CuO–SnO2 reverse cubic heterojunctions as high-performance supercapacitor electrodes

Abstract

CuO–SnO₂ reverse cubic heterojunctions are successfully synthesized by a hydrothermal reaction and a subsequent heat treatment method. CuO–SnO₂ heterojunctions not only manifest a large specific capacitance of 1972 F g⁻¹ even at 1.0 A g⁻¹, but also fine rate properties with 1695 F g⁻¹ at 10 A g⁻¹ and an excellent capacitance retention of nearly 96.05% over 10 000 cycles in 6 M KOH electrolyte. In addition, the specific capacitance of CuO–SnO₂ heterojunctions presents a parabolic trend with the increase of SnO₂ concentration. The asymmetrical supercapacitor made from the CuO-9 wt% SnO₂ heterojunction demonstrates a remarkable energy density of 117.32 W h kg⁻¹ at a power density of 13 624.26 W kg⁻¹. It is noteworthy that even at a high power density of 36 663.16 W kg⁻¹, the energy density can reach 96.75 W h kg⁻¹. The higher specific capacitance of the CuO–SnO₂ heterojunctions mainly comes from their high conductivity which is improved by the high electron hole state in the heterojunctions. The excellent electrochemical properties of CuO–SnO₂ heterojunctions can be attributed to their unique band structures and great conductivity, which allows efficient charge transport and electrolyte diffusion.