Interparticle Distance-Driven Diffusion Field Transforming Selectivity in Oxygen Reduction Reaction

Abstract The oxygen reduction reaction (ORR) on platinum (Pt) electrodes in acidic electrolytes can occur via two pathways, with the four-electron (4e−) pathway predominantly prevailing. However, the research on the fundamental reasons for the switching of reaction pathways has largely focused on structure-activity relationships, while neglecting the impact of mass transport. The influence of macroscopic mass transport from the bulk to the diffusion layer has been studied by controlling the rotating speed. However, regulating mesoscopic transport by altering macroscopic hydrodynamics remains challenging. In this study, we varied the loading of Pt nanoparticles to produce Pt with nearly identical physicochemical properties but differing interparticle distances. Increasing the interparticle distance from 58.6 nm to 117.0 nm significantly enhanced the selectivity towards H2O2 in an acidic environment, with the selectivity increasing from 4.6% to 81.5%. Utilizing electrochemical im-pedance spectroscopy, we demonstrate that interparticle distance modulates the O2 diffusion field around Pt nanoparticles, consequently affecting H2O2 adsorption and determining the electron transfer numbers of the ORR. Our findings highlight that mesoscopic mass transport influences not only the total current but also the reaction pathways. These results emphasize the importance of the spatial distribution density of nanoparticles in regulating mesoscopic mass transport, thereby controlling the adsorption of intermediates and enhancing electrocatalytic performance.