Deep Insight into the Origin of the Size Effect of Pt Nanoparticles on Oxygen Reduction Electrocatalysis

Here, employing the kinetic current (I_k) of the exposed electrochemical surface area (exposed ECSA) to assess the real activity and in situ X-ray absorption spectroscopy to assess the electronic/local structure, we report a new mechanism for the size effect of Pt nanoparticles (NPs) on the oxygen reduction reaction (ORR). The results show that I_k of the exposed ECSA of large-sized Pt has a smaller decrease with increased potentials than that of small-sized Pt. Correspondingly, the electron vacancy and strain relaxation of large-sized Pt have a smaller increase with increased potentials than those of small-sized Pt. The d-band center theory verifies that the decreased extent in I_k of the exposed ECSA is the perfect reflection of the increased extent in electron vacancy and strain relaxation of Pt NPs. These findings identify that the potential-induced structural changes of Pt NPs engender the deactivation of the exposed ECSA, which dominates the size effect of Pt NPs on the ORR.