Mechanisms and kinetics of aqueous formic acid and formate ion dehydrogenation on platinum and subsequent reaction of adsorbed hydrogen

Abstract

The opencircuit chemical behavior of dissolved HCOOH and HCOONa at Pt electrodes was studied. A doublepulse electrochemical anodic charging technique was used to first strip the surface and to then quantitatively determine the amount of atomic hydrogen formed on the clean electrode from the dissociation of formic acid and formates and the net rate at which this atomic hydrogen was removed from the electrode surface by reaction with formate species. The integrated rates of the reaction of PtO ads with hydrogen and/or formate species, of the dehydrogenation of formic acid and formates on clean Pt, and of the atomic hydrogen removal were measured. The kinetics of the net atomic hydrogen removal process were determined and shown to be first order in respect to hydrogen atom concentration at the surface. The formation of residues from the organic free radicals which were the products of dehydrogenation retarded the further dissociation of formic acid and formates. Sulfuric acid solutions of very low pH values and molecular hydrogen could strongly affect the reaction rates and retarded the rate of hydrogen atom removal from the electrode surface. Generalizations concerning fuel cell anodic reactions are made.