Bridging Energy Conversion and Storage: Precursor-Engineered Co@CoO-Y2O3 Heterostructures for Oxygen Reduction Reaction and Battery-Type Supercapacitor Applications

Abstract

The escalating consumption of fossil fuels and the intermittency of renewable power have intensified the need for multifunctional electrochemical materials that can couple efficient energy conversion and durable energy storage while avoiding device-level complexity and reliance on Pt. Herein, we report a non-noble metal-based Co@CoO-Y2O3 (CCY) heterostructured composite synthesized via the pyrolysis of a well-defined cobalt-yttrium single-crystal precursor complex. Structural and spectroscopic analyses confirm the coexistence of metallic Co, CoO, and Y2O3 phases, with strong Co-O-Y interfacial coupling and oxygen-vacancy-rich heterointerfaces arising from rare-earth oxide incorporation. The CCY composite exhibited hierarchical mesoporosity, facilitating mass transport and active site accessibility. In alkaline media (1 M KOH), CCY demonstrates competitive oxygen reduction reaction (ORR) activity, delivering a half-wave potential of 0.728 V (vs. RHE), an onset potential of 0.602 V, and stable operation for over 24 h. Koutecky-Levich analysis indicates a predominantly two-electron ORR pathway with high peroxide selectivity, highlighting its suitability for non-Pt catalytic systems. Simultaneously, when employed as a battery-type supercapacitor electrode, CCY exhibited electrolyte-dependent faradaic charge storage, achieving specific capacitances of 22, 18.74, and 10.12 F g⁻¹ at 0.1 A g ⁻ 1 in KOH, NaOH, and LiOH electrolytes, respectively, along with a low charge-transfer resistance and ~99% capacitance retention over 10,000 cycles. The incorporation of Y2O3 stabilizes the Co@CoO framework by suppressing cobalt dissolution and inducing interfacial electronic modulation and oxygen vacancy formation. This study establishes a scalable, precursor-driven strategy for designing rare-earth-modified bifunctional materials for integrated energy conversion and storage applications.