Cobalt-Porphyrin Modified Three-Dimensional Graphene Hydrogel Electrode for High Performance Asymmetric Supercapacitors

Abstract

Three-dimensional (3D) graphene-based materials have attracted much attention in the field of supercapacitors for their large surface areas and fast electronic conductivity capability. Faradaic pseudo-capacitance materials inside the architecture can enlarge the electrochemical performance of the electrode. Additionally, metal porphyrins are negative electrode active materials for supercapacitors as they have potential high pseudo-capacitance, conductivity and N-doping. The design and preparation of the 3D cobalt-porphyrin modified graphene hydrogels (3D CoP/GHs) is an interesting topic. Here, we have fabricated the 3D CoP/GH by a two-step method. The composite electrode reaches a specific capacitance of 335[Formula: see text]F[Formula: see text]g[Formula: see text], twice that of pure GHs. At the same time, resistance of the electrode material decreases and the ion transfer is accelerated due to the addition of cobalt-porphyrin. After 10[Formula: see text]000 cycles, the 3D CoP/GH maintains its stable specific capacitance retention of 94.11% indicating its excellent cycle life. The cycle life is much better than that of a hydrogel that has not been doped (81.63%) according to our previous work. Then we fabricated an asymmetrical supercapacitor which uses both the 3D CoP/GH and GH as the two electrodes (3D CoP/GH[Formula: see text]GH), and reaches an outstanding energy density of 30.40[Formula: see text]Wh[Formula: see text]kg[Formula: see text] at a current density of 1[Formula: see text]A[Formula: see text]g[Formula: see text] while the power density is 749.5[Formula: see text]W[Formula: see text]kg[Formula: see text].