Combinatorial Screening of Pd–Co–Au and Pd–Zr–Cu Systems as Potential Catalysts for Formic Acid Oxidation

This study presents a systematic investigation of two optimized Pd-based alloy catalysts, Pd2Co6Au2 and Pd8Zr2, for the formic acid oxidation reaction (FAOR). Scanning electrochemical microscopy was employed to screen Pd–Co–Au and Pd–Zr–Cu catalyst arrays, leading to the identification of compositions with the highest FAOR activity for subsequent evaluation. Structural and electrochemical analyses reveal that Pd2Co6Au2 possesses a CoO-enriched interfacial surface, which promotes OH adsorption and facilitates CO oxidation, thereby enhancing the CO tolerance and long-term stability. In contrast, Pd8Zr2 benefits from ZrO2-induced modulation of the Pd electronic structure, exhibiting high initial activity but diminished durability due to CO accumulation. Overall, Pd2Co6Au2 achieves an optimal balance among catalytic activity, CO tolerance, and operational stability. Although Pd8Zr2 exhibits higher initial mass and specific activities, it suffers from a more rapid performance degradation. Both catalysts outperform pure Pd, underscoring their potential for efficient FAOR. Notably, the direct formic acid fuel cell employing Pd2Co6Au2 delivers a maximum power density of 116.71 mW cm–2 at a current density of 389.04 mA cm–2.