Direct Interfacial Growth of MnO2 Nanostructure on Hierarchically Porous Carbon for High-Performance Asymmetric Supercapacitors

Abstract

Developing a composite electrode composed of a carbon-based material and a transition metal oxide is an effective way to address the problems such as poor conductivity and low porosity created by transitional metal oxide electrodes for supercapacitors. In this work, the activated carbon (AC) prepared from enteromorpha prolifera (ACEP) with typical hierarchically porous structure, was used as a substrate to grow MnO2 nanostructures via wet chemical reaction process. The morphology and crystalline phase of the MnO2 could be controlled by facilely adjusting reaction time. For instance, δ-MnO2 nanosheets were anchored on the ACEP in the initial stage (1–6 h), but α-MnO2 nanowires were obtained with the extension of reaction time (7–12 h). The electrode prepared from ACEP@δ-MnO2 nanosheets displays high specific capacitance (345.1 F g–1 at 0.5 A g–1) and excellent cycle stability (i.e., a capacitance retention of 92.8% after 5000 cycles). Moreover, an asymmetric supercapacitor was assembled by using as-prepared ACEP@δ-MnO2 composite as positive electrode and AC as negative electrode. The assembled AC//δ-ACEP@MnO2 supercapacitor is shown to work in a wide voltage range of 0–2.0 V and delivered a high energy density of 31.0 Wh kg–1 at a power density of 500.0 W kg–1.