Modulation of the electronic structure of nickel selenide <i>via</i> iron doping for energy-saving hydrogen production coupled with sulfion upgradation

Hybrid water electrolysis is a promising approach for energy-saving hydrogen (H₂) generation by replacing the oxygen evolution reaction with the thermodynamically advantageous sulfion oxidation reaction (SOR). Herein, we designed iron-modified nickel selenide nanosheet arrays (Fe-Ni_0.85Se) and used them as an electrocatalyst in bifunctional hydrogen evolution reaction (HER) and SOR to simultaneously facilitate H₂ production and sulfion conversion into a valuable sulfur product. Fe-Ni_0.85Se requires a low overpotential of 114 mV for the HER and a working potential of 0.340 V for the anodic SOR to attain 10 mA cm^-2. Moreover, the two-electrode hybrid electrolysis cell employing Fe-Ni_0.85Se as the cathode and anode requires a small voltage of 0.439 V at 10 mA cm^-2, which greatly reduces the operating voltage by 1.186 V compared with that for overall water splitting, realizing energy-saving H₂ production and high-value-added sulfur production. Theoretical calculations prove that Fe modification can accelerate water dissociation, optimize the adsorption behavior of hydrogen adsorption and sulfion, and promote the conversion process of sulfur intermediates. This study offers a simple approach to develop bifunctional catalytic electrodes for economically viable H₂ generation and sulfur recovery.