Ultrafine intermetallic platinum-cobalt with a contracted Pt–Pt pair for efficient acidic oxygen reduction reactions

Ultrafine ordered intermetallic nanoparticles are emerging as promising electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. However, they are difficult to obtain because high-temperature annealing inevitably leads to metal sintering, resulting in larger crystallites. Additionally, the resulting electronic effects are difficult to control, limiting both performance and stability improvements. Herein, we present an ultrafine ordered intermetallic platinum-cobalt alloy encaged in nitrogen-doped carbon (Pt₃Co/NC) with a small particle size of 4.18 ± 1.00 nm and a high electrochemically active surface area (ECSA) of 73.16 m² g_Pt^-1. The contraction of the Pt-Pt pair induces strong electron coupling, resulting in electron transfer from Co to Pt. Using <i>in situ</i> spectroscopies, we revealed that incorporating the cost-effective transition metal Co into the Pt lattice induces Pt-Pt contraction and generates additional Pt d-band occupancy, which accelerates the protonation of *O to *OH, thereby significantly enhancing the kinetics of the four-electron ORR process. The meticulously designed catalyst achieves a superior half-wave potential of 0.89 V <i>versus</i> RHE and a remarkable mass activity of 0.79 A mg_Pt^-1. More importantly, after 10 000 cycles, the particle size expansion is marginal (5.01 ± 0.92 nm), alongside slight reductions in mass activity (6%) and specific activity (2%), demonstrating excellent catalytic stability in an acidic medium.