Joghee Prabhuram

Electrochemical Reactions in a DMFC under Open-Circuit Conditions

Department of Mechanical Engineering, The Hong Kong University of Science and Technology,Clear Water Bay, Kowloon, Hong Kong, ChinaGas evolution, principally consisting of carbon dioxide and hydrogen, was observed in the anode flow field of a direct methanolfuel cell ~DMFC! running under open-circuit conditions and at low oxygen flow rates. This finding is contrary to conventionalwisdom that electrochemical reactions cease as an external load is removed. The mechanism leading to this peculiar phenomenonis explained theoretically and confirmed experimentally.© 2004 The Electrochemical Society. @DOI: 10.1149/1.1836111# All rights reserved.Manuscript submitted July 17, 2004; revised manuscript received August 28, 2004. Available electronically November 29, 2004.

Possibilities of prevention of formation of poisoning species on direct methanol fuel cell anodes

Abstract Porous unsupported Pd, Pt and Pt–Ru single phase alloy electrodes with different compositions viz. 9:1, 7:3 and 5:5 were prepared by NaBH 4 reduction method at room temperature. Extensive cyclic voltammetric investigations in different solutions have been performed on these electrodes, as well as on smooth electrodes, with the aim of identifying suitable combinations of electrode structure and electrolyte/methanol mixtures which can prevent the formation of organic poisoning species. Various electrochemical processes occurring in different potential regions are discussed. Meanings of the appearance/disappearance of oxidation peaks during both forward and backward sweeps on the present electrodes are pointed out.

Pd and Pd-Cu alloy deposited nafion membranes for reduction of methanol crossover in direct methanol fuel cells

Department of Mechanical Engineering, The Hong Kong University of Science and Technology,Clear Water Bay, Kowloon, Hong Kong, ChinaTo reduce methanol crossover in direct methanol fuel cells ~DMFCs!, Nafion 115 membrane was modified by sputtering a thinlayer of Pd or a thin layer of Pd-Cu~60:40! alloy. The sputtered membranes were characterized by using a scanning electronmicroscope, an energy-dispersive X-ray spectrometer, and X-ray diffraction analysis. At room temperature, the modified mem-branes showed significant improvements in both the open-circuit voltage~OCV! and cell performance as compared with the bareNafion 115 membrane; and Pd-sputtered membrane performed better than the Pd-Cu-sputtered membrane in OCV and cellperformance. The methanol permeation rate studied by the voltammetric method in a DMFC configuration under the open-circuitcondition indicated that the improvements in the cell performance occurred because the methanol crossover was lower with themodified membranes than with the bare membrane. At a higher cell operating temperature~70°C!, the Pd-sputtered membraneshowed higher OCV and higher performance only at low current densities, but the performance was found to decline at highcurrent densities. It was also found that at this higher temperature operation, the Pd-Cu-sputtered membrane at high currentdensities exhibited a better performance than the bare Nafion 115 membrane did.© 2005 The Electrochemical Society. @DOI: 10.1149/1.1926671# All rights reserved.Manuscript submitted August 26, 2004; revised manuscript received January 24, 2005. Available electronically June 10, 2005.