Roles of structural defects in polycrystalline platinum nanowires for enhanced oxygen reduction activity

Abstract

Nanocatalysts have uneven reactivity and lively change in reactions, challenging revealing catalytic origins. Phenomenologically, Pt-based nanowires, one of the most important nanostructures, have displayed high activity for oxygen reduction reaction (ORR); however, the fundamentally catalytic origin behind such high performance remains elusive and was implicitly ascribed to one-dimensional structure and/or low-index facets. Here, with molecular-level and operando spectroscopic evidence, we reveal that the polycrystalline platinum nanowires with enhanced ORR activity are closely correlated with structural defects including grain boundaries (GBs), atomic steps, and a few amorphous regions, which is previously neglected or simplified. The local micro-strain is induced by GBs and increases with misorientation angles of GBs. Despite the same coordination number between edge sites and atomic steps, the latter together with a few amorphous regions disturb interfacial water networks via preferably hydrogen bonding, which destabilizes ORR intermediates on terraces and presumably promotes proton transfer.