Regulating the Electronic Structure of ZnCo ₂ O ₄ with CoS for Urea-Assisted Alkaline Water Electrolysis

To address the global energy crisis and environmental concerns, the development of low-cost, earth-abundant electrocatalysts for urea-assisted alkaline water splitting is essential. Herein, ZnCo2O4 and ZnCo2O4/CoS nanosheet electrocatalysts were synthesized through a facile, cost-effective hydrothermal approach. The optimized ZnCo2O4/CoS heterostructure demonstrates a prominent urea oxidation reaction (UOR) performance, achieving a current density of 50 mA cm–2 at 1.47 V vs RHE, and delivers a current density of 10 mA cm–2 at a low cell voltage of 1.50 V in a full-cell configuration. X-ray absorption spectroscopy (XAS) and scanning transmission X-ray microscopy (STXM) studies reveal that enhanced catalytic activity arises from an increased surface area and a higher Co3+/Co2+ ratio in ZnCo2O4/CoS. In fact, the introduction of Co–S bonds increases covalency via stronger Co 3d-S 3p hybridization. Subsequently, conductivity enhancement arises from improved electronic coupling rather than oxygen-vacancy-mediated transport. Further, in situ Raman analysis directs the dynamic formation of active cobalt (oxy)hydroxide (Co-OOH) intermediates in ZnCo2O4/CoS, which collectively accelerate OER kinetics. These features promote improved electronic conductivity and a greater number of active sites. Remarkably, ZnCo2O4/CoS maintains excellent stability performance for over 96 h at current densities of 10 mA cm–2. This work highlights valuable insights into the rational design of efficient, stable, and non-noble metal-based electrocatalysts for sustainable energy conversion applications.