Designing M–N–O–N Basalt Fibers for Overall Water Splitting with Significant Regenerative Efficiency: Operando EIS and Temperature-Dependent Analyses

The development of economical bifunctional electrocatalysts with high activity and significant durability can provide a key to increasing energy demands. Herein, we report a stable overall water-splitting assembly, cobalt nitride-vanadium oxynitride (CoN-VON), which produced higher water oxidation kinetics, rapid proton reduction, and total water-splitting performance compared to monometallic CoN, VON, and noble metal catalyst systems. The optimized CoN-VON exhibits eye-catching OER activity along with HER activity, requiring only 281 and 164 mV electrode potential, with Tafel slopes of 84 and 48 mV dec^-1, respectively. The kinetics of CoN-VON, evaluated via operando EIS, inferred improved kinetics, reduced resistance, and higher conductivity. The improved activity was sustained, as confimed by the Bode study carried out at various potentials. The CoN-VON showed an activation energy (2.06 kJ/mol) lower than that of CoN (3.49 kJ/mol). The higher rate constant for CoN-VON at various pH, levels, derived from the Trumpet plot, inferred the rapid evolution of O₂ gas. Finally, an alkaline-/solar-driven electrolyzer was explored for overall water splitting at 1.62 V with long-term stability for 60 h. This study affords an effective energ-saving strategy to prepare nitride-oxynitride mechanochemically, promoting electron rearrangement with lowering of the energy barrier to enhance catalytic activity, and is believed to make hydrogen production more economical and sustainable.