Tailoring the Morphology of Cu₂O Microcrystals in Cu₂O/rGO Composites for Achieving Enhanced Supercapacitor Performance

Cuprous oxide/reduced graphene oxide (rGO) composites have attracted considerable attention for energy applications because of the high theoretical specific capacitance of Cu₂O and the decent electrical conductivity of rGO. Moreover, Cu₂O crystals have intriguing facet-dependent electrical and photocatalytic properties. Although some studies have explored the facet-dependent photocatalytic activity of Cu₂O crystals, limited research has investigated the use of Cu₂O with tunable crystal shapes in supercapacitor applications. In this study, we present a facile one-step hydrothermal process for preparing Cu₂O-based rGO composites under alkaline conditions without additional reducing agents. By adjusting the synthesis parameters, we obtained Cu₂O/rGO composites containing cubic, truncated cubic, concave octahedral, and octahedral Cu₂O crystals. Comprehensive electrochemical analyses demonstrated that these composites displayed noticeable pseudocapacitive properties. Among them, the O-Cu₂O/rGO composite with octahedral Cu₂O crystals exhibited the highest specific capacitance (525 F/g at 1 A/g) and decent electrochemical stability. This superior pseudocapacitive performance is attributed to the high conductivity and low charge transfer resistance of Cu₂O octahedrons as well as the favorable interfacial contact between negatively charged rGO and the positively charged {111} facets of Cu₂O octahedrons. Our findings provide valuable insights for designing other promising metal oxide/rGO composites for supercapacitor applications.