Oral: Electrocatalytic Oxygen Reduction Reaction at the Platinum Grain Boundaries

Grain boundaries in platinum catalysts are recognized as pivotal sites for enhancing oxygen reduction reaction (ORR) activity in acidic environments. In this work, scanning electrochemical cell microscopy (SECCM) was employed to map ORR current at the nanoscale, allowing high-resolution spatial correlation of electrocatalytic activity with the underlying platinum microstructure. SECCM revealed a significant rise in ORR current at platinum grain boundaries compared to adjacent grains. However, atomic force microscopy (AFM) mapping demonstrated that the electrolyte droplet contact area at grain boundaries can be larger than on grains, complicating straightforward current normalization. To accurately assess intrinsic activity, the measured electrochemical currents were normalized using the true surface area obtained from colocalized AFM topography, rather than relying on geometric estimates a critical advance for quantitative electrocatalysis at heterogeneous interfaces.

Our analysis further differentiated between high-angle and low-angle grain boundaries, with SECCM measurements showing that high-angle boundaries consistently exhibit greater ORR activity than low-angle boundaries. This enhanced activity suggests unique electronic or structural effects associated with high-angle boundary defects. The synergy of SECCM and AFM allows a more rigorous normalization and direct structure-activity mapping across individual grain boundaries. These insights elucidate the fundamental role of grain boundary engineering in optimizing catalyst design, providing new directions for the targeted fabrication of more active ORR electrocatalysts. The combination of SECCM and AFM presented here offers an advanced approach for interrogating nanoscale electrocatalytic processes, potentially extending to other energy-related reactions and materials systems.