Modeling the electroreduction of hydrogen peroxide in alkaline media

Contrary to the hydrogen peroxide (H202) reduction reaction (HPRR) in acidic solutions, the kinetic mechanism in alkaline media is still unclear. ln this study we propose, for the first time, a model to describe HPRR in alkaline media taking in account the effect of metallic cation (C+) in the electrolyte. H202 is mainly found as deprotonated hydrogen peroxide (H02-) due to alkaline media. The reduction process initiates by a dissociative adsorption (asterisks represent free active sites) of HO2- (r1 ), that produces adsorbed oxygenated species (OHad and Üad). As they are unstable adsorbates it is assumed that, as soon as they are formed, Üad promptly reacts with water to form OHad (r2) and OHad is reduced to OH- (r3). Water, which is an abundant molecule, is constantly adsorbing (r5) and desorbing (r6) at the surface. The water reduction step (r7) promotes the formation of Had that acts as a blocking agent for HPRR and generates H2 (r9). The effectiveness for water reduction is correlated with noncovalent interactions between cation and adsorbed water (r10). As the coverage of H2Oad is stabilized by e +, the formation of Had can be enhanced (r12), the poisoning effect induced by these interactions could result in a decrease of the faradaic current and the oscillatory frequency because of the formation of Had. To verify the coherency of the proposed mechanism numeric simulations of electrochemical kinetics of HPRR is being currently developed under conventional and oscillatory conditions.