Stable Hexagonal Close-Packed CoRu/C Nanocrystals for Highly Efficient Hydrogen Oxidation Electrocatalysis

The hydrogen oxidation reaction (HOR) in alkaline media, a critical anode process of anion exchange membrane fuel cells (AEMFCs), suffers from intrinsically sluggish kinetics and limited CO tolerance, hindering practical applications. The hexagonal close-packed (hcp) Co exhibits great potential, while crystallographic phase engineering of Co-based nanomaterials remains largely uncharted territory for boosting HOR activity. Here, we demonstrate that hcp CoRu nanocrystals anchored on C nanosheets exhibit enhanced alkaline HOR performance compared to their face-centered cubic (fcc) counterparts. The hcp CoRu/C catalyst achieves a higher mass activity of 886 A g_Ru^-1 at 50 mV, surpassing fcc CoRu/C (2.13×), Pt/C (10.6×), and Ru/C (18.1×), while maintaining 77.3% current retention over 20,000 s and high CO tolerance (94.9% activity retention in H₂/1000 ppm of CO). Density functional theory (DFT) calculations indicate that the hcp phase stabilizes Ru sites by downshifting their d-band center, simultaneously weakening hydrogen binding energy (HBE) and optimizing hydroxyl adsorption energy (OHBE). This dual modulation synergistically accelerates the rate-limiting Volmer step and mitigates CO poisoning. Our work demonstrates crystallographic phase engineering as a viable strategy for designing robust HOR electrocatalysts, offering an alternative to traditional composition-based approaches for advancing alkaline fuel cell technologies.