High-Efficiency Hydrogen Oxidation for Hydroxide Exchange Membrane Fuel Cells Catalyzed by Fivefold-Twinned Nickel...

The independent regulation of multiple intermediates is critically important for optimizing the electronic structure of nickel (Ni), thereby improving its catalytic performance in the hydrogen oxidation reaction (HOR). However, conventional regulation strategies based on the Hammer-Nørskov d-band model often change the hydrogen binding energy (HBE) and hydroxyl binding energy (OHBE) in a synchronized manner. Herein, we find that a catalyst consisting of fivefold-twinned ultrasmall Ni nanoparticles could tune HBE and OHBE individually via the strain effect. Experimental and theoretical calculations suggest that tensile strain in proximity to the twin boundary (TB) significantly enhances OHBE, allows for adjustable HBE due to unique geometric effects, and greatly reduces HBE at specific sites, enabling an unprecedented HOR activity. The catalyst has a high j_k,m value of 106.6 mA mg_Ni ^-1, which is 24.2 times greater than that of Ni/C. The hydroxide exchange membrane fuel cell (HEMFC) with fivefold-twinned Ni nanoparticles anode delivers a peak power density (PPD) of 805 mW cm^-2 with H₂/O₂ gas feed, which is the highest among Ni-based electrocatalysts reported thus far. Furthermore, the catalyst also exhibits excellent long-term cycling performance, taking a giant step forward toward the commercialization of platinum group metal (PGM)-free HEMFCs.