LAUSR

Abstract Transition-metal oxides and phosphates can engage oxidation states that enhance reduction-oxidation (redox) reactions and can lead to excellent pseudo-capacitance behavior. In this study, amorphous Ar–Co3(PO4)2 (Ar ​= ​amorphous) was combined with the mixed valence cobalt oxide Co3O4 (or CoIICoIII2O4) to form a composite with a higher specific capacitance (531. 4 ​F/g) than pure Co3O4 (302.8 ​F/g) at 3 ​mV/s in 3 ​M KOH. The material was synthesized using an in-situ precipitation reaction of ammonium cobalt phosphate on Co3O4 followed by thermal treatment at 550 ​°C. Studies into the mechanism showed improved charge storage was linked to Co3O4 having rapid redox reactions on its surface. Cyclic stability studies revealed that the Ar–Co3(PO4)2/Co3O4 composite showed better stability with capacitance retention of 89.1% than when compared to pure Co3O4 at 76.5%. Both pure Co3O4 and Ar–Co3(PO4)2/Co3O4 contain mesopores with the former having a larger average pore volume. These findings demonstrate the potential of Ar–Co3(PO4)2 and Co3O4 as a promising electrode composite material in the fabrication of high-performance supercapacitor devices.