and reversible H2 and D2 storage capacities with the absorption values up to 0.61 and 0.595 at room temperature. The hydrogen isotope storage capacities increase with the ligament sizes of the NP-Pd samples, which have been high temperature annealed with the larger ligament size more than 10 nm. While for the fresh dealloyed NP-Pd samples with rough surface and ligament size much smaller than 10 nm, the capacity does not follow this behavior. Therefore, a theoretical model based on the existence of the different storage sites at subsurface and interior region is established, which can be used to predict the hydrogen absorption capacity of nanoporous Pd with different structure size. This work reveals both fundamental insights and practical guidance for nanoporous materials design and fabrication, which can be applied in hydrogen isotope separation and storage applications in green energy fields.
... For example, silver can be selectively dissolved from Ag-rich Ag-Au alloys to form nanoporous Au because Ag is much more easily oxidized than Au. Other examples of nanoporous materials made by electrochemical dealloying include nanoporous precious metals, such as Pt [11], Pd [12] and Ag [8], and other relatively noble metals, such as Cu [7,13] and Ni [14]. The underlying kinetics of electrochemical dealloying were not fully elucidated until 2001 when Erlebacher et al. published a new model for porosity evolution that successfully predicted the characteristic length scale, the average distance between ligaments, of the nanoporous structure [6]. ...
Article
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The physical architecture of materials plays an integral role in determining material properties and functionality. While many processing techniques now exist for fabricating parts of any shape or size, a couple of techniques have emerged as facile and effective methods for creating unique structures: dealloying and additive manufacturing. This review discusses progress and challenges in the integration of dealloying techniques with the additive manufacturing (AM) platform to take advantage of the material processing capabilities established by each field. These methods are uniquely complementary: not only can we use AM to make nanoporous metals of complex, customized shapes—for instance, with applications in biomedical implants and microfluidics—but dealloying can occur simultaneously during AM to produce unique composite materials with nanoscale features of two interpenetrating phases. We discuss the experimental challenges of implementing these processing methods and how future efforts could be directed to address these difficulties. Our premise is that combining these synergistic techniques offers both new avenues for creating 3D functional materials and new functional materials that cannot be synthesized any other way. Dealloying and AM will continue to grow both independently and together as the materials community realizes the potential of this compelling combination.
... a The photograph of dealloyed samples. SEM images of b a dealloyed sample, c the one that has been solidified by cooling in liquid N 2 , and d porous Pb prepared by etching Ga from Pb/Ga composites shown in ac. e Ligament sizes plotted as a function of homologous temperature, T H = T dealloy /T M , for porous materials prepared by electrochemical dealloying (Au [38], Pt [39], Cu [40], Pd [41], Ag [42],Pb [43], Sn [43], Cd [43], Bi [43], Ni [44], Rh [45], Ru [46], Ir [47] and Al [48]) and liquid meal dealloying (TiFe [17], TiNb [17], Ti [18], Fe [19], Cr [19], Ta [25], Nb [28], Si [22], Ni [49], TiHf [50], TiZr [51], and TiVNbMoTa HEA [52]). For a fair comparison, only relatively stabilized structure sizes are included (with dealloying time of order 10 3 s or even beyond, for both types of dealloying). ...
Article
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In liquid metal dealloying, it is assumed that the corrosion product (dealloyed porous solids) is wetted by the liquid metal; otherwise, the dealloying may be halted due to liquid metal expulsion. Here, we report the first observation of liquid metal expulsion in liquid metal dealloying—liquid Ga rushes out of porous C when the dealloying of Mn–C alloy in liquid Ga is complete. On the contrary, similar to all previous reports, liquid Ga is trapped in porous Pb when In–Pb is dealloyed in liquid Ga. It suggests that liquid metal dealloying can proceed although the corrosion product is repelled by the liquid metal. Our study also reveals that the wettability and solid/liquid interface significantly influence the morphology of dealloyed porous structure, which has been largely unexplored in dealloying.
... These porous structures can be obtained from various methods. Eletrochemical dealloying enables to produce very fine nanoporous structures but is limited to noble metals such as gold, palladium or copper [1,[9][10][11]. Recently, this limitation has been overcome with the development of liquid metal dealloying, that consists in using a molten metal to selectively dissolve one component out of a binary alloy [12]. This processing technique presents the advantage of being applicable to a wide range of metals including titanium [13], iron [14], niobium [15], and tantalum [16,17], or semiconductors such as silicon [18]. ...
Article
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Nano and microporous connected structures have attracted increasing attention in the past decades due to their high surface area, presenting interesting properties for a number of applications. These structures generally coarsen by surface diffusion, leading to an enlargement of the structure characteristic length scale. We propose to study this coarsening behavior using a phase-field model for surface diffusion. In addition to reproducing the expected scaling law, our simulations enable to investigate precisely the evolution of the topological and morphological characteristics along the coarsening process. In particular, we show that after a transient regime, the coarsening is self-similar as exhibited by the evolution of both morphological and topological features. In addition, the influence of surface anisotropy is discussed and comparisons with experimental tomographic observations are presented.
... For instance, a large surface to volume ratio of nanoporous palladium has been utilized in the electrocatalytic hydrogenolysis of chlorinated organic compounds [4]. A number of groups have shown that nanoporous palladium can be produced using a variety of dealloying processes [5,6]. The evolution of the porous structure during dealloying is dominated by both dissolution of the less noble component and surface diffusion of the more noble component. ...
... In this section, we demonstrate the fabrication of hierarchical nanoporous Al with ultrafine ligament/pore structures using a novel air-free electrolytic dealloying route in non-aqueous electrolytes. 37 Although a wide range of nanoporous metals [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] and nanoporous metalloids [54][55][56][57] have been fabricated using the conventional chemical and electrolytic dealloying route in "aqueous" electrolytes, these aqueous electrolytes are not suitable for the fabrication reactive nanoporous metals, 22 such as nanoporous Al, because ionic species such as H + and OHpresent in aqueous electrolytes will spontaneously react with Al. In a first attempt to overcome this limitation, Detsi and Tolbert demonstrated the fabrication of ultrafine nanoporous Al with ligament size in the range of ~10 nm by galvanic replacement in non-aqueous electrolytes. ...
Article
There are still many scientific and engineering challenges that need to be addressed before a true sustainable hydrogen economy can be realized. Three of these challenges include sustainable hydrogen generation without CO2 emissions, effective storage of this hydrogen for specific applications, and expanding the limited existing hydrogen infrastructure. Here we demonstrate: (i) The fabrication of hierarchical bulk nanoporous aluminum with the coexistence of macroscopic and mesoscopic ligament/pore structures, with the mesoscopic ligaments in the range of 10-20 nm; (ii) The use of this aluminum to produce hydrogen on-site with a yield of ~52-90 % by hydrolysis with “pure” water, without incorporation of any catalyst or reaction promoter in the aluminum-water system; and (iii) The combustion of this aluminum in air under ambient conditions, which implies that this material could be attractive as a combustion fuel catalyst, e.g., to enhance the ignition and combustion of solid propellants
... On the Bpseudo This phenomenon corresponds to a dealloying of the starting CoSb 3 intermetallic phase. Numerous examples of dealloying can be found in the recent literature, leading most of the time to the formation of a nanostructured metallic network [22][23][24], as a consequence of the selective dissolution of one element. But few references deal with the formation of simple oxide on alloys by dealloying under the effect of anodic polarization [25,26]. ...
Article
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The electrochemical behavior of pure Co, pure Sb, and CoSb3 has been investigated over a large anodic potential range (0 to 40 V) in two acids, i.e., oxalic acid or sulfuric acid at different concentrations (0.01 to 1 M). Potentiodynamic polarizations performed on CoSb3 plates reveal the possible formation of a passive layer between 1 and 3 V (vs SCE), on a passivation plateau. The oxidation of CoSb3 at 2 V in sulfuric and oxalic acids results in the growth of an anodic conversion layer. This coating is mainly made of a porous layer of amorphous antimony oxides due to dealloying of CoSb3. In the specific case of oxalic acid, rods of crystallized oxalates are tangled between the oxide sheets.
... Templates act as a support scaffold for metallization procedures in the fabrication of porous metals, enabling a robust processing approach which addresses fundamental difficulties in nanoporous metal assembly and FIG. 1. Sample dimensions and pore sizes of nanoporous metals (or templates) fabricated by various methods, including Ni from polymer templates prepared by BCP self-assembly, 2,68 Au lattice from polymer templates prepared by two-photon lithography, 37 Ti from powder sintering, 69,70 Cu from electrodeposition, 25,26 Fe, Cu, Ag, Co from combustion, 4 Au, 3,15,16,[71][72][73][74][75][76][77][78][79][80] Ag, 18,[80][81][82][83][84] Pt, 80,85 Pd, 17,80,[86][87][88][89] Cu, 20,[90][91][92][93][94] and Ni 19,95-98 from dealloying, as well as carbon template, 31,33,99 and polymer templates fabricated by foaming, 45 melt mixing, 44 and BCP self-assembly. 38,42,[47][48][49]68 Lines in the figure represent a range of pore sizes or sample sizes. ...
Article
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Nanoporous metallic foams with high surface area and novel functional behavior are positioned to stimulate new multifunctional and metamaterial applications. However, there are fundamental challenges in achieving uniform nanopores and tailorable morphology. Emerging templating methods offer a wide range of applicable metallic species while enhancing control of pore morphology, uniformity, and interconnectivity. Here, a critical review of nanoporous metal fabrication is presented, with focus on templating methods utilizing nanoporous polymeric templates. Metals are introduced into percolative nanochannels of sacrificial templates by deposition, and subsequent removal of templates yields ordered nanoporous metals. We introduce approaches for preparing nanoporous templates, including utilizing block copolymer self-assembly that yields periodic gyroid networks. While metallization of templates by electrodeposition has been demonstrated, electroless deposition permits uniform deposition by many metallic species and infiltration of narrow pores. Examples of nanoporous metals with uniform pore sizes below 50 nm fabricated by templating methods are examined. Copyright © Materials Research Society 2017 This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
... Thus, great efforts have been introduced to prepare bulk nanoporous metals. So far, majority of studies have been started out to dealloying conventionally solidified bulk master alloy ingots [19][20][21]. Specifically, Qi and Weissmü ller produced hierarchical nested-network Au nanostructure by electrochemical dealloying and annealing strategy, which show faster charge transport rate than nanoporous Au [22]. Shi et al. [23] reported a strategy for preparing macroscopic samples of nanoporous Pd by electrochemical dealloying and explored its actuation properties through electrochemically controlled hydrogen sorption. ...
Article
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In the present study, bulk nanoporous Cu materials with hierarchical porous structure and fine ligaments have been facilely fabricated through chemical dealloying of CuAl alloy that prepared by suction casting. Effect of dealloying temperature on the formation of nanoporous Cu was investigated. Results reveal that robust bulk nanoporous Cu with no noticeable volume shrinkage can be prepared. The Fe adatoms may act as activation barrier for the surface diffusion of Cu adatoms, which is beneficial for the refinement of nanoporous Cu. Moreover, thermal coarsening behavior of nanoporous Cu was also investigated.
... 6,10 In this method, one or more base constituents of an alloy are removed by selective corrosion in an acid or alkaline solution, resulting in the formation of noble nanoporous metals with fine and homogeneous structures. This method is most effective for preparing relatively noble nanoporous metals such as those of Au, 10 Pt, 11 Pd, 12 Cu, 13 and Ni 14 and so on. ...
... 6,10 In this method, one or more base constituents of an alloy are removed by selective corrosion in an acid or alkaline solution, resulting in the formation of noble nanoporous metals with fine and homogeneous structures. This method is most effective for preparing relatively noble nanoporous metals such as those of Au, 10 Pt, 11 Pd, 12 Cu, 13 and Ni 14 and so on. ...
... The cracks imply brittleness even in compression, raising the question if the material has the load-bearing capability that is required for actuation. Np-Pd with the more homogeneous pore structure that results from dealloying uniform single-phase master alloys, as in Ref. [13][14][15], promise improved mechanical performance. Yet, mechanical tests for np-Pd remain yet to be reported. ...
Article
We report a strategy for preparing macroscopic samples of nanoporous (np-) Pd by electrochemical dealloying. Starting out with the master alloy , single-step dealloying in 1 M at C provides a hierarchical network structure with two well-defined ligament sizes, 35 and 10 nm. The material is distinguished by its uniform microstructure and its excellent mechanical deformability. Thereby, it may provide an alternative to dealloying-made nanoporous gold as a model system for nanoscale functional materials. Our study exemplifies this by exploring actuation through electrochemically controlled hydrogen sorption. Hydrogen underpotential deposition, bulk sorption isotherms and the concentration strain coefficient are found to agree closely with previous studies of H adsorption on planar surfaces and of hydrogen absorption in bulk, respectively. The actuation strain reaches amplitudes up to 4.0%. Even though each strain cycle brings the np-Pd-H through the phase transformation, the strain amplitude remains stable during much more than 1000 cycles. Furthermore, in view of the macroscopic sample size in all three dimensions, the switching time for actuation is remarkably fast.
... 6,10 In this method, one or more base constituents of an alloy are removed by selective corrosion in an acid or alkaline solution, resulting in the formation of noble nanoporous metals with fine and homogeneous structures. This method is most effective for preparing relatively noble nanoporous metals such as those of Au, 10 Pt, 11 Pd, 12 Cu, 13 and Ni 14 and so on. ...
Article
We present a novel route to fabricate 3D nanoporous α-Ti foams by dealloying of TiCu master alloy in solid state using Mg powders. Pure open-cell nanoporous α-Ti foams are fabricated with BET surface area of 34.4 ± 0.8 m²/g and pore size in the range of 2–50 nm. The dealloying using powders is a solid state chemical reaction process to form Cu2Mg phase and Ti/Mg nanocomposites. The constituent of Cu in the TiCu alloy was dissolved into Mg powders thanks to the kinetics of interface reaction and volume diffusion. The pore-forming mechanism is a solid-state interdiffusion process. The ligament coarsening is from 492 to 650 nm with increasing of the dealloying temperature. The hardness and elastic modulus in nanoporous α-Ti foam follow linear decay fit with ligament size increasing. Our results demonstrate a facile strategy for the fabrication of nanoporous Ti foams with novel nanostructures and tailored properties.
... Nanoporous metals have attracted great attention in many technological applications, including sensing, catalysis, photonics, energy storage, etc. [1][2][3][4][5][6] Chemical or electrochemical dealloying is a superior route to prepare nanoporous metals via selective dissolution of one or more components out of an alloy, [7][8][9] and various nanoporous metals such as gold, platinum, palladium and silver have been synthesized by dealloying method. [10][11][12][13] However, wide industrial applications of nanoporous noble metals have been greatly limited by their high cost. The development of low-cost nanoporous transitional metals, such as copper and nickel, is gaining more interests. ...
Article
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Free-standing nanoporous nickel (np-Ni) ribbons were directly synthesized by dealloying Mg90-xNixY10 metallic glass ribbons in citric acid aqueous solutions under free conditions. Due to the amorphous nature of the Mg90-xNixY10 precursors, the as-dealloyed samples exhibit a uniform nanoporous structure with the ligament size of ∼7 nm. Effects of alloy composition, leaching time, and acid concentration on the resulting nanoporous microstructure were discussed. The lower limit of Ni content in Mg90-xNixY10 precursors was identified to be 20%, below which the nanoporous Ni could not be formed. Besides, a linear relationship was established between the ligament size and the leaching time on a logarithmic scale. The ultrafine structure of the obtained np-Ni was associated with the stabilizing effect of citric acid. The as-dealloyed samples with the naturally formed oxide surface of NiO were directly examined as binder-free electrodes for high-performance supercapacitors.
... Nanoporous metals play an important role in the functional materials because of their novel optical, catalytic, electronic and sensing properties [1][2][3][4][5][6]. So far, the dealloying method has been widely adopted to prepare the nanoporous metals [7][8][9]. The raw alloy powders in millimeter or micrometer size are usually prepared by atomizing technique or by casting-crashing technique. ...
Article
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The Co-61.8wt% Al nanoparticles of 45 nm were prepared by hydrogen plasma-metal reaction (HPMR) method. The nanoparticles display core shell structure with Al13Co4 and CoAl core and aluminum oxide shell (about 2nm). Under ultrasonic irradiation, nanoporous fcc-Co nanoparticles were produced successfully by chemically dealloying the Co-Al nanoparticles at room temperature, whereas, without ultrasonic irradiation CoAl phase could hardly react with sodium hydroxide solution. At 323K the Co-Al nanoparticles could be dealloyed to fcc-Co and hcp-Co phases even without ultrasonic irradiation. The surface area of the dealloyed nanoparticles under ultrasonic irradiation was larger than that of the dealloyed sample without ultrasonic irradiation at the same temperature. It is believed that the microjet and shock-wave induced by ultrasonic irradiation give rise to particles size reduction, interparticle collision and surface cleaning, and accelerate the dealloying process and the phase transformation.
... Cu, 23 Pd, 24 Au, 25 etc.) and alloys (e.g. PdNi, 26 PdCo, 27 PtCu, 28 PtRuCuOsIr, 29 etc.) have been successfully synthesized through selectively dissolving Al from Al-based precursor alloys. However, these Al-based precursors are always composed of multiple intermetallic phases, which would apparently have an impact on the uniformity and quality of the resulting nanoporous alloys. ...
Article
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Pt-based electrocatalysts play a crucial role in both the anode and cathode reactions of direct methanol fuel cells (DMFCs), but their activity/durability and cost are still the main issues to be addressed. Through the combination of mechanical alloying with dealloying, here we have fabricated a nanoporous PtCuTi (np-PtCuTi) alloy with a low Pt content from a Cu-based precursor. The np-PtCuTi alloy exhibits a three-dimensional bi-continuous interpenetrating ligament/channel structure with a ligament size of 3.1 ± 0.6 nm. Electrochemical measurements show that the np-PtCuTi alloy exhibits superior electrocatalytic activities (CO tolerance, specific and mass activity) towards methanol oxidation at the anode, compared to commercial PtC catalysts. Moreover, the np-PtCuTi catalyst shows an enhancement of 1.9 and 4.2 times in the mass and specific activity towards the oxygen reduction reaction (ORR) at the cathode compared to PtC, respectively. More importantly, the np-PtCuTi catalyst shows excellent catalytic durability for the ORR, and the mass activity retains 91.8% of the initial value after 20:000 cycles. In addition, the mechanisms for the activity enhancement of np-PtCuTi have been rationalized on the basis of the structural effect, alloying effect and electronic effect through experiments and density functional theory calculations.
Article
Nanoporous metals have emerged as a new class of functional materials with unique structures and properties. Compared to conventional metals and alloys, nanoporous metals possess a high surface area, unique pore size distribution and enhanced catalytic activity, making them highly desirable for a wide range of applications, such as photonics, sensing, supercapacitors and catalysis. In this review paper, we aim to summarize recent advances in the fabrication, structural regulation and functional applications of nanoporous metals and their composites via the dealloying of metallic glasses. Particularly, we will discuss the factors that affect the nanoporous structure, including precursor composition, dealloying conditions and post-treatment methods. We will also cover topics such as the preparation of immiscible nanoporous metals and the control of hierarchical nanoporous structures. Finally, we will provide a brief overview of the current situation and discuss the current challenges and potential research directions in the field.
Article
Dealloying, which is traditionally originated in the research of alloy corrosion, has recently been developed as a robust and generic method for fabricating functional 3D nanoporous materials. Endorsed by the unique 3D bicontinuous porous structure, they exhibit remarkable properties such as large surface area, high conductivity, efficient mass transport, and high catalytic activity, which render them as advanced nanomaterials with enormous potential for a variety of applications. In this review, we summarize recent progress in the development of dealloying and dealloyed nanoporous materials for electrochemical energy conversion and storage. Beginning with an overview of the modern understanding of dealloying mechanisms, the unique structural and physical properties of dealloyed nanoporous materials are introduced. Then, we discuss the established dealloying techniques and how they enable the versatile fabrication of a diverse variety of nanoporous materials, ranging from unary metals and alloys to the latest high-entropy alloys and two-dimensional materials. Following that, the electrochemical applications of dealloyed nanoporous materials for fuel cells, supercapacitors, metal-ion batteries, alkali metal batteries, non-aqueous metal-oxygen batteries, electrochemical CO2 reduction, and electrocatalytic N2 reduction are highlighted. Finally, we discuss remaining challenges in this field and offer perspectives on potential directions for future research.
Article
Bimodal nanoporous structure shows great potential in a wide variety of applications. So far, however, a scalable fabrication method for bimodal nanoporous structure with controllable morphology and size remains a critical challenge. Herein, we prepare a homogeneously bimodal nanoporous copper which consists of nanoslit and nanopore through combined laser processing and dealloying. The nanoslit and nanopore size can be easily altered by simply controlling the laser processing parameters. With decreased heat input during laser processing, the width of nanoslit decreases from 200 nm to 100 nm and the average size of nanopore decreases from 23.7 to 14.0 nm. The bimodal nanoporous copper is found to be principally influenced by metallurgical reaction during laser-material interaction. Compared with equilibrium-solidified as-cast alloy, phase separation and refined microstructure induced by non-equilibrium solidification through laser processing facilitates corrosion rate during dealloying and induces bimodal nanoporous structure after dealloying.
Chapter
A large variety of electrochemical methods can be used to obtain porous nanostructures. The first part of this chapter deals with bottom-up methods such as dynamic bubble templating and direct deposition of porous layers, completed with post-deposition surface modification methods. The second part of the chapter yields an overview on dealloying, which is a top-down method to obtain porous nanostructures. In each part, combinative routes by applying various electrochemical and non-electrochemical methods are also be presented.
Article
This book summarizes the electrochemical routes of nanostructure preparation in a systematic and didactic manner. It provides a comprehensive overview of electrodeposition, anodization, carbon nanotube preparation and other methods of nanostructure fabrication, combining essential information on the physical background of electrochemistry with materials science aspects of the field. The book includes a brief introduction to general electrochemistry with an emphasis on physico-chemical aspects, followed by a description of the sample preparation methods. In each chapter, an overview of the particular method is accompanied by a discussion of the relevant physical or chemical properties of the materials, including magnetic, mechanical, optical, catalytic, sensoric and other features. While some preparation methods are discussed in connection with the theories of physical electrochemistry (e.g. electrodeposition), the book also covers methods that are more heuristic but nonetheless utilize electric current (e.g. anodization of porous alumina or synthesis of carbon nanotubes by means of electric arc discharge).
Article
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Nanoporous metals show great potentials in various applications including catalysis, sensing, actuation and supercapacitors. The liquid Ga-assisted alloying/dealloying strategy is a feasible and scalable way to fabricate substrate-supported nanoporous metals. However, the influence of intrinsic alloying mode and mechanism on the formation and modulation of nanoporous structure has not been thoroughly explored before. In this work, after painting liquid Ga on Ag foil, both the bulk-like Ag3Ga (in the Ag-rich zone) and wire-like Ag3Ga (in the liquid Ga-rich zone) form owing to the interdiffusion of Ag and Ga atoms. Correspondingly, the bimodal wire-like and unimodal bulk-like nanoporous Ag is obtained because of the structure inheritance during dealloying. In addition, the thickness of alloy layer (nanoporous layer) versus mass loading of liquid Ga follows a good linear relationship. The in-situ X-ray diffraction of dealloying from Ag3Ga to nanoporous Ag illustrates no other intermetallic phase appears and the dealloying process can be described by the dissolution-surface diffusion model. More importantly, the substrate-supported nanoporous Ag exhibits excellent mechanical properties which are of great importance to the future applications of nanoporous metals.
Article
This article describes the synthesis of nanoporous silver submicrocubes (Np-Ag) capped with poly(allylamine hydrochloride) PAH/poly(styrenesulfonate) PSS bilayers (Np-Ag(PAH/PSS) n , 1 ≤ n ≤ 4) via layer-by-layer (LBL) assembly for the electrochemical glucose sensing. The consecutive LBL encapsulation of Np-Ag (average size ≈530 nm) with positively charged PAH and negatively charged PSS layers was monitored by using ζ-potential analyses, which showed that the sign of the ζ-potential became positive (+10 mV) or negative (-22 mV) depending on the charge of the encapsulating species. The thickness of two PAH/PSS bilayers on the Np-Ag was estimated to be ∼4 nm (consistent with a literature value of ∼1 nm per PAH or PSS layer) on the basis of a high-resolution transmission electron microscopy image of the Np-Ag(PAH/PSS)2. Moreover, the high quality of the polyelectrolyte capping on Np-Ag was evidenced by the elemental mapping analysis of particles (obtained by using high-angle annular dark-field scanning transmission electron microscopy), which showed a uniform spatial distribution of C, N, and S (derived from PAH and PSS layers). Among the four different Np-Ag(PAH/PSS)n (1 ≤ n ≤ 4) electrodes, Np-Ag(PAH/PSS)2 exhibited the highest electrocatalytic activity toward glucose because of the optimal thickness and density of its polyelectrolyte films (fabricated onto Np-Ag). The (Np-Ag(PAH/PSS)2 electrode demonstrated a detection limit of 20 μM, a sensitivity limit of 472.15 μA mM-1 cm-2, and a wide range of detection for glucose at concentrations as high as 23.3 mM along with good selectivity toward glucose. The findings of this study are expected to contribute to improvements in the fabrication and stability of various particle-type catalysts on an electrode surface and to efforts to optimize the device performance using the LBL encapsulation technique.
Article
Lights interact with nanoporous gold (NPG) brings versatile applications, requiring the fundamental understanding the dynamic process that how this nanoporous material converts photon energy. In this work, we conducted a comprehensive research to capture the ultrafast dynamic process of NPG with different structures responding different light wavelengths and intensities. The elevated annealing temperature was controlled to adjust the nanostructures, mainly featured by the size of ligament and the porosity. Ultrafast dynamic results showed that the energy exchange faster in electron-electron coupling and slower in electron-phonon coupling when the samples were excited at plasmonic resonance (~2.21 eV) and higher excitation energy compared to other light parameters. Smaller ligament size and higher porosity gave rise to larger time constants of both electron-electron and electron-phonon coupling. And for vibration modes, the low-frequency component dominates the vibration modes. The results suggest that light and structure parameters could significantly alter the light induced electronic excitation dynamics inside NPG, thus is fundamentally important for the light modulated properties of NPG materials.
Article
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Electrochemical reactions represent a promising approach to control magnetization via electric fields. Favorable reaction kinetics have made nanoporous materials particularly interesting for magnetic tuning experiments. A fully reversible ON and OFF switching of magnetism in nanoporous Pd(Co) at room temperature is demonstrated, triggered by electrochemical hydrogen sorption. Comprehensive magnetic characterization in combination with high‐resolution scanning transmission electron microscopy reveals the presence of Co‐rich, nanometer‐sized clusters in the nanoporous Pd matrix with distinct superparamagnetic behavior. The strong magneto‐ionic effect arises from coupling of the magnetic clusters via a Ruderman–Kittel–Kasuya–Yoshida‐type interaction in the Pd matrix which is strengthened upon hydrogen sorption. This approach offers a new pathway for the voltage control of magnetism, for application in spintronic or microelectromagnetic devices.
Article
Nanoporous metal-based catalysts with the specific bicontinuous interconnected ligaments/pores network exhibit highly active performances in application for energy conversion, which represent a broader trend in the design of catalyst materials. These promising nanomaterials commendably provide highly conductive porous morphologies with reduced contact resistances, large electrochemical surface areas with enhanced catalytic efficiency, and controllable synthesis for regulating the performances. Thus, we highlight recent designs of nanoporous metals, alloys, transition metal compounds and hierarchical structures mainly employed in catalysis process. We discuss applied strategies to utilize characteristics of nanoporous metals in the energetic field of catalytic reactions. Moreover, development and evolution of novel controllable synthesis methods are applied in preparation of nanoporous non-noble metals and transition metal compounds. Finally, we present some outlooks and perspectives on the nanoporous metal catalyst and suggest ways for achieving alternative materials in catalysis applications.
Article
The formation of nanoporous Pd was studied by electro-chemical dealloying a rapidly-quenched Al 70 Pd 17 Fe 13 quasicrystal alloy in dilute NaCl aqueous solution, and the electro-catalytic activity of the nanoporous Pd towards methanol electro-oxidation was evaluated by cyclic voltammetry in 1 mol/L KOH solution. XRD and TEM analyses revealed that nano-decomposition of quasicrystal grains occurred in the initial stage of dealloying, and the fully dealloyed sample was composed of FCC-Pd phase. Scanning electron microscopy observation indicated that a maze-like nanoporous pattern was formed in the dealloyed sample, consisting of percolated pores of 5−20 nm in diameter in a skeleton of randomly-orientated Pd nano-ligaments with a uniform thickness of ~5 nm. A retention of ~12 at.% Al in the Pd nano-ligments was determined by energy dispersive X-ray spectroscopy (EDS). The nanoporous Pd demonstrated obvious electro-catalytic activity towards methanol electro-oxidation in alkaline environment.
Thesis
Nanoporous metals have attracted considerable attention for their excellent functional properties. The first developed technique used to prepare such nanoporous noble metals is dealloying in aqueous solution. Porous structures with less noble metals such as Ti or Fe are highly desired for various applications including energy-harvesting devices. The less noble metals, unstable in aqueous solution, are oxidized immediately when they contact water at a given potential so aqueous dealloying is only possible for noble metals. To overcome this limitation, a new dealloying method using a metallic melt instead of aqueous solution was developed. Liquid metal dealloying is a selective dissolution phenomenon of a mono-phase alloy solid precursor: one component (referred as soluble component) being soluble in the metallic melt while the other (referred as targeted component) is not. When the solid precursor contacts the metallic melt, only atoms of the soluble component dissolve into the melt inducing a spontaneously organized bi-continuous structure (targeted+sacrificial phases), at a microstructure level. This sacrificial phase can finally be removed by chemical etching to obtain the final nanoporous materials. Because this is a water-free process, it has enabled the preparation of nanoporous structures in less noble metals such as Ti, Si, Fe, Nb, Co and Cr. The objectives of this study are the fabrication and the microstructure and mechanical characterization of 3 different types of materials by dealloying process : (i) metal/metal composites (FeCr-Mg), (ii) porous metal (FeCr) (iii) metal/polymer composites (FeCr-epoxy resin). The last objective is the evaluation of the possibilities to apply liquid metal dealloying in an industrial context. The microstructure study was based on 3D observation by X-ray tomography and 2D analysis with electron microscopy (SEM, SEM-EDX, SEM-EBSD). To have a better understanding of the dealloying, the process was followed in situ by X-ray tomography and X-ray diffraction. Finally the mechanical properties were evaluated by nanoindentation and compression.
Article
Nanoporous gold (np-Au), produced by dealloying in silver nitrate solution exhibits extraordinary high surface-to-volume ratios of more than 20 m^2/g which represents an excellent prerequisite for property tuning by surface charging. Upon electrochemical charging in aqueous KOH solution, the electrical resistance is observed to vary reversibly by up to 88 %. The charge coefficient, thus the sensitivity of the resistance towards the imposed charge per mol, is however significantly smaller compared to conventionally prepared np-Au, prepared in nitric acid solution. While the strong resistance variation observed in the present work can directly be related to the high charge transfer due to extraordinary fine porosity, the charge coefficients can be understood with regards to the matrix resistance of the respective materials, which is strongly influenced by dealloying residuals.
Chapter
Taking the Ni–Mn alloy with 25% Ni as the precursor, nanoporous nickel (NPN) was fabricated by electrochemical dealloying, and the effect of corrosion potential on the material microstructure and electrochemical performance was studied in the article. Morphology, element species, content and phase of the sample were characterized and analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). Different from the previously report that the material surface presented the structure of “mud crack”, materials prepared in this article remained the porous skeleton structure, but also reduced the large cracks and increased the hairline cracks. After a deep research, it is found that the corrosion potential determines the morphology and structure of porous material. This was due to the fact that corrosion rate became quicker when the corrosion voltage was higher and the degree of corrosion increased accordingly; precursor alloy defects increased as the dissolution of Mn, and the internal stress increased as a result; in addition, the diffusion rate of Ni was so low that it couldn’t refill the vacancy of Mn timely, and then more cracks occurred, therefore there were significant differences for the number and size of cracks. In order to further understand the electrochemical performance of the electrode material prepared under a proper potential, cyclic voltammetry and charge-discharge technology were used to characterize the electrochemical performance of NPN. The results show that the specific capacitance of NPN was 1.69 F cm⁻² which is 3 times of that of the nanoporous nickel martial reported previously. Therefore the prepared nanocomposite nickel in this article is a high-quality electrode capacitor material.
Article
Porous metals have been under development for nearly a century, but commercial adoption remains limited. This development has followed two primary routes: liquid state or solid state processing. Liquid state foaming introduces porosity to a liquid or semi-solid metal, and solid state foaming introduces porosity to a metal, which is fully solid. Either method may create pores by internal gas pressure or introducing metal around a template directly control porosity. Process optimization and commercial output has been primarily related to liquid state methods, as solid state processing is often more complex, diverse, and with lower throughput. Solid state methods, however, are often more versatile and offer greater control of pore characteristics. Ongoing advancements in solid state foaming have allowed for a wide array of metals and alloys to be made porous and the three-dimensional structure to be precisely tailored. In general, solid state processing remains limited to niche applications, often with modest dimensions (cm scale). “Traditional” solid state processes are being further refined and extended, and continuing developments to reduce cost, increase output, and control pore characteristics are likely to produce important advancements in coming years. The extensive variability of pore quantity and morphology makes solid state processes suitable, and often preferable, for an assortment of functional and structural applications, with electrodes and biomedical devices being among the most popular in current research. Various techniques for introducing porosity, the way these methods are applied, important considerations, typical outcomes, and current applications are reviewed.
Article
In the present study, porous bulk palladium samples were prepared by sodium chloride salt powder spacer incorporation and removal combined with dealloying. The obtained porous Pd bulks were characterized by X-ray diffraction, field-emission scanning electron microscopy and N2 adsorption isotherm measurements. The prepared porous Pd bulk samples showed a hierarchical pore structure, a high porosity of ∼88%, a high surface area of ∼54 m²/g, and a compression strength of ∼0.5 MPa. Electrochemical measurements were performed to evaluate the electrocatalytic properties of the porous Pd bulk samples, revealing their effectiveness for ethanol oxidation.
Article
The fabrication of three-dimensional (3D) porous bismuth by electrochemical dealloying of two-phase Sn–Bi alloys was investigated. The results show that the resulting porous bismuth changes from a microporous structure composed of bismuth microparticles to an aligned nanowire matrix composite as the Bi content in the Sn–Bi master alloy decreases. Single-crystal bismuth nanowires growing in the [110] direction were fabricated by the selective dissolution of the Sn phase from an alloy with ultralow Bi content. The influence of the two states of elemental Bi existing in smelted Sn–Bi alloys during dealloying was systematically analyzed and discussed. This report presents a novel strategy for direct fabrication of bismuth nanowires by electrochemical dealloying.
Article
A thin layer of copper (40-70 μm) was deposited on the surface of a nanoporous copper (NPC) matrix via a chemical deposition method that utilized the catalytic activity of the NPC itself to fabricate a new sandwich-type NPC (ST NPC) composite material. The effects of NPC aperture, chemical deposition time, and heat treatment on the mechanical properties of the ST NPC were studied. The results showed that an NPC matrix aperture of 150-160 nm helps to improve the mechanical properties of the sandwich-type NPC. On changing the deposition time, although the deposition thickness increases with the increase of time, the mechanical parameters of ST NPC become unstable because the deposited layer peels off from the surface of substrate NPC. Heat treatment greatly improved the interfacial adhesion between the panel and the interior pores, thus greatly improving the mechanical properties of the ST NPC. Besides mechanical properties, the thermal stability and corrosion resistance of the ST NPC were superior to those of the NPC substrate. However, catalytic performance of ST NPC was reduced owing to the as-obtained deposition layer, which increased the pore wall and decreased the porosity.
Article
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A low-temperature dealloying technique was developed to tailor the characteristic length scale of nanoporous gold for advanced functional applications. By systematically investigating the kinetics of nanopore formation during free corrosion, the authors experimentally demonstrated that the dealloying process is controlled by the diffusion of gold atoms at alloy/electrolyte interfaces, which strongly relies on the reaction temperatures. Low dealloying temperatures significantly reduce the interfacial diffusivity of gold atoms and result in an ultrafine nanoporous structure that has been proved to be useful with improved chemical and physical properties.
Article
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This paper gives results demonstrating the production of nanoporous platinum through the de-alloying of Cu0.75Pt0.25 alloy in 1 M H2SO4. Both field emission scanning electron microscopy and small angle neutron scattering confirm the presence of porosity with a diameter of approximately 3.4 nm. This is the smallest porosity quantitatively reported from a de-alloying process to date. The small size is attributed to the extremely small values of surface diffusivity expected for Pt at room temperature, effectively eliminating room-temperature coarsening processes. The results also show that larger length scales can be achieved through coarsening at elevated temperatures. The ease of production of porous platinum makes it attractive for possible applications, such as high surface area electrodes for biomedical devices or as catalyst materials.
Article
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The electrical conductivity of nanoporous gold was measured in situ during the charging and decharging of the surface of the metal. The nanoporous gold samples were prepared by the process of selective dealloying of Ag from Au–Ag alloy. Charge was induced on the surface by making the sample a working electrode in an electrochemical cell. The conductivity was observed to vary reversibly with the induced surface charge.
Article
For the first time, the latent heat of fusion \DeltaHm{}{H}_{m} for Sn particles formed by evaporation on inert substrate with radii ranging from 5 to 50 nm has been measured directly using a novel scanning nanocalorimeter. A particle-size-dependent reduction of \DeltaHm{}{H}_{m} has been observed. An ``excluded volume'' is introduced to describe the latent heat of fusion from the enhanced surface melting of small particles. Melting point depression has also been found by our nanocalorimetric technique.
Article
Microscopic observations of the surface structure and composition of thin films of silver-gold alloys are used to deduce the processes involved in the dissolution of these alloys in nitric acid solutions. The micromorphology consists of an island-and-channel structure whose formation depends in detail on the initial overall composition of the alloy. It also depends on the strength of the acid. The micromorphology can be modified by annealing for short times at elevated temperature, by storage for long periods at room temperature, or by increasing the strength of the acid during corrosion, giving very similar results. These observations can be explained in terms of a model in which corrosion proceeds by selective dissolution of the less noble component, thereby creating a disordered surface layer which subsequently reorders by surface diffusion.
Article
Thermal instability and melting behavior of tin nanowires were studied with a decrease of wire radius(rNW = 7–30 nm) via differential scanning calorimetry (DSC). Two sequential DSC measurements showed a 1/rNW dependency of the melting temperature depression; the first melting temperature decreased from 502 to 486 K with 1/rNW whereas the second one was more depressed between 0.8 and 5 K. The melting temperature difference between the first and second cycles increased linearly with 1/rNW. This variation was attributed to fragmentation of nanowires due to Rayleigh instability. Here, fragmentation of long nanowires was suppressed by a template confinement, resulting in the formation of short nanorods.
Article
Nanoporous metals with a pore (and ligament) size of several to 500 nm emerge as novel materials that can be fabricated by dealloying [1]. In dealloying, a less noble element selectively dissolves from a binary alloy, and the remaining more noble element self-organizes an open-cell nanoporous structure. Many studies have examined the dealloying mechanism in an Au–Ag alloy [2], [3] and [4] and the interesting properties of the resulting nanoporous Au [5], [6], [7] and [8]. Nanoporous Au has potential applications in chemical microactuators [7], microreactors [9], filters [10] and catalyst support [11].
Article
Dissolution rates as a function of potential and the corrosion potentials for Cu and five Cu‐Pd alloys with varying compositions in the range of (0–30%) Pd were measured. The Auger spectra of the alloy surface and fresh surfaces obtained by argon ion bombardment to a depth up to 30 nm were obtained. Cu dissolves from the alloy and the rate of dissolution of Pd is negligible. The Cu dissolution follows the same laws as from pure Cu. Below a certain critical potential, the initially observed dissolution current decayed towards zero. The electrode potential at zero current follows the surface composition. At zero current the bulk alloy composition was found to have been modified to a depth of about 20 nm. An approximate calculation of for Cu dissolution of the alloy as a function of composition showed that value is reduced by some ten orders of magnitude compared with that of pure Cu. Corrosion is reduced in a manner consistent with these reductions when the cathodic reaction is not rate controlling.
Article
Anodic dissolution of AgPd alloys in 12 M LiCl is being investigated using Auger electron spectroscopy and coulometry for the determination of Pd surface enrichment. Under steady state conditions Ag dissolved selectively in alloys containing <5% Pd, while both components dissolve in stoichiometric proportion in alloys >10% Pd. Initial surface enrichment of Pd occurs in both cases, the degree of enrichment decreasing with increasing Pd content. Pd in the alloy may dissolve at potentials below those observed for the pure metal. A procedure for the determination of surface excess from Auger depth profiles taking into account sputtering effects is described.
Conference Paper
These proceedings collect papers presented at a symposium on alloy phase diagrams. Topics include: Crystal phase transformations; order-disorder transformations; crystal lattices; metallic glasses; metastable states; solubility; binary alloy systems; and alloys of iron, tantalum, silicon, aluminum, germanium, palladium, copper, and nickel.
Article
Empirical relations are established between the cohesive energy, surface tension, and melting temperature of different bulk solids. An expression for the size-dependent melting for low-dimensional systems is derived on the basis of an analogy with the liquid-drop model and these empirical relations, and compared with other theoretical models as well as the available experimental data in the literature. The model is then extended to understand (i) the effect of substrate temperature on the size of the deposited cluster and (ii) the superheating of nanoparticles embedded in a matrix. It is argued that the exponential increase in particle size with the increase in deposition temperature can be understood by using the expression for the size-dependent melting of nanoparticles. Superheating is possible when nanoparticles with a lower surface energy are embedded in a matrix with a material of higher surface energy in which case the melting temperature depends on the amount of epitaxy between the nanoparticles and the embedding matrix. The predictions of the model show good agreement with the experimental results. A scaling for the size-dependent melting point suppression is also proposed.
Article
Colloidal solutions of metal nanoparticles are currently among the most studied substrates for sensors based on surface-enhanced Raman scattering (SERS). However, such substrates often suffer from not being cost-effective, reusable, or stable. Here, we develop nanoporous Au as a highly active, tunable, stable, biocompatible, and reusable SERS substrate. Nanoporous Au is prepared by a facile process of free corrosion of AgAu alloys followed by annealing. Results show that nanofoams with average pore widths of ∼ 250 nm exhibit the largest SERS signal for 632.8 nm excitation. This is attributed to the electromagnetic SERS enhancement mechanism with additional field localization within pores.
Article
Monolithic nanoporous copper was synthesized by dealloying Mn0.7Cu0.3 by two distinct methods: potentiostatically driven dealloying and free corrosion. Both the ligament size and morphology were found to be highly dependent on the dealloying methods and conditions. For example, ligaments from 16 nm–125 nm were obtained by dealloying either electrochemically or by free corrosion, respectively. Optimization of the starting Mn–Cu alloy microstructure allowed us to synthesize uniform porous structures; but we found cracking to be unavoidable. Despite the presence of unavoidable defects, the nanoporous material still exhibits higher than expected yield strength.
Article
We report the preparation of composite foils consisting of two layers, one solid gold and one nanoporous gold. Tip displacements of several millimeters are observed when the foils are immersed in aqueous electrolytes and the electrochemical potential varied. This suggests that nanoporous metals could be used as the active component in actors, and it demonstrates for the first time that changes in the surface stress f of the metal−electrolyte interface can induce a macroscopic strain, orders of magnitude larger than the amplitudes which are reached in conventional cantilever bending experiments used to measure f.
Article
The size dependencies of the hydrogen-storage properties in polymer-coated Pd nanoparticles with diameters of 2.6 ± 0.4 and 7.0 ± 0.9 nm were investigated by a measurement of hydrogen pressure-composition isotherms. Their storage capacities per constituent Pd atom in the particles decreased with decreasing particle size, whereas the hydrogen concentrations in the two kinds of nanoparticles were almost the same and 1.2 times as much, respectively, as that in bulk palladium after counting zero hydrogen occupancy on the atoms in the first surface layer of the particles. Furthermore, apparent changes in hydrogen absorption behavior with decreasing particle size were observed, that is, a narrowing of the two-phase regions of solid-solution and hydride phases, the lowering of the equilibrium hydrogen pressure, and a decrease in the critical temperature of the two-phase state. By analyzing the isotherms, we quantitatively determined the heat of formation (ΔHα→β) and the entropy change (ΔSα→β) in the hydride formation of the nanoparticle. ΔHα→β and ΔSα→β for the 2.6 ± 0.4 nm diameter Pd nanoparticle were −34.6 ± 0.61 kJ(H2 mol)-1 and −83.1 ± 1.8 J(H2 mol)-1K-1, whereas for the 7.0 ± 0.9 nm diameter Pd nanoparticles the values were −31.0 ± 1.8 kJ(H2 mol)-1 and −67.3 ± 5.1 J(H2 mol)-1K-1, respectively. These quantities gave us a prospective picture of hydrogen absorption in Pd nanoparticles and the peculiarities in the formation of a single nanometer-sized hydride.
Article
The synthesis of nanoporous palladium by electrochemically dealloying multicomponent Pd30Ni50P20 ribbons were produced by single-roller melt-spinning in vacuum which was introduced in detail elsewhere. X-ray diffraction (XRD) and transmission electron microscopy (TEM) demonstrated that the as-obtained ribbons are fully amorphous with a uniform structure and composition down to subnanoscale. The electrochemical dealloying process of the Pd30Ni50P20 metallic glass was monitored by the cross-sectional SEM micrographs. Nanoporous palladium with a rather uniform structure was obtained. It was observed that nanoporosity formation is mainly controlled by the dissolution process of the less noble Ni and P in the metallic glass system rather than by the surface diffusion of Pd in the acid during electrochemical dealloying.
Article
In this paper, nanoporous platinum films with an enhanced surface area were obtained through a facile route by selective anodic dissolution of Cu from PtCu alloy. A homogeneous PtCu alloy was electrochemically deposited at a glassy carbon electrode at room temperature, then Cu was electrochemically etched from the PtCu alloy resulting in the fabrication of a nanoporous platinum film with a much higher surface area. The surface area of the dealloyed nanoporous platinum film was highly enhanced by up to 500 times compared with that of a polycrystalline platinum electrode. This nanoporous platinum film exhibited high stability and remarkable catalytic activity for oxygen electro-reduction and methanol electro-oxidation, with promising applications in fuel cells and biosensors, etc.
Article
The size dependence of the melting point of tin has been studied by means of transmission electron diffraction and microscopy. In accordance with the observations of other workers, it has been found that the melting point of a spherical particle of tin decreases as the radius Rm of the particle decreases. However, the decrease does not depend linearly on 1/Rm. The experimental results are explained in terms of a thermodynamic treatment which allows for the fact that a liquid cannot be subdivided indefinitely. The theory ceases to give correct results for the melting point of particles with radii less than about 50 Å, the calculated temperatures being less than those observed. For particles to which the theory is applicable it is found that the surface tension at the interface between solid and liquid tin is σ1 = 622 ± 10 dyn cm-1.
Article
A nanoporous Pd film sensor fabricated on a carbon-coated AAA template has been found to have a unique H2 sensing performance compared to traditional dense Pd film sensors. Nanostructured Pd materials have been developed to improve H2-sensing performance, and they have demonstrated a much quicker response to hydrogen gas. There is always a slight drift in the film resistance for nanoporous Pd film sensors in balancing atmosphere of nitrogen. The pyrolytic, carbon-supported, nanoporous Pd film sensor is effective in detecting both dilute and high concentration of H 2 gas because of its nanoporous, structure-enhanced, H 2-sensing ability. Various nanoporous H2-sensitive materials such as Pd, Pt, Ni, and their alloys are expected to work based on the nanoporous-structure enhanced H2-sensing mechanism.
Article
A latest method to produce nanoporous gold leaf (NPGL) is discussed. It is formed by a spontaneous pattern-forming in a porous media during etching. The technique allows precise control over pore size and microstructure and the porosity can be adjusted through simple room temperature post processing. The porosity of nanoporous gold can be adjusted from less than 10 nm up to the microscopic scale of the original starting material. Since the NPGL is mechanically rigid, chemically stable and bio-compatible, it can be used for various applications.
Article
Ordered hole-array membranes of Pd were fabricated using two-step replication of anodic porous alumina. Electroless deposition of Pd on negative anodic porous alumina of polymethyl methacrylate resulted in a Pd hole-array structure with straight holes of nanometer dimensions. The controlled change of the size of hole openings in the Pd electrode was achieved after cathodic polarization in H2SO4, as a result of the deformation of the opening of the holes caused by hydrogen absorption at Pd.
Article
The corrosion properties of micro- and nanocrystalline Co and Co–1.1 wt% P alloys were studied in deaerated 0.1 M H2SO4 solution using open-circuit potential measurement, polarization tests, ac impedance measurements and XPS. The potentiodynamic polarization tests revealed that all samples exhibited active anodic dissolution without a distinct transition to passivation up to −0.1 VSCE. While the anodic polarization curve of the nanocrystalline Co was almost identical to that of its microcrystalline Co, the cathodic kinetics of the nanocrystalline Co increased. For both micro- and nano Co, an inductive loop was observed in the low frequency and this could be attributed to the adsorption behaviour. Compared to the nanocrystalline Co, impedance measurement showed that addition of P resulted in an increase of the interfacial impedance at the open-circuit potential. This enhanced corrosion resistance was closely related to an enrichment of elemental P on the electrode surface and was confirmed by X-ray photoelectron spectroscopy (XPS). However, superior corrosion resistance did not last due to the formation of a non-protective surface film at higher anodic potentials.
Article
A comprehensive study on the relationship between yield strength, relative density and ligament sizes is presented for nanoporous Au foams. Depth-sensing nanoindentation tests were performed on nanoporous foams ranging from 20% to 42% relative density with ligament sizes ranging from 10 to 900 nm. The Gibson and Ashby yield strength equation for open-cell macrocellular foams is modified in order to incorporate ligament size effects. This study demonstrates that, at the nanoscale, foam strength is governed by ligament size, in addition to relative density. Furthermore, we present the ligament length scale as a new parameter to tailor foam properties and achieve high strength at low densities.
Article
A systematic study of the corrosion and passivation behaviour of cobalt in aqueous solutions of different pH was carried out. Open circuit potential measurements, polarization experiments and electrochemical spectroscopic (EIS) investigations were employed. The experimental results show that the metal surface is always covered by a native passive film which consists of CoO. The formation of the oxide film obeys a two-electron charge transfer process. The dissolution of the barrier film is controlled by the pH of the solution. In neutral and basic solutions the barrier film is stable. In these media a barrier film thickening with the formation of secondary layer is considered. In acidic solutions, the passive film is unstable and dissolves via a pure chemical process. The mechanism of the corrosion and passivation processes taking place at the electrode/electrolyte interface in the different solutions is discussed. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the electrochemical measurements and the suggested mechanisms.
Article
In this work, we study the preparation, structural characterization, and electrocatalytic analysis of robust Pt and Pd-containing catalyst structures for silicon-based formic acid micro fuel cells. The catalyst structures studied were prepared and incorporated into the silicon fuel cells by a post CMOS-compatible process of electrodeposition, as opposed to the more common introduction of nanoparticle-based catalyst by ink painting. Robust, high surface area, catalyst structures consisting of pure Pt, pure Pd, and Pt/Pd = 1:1 were obtained. In addition, Pt/Pd catalyst structures were obtained via spontaneous deposition on the electrodeposited pure Pt structure. The catalyst structures were characterized electrochemically using cyclic voltammetry and chronoamperometry. All Pd-containing catalyst structures facilitate formic acid oxidation at the lower potentials and deliver higher oxidation currents compared to pure Pt catalyst structures. Fuel cells of these catalyst structures show that pure Pd catalyst structures on the anode exhibit the highest peak power density, i.e. as high as 28.0 mW/cm2. The MEMS compatible way of catalyst electrodeposition and integration presented here has yielded catalyst structures that are highly active towards formic acid oxidation and are sufficiently robust to be compatible with post-CMOS processing.
Article
The anodic dissolution behavior of the binary single phase alloys CuPd, NiPd and AgAu in 12 M LiCl is being investigated on a rotating disk electrode. Auger electron spectroscopy is employed to study the influence of applied charge on the surface composition of Cu20Pd and Ni20Pd and results are compared to previous data for AgPd alloys. Results show the dissolution mode, selective or simultaneous, to depend on noble metal content. Similarities and differences in the behavior of different alloy systems are discussed.
Article
Recently, small particles have been shown to exhibit a melting temperature which depends on the particle size. The various possible experimental methods have been compared and measurements of the melting points of small gold particles have been made using a scanning electron-diffraction technique. This method was applied to particles having diameters down to 20 Å. Consideration of the size distribution over an entire sample makes it necessary to carry out a careful analysis of the experimental results in order to deduce the melting temperature of particles having a well-defined diameter. The experimental results are quantitatively in good agreement with two phenomenological models. The first model describes the equilibrium condition for a system formed by a solid particle, a liquid particle having the same mass, and their saturating vapor phase. The second model assumes the preexistence of a liquid layer surrounding the solid particle and describes the equilibrium of such a system in the presence of the vapor phase. In order to permit a better comparison between both models, a new expression for the thermodynamic equilibrium condition has been derived in the present work. In the case of the first model, the agreement was obtained using only the physical constants of massive gold. In applying the second model, however, one is compelled to assume the existence of a liquid layer having a thickness of about 6 Å.
Article
The way that small particles melt is a crucial clement in the construction of a thermodynamic treatment of the relation between particle size and melting temperature. There are indications that melting is initiated at the surface and that the solid-liquid interface sweeps rapidly through the solid at the melting temperature. The formal and physical elements of the indicated nucleation and growth criterion for melting are discussed and the existence of upper and lower limits on the melting temperature is outlined. Theoretical predictions show satisfactory agreement with experimental observations.
Article
Chemisorption from the gas or liquid phase can result in a measurable resistance change in a metallic material when at least one dimension is smaller than the mean free path for electrons. Here we report on the fabrication of single nanoporous gold nanowires and demonstrate that adsorption of an alkanethiol can be monitored in real time. Single nanowire devices were fabricated by in situ etching of Au0.18Ag0.82 alloy nanowires in dilute nitric acid. The evolution of the porous structure was characterized by monitoring the resistance change and comparing to cross-sectional images. The feature size of about 10 nm is less than the mean free path for electrons in bulk gold, and hence the resistance is dominated by surface scattering. Adsorption of a monolayer of octadecanethiol onto the nanoporous gold nanowire results in a resistance change of about 3%. The sensitivity factor of 1.0x10(-16) cm2 is comparable to values reported for adsorption at ultrathin films.
Article
We report a macroscopic shrinkage by up to 30 vol % during electrochemical dealloying of Ag-Au. Since the original crystal lattice is maintained during the process, we suggest that the formation of nanoporous gold in our experiments is accompanied by the creation of a large number of lattice defects and by local plastic deformation.
Article
Supported Au nanoclusters are well-known for their unusual properties in catalysis. We describe here that nanostructured porous Au made via dealloying represents a new class of unsupported catalysts with extraordinary activities in important reactions such as CO oxidation. Although nanoporous Au may contain some oxides on the surface, our results demonstrate that it is metallic Au that plays the main role in this catalytic reaction. Furthermore, this material has good low-temperature catalytic stability and is extremely CO tolerant.
Article
Dealloying is a common corrosion process during which an alloy is "parted" by the selective dissolution of the electrochemically more active elements. This process results in the formation of a nanoporous sponge composed almost entirely of the more noble alloy constituents . Even though this morphology evolution problem has attracted considerable attention, the physics responsible for porosity evolution have remained a mystery . Here we show by experiment, lattice computer simulation, and a continuum model, that nanoporosity is due to an intrinsic dynamical pattern formation process - pores form because the more noble atoms are chemically driven to aggregate into two-dimensional clusters via a spinodal decomposition process at the solid-electrolyte interface. At the same time, the surface area continuously increases due to etching. Together, these processes evolve a characteristic length scale predicted by our continuum model. The applications potential of nanoporous metals is enormous. For instance, the high surface area of nanoporous gold made by dealloying Ag-Au can be chemically tailored, making it suitable for sensor applications, particularly in biomaterials contexts.
  • M Yamauchi
  • R Ikeda
  • H Kitagawa
  • M Takata
M. Yamauchi, R. Ikeda, H. Kitagawa and M. Takata: J. Phys. Chem. C 112 (2008) 3294–3299.
  • C Xu
  • J Su
  • X Xu
  • P Liu
  • H Zhao
  • F Tian
  • Y Ding
C. Xu, J. Su, X. Xu, P. Liu, H. Zhao, F. Tian and Y. Ding: J. Am. Chem. Soc. 129 (2007) 42–43.
  • F Jia
  • C Yu
  • K Deng
  • L Zhang
F. Jia, C. Yu, K. Deng and L. Zhang: J. Phys. Chem. C 111 (2007) 8424-8431.
Honoring Doctor Norman Hackerman on His Seventy-Fifth Birthday
  • B Kabius
  • H Kaiser
  • H Kaesche
B. Kabius, H. Kaiser and H. Kaesche: Surfaces, Inhibition, and Passivation: Proc. Int. Symp. Honoring Doctor Norman Hackerman on His Seventy-Fifth Birthday, ed. by E. McCafferty, R. J. Brodd, (Electrochemical Society, Pennington, 1986) pp. 562-573.
  • D V Pugh
  • A Dursun
  • S G Corcoran
D. V. Pugh, A. Dursun and S. G. Corcoran: J. Mater. Res. 18 (2003) 216-221.
  • K Sieradzki
  • N Dimitrov
  • D Movrin
  • C Mccall
  • N Vasiljevic
  • J Erlebacher
K. Sieradzki, N. Dimitrov, D. Movrin, C. McCall, N. Vasiljevic and J. Erlebacher: J. Electrochem. Soc. 149 (2002) B370-B377.
  • R Li
  • K Sieradzki
R. Li and K. Sieradzki: Phys. Rev. Lett. 68 (1992) 1168-1171.
  • D Ding
  • Z Chen
D. Ding and Z. Chen: Adv. Mater. 19 (2007) 1996-1999.
  • R B Diegle
  • N R Sorensen
  • C R Clayton
  • M A Helfand
  • Y C Yu
R. B. Diegle, N. R. Sorensen, C. R. Clayton, M. A. Helfand and Y. C. Yu: J. Electrochem. Soc. 135 (1988) 1085-1092.
  • J Yu
  • Y Ding
  • C Xu
  • A Inoue
  • T Sakurai
  • M Chen
J. Yu, Y. Ding, C. Xu, A. Inoue, T. Sakurai and M. Chen: Chem. Mater. 20 (2008) 4548–4550.
  • D Kramer
  • R N Viswanath
  • J Weissmüller
D. Kramer, R. N. Viswanath and J. Weissmüller: Nano Lett. 4 (2004) 793–796.
  • Z Liu
  • P C Searson
Z. Liu and P. C. Searson: J. Phys. Chem. B 110 (2006) 4318-4312.
  • J A L Dobbelaar
  • E C M Herman
  • J H W De Wit
J. A. L. Dobbelaar, E. C. M. Herman and J. H. W. De Wit: Corr. Sci. 33 (1992) 765-778.
  • S Trasatti
  • O A Petrii
S. Trasatti and O. A. Petrii: J. Electroanal. Chem. 327 (1992) 353-376.
  • J R Hayes
  • A M Hodge
  • J Biener
  • A V Hamza
  • K Sieradzki
J. R. Hayes, A. M. Hodge, J. Biener, A. V. Hamza and K. Sieradzki: J. Mater. Res. 21 (2006) 2611-2616.