Heteroatom doping has emerged as an effective strategy to enhance the performance of electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Traditional doping methods often involve harsh chemical treatments and tedious procedures, hindering their widespread applications. Furthermore, although dynamic surface reconstruction in alkaline media is commonly observed in bimetallic compounds, strategies to regulate this reconstruction behavior for enhanced HER and OER performances remain inadequately explored. Herein, we report an ultrafast (≤ 300s) and mild electrochemical doping approach to fabricate Se-doped NiCo₂S₄ hollow nanoarrays on carbon fiber papers (a-NiCo₂(S_1-xSe_x)₄), investigating the role of Se in enhancing overall water splitting performance. Under HER conditions, a-NiCo₂(S_1-xSe_x)₄ demonstrates remarkable stability, with Se tuning the electronic structure to optimize intermediate adsorption and facilitate H₂O dissociation. While under OER conditions, Se doping lowers the energy barrier for reconstruction and promotes transformation into active Se, S co-doped Ni_0.33Co_0.67OOH nanosheets. The optimal samples exhibit superior HER and OER activity, requiring a cell voltage of 1.578 V to deliver a current density of 100 mA cm⁻² for overall water splitting. This work not only introduces a facile method for Se doping but also provides comprehensive insights into the structure–composition–activity relationship for Se-doped bimetallic sulfide.

With practical electrocatalytic hydrogen production frequently involving the splitting of water in various pH media, there is an urgent need but still a technical challenge to develop low-cost, highly active, and stable electrocatalysts for pH-universal hydrogen evolution reaction (HER). We report herein the adoption of a hydrothermal reaction combined with a post gas-phase doping strategy to fabricate P-doped NiCo₂Se₄ hollow nanoneedle arrays on carbon fiber paper (i.e., P-NiCo₂Se₄/CFP). Notably, the optimal arrays (P_8.71-NiCo₂Se₄/CFP) can afford an outstanding pH-universal HER performance, with an overpotential as low as 33, 57, and 69 mV at 10 mA·cm⁻² and corresponding Tafel slopes down to 52, 61, and 72 mV·dec⁻¹ in acidic, alkaline, and neutral media, respectively, outperforming most state-of-the-art nonprecious catalysts and even the commercial Pt/C catalyst in both neutral and alkaline media at large current densities. Impressively, P_8.71-NiCo₂Se₄/CFP also displays good durability toward long-time stability testing in harsh acidic and alkaline electrolytes. Experimental and theoretical studies further reveal that the doping of P atoms into NiCo₂Se₄ can simultaneously optimize its H* adsorption/desorption energy, water adsorption energy, and water dissociation energy by adjusting the local electronic states of various active sites, thus accelerating the rate-determining step of HER in different pH media to endow P-NiCo₂Se₄ with an outstanding pH-universal HER performance. This work provides atomic-level insights into the roles of active sites in various electrolysis environments, thereby shedding new light on the rational design of highly efficient pH-universal nonprecious catalysts for HER and beyond.