Decoding systematic effects and mass transport in H2O2 production via Aux/C ORR electrocatalysis

Traditionally, evaluating a catalyst's activity has focused on its intrinsic properties. However, the observed catalytic behavior can be significantly influenced by both systematic parameters and mesoscopic mass transport limitations. Although the independent roles of various factors are known, their intricate interplay within electrocatalysis remains elusive. This work presents a comprehensive investigation into the interplay between these factors in the selective generation of hydrogen peroxide (H 2 O 2 ) via the oxygen reduction reaction (ORR) using Au x /C catalysts with varying particle sizes. By considering the exchange of surface-bound reaction intermediates between the electrode and bulk electrolyte, we reveal how the catalyst's surface area can influence selectivity through kinetic competition. This effect becomes particularly relevant for technologically important reactions such as the ORR, where multiple product pathways exist. This study underscores the need for a multi-scale approach that considers all these factors, especially for reactions involving multiple reaction pathways. Precise tuning of these parameters is essential for achieving a reliable and equitable assessment of electrocatalysts, paving the way for optimizing H 2 O 2 production and similar multi-step electrocatalytic reactions. • Smaller Au NPs exhibit enhanced activity and favour reducing O 2 to water over H 2 O 2 . • Increasing interparticle distance boosts H 2 O 2 selectivity, especially at higher Au loadings. • Thicker catalyst layers trap H 2 O 2 , slowing mass transport and boosting re-adsorption. • Intermediates' residence time and active site interactions, driven by oxygen affinity, affect selectivity.