Eu-modulated electronic structure of cobalt oxide for high-performance self-supporting supercapacitor cathodes

In this study, the electrochemical performance of cobalt oxide was significantly enhanced through europium (Eu) doping. Nanoneedle-shaped Eu-doped Co 3 O 4 (ECO) was synthesized via a solvothermal method followed by annealing. ECO exhibited a specific capacitance of 1496 F g −1 at a current density of 1 A g −1 , which is superior to that of pristine Co 3 O 4 . Aberration-corrected scanning transmission electron microscopy (AC-STEM) confirmed the successful incorporation of Eu into the crystal lattice. Density functional theory (DFT) calculations revealed that Eu doping narrowed the bandgap, thereby improving electrical conductivity and reaction kinetics. The resultant asymmetric supercapacitor device achieved an energy density of 47.5 Wh k g −1 at a power density of 750 W k g −1 , while maintaining 91.2% of its initial capacitance after 10,000 cycles. This work highlights the potential of ECO as a high-performance electrode material for supercapacitors.