In situ detection with interdigitated array electrodes towards the platinum-catalyzed oxygen reduction reaction: Size effect and the reaction pathway

Platinum has long been recognized as a vital catalyst in energy conversion and utilization, particularly in oxygen reduction reaction (ORR), due to its exceptional catalytic activity. However, its exorbitant cost and scarcity have motivated researchers to explore the size-activity correlation of Pt catalysts in ORR, aiming to reduce Pt loading density while preserving high catalytic performance. In this work, we concentrate on the interdigitated-array(IDA)-electrodes-based precise detection of the influence of Pt cluster size on catalytic ability, focusing on (1) Direct synthesis of Pt catalyst onto electrodes surface, rather than offline preparation and pasting, to avoid interference from other chemicals and changes to the surface status of catalyst particles; (2) Use of IDA electrodes with largely improved sensitivity for in-situ detection of reaction intermediates (H₂O₂) and provide insight into the reaction pathway and electron transfer process. It indicates that the specific activity and mass activity are larger for the smaller-sized Pt cluster. Specifically, the proportion of different electron transfer pathways was analyzed with IDA results, and with the same amount of Pt catalyst loading, the smaller-sized Pt cluster produces a higher percent of H₂O₂; the smaller-sized Pt catalyzed ORR undergoes less proportion of 4-electron pathway than the larger-sized Pt catalyst (about 43% total catalytic current is contributed by the 4-electron pathway for the #6 Pt catalyst, and this number raises to 98% for the #1 Pt catalyst).