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

Xiaoyu Li,Zhiqiang Gong,Zhenbo Wang,Dong Han

doi:10.3390/nano11102715

Abstract

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.

Highlights

Electrical energy storage systems have drawn great attention in recent decades such as conventional capacitors and batteries, Li-ion batteries, and supercapacitors [1]
The content and morphology of MnO2 in the as-received MPC could be controlled by varying the reaction time
As for MPC-A-5 (Figure 2c), the hierarchical porous structure of the hierarchical porous carbon (HPC)-A substrate was almost completely covered by the surface MnO2 nanostructure due to the over-reaction between carbon and KMnO4

Summary

Introduction

Electrical energy storage systems have drawn great attention in recent decades such as conventional capacitors and batteries, Li-ion batteries, and supercapacitors [1]. Supercapacitors can be classified into electric double-layer capacitors (EDLC) and pseudo capacitors, according to the different energy storage mechanisms. The capacitance in EDLCs is controlled by the surface electrical double layers between the electrode and electrolyte, while in pseudo capacitors, the energy is stored by the fast and reversible faradaic redox reactions in the electrode, which are controlled by diffusion. As is known to all, pseudo capacitors usually provide higher specific capacitances (Cs ) and energy densities, but suffer from some shortcomings such as poor electrical conductivity and cycling stability, while EDLCs are the opposite. The plans to realize the synergistic effect of the advantages of both EDLC and pseudo capacitor are highly desirable to improve the electrochemical performance [4]

Methods

Results

Conclusion