Expanding our view on active sites in electrocatalysis

Abstract

At the heart of electrocatalyst design and development lies the concept of active sites that are usually identified as those sites for adsorption where the conversion of interest occurs. However, electrochemical interfaces are complex systems where the exact structure and dynamics of interfacial species during a reaction greatly depend on the local reactive microenvironment, including co-adsorbates and solvent molecules, that may include structural transformations upon adsorption, the charge-transfer dynamics, and/or the x,y charge-induced electric field distribution. We review the concept of active sites in electrocatalysis within these lines in light of recent studies that point out the necessity to expand the still widely spread idea of quasi-static atomic-scale sites toward the picture of a dynamically reactive microenvironment: the active site can extend over several tens on nanometers due to surface structural transformations during the reaction, includes interdependent components such as electrode and electrolyte as well as target reactant geometric and electronic structures, and often spontaneously rearranges during the electrocatalytic reaction. Thus, to define optimal reactions conditions, the reactive microenvironment as a whole needs to be considered.