Enriching Oxygen Vacancy in Co₃O₄ by Solution Combustion Synthesis for Enhanced Supercapacitive Property

Transition-metal oxides show great promise as electrode materials for supercapacitors due to their ease of synthesis, affordability, adequate redox stability, and high theoretical capacity. However, their inherent poor electrical conductivity and sluggish reaction kinetics typically lead to low specific capacity, reduced energy and power density, and sluggish rate capability in energy storage devices. In this study, we have re-engineered common Co 3 O 4 using a controlled solution combustion method to enhance oxygen vacancy within the oxide materials. We compared this approach with other calcination-based preparation techniques. Notably, the solution combustion-derived Co 3 O 4 (SCS) exhibited the most significant oxygen vacancy along with higher surface area and smaller crystallite size compared to calcination-derived Co 3 O 4 (CLS) and Co 3 O 4 (ZIF). The Co 3 O 4 (SCS)-modified electrode demonstrated a remarkable specific capacitance of 688.3 F/g at a current density of 1 A/g in a three-electrode electrochemical system─nearly four times of Co 3 O 4 (ZIF) (173.3 F/g). Furthermore, the solid-state asymmetric supercapacitor constructed with Co 3 O 4 (SCS) [Co 3 O 4 (SCS) @ITO//ITO] exhibited a specific capacitance of 232 F/g at a 1 A/g current density, along with high energy densities across a wide range of power densities (e.g., 93.12 Wh/kg at 848.2 W/kg and 79.07 Wh/kg at 4248.55 W/kg), surpassing the performance of most reported hybrid supercapacitors. As a proof-of-concept, we further improved the oxygen vacancy in Co 3 O 4 (SCS) through H 2 treatment, resulting in reduced Co 3 O 4 (SCS-R) with an enhanced specific capacitance of 278 F/g, an energy density of 111.58 Wh/kg, and a power density of 869.45 W/kg at a 1 A/g current density. This modified material also demonstrated exceptional capacitive efficiency (90%) and Coulombic efficiency (90.2%) retention even after 6000 cycles. Ultimately, this report introduces a straightforward solution combustion synthesis strategy for generating oxygen vacancies in metal oxides, holding significant promise for enhancing their energy storage properties.