Activity Descriptor Identification for Oxygen Reduction on Platinum-Based Bimetallic Nanoparticles: <italic>In Situ</italic> Observation of the Linear Composition–Strain–Activity Relationship

E xtensive efforts have been dedicated to the development of polymer electrolyte membrane fuel cells (PEMFCs) as promising alternatives to fossil fuels owing to their high energy efficiency and low emissions. 3 The main bottlenecks for PEMFC technology are the sluggish oxygen reduction reaction (ORR) and the high cost of platinum required to accelerate the ORR in the highly acidic and oxidizing environment of a PEMFC cathode. 6 The development of active and durable catalysts with reduced Pt content is of paramount importance for PEMFC commercialization. Much progress has been made in reducing the Pt loading by alloying Pt with transition metals such as Co, Ni, Cu, etc., as not only is less Pt wasted in the core, but the Pt-based alloys (PtM) often exhibit enhanced activity and durability compared to pure Pt. 11 The promoting effects induced by the transition metal are to weaken the binding energies of oxygen-containing ORR intermediates (e.g., O, OH, OOH) via altering the electronic property (such as the d-band center or vacancy) of the Pt-rich shell. 15 This is primarily induced by two effects: the geometric or the strain effects that refer to the changes in the Pt Pt bond distance on the surface, 18 and the electronic or * Address correspondence to [email protected].