Effects of heat treatment on the catalytic activity and methanol tolerance of carbon-supported platinum alloys

This work studies the effect of heat treatment of carbon-dispersed platinum and platinum alloys on its methanol tolerance and catalytic activity as gas diffusion electrodes for oxygen reduction reaction (ORR) in acid medium. The catalyst powders were subjected to heat treatments at three different temperatures for a fixed period at controlled atmospheres. Differences in catalyst morphology were characterized using X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscope techniques. The electrochemical characteristics and activity of the electro-catalysts were evaluated for ORR and methanol tolerance using cyclic voltammetry, in the form of gas diffusion electrodes. The optimum heat-treatment temperature is found to be strongly dependent on the individual catalyst. The maximum ORR activity and better methanol tolerance for the oxygen reduction reaction (ORR) was observed in Pt-Fe/C and Pt-Cu/C catalysts subjected to heat treatment at 350 °C.A trend of catalytic activity for oxygen reduction reaction (ORR) was obtained: Pt-Cu/C (350°C)>Pt-Fe/C (350°C) > Pt-Ni/C (350°C) > Pt-Co/C (250°C) > Pt/C (350°C), showing that Pt-Cu/C-type catalysts had a higher catalytic activity with reasonable methanol tolerance

Effect of Diffusion-Layer Morphology on the Performance of Solid-Polymer-Electrolyte Direct Methanol Fuel Cells

The performance of solid-polymer-electrolyte direct methanol fuel cells (SPE-DMFCs) is substantially influenced by the morphology of the gas diffusion-layer in the catalytic electrodes. Cells utilising gas diffusion-layers made with high surface-area Ketjen Black carbon, at an optimised thickness, show better performance compared with cells utilising Vulcan XC-72 carbon or ‘acetylene black’ carbon in the diffusion-layer. The cells with a hydrophilic diffusion-layer on the anodes and a hydrophobic diffusion-layer on the cathodes yield better performance. The cells with oxygen or air as the oxidant gave power density of 250 or 105 mW cm^ - ^2, respectively, at an operational temperature of 90 °C and 2 bar pressure

Unsupported Cu-Pt Core-Shell Nanoparticles: Oxygen Reduction Reaction (ORR) Catalyst with Better Activity and Reduced Precious Metal Content

An unsupported Cu-Pt core-shell catalyst is prepared by a transmetalation reaction between copper and Pt2+ ions, and a Cu-Pt bimetallic alloy catalyst by a simultaneous reduction reaction. Both catalysts are subjected to electrochemical leaching without further treatment and their electrochemical characteristics and ORR activities are compared to that of a standard Pt black catalyst. Potential cycling in 0.1 M HClO4 and 0.5 M H2SO4 shows that the core-shell catalyst is highly stable and the electrochemical features show that it is purely Pt on the catalyst surface. The electrochemical surface area of the Cu-Pt core-shell catalyst is much higher than that of the Pt black. When the Pt loading on the electrode is increased with Pt black catalyst to match its geometric electrochemical surface area (cm(2)/electrode area (cm(2))) with that of Cu-Pt core-shell catalyst, the activity of the latter is still higher. The mass activities of Pt black, Cu-Pt binary alloy, and Cu-Pt core-shell catalysts measured using a rotating disk electrode are 0.053, 0.153 and 0.262 A mg(-1) Pt, and their respective specific activities are 197, 496, and 710 mu A cm(-2) Pt. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.039207jes] All rights reserved

A high-performance phosphoric acid fuel cell

Although, phosphoric acid fuel cell technology is now nearly commercially mature, it is mandatory to make it cost competitive with existing power technologies. Since, the cost and power density of fuel cells are linked to each other, attempts are being made to enhance the power density of phosphoric acid fuel cells. This study demonstrates that phosphoric acid fuel cells with power density values as high as $560 \hspace{2mm}mW cm^{-2}$ are realizable by employing a combination of SiC and $ZrSiO_4$ as an electrolyte matrix, and Pt-Co/C as a cathode catalyst

A high-performance phosphoric acid fuel cell

Although, phosphoric acid fuel cell technology is now nearly commercially mature, it is mandatory to make it cost competitive with existing power technologies. Since, the cost and power density of fuel cells are linked to each other, attempts are being made to enhance the power density of phosphoric acid fuel cells. This study demonstrates that phosphoric acid fuel cells with power density values as high as 560 mW cm-2 are realizable by employing a combination of SiC and ZrSiO4 as an electrolyte matrix, and Pt-Co/C as a cathode catalyst

Effect of diffusion-layer morphology on the performance of solid-polymer-electrolyte direct methanol fuel cells

The performance of solid-polymer-electrolyte direct methanol fuel cells (SPE-DMFCs) is substantially influenced by the morphology of the gas diffusion-layer in the catalytic electrodes. Cells utilising gas diffusion-layers made with high surface-area Ketjen Black carbon, at an optimised thickness, show better performance compared with cells utilising Vulcan XC-72 carbon or 'acetylene black' carbon in the diffusion-layer. The cells with a hydrophilic diffusion-layer on the anodes and a hydrophobic diffusion-layer on the cathodes yield better performance. The cells with oxygen or air as the oxidant gave power density of 250 or 105 mW cm-2, respectively, at an operational temperature of 90 ° C and 2 bar pressure

Carbon-supported Pd-Fe electrocatalysts for oxygen reduction reaction (ORR) and their methanol tolerance

Carbon-supported palladium-iron bimetallic electrocatalysts of different Pd to Fe ratios (1:1, 2:1, 3:1) were prepared by a low temperature single step co-reduction method in alkaline media without any stabilizing agents. The physical characterizations of catalysts were done using XRD and TEM. The electrochemical characterizations were done using underpotential deposition (upd) of hydrogen and copper. Electrocatalytic activities for oxygen reduction reaction (ORR) were investigated and compared to that of standard Pt/C catalyst. The carbon-supported Pd-Fe bimetallic catalysts showed higher surface area than that of pure Pd/C. The half-wave potential of ORR on as-prepared palladium-iron bimetallic catalysts was shifted positively by similar to 75-100 mV from that of Pd/C in oxygen saturated 0.1 M HClO(4) solution. The highest catalytic activity was obtained with Pd(3)Fe/C - catalyst and it was close to that of standard Pt/C. XRD analysis did not show any noticeable shift in peak position due to alloying. In presence of methanol, carbon-supported Pd and Pd-Fe bimetallic catalysts showed superior ORR selectivity and activity unlike Pt/C. The peroxide generation on Pd(3)Fe/C - the best of Pd based electrocatalyst - was comparable to that on Pt/C. These catalysts, prepared at low temperature and without any further heat-treatment, gave activities that were free from effects of crystallite size, segregation, and enrichment of precious metal content that might happen at high temperature. (C) 2011 Elsevier B.V. All rights reserved

Mg-C Interaction Induced Hydrogen Uptake and Enhanced Hydrogen Release Kinetics in MgH2-rGO Nanocomposites

Hydrogen uptake at 250 degrees C, P-H2 > 15 bar and release at 320, 350 degrees C by MgH(2 )mixed with 10 wt % rGO alleviates the incubation period (slow kinetics) encountered during hydrogen release by pure MgH2. Ball milling establishes Mg-C interactions (similar to 283 eV) in these nano-composites through electron-transfer from Mg to pi* of C and weakens the C-C pi bond. These Mg-C interactions persist in the nanocomposites upon subsequent hydrogen uptake and release. These interactions change the hybridization of C from sp(2) to sp(3), aiding hydrogen uptake by C (C-H). On hydrogen release, H releases from C-H, and electrons are donated back from C to Mg. This electron back-donation weakens the Mg-H bond and enhances hydrogen release from MgH2. The persistent Mg-C interactions are crucial for alleviating the incubation period. For the present study, X-ray diffraction, Raman, X-ray photoelectron spectroscopy (C-1s core level, valence band), and Fourier transform infrared spectroscopy are used

Sodium borohydride treatment: a simple and effective process for the removal of stabilizer and capping agents from shape-controlled palladium nanoparticles

The inherent property of palladium to form hydride is effectively exploited for the removal of adsorbed stabilizer and capping agents. Formation of hydride on exposure of Pd nanoparticles to sodium-borohydride weakens the metal's interaction with the adsorbed-impurities and thus enables their easy removal without compromising the shape, size and dispersion