Heterogeneous CoO–Pd interface along with oxygen vacancies boosts the oxygen reduction reaction performance of Pd nanoparticles

Abstract

The rational design of low-Pd catalysts for the oxygen reduction reaction (ORR) remains a central challenge toward cost-effective fuel cell technologies. Here, we report a multiwalled carbon nanotubes supported binary CoPd catalyst with an ultralow Pd loading of only 5 wt% and abundant oxygen vacancies in CoO domains (denoted as CoPd-O^V). As prepared CoPd-O^V catalyst delivers an impressive half-wave potential (E_1/2) of 0.883 V versus RHE and a kinetic current density (J_K) of 12.35 mA cm⁻² in alkaline ORR (0.1 M KOH), significantly surpassing the benchmark J.M.-Pt/C catalyst wit 20 wt% Pt loading (E_1/2 = 0.844 V vs. RHE, J_k = 4.37 mA cm⁻²). In situ X-ray absorption spectroscopy (XAS) at the Co K-edge reveals that oxygen vacancies in CoO promote O₂ bond activation and splitting, while the neighboring Pd domains facilitate the subsequent hydration step through a strong electron relocation effect from Co-to-Pd. A control CoPd catalyst with similar Pd content but lacking oxygen vacancies shows markedly suppressed ORR activity, confirming the synergistic role of O^Vs and Pd. These findings establish a powerful strategy for engineering vacancy–metal interfaces, enabling high-performance ORR electrocatalysis at minimal noble metal cost.