Nest-Like MnO₂ Nanowire/Hierarchical Porous Carbon Composite for High-Performance Supercapacitor from Oily Sludge

In the aim to go beyond the performance tradeoffs of classic electric double-layer capacitance and pseudo-capacitance, composites made out of carbon and pseudo-capacitive materials have been a hot-spot strategy. In this paper, a nest-like MnO₂ nanowire/hierarchical porous carbon (HPC) composite (MPC) was successfully fabricated by a controllable in situ chemical co-precipitation method from oily sludge waste. Due to the advantages of high surface area and fast charge transfer for HPC as well as the large pseudo-capacitance for MnO₂ nanowires, the as-prepared MPC has good capacitance performance with a specific capacitance of 437.9 F g^-1 at 0.5 A g^-1, favorable rate capability of 79.2% retention at 20 A g^-1, and long-term cycle stability of 78.5% retention after 5000 cycles at 5 A g^-1. Meanwhile, an asymmetric supercapacitor (ASC) was assembled using MPC as the cathode while HPC was the anode, which exhibits a superior energy density of 58.67 W h kg^-1 at the corresponding power density of 498.8 W kg^-1. These extraordinary electrochemical properties highlight the prospect of our waste-derived composites electrode material to replace conventional electrode materials for a high-performance supercapacitor.