Bifunctional oxygen reduction and urea oxidation reactions catalyzed by Co-Ni sulfides: Boosting kinetics via electronic modulation

The current study develops a transition metal-based sulfide (TMS), as a bifunctional electrocatalyst (EC) towards its application in oxygen reduction reaction (ORR) and urea oxidation reaction (UOR). Herein, microspheres of Co-Ni sulfide were synthesized using a facile hydrothermal method. The hierarchical sheet-on-sphere morphology of the C1N1S catalyst ensures high active site exposure. Beyond morphology, the superior activity is rooted in the synergistic electronic modulation of the mixed-valence Co and Ni sites, specifically through the distortion-induced t 2g 5 e g 1 state of Co 3+ and the t 2g 6 e g 1 state of Ni 3+ . These electronic characteristics promote efficient electron transfer between the catalyst surface and adsorbed intermediates. The synergy between the Co 2+ /Co 3+ and Ni 2+ /Ni 3+ aided the C1N1S to achieve the highest E onset i.e. 0.90 V vs. RHE for ORR, and also promoted an early 1.34 V (vs. RHE) potential to reach a current density of 10 mA cm −2 , exhibiting an excellent narrow potential gap (ΔE) of only 0.52 V. The work provides a promising strategy for utilizing electronic structure tailoring to develop high-performance TMS for the application in renewable energy conversion technologies.