Cobalt–Vanadium Bimetallic Heterojunction Stabilizes High-Spin Co 3+ for Efficient Water Oxidation

High-spin cobalt-based catalysts represent promising candidates for the oxygen evolution reaction (OER) under alkaline conditions. However, during the OER process, the irreversible transformation of the high-spin Co 3+ (HS-Co 3+ ) species to a low-spin state due to insufficient sustainable electron compensation is a key factor leading to catalyst deactivation. We report a Co 2 VO 4 /VN heterojunction exhibiting a three-dimensional layered porous micronanostructure resembling puffed-rice-sphere. The interfacial structure anchored by strong V–N covalent bonds reduce crystal field splitting energy, promotes e g orbitals occupation, and stabilizes HS-Co 3+ . Concurrently, dynamic charge compensation from the V 4+ /V 5+ redox pair serves as an electron reservoir for Co sites, thereby suppressing the transition to low-spin states. Results demonstrate that the Co 2 VO 4 /VN catalyst achieves an ultralow OER overpotential of 253.2 mV at 10 mA·cm –2 in alkaline media, maintaining a stable current density of 1 A cm –2 at 1.866 V for 500 h in 1.0 M KOH. Through a life cycle assessment (LCA) of its preparation and application, the carbon footprint of the catalyst synthesis process is only 48.47 kg CO 2 -eq This work demonstrates that heterostructure engineering can overcome spin relaxation induced deactivation in high-spin cobalt catalysts, offering a general strategy for designing spin state-tuned electrocatalysts that combine high activity with extended lifetime.