Regulating crystal surface of Cu2O distributed in graphene film to explore supercapacitive performance in liquid or gel electrolyte

Abstract

The morphologies of transition metal oxides have a decisive impact on the performance of their applications. In this work, two kinds of Cu2O nanocrystals with preferentially exposed {100} and {111} facets corresponding to Cu2O nano-cube (Cu2O NC) and Cu2O nano-octahedron (Cu2O NO) were designed. Then the different crystallographic Cu2O nanocrystals were self-assembled to be flexible self-supporting Cu2O and reduced graphene oxide films. By the comparison of the kinetic study of Cu2O nanocrystal with two different exposure facets, the nanocrystal with preferentially exposed {111} behaves a larger proportion of surface-confined charging process, indicating faster ion adsorption and transferability. The specific capacity of an electrode with different exposed facets behaves as an obvious shape-dependence in the aqueous two-electrode system. In contrast with the hydrogel electrolyte system, the shape-dependence disappeared due to the sufficient ions adsorb in the slow ion diffusion electrolyte. Based on the intrinsic crystallographic plane of the cuprite Cu2O, the charge-storage mechanism was elucidated. The so-called “crystallography-dependence” is relevant to the dangling bonds from the exposed {111} facets, which can act as active sites for electrochemical energy storage. Furthermore, the composite of Cu2O NO/rGO shows a high capacity of 737.4 F g−1. The Cu2O NO/rGO film with exposure {111} facets demonstrated preferential adsorption of electrostatic charges on the planes and showed better charge-storage capability. In other words, there is a crystallography-dependent adsorption ability during energy storage.