The development of precious-metal-free electrocatalysts with high-efficiency for hydrogen evolution reaction (HER) at all pHs is of great interest for the development of electrochemical overall splitting technologies. Despite that intense efforts have been made to developing cost-effective electrocatalysts toward HER under both acidic and alkaline electrolytes with high efficiency, electrocatalysts with remarkable performance in neutral media are rare. Herein, N atoms doped Co2P nanorod arrays grown on carbon cloth (N–Co2P/CC) have been successfully synthesized and further used as efficient electrocatalysts for HER at all pH values. Specially, the N–Co2P/CC exhibits an overpotential of 42 mV at the current density of 10 mA cm –2 with long-term stability in 1.0 M PBS (phosphate-buffered solution), which is comparable to the benchmark Pt/CC. Density functional theory (DFT) calculations suggest nitrogen doping could tailor the electronic structure of Co2P, leading to optimized adsorption free energies of water (ΔG *H2O) and hydrogen (ΔG *H), facilitating hydrogen generation through the Volmer–Heyrovsky mechanism.

The hydrogen evolution reaction (HER) on Pt and other noble metals often undergo ~2 orders of magnitude decrease in reaction kinetics when changing the electrolyte pH from acid to alkaline regime. The origin of this kinetic pH effect remains far from a consensus, hindering the rational design of pHspeci c electrocatalysts. Herein, by meticulously comparing the electric double layer (EDL) structures of acid and alkaline interfaces from the ab initio molecular dynamics (AIMD) simulations, and the computational vibration spectra of water molecules in the AIMD-simulated interfaces with the results of in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), we conclude that neither the hydrogen adsorption strength nor the water dissociation barrier is responsible for the greatly reduced HER kinetics on Pt in alkaline media, because the alkaline interface could have more favorite hydrogen adsorption strength and lower barriers for individual Volmer reactions; it is the signi cantly different connectivity of hydrogen bond networks in EDL that cause the huge kinetic pH effect of HER. What's further, using Pt-Ru alloy as model, our results reveal an unprecedented role of OH adsorption in improving the kinetics of alkaline hydrogen electrocatalysis on Pt-based catalysts, namely, by increasing the connectivity of hydrogen bond networks in EDL rather than by directly affecting the energetics of surface steps. These ndings should add signi cant new insights into the key roles of EDL structures in electrocatalysis. Meanwhile, this study offers a referential research paradigm for exploring the atomic structures of electrochemical interfaces by combining AIMD simulations, computational spectroscopy, and experimental spectroscopy.

Precisely tailoring the electronic structures of electrocatalysts to achieve an optimum hydroxide binding energy (OHBE) is vital to the alkaline hydrogen oxidation reaction (HOR). As a promising alternative to the Pt-group metals, considerable efforts have been devoted to exploring highly efficient Ni-based catalysts for alkaline HOR. However, their performances still lack practical competitiveness. Herein, based on insights from the molecular orbital theory and the Hammer–Nørskov d-band model, we propose an ingenious surface oxygen insertion strategy to precisely tailor the electronic structures of Ni electrocatalysts, simultaneously increasing the degree of energy-level alignment between the adsorbed hydroxide (*OH) states and surface Ni d-band and decreasing the degree of anti-bonding filling, which leads to an optimal OHBE. Through the pyrolysis procedure mediated by a metal–organic framework at a low temperature under a reducing atmosphere, the obtained oxygen-inserted two atomic-layer Ni shell-modified Ni metal core nanoparticle (Ni@Oi-Ni) exhibits a remarkable alkaline HOR performance with a record mass activity of 85.63 mA mg–1, which is 40-fold higher than that of the freshly synthesized Ni catalyst. Combining CO stripping experiments with ab initio calculations, we further reveal a linear relationship between the OHBE and the content of inserted oxygen, which thus results in a volcano-type correlation between the OH binding strength and alkaline HOR activity. This work indicates that the oxygen insertion into the top-surface layers is an efficient strategy to regulate the coordination environment and electronic structure of Ni catalysts and identifies the dominate role of OH binding strength in alkaline HOR.

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