Effect of Electrolyte Ions on Iridium Oxide-Based Water Oxidation Catalysis

The oxygen evolution reaction often limits the efficiency of renewable fuel syntheses due to its sluggish reaction kinetics. Of the factors that have been studied to improve this important reaction is how the choice of the electrolyte may alter the reaction kinetics. Despite its importance, systematic studies of this effect have been relatively rare. Herein, we report an effort toward correcting this deficiency by investigating the effect of nitrate on water oxidation catalyzed by IrOx. The results show that nitrate can suppress the reaction, resulting in a decrease in the rate and an increase in the Tafel slope. The effect was found to be consistent with a microkinetic model incorporating competitive adsorption between reaction intermediates and nitrate, suggesting that the reaction mechanism was unaffected by the anion identity. Moreover, this blocking effect exhibited dependence on the cations, following a trend of Li+ ≈ Na+ ≈ K+ > Cs+ > TEA+. The results are expected to have broad applications in electrocatalysis.