Anion exchange membrane fuel cells are limited by the slow kinetics of alkaline hydrogen oxidation reaction (HOR). Here, we establish HOR catalytic activities of single-atom and diatomic sites as a function of *H and *OH binding energies to screen the optimal active sites for the HOR. As a result, the Ru-Ni diatomic one is identified as the best active center. Guided by the theoretical finding, we subsequently synthesize a catalyst with Ru-Ni diatomic sites supported on N-doped porous carbon, which exhibits excellent catalytic activity, CO tolerance, and stability for alkaline HOR and is also superior to single-site counterparts. In situ scanning electrochemical microscopy study validates the HOR activity resulting from the Ru-Ni diatomic sites. Furthermore, in situ x-ray absorption spectroscopy and computational studies unveil a synergistic interaction between Ru and Ni to promote the molecular H ₂ dissociation and strengthen OH adsorption at the diatomic sites, and thus enhance the kinetics of HOR.

Significance: The production of solar fuels from CO ₂ using sunlight and electricity provides one promising route for reducing atmospheric carbon emissions and storing intermittent solar energy. The rational design of an efficient and inexpensive electrocatalyst is the key. We developed a binary copper−iron catalyst for photoelectrochemical CO ₂ reduction toward methane. The theoretical calculations suggest that Cu and Fe in the binary system can work in synergy to spontaneously favor CO ₂ activation and conversion for methane synthesis. The earth-abundant CuFe catalyst exhibits a high current density with an impressive methane Faradaic efficiency using industry-ready planar silicon photoelectrodes under one-sun illumination. This work presents a unique, highly efficient, and inexpensive route for solar fuels synthesis.

Hydrogen embrittlement of metals is widely observed, but its atomistic origins remain little understood and much debated. Combining a unique identification of interstitial sites through polyhedral tessellation and first-principles calculations, we study hydrogen adsorption at grain boundaries in a variety of face-centered cubic metals of Ni, Cu, $\gamma \text{−}\mathrm{Fe}$, and Pd. We discover the chemomechanical origin of the variation of adsorption energetics for interstitial hydrogen at grain boundaries. A general chemomechanical formula is established to provide accurate assessments of hydrogen trapping and segregation energetics at grain boundaries, and it also offers direct explanations for certain experimental observations. The present study deepens our mechanistic understanding of the role of grain boundaries in hydrogen embrittlement and points to a viable path towards predictive microstructure engineering against hydrogen embrittlement in structural metals.