Structural and Electronic Effects of Carbon‐Supported Pt x Pd 1− x Nanoparticles on the Electrocatalytic Activity of the Oxygen‐Reduction Reaction and on Methanol Tolerance

We report a systematic investigation on the structural and electronic effects of carbon‐supported Pt x Pd 1− x bimetallic nanoparticles on the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in acid electrolyte. Pt x Pd 1− x /C nanocatalysts with various Pt/Pd atomic ratios ( x =0.25, 0.5, and 0.75) were synthesized by using a borohydride‐reduction method. Rotating‐disk electrode measurements revealed that the Pt 3 Pd 1 /C nanocatalyst has a synergistic effect on the ORR, showing 50 % enhancement, and an antagonistic effect on the MOR, showing 90 % reduction, relative to JM 20 Pt/C on a mass basis. The extent of alloying and Pt d‐band vacancies of the Pt x Pd 1− x /C nanocatalysts were explored by extended X‐ray absorption fine‐structure spectroscopy (EXAFS) and X‐ray absorption near‐edge structure spectroscopy (XANES). The structure–activity relationship indicates that ORR activity and methanol tolerance of the nanocatalysts strongly depend on their extent of alloying and d‐band vacancies. The optimal composition for enhanced ORR activity is Pt 3 Pd 1 /C, with high extent of alloying and low Pt d‐band vacancies, owing to favorable OO scission and inhibited formation of oxygenated intermediates. MOR activity also shows structure dependence. For example, Pt 1 Pd 3 /C with Pt rich−core Pd rich−shell structure possesses lower MOR activity than the Pt 3 Pd 1 /C nanocatalyst with random alloy structure. Herein, extent of alloying and d‐band vacancies reveal new insights into the synergistic and antagonistic effects of the Pt x Pd 1− x /C nanocatalysts on surface reactivity.