Oxygen vacancy engineering in cobalt-nickel oxide via simple chemical reduction for boosted supercapacitor performance

Cobalt-nickel transition metal oxides are promising supercapacitor electrodes due to their high theoretical capacity, yet their practical application is hindered by poor intrinsic conductivity and sluggish ion diffusion kinetics. Herein, we report a facile strategy to simultaneously engineer the morphology of CoNiO 2 and introduce oxygen vacancies in CoNiO 2 via NH 4 F-mediated hydrothermal synthesis followed by a simple impregnation treatment. The synergistic effects of NH 4 F dosage and impregnation time on the structural and electrochemical properties were systematically investigated. The optimal sample, Ov-CoNiO 2 -3, obtained with 12 mmol NH 4 F and 2 h impregnation, delivers a high specific capacitance of 2184 F g −1 at 1 A g −1 , which is 140% higher than that of the pristine CoNiO 2 . XPS and EPR analyses confirm the successful introduction of oxygen vacancies, while DFT calculations reveal that oxygen vacancies create defect states near the Fermi level, enhancing electronic conductivity. An asymmetric supercapacitor (Ov-CoNiO 2 //BC) was fabricated with Ov-CoNiO 2 -3 as the positive electrode and coal-derived carbon as the negative electrode. It delivers 384 F g −1 at 5 mV s −1 and retains 82% of its initial capacitance after 8,000 cycles, demonstrating good performance. These results reveal the great potential of oxygen vacancies in enhancing electrochemical performance for future electrode material design.