Eu3+-doped MnCo2O4 nanoneedle arrays as a high-performance bifunctional electrode for supercapacitors and aqueous zinc-ion batteries

This study proposes a multi-scale rare-earth engineering strategy that integrates Eu 3+ doping into MnCo 2 O 4 nanoneedle arrays grown on nickel foam, enabling simultaneous modulation of electronic structure, defect chemistry, and nanoscale morphology. A synergistic combination of in situ Raman spectroscopy, ex situ XRD/XPS, and electrochemical analysis reveals that Eu 3+ preferentially substitutes for Co 3+ , simultaneously boosting the conductive Co 2+ population, generating abundant oxygen vacancies, and stabilizing a reversible H + -driven MnOOH phase transformation during cycling. This modulation yields a specific capacitance of 500 F/g for supercapacitors and a specific capacity of 390 mAh/g for aqueous zinc-ion batteries at 1 A/g. The assembled asymmetric supercapacitor delivers 100 Wh/kg with ∼93% capacitance retention after 4000 cycles, while the zinc-ion battery retains ∼96% capacity over 5000 cycles. This study establishes a coherent “atomic-to-nanoscale” design strategy for developing durable, high-performance electrodes, offering a scalable and materials-efficient route toward next-generation energy storage systems with potential for integration into portable electronics and grid-level storage.