Abstract: A transition metal electrocatalyst surface (e.g. a porous surface of finely divided Group VIII or Group I-B metal with an attached current collector) is modified by a sulfur treatment, using an oxidized sulfur species of average sulfur oxidation state of about 4 or less, e.g. SO.sub.2 dissolved in aqueous acid. Treatment of the transition metal with SO.sub.2 or the like typically provides up to 100% coverage of the surface electrocatalyst sites with chemisorbed sulfur-containing species and perhaps subsurface effects as well, but washing or other non-electrochemical techniques can remove 5-90% (e.g. 25-70%) of the chemisorbed SO.sub.2 or the like from the surface, leaving substantially only a very strongly bound form of the sulfur-containing species. The strongly bound sulfur-containing species can then be reduced to form a highly beneficial, selectively-improving pattern of sites containing reduced -S (e.g. sulfur or sulfide) on the electrocatalyst surface.

Abstract: A transition metal electrocatalyst surface (e.g. a porous surface of finely divided Group VIII or Group I-B metal with an attached current collector) is modified by a sulfur treatment, using an oxidized sulfur species of average sulfur oxidation state of about 4 or less, e.g. SO.sub.2 dissolved in aqueous acid. Treatment of the transition metal with SO.sub.2 or the like typically provides up to 100% coverage of the surface electrocatalyst sites with chemisorbed sulfur-containing species and perhaps subsurface effects as well, but washing or other non-electrochemical techniques can remove 5-90% (e.g. 25-70%) of the chemisorbed SO.sub.2 or the like from the surface, leaving substantially only a very strongly bound form of the sulfur-containing species. The strongly bound sulfur-containing species can then be reduced to form a highly beneficial, selectivity-improving pattern of sites containing reduced --S (e.g. sulfur or sulfide) on the electrocatalyst surface.