Hydrogen oxidation reaction in alkaline media: Relationship between electrocatalysis and electrochemical double layer structure
Abstract Enhancing the sluggish kinetics of electrochemical hydrogen oxidation reaction in high pH environments is of crucial importance considering its applications in alkaline membrane fuel cells (AMFC) and regenerative hydrogen electrodes for energy storage. Alkaline H 2 oxidation to form water involves reaction between H adsorbed intermediates and hydroxide anions wherein the nature/source of the latter plays a crucial role. Here, we take a systematic approach to understand why H 2 oxidation kinetics is slower in alkaline media compared to acid. While recently reported models focus on surface adsorbate bond strength optimization, we herein show that the alkaline H 2 oxidation mechanism is fundamentally different due to a complex interplay between electrocatalysis and electrochemical double layer structure. A heretofore unknown modern rendition of the double layer structure is proposed wherein specifically adsorbed (M OH ad and quasi specifically adsorbed (M H ad/upd OH q ad reactive hydroxide species localized in the compact part of the electrochemical double layer is shown to define H 2 oxidation kinetics on monometallic and bimetallic catalyst surfaces at high pH.