Pd₁Ni₂ Trimer Sites Drive Efficient and Durable Hydrogen Oxidation in Alkaline Media

Anion-exchange membrane fuel cell (AEMFC) is a cost-effective hydrogen-to-electricity conversion technology under a zero-emission scenario. However, the sluggish kinetics of the anodic hydrogen oxidation reaction (HOR) impedes the commercial implementation of AEMFCs. Here, we develop a Pd single-atom-embedded Ni₃N catalyst (Pd₁/Ni₃N) with unconventional Pd₁Ni₂ trimer sites to drive efficient and durable HOR in alkaline media. Integrating theoretical and experimental analyses, we demonstrate that dual Pd₁Ni₂ sites achieve a "*H on Pd₁Ni₂-H_V + *OH on Pd₁Ni₂-H_N" adsorption mode, effectively weakening the overstrong *H and *OH adsorptions on pristine Ni₃N. Owing to the unique coordination mode and atomically dispersed catalytic sites, the resulting Pd₁/Ni₃N catalyst delivers a high intrinsic and mass activity together with excellent antioxidation capability and CO tolerance. Specifically, the HOR mass activity of Pd₁/Ni₃N reaches 7.54 A mg_Pd^-1 at the overpotential of 50 mV. The AEMFC employing Pd₁/Ni₃N as the anode catalyst displays a high power density of 31.7 W mg_Pd^-1 with an ultralow anode precious metal loading of only 0.023 mg_Pd cm^-2. This study provides guidance for the design of high-performance alkaline HOR catalytic sites at the atomic level.