Bimetallic Palladium–Nickel Nanoparticles Anchored on Carbon as High-Performance Electrocatalysts for Oxygen Reduction and Formic Acid Oxidation Reactions

Herein, we report the synthesis of carbon-supported palladium–nickel electrocatalysts (ECs) (Pd4–xNix/C ECs, x = 1–3) as an important class of non-platinum ECs, for both oxygen reduction reaction (ORR) and formic acid oxidation (FAO) reactions. Among various as-synthesized ECs, the Pd3Ni/C catalyst exhibited the best performance, which outperforms the benchmark Pt/C and Pd/C catalysts. For ORR, the onset potential of Pd3Ni/C EC (0.96 V) is 40 and 80 mV more positive than that of the benchmark Pt/C (0.92 V) and Pd/C (0.88 V) catalysts, suggesting its remarkable ORR behavior. All Pd4–xNix/C (x = 1–3) compositions favored the “4e” reduction pathway during ORR in alkaline media. Furthermore, the ECs are very efficient toward the FAO reaction, which proceeds via the “dehydrogenation” pathway. The electrochemically active surface area of Pd3Ni/C EC is found to be ∼2-, ∼4-, ∼5-, and ∼35-fold higher than that of PdNi/C, PdNi3/C, Pd/C, and standard Pd/C ECs, respectively. The remarkable ORR/FAO activity of the synthesized ECs can be ascribed to the homogeneous dispersion of smaller palladium–nickel alloy nanoparticles over the carbon support, downshift of Pd d-band center, as well as synergistic effect between the metals that makes electron transfer easier. Meanwhile, the downshift of the Pd d-band center after alloying with Ni was confirmed via density functional theory calculations, which unveiled the superiority of Pd3Ni/C over other ECs and the benchmarks. Thus, this work represents a cost-effective and ecofriendly approach for designing high-performance anode as well as cathode catalytic materials for practical applications.