[Show abstract][Hide abstract] ABSTRACT: High durability and hydroxide ion conducting pore-filled anion exchange membranes is developed.Figure optionsDownload full-size imageDownload as PowerPoint slide
Journal of Power Sources 12/2014; 269:1–6. · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Carbon-coated titanium dioxide (TiO2–C) has received much attention as a catalyst support in proton exchange membrane fuel cells. In this study, TiO2 nanorod arrays (NRs) are hydrothermally grown on carbon paper and converted into TiO2–C NRs by heat treatment at 900 °C under methane atmosphere. Then, platinum nanoparticles are sputtered onto the TiO2 NRs by physical vapor deposition to produce Pt–TiO2–C. The as-prepared Pt–TiO2–C exhibits high stability during accelerated durability tests. As compared with the commercial gas diffusion electrode (GDE, 34.4% decrease), a minor reduction in the electrochemically active surface area of the Pt–TiO2–C electrode after 1500 cycles (10.6% decrease) is observed. When the as-prepared electrode with ultra-low platinum content (Pt loading: 28.67 μg cm−2) is employed as the cathode of a single cell, the electrode generates power that is 4.84 × that of the commercial GDE (Pt loading: 400 μg cm−2). An electrode that generates power of 11.9 kW gPt−1 (as the cathode) is proposed. The fabricated Pt–TiO2–C electrode can be used in proton exchange membrane fuel cells.
Journal of Power Sources 11/2014; · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The wheatear-like catalysts were prepared on the Co-OH-CO3 nanowires to design an ultra-thin catalyst layer (UTCL). Without any ionomer, the UTCL exhibited a maximum power density of 481 mW cm-2 at ultra-low Pt loading of 43 μg cm-2Pt, resulting in a relatively high Pt utilization of 11.2 kW g-1Pt. It is expected that the nanostructured thin film materials will lead to further technological advancements in fuel cells and applications.
[Show abstract][Hide abstract] ABSTRACT: A new method of preparing microporous layer (MPL) for proton exchange membrane fuel cell (PEMFC) was presented in this paper. Considering the bad dispersion of PTFE aqueous suspension in the carbon slurry based on ethanol, polyvinylpyrrolidone (PVP) aqueous solution was used to prepare carbon slurry for microporous layer. The prepared gas diffusion layers (GDLs) were characterized by scanning electron microscopy, contact angle system and pore size distribution analyzer. It was found that the GDL prepared with PVP aqueous solution had higher gas permeability, as well as more homogeneous hydrophobicity. Moreover, the prepared GDLs were used in the cathode of fuel cell and evaluated with fuel cell performance and EIS analysis, and the GDL prepared with PVP aqueous solution indicated better fuel cell performance and lower ohmic resistance and mass transfer resistance.
International Journal of Hydrogen Energy 09/2014; 39(28):15681–15686. · 3.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: With UV irradiation, the photo-generated hydroxyl groups further the back diffusion and decrease the proton transport resistance, which improve the performance at the low-humidity condition for PEMFC system.
[Show abstract][Hide abstract] ABSTRACT: The key factors influencing the low-temperature electrochemical performances of LiFePO4 cathode materials are systematically investigated by measuring and comparing the amount of surface carbon, particle size, and conductivities of LiFePO4, LiFePO4/C and electrolyte in the temperatures range of −20 to 40 °C. It is found that the low-temperature electrochemical performance of the material is improved obviously by coating the surface of LiFePO4 with carbon. At −20 °C, the discharge specific capacity of LiFePO4/C with 4 wt% surface carbon is 81.4 mAh/g, while the uncoated LiFePO4 only delivers the discharge specific capacity of 27.7 mAh/g. The low-temperature electrochemical performance of LiFePO4/C has no significant change as increasing the carbon content, but is further improved by reducing the particle size. In order to understand the difference of low-temperature electrochemical performance between the carbon-coated and uncoated LiFePO4 cathodes, the ionic conductivity of electrolyte, the electronic/ionic conductivities of LiFePO4 and LiFePO4/C at various temperatures were measured. The electronic conductivity of LiFePO4 with 4.9 × 10−11 S/cm at −20 °C is found to be responsible for its poor low-temperature electrochemical performance. However, for the LiFePO4/C, the low-temperature electrochemical performance is mainly determined by its ionic conductivity, therefore, the decrease of the particle size can increase the low-temperature electrochemical performance.
Journal of the Taiwan Institute of Chemical Engineers 07/2014; 45(4):1321–1330. · 2.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: LiNi0.5Mn1.5O4 nanoplates were prepared using a two-step method composed of a hydrothermal method and a solid-state reaction. At first, bimetal–organic coordination-polymers containing Ni2+ and Mn2+ were synthesized using the ligand 3,4,9,10-perylenetetracarboxylic dianhydride (ptcda) by a template-assisted self-assembly method in a hydrothermal atmosphere. This was followed by thermal treatment to remove the organic components and then calcination with lithium acetate, and nanoplate-stacked LiNi0.5Mn1.5O4 was obtained. The nanoplate structure shortens the diffusion path of the lithium ions in the bulk of LiNi0.5Mn1.5O4 and then promotes fast charge–discharge properties of the material. In addition, an amorphous Li2CO3 layer with nanometer thickness in situ generated on the surface of the LiNi0.5Mn1.5O4 particles was confirmed by TEM and XPS. This is helpful for suppressing the interfacial side reactions and thereby improving the cycling stability of the material. Owing to these advantages, the LiNi0.5Mn1.5O4/Li2CO3 material exhibits excellent rate capability and cycling stability. The as-prepared material delivers 129.8 mA h g−1 at a 1 C rate and retains 86.4% of the initial capacity even after 1000 cycles of charge–discharge at 25 °C. Even at a high discharge rate of 40 C, the specific capacity of the material is 120.9 mA h g−1, and the capacity retention is 84.7% over 500 cycles. The high-temperature stability of the material is also superior. When operating at 55 °C, the capacity loss by cycle is only 0.037% throughout 250 cycles.
[Show abstract][Hide abstract] ABSTRACT: Ti0.7Sn0.3O2 nanoparticles with high surface area are used as Pt catalyst supports for the oxygen reduction reaction. Pt/Ti0.7Sn0.3O2 exhibits excellent electrochemical stability compared to Pt/XC-72 under high potential electrooxidation and potential cycling.
Journal of Energy Chemistry. 05/2014; 23(3):331–337.
[Show abstract][Hide abstract] ABSTRACT: The unique bimodal mesoporous structure in the carbon framework MC-2 has been shown to contribute to the excellent electrochemical performances of S/MC-2 composite for the Li-S battery cathode.
Journal of Energy Chemistry. 05/2014; 23(3):391–396.
[Show abstract][Hide abstract] ABSTRACT: Hydrophobicity treatment under vacuum resulted in a more even polytetrafluoroethylene (PTFE) distribution in the gas diffusion layer, which inhibits water flooding in proton exchange membrane fuel cells.
Chinese Journal of Catalysis 04/2014; 35(4):468–473. · 1.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Over the past several decades, tremendous effort has been put into developing cost-effective, highly active and durable electrocatalysts for oxygen evolution reaction (OER) in the proton exchange membrane water electrolyzer. This report explores an advanced and effective “soft” material-assistant method to fabricate Ir0.6Sn0.4O2 electrocatalysts with a 0.6/0.4 ratio of Ir/Sn in precursors. Adopting a series of characterization methods, the collective results suggest that the surfactant-material F127 content, as an important factor, can efficiently control the formation of Ir–Sn oxides with varying surface properties and morphologies, such as the grainy and rod-shaped structures. Associating with the half-cell and single electrolyzer, it is affirmed that the optimal ratio of (Ir + Sn)/F127 is 100 for the preparation of S100-Ir0.6Sn0.4O2 with obviously enhanced activity and sufficient durability under the electrolysis circumstances. The lowest cell voltages obtained at 80 °C are 1.631 V at 1000 mA cm−2, and 1.820 V at 2000 mA cm−2, when applying S100-Ir0.6Sn0.4O2 OER catalyst and Ti-material diffusion layer on the anode side and Nafion® 115 membrane. Furthermore, the noble-metal Ir loading in the same cell decreases to 0.77 mg cm−2. These results highlight that Ir–Sn oxide synthesized by the soft-material method is a promising OER electrocatalyst.Graphical abstractFigure optionsView in workspaceprs.rt("abs_end");KeywordsLow noble-metal loading; Iridium–tin oxide electrocatalyst; Oxygen evolution reaction; Proton exchange membrane water electrolyzer; Triblock polymer surfactantFigures and tables from this article:Fig. 1. TEM images of (a) as-synthetic S100-Ir0.6Sn0.4O2, (b) S100-Ir0.6Sn0.4O2, (c) S40-Ir0.6Sn0.4O2 and (d) N-Ir0.6Sn0.4O2.Figure optionsView in workspaceFig. 2. HRTEM images of (a) S100-Ir0.6Sn0.4O2, (b) S100-Ir0.6Sn0.4O2 at a higher magnification after exposing the electron beam for over 5 min at an accelerated voltage of 300 kV, (c) S100-Ir0.6Sn0.4O2 and (d) N-Ir0.6Sn0.4O2.Figure optionsView in workspaceFig. 3. XRD patterns of the prepared Ir0.6Sn0.4O2 samples. Stick reference patterns for rutile IrO2 and SnO2 are also included.Figure optionsView in workspaceFig. 4. XPS spectra for (a) Ir4f and (b) Sn3d in the prepared Ir0.6Sn0.4O2 samples. Solid circle – raw data; (Symbol+) line – fit data. Background lines for Ir4f and Sn3d5/2 are also included.Figure optionsView in workspaceFig. 5. CV curves of the prepared Ir0.6Sn0.4O2 and IrO2 samples at 50 mV s−1 in 0.5 M H2SO4 at room temperature.Figure optionsView in workspaceFig. 6. The reversibility of the pseudo-capacitance process of the prepared Ir0.6Sn0.4O2 and IrO2 samples.Figure optionsView in workspaceFig. 7. Dependence of voltammetric charges of the prepared Ir0.6Sn0.4O2 and IrO2 samples on scan rates in 0.5 M H2SO4 (a) before and (b) after the 2000th CV tests at 100 mV s−1.Figure optionsView in workspaceFig. 8. (a) LSV curves of the prepared Ir0.6Sn0.4O2 and IrO2 samples at 2 mV s−1 in 0.5 M H2SO4, and (b) Tafel plots (data extracted from LSV measurements) for OER, and (C) LSV curves after the 2000th CV test.Figure optionsView in workspaceFig. 9. Impedance spectra for the PEMWE cells at 1.45 V in a sweeping frequency range from 0.1 Hz to 10 kHz, and with an alternate signal of 10 mV. Point – raw data; line – fit data.Figure optionsView in workspaceFig. 10. Steady state polarization curves of the PEMWE cells using Nafion® 115 membrane and the prepared Ir0.6Sn0.4O2 samples as anode catalyst at 80 °C.Figure optionsView in workspaceFigure optionsView in workspaceTable 1.
Physical properties of various catalyst samples.View Within ArticleTable 2.
XPS analysis for the prepared Ir0.6Sn0.4 samples.
Journal of Power Sources 03/2014; 249:175–184. · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A ionic liquid doped polybenzimidazole (PBI) proton conducting membrane for anhydrous H2/Cl2 fuel cell has been proposed. Compared with other ionic liquids, such as imidazole type ionic liquids, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]) showed better electrode reaction kinetics (H2 oxidation and Cl2 reduction reaction at platinum), and was more suitable for H2/Cl2 fuel cell. PBI polymer and [dema][TfO] were compatibility with each other and the hybrid membranes exhibited high stability, and good ionic conductivity, reaching to 20.73 mS cm-1 at 160 oC. We also analyzed the proton transfer mechanism in this ionic liquid based membrane and considered that both proton hopping and diffusion mechanisms were existed. In addition, this composite electrolyte worked well in H2/Cl2 fuel cell under non-water condition. This work would give a good path to study the novel membranes for anhydrous H2/Cl2 fuel cell application.
[Show abstract][Hide abstract] ABSTRACT: Nickel hydroxide consisting of loosely packed nanospheres was synthesized as positive electrode material for an asymmetric capacitor based on Ni(OH)2 and activated carbon (AC). Two series of supercapacitors were fabricated to investigate the effects of the single electrodes of Ni(OH)2 and AC on the electrochemical performance of asymmetric Ni(OH)2–AC capacitor. Parameters including cell voltage window, specific capacitance and cyclic stability were assessed. In one series of supercapacitors, mass of Ni(OH)2 was excessive while mass of AC was varied, the AC electrode thus constrained both the capacitance and the upper limit of cell voltage. Deficiency of AC resulted in lower specific capacitance and narrower cell voltage window but benefited to cyclic stability. In the other series of supercapacitors, the mass of AC was excessive whereas the mass of Ni(OH)2 was changeable in each cell, Ni(OH)2 electrode thus dominated both the capacitance and the lower limit of cell voltage. As a consequence, deficiency of Ni(OH)2 led to higher specific capacity and wider cell voltage window as well as lower cyclic stability. These results can contribute to improving understanding of and optimizing performance of asymmetric Ni(OH)2–AC capacitor.
Materials Chemistry and Physics 02/2014; 143(3):1164–1170. · 2.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We reported a facile adjusted method for the synthesis of high surface area nanorod hematite film as a photoanode for application in water splitting. Crystalline hematite nanorods (EG-α-Fe2O3) are fabricated by electrodeposition in Fe(2+) precursor solution with the addition of ethylene glycol (EG) and followed by annealing at 450 °C. The nanorod hematite film fabricated by the modified electrodeposition approach exhibits a more uncompact structure than α-Fe2O3 obtained by directly electrodepositing on the FTO substrate. The optical and structural characteristics of the obtained film are also tested. The results infer that EG can tune the morphology of hematite and improve the photoabsorption in the visible light region due to its inducement of one-dimensional growth of crystal hematite. It also enhances the photoresponse activity of hematite in water splitting by improving the activities at the semiconductor/solution interface. The photocurrent density of EG-α-Fe2O3 nanorods increased to 0.24 mA cm(-2) at 1.4 V vs. RHE in 1 M KOH (pH = 13.6), almost 5 times higher than the original α-Fe2O3 (0.05 mA cm(-2), measured under the same conditions).
Physical Chemistry Chemical Physics 01/2014; · 4.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A 9-cell proton exchange membrane (PEM) water electrolysis stack is developed and tested for 7800 h. The average degradation rate of 35.5 μV h−1 per cell is measured. The 4th MEA of the stack is offline investigated and characterized. The electrochemical impedance spectroscopy (EIS) shows that the charge transfer resistance and ionic resistance of the cell both increase. The linear sweep scan (LSV) shows the hydrogen crossover rate of the membrane has slight increase. The electron probe X-ray microanalyze (EPMA) illustrates further that Ca, Cu and Fe elements distribute in the membrane and catalyst layers of the catalyst-coated membranes (CCMs). The cations occupy the ion exchange sites of the Nafion polymer electrolyte in the catalyst layers and membrane, which results in the increase in the anode and the cathode overpotentials. The metallic impurities originate mainly from the feed water and the components of the electrolysis unit. Fortunately, the degradation was reversible and can be almost recovered to the initial performance by using 0.5 M H2SO4. This indicates the performance degradation of the stack running 7800 h is mainly caused by a recoverable contamination.
Journal of Power Sources 01/2014; 267:515–520. · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Proton exchange membrane fuel cells (PEMFCs) with a dead-ended anode
(DEA) can obtain high hydrogen utilization by a comparatively simple
system. Nevertheless, the accumulation of the nitrogen and the water in
the anode channels can lead to a local fuel starvation, which degrades
the performance and durability of PEMFCs. In this paper, the behaviors
of PEMFCs with a DEA are explored experimentally by detecting the
current distribution and the local potentials. The results indicate that
the current distribution is uneven during the DEA operation. The local
current firstly decreases at the region near the anode outlet, and then
extends to the inlet region along the channels with time. The complete
fuel starvation near the anode outlet leads to a high local potential
and carbon corrosion on the cathode side. The SEM images of the cathode
electrode reveal that the significant thickness reduction and the
collapse of the electrode's porous structure happen in the cathode
catalyst layer, leading to the irreversible decline of the performance.
The comparison of the experiments with different oxidants and fuels
reveals that the nitrogen crossover from cathode to anode is the
dominant factor on the performance decline under the DEA operations.
Journal of Power Sources 01/2014; · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Partially graphitized hierarchically porous carbons (denoted as GHPCs) were prepared by using ordered mesoporous nickel oxide as template. The mesoporous nickel oxide, which is different from the inert template such as mesoporous silica SBA-15, plays an important role in the synthesis of the carbons with partially graphitized nanostructures at high temperature. X-ray diffraction, transmission electron microscopy and nitrogen adsorption were employed to characterize the structure of GHPCs. It is shown that the GHPC obtained by calcinating the precursor at 700 °C has a hierarchically porous structure with the pore size distributions at 8 and 30 nm. Partially graphitized structure leads to the high electrical conductivity of GHPCs. The GHPC prepared at 700 °C (GHPC700) shows outstanding high rate performance. Its specific capacitance reaches 91 F g−1 at a potential scan rate of 500 mV s−1. Meanwhile the specific capacitance for the GHPC prepared at 600 °C (GHPC600) is only 46 F g−1 at the same scan rate. Synergistic effect of the efficient ion transport in hierarchically porous structure and the high electrical conductivity owing to the partially graphitic structure is contributed to the attractive electrochemical performance of GHPC700.
Journal of Materials Science 01/2014; 49(1). · 2.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Na+ is a likely intrinsic impurity in water and is a potential cation impurity in the solid polymer electrolyte water electrolysis. In this paper, the dynamic-state effect of low concentration of Na+ is studied by adding Na+ into the deionized water fed in the SPE water electrolyser. The dynamic variation of cell voltage results show that the cell performance degraded more severely in the presence of Na+ impurity by anode poisoning than by cathode poisoning. The severity and poisoning rate of the cell depend on the Na+ concentration, water flow rate and cell temperature. However, the current density does not impact the extent of the cell voltage increase. In the meantime, an external reference electrode is used to measure the anode and cathode potentials. The performance degradation is mainly ascribed to the increase in cathode overpotential by anode poisoning. EIS measurements show that the performance difference primarily comes from the kinetics loss rather than the ohmic loss. The decrease of available protons in the three phase boundaries may lead to the increase in charge transfer resistance. The electron probe microanalysis tests show that Na+ remains in CCM even recovered with deionized water, which results in only partially recovered cell performance.
Journal of Power Sources 11/2013; 241:341–348. · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Glucose-derived activated carbon (GAC)/reduced graphene oxide (RGO) composites are prepared by pre-carbonization of the precursors (aqueous mixture of glucose and graphene oxide) and KOH activation of the pyrolysis products. The effect of the mass ratio of graphene oxide (GO) in the precursor on the electrochemical performance of GAC/RGO composites as electrode materials for electrochemical capacitors is investigated. It is found that the thermally reduced graphene oxide sheets serves as a wrinkled carrier to support the activated carbon particles after activation. The pore size distribution and surface area are depended on the mass ratio of GO. Besides, the rate capability of GAC is improved by the introduction of GO in the precursor. The highest specific capacitance of 334 F g−1 is achieved for the GAC/RGO composite prepared from the precursor with a GO mass ratio of 3 %.
Journal of Solid State Electrochemistry 11/2013; 17(11). · 2.28 Impact Factor