Hydrogen Sulfide Poisoning of Platinum Anode in Phosphoric Acid Fuel Cell Electrolyte

Abstract

A s tudy has been made of the effect of H2S on the anodic ox idat ion of hydrogen on Pt in concentrated phosphor ic acid fuel cell electrolyte over a temperature range of 25~176 The anodic current vs. potent ia l curves of a stat ionary Pt elec-t rode in 94 weight percent (w/o) H3PO4 were measured with a half-cell setup, and the cyclic vo l tammetry was used to char-acterize the Pt surface in the presence of H2S. It was found that the in t roduct ion of H2S into hydrogen gas caused a rapid decrease in the anodic cur rent due to the adsorpt ion of H2S on Pt. The extent of H2S po ison ing appeared to decrease wi th increas ing temperature and to increase with increas ing potential. The cyclic vo l tammogram revealed that adsorbed H2S species b locked the active sites avai lable for the adsorpt ion/desorpt ion of H and thus retarded the rate of hydrogen oxida-t ion react ion on Pt. At suff iciently h igh anodic potentials, a layer of adsorbed e lementa l sulfur formed on the electrode sur-face and suppressed the format ion of p la t inum oxide at the oxygen adsorpt ion potentials. The Un i ted States Army is p lann ing to conver t logist ic hydrocarbon fuels (i.e., diesel oil, gasol ine, JP4, etc.) to a hydrogen- r ich gas as the anode reactant in the tactical fuel cell power plants. One of the crit ical impur i t ies in this feed gas, wh ich can cause the fa i lure of fuel cells, is hydrogen