Waste cotton stalk-derived carbon-supported Ni/NiO composite as an efficient bifunctional electrocatalyst for urea-assisted alkaline overall water splitting

Coupling waste biomass-derived carbon-supported transition metal oxide electrocatalysts with urea-assisted alkaline water splitting helps to reduce waste and pollution, while improving the efficiency of electrocatalytic hydrogen production. Herein, we report a waste cotton shell-derived carbon-supported Ni/NiO composite (Ni/NiO@C) synthesized via a straightforward pyrolysis strategy, enabling efficient valorization of agricultural biomass while significantly reducing catalyst cost. The optimized Ni/NiO@C-2 delivers exceptional bifunctional electrocatalytic activity, achieving a remarkably low overpotential of 117 mV for the urea oxidation reaction (UOR) and 228 mV for the hydrogen evolution reaction (HER) at 10 mA cm −2 , with the UOR exhibiting a Tafel slope as low as 22.18 mV dec −1 , underscoring its superior reaction kinetics. Notably, when employed as both the anode and cathode in a urea-assisted water electrolyzer, Ni/NiO@C-2 requires a cell voltage of only 1.55 V to achieve 10 mA cm −2 —substantially lower than that of conventional water splitting—while maintaining exceptional operational stability over prolonged electrolysis. The remarkable performance is attributed to the synergistic interplay between the hierarchically porous carbon architecture derived from natural cotton stalk, which ensures uniform dispersion of active Ni/NiO nanoparticles, and the enhanced charge transfer enabled by the well-integrated hybrid interface. This work not only establishes a sustainable platform for converting agricultural waste into high-performance electrocatalysts but also provides a viable pathway toward energy-saving hydrogen production through urea-assisted water splitting, offering a compelling strategy for simultaneous clean energy generation and wastewater treatment.