The fivefold-twinned nickel (Ni) nanoparticles exhibit a pronounced pull-up strain near the twin boundary (TB), with a gradual increase in the strain effect near the TB. The fivefold-twinned nanoparticles demonstrate an increased hydroxyl binding energy (OHBE) and stable hydrogen binding energy (HBE) at the TB due to the strain effect, generating abundant and highly active sites in proximity to the TB. Special strain effect plays a crucial role in accelerating the hydrogen oxidation reaction (HOR) process.

Abstract

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.