Composite Aerogels of Carbon Nanocellulose Fibers and Mixed-Valent Manganese Oxides as Renewable Supercapacitor Electrodes.

Xiaoyu Guo,Haipeng Yu,Qi Zhang,Qing Li,Yixing Liu

doi:10.3390/polym11010129

Abstract

Bio-waste derived nanocelluloses show excellent mechanical flexibility and self-aggregated capability, which enable them to be good supporting substrates for the synthesis of electroactive materials. Herein, we present a facile route for fabricating composite aerogels consisting of carbonized nanocellulose fibers (CNF) and mixed-valent manganese oxide (MnOx), toward supercapacitor applications. Mixed solutions of nanocellulose and manganese acetate with different ratios were prepared and freeze-dried into hybrid aerogels. The hybrid aerogels were then transformed into CNF/MnOx composites by a calcination process. The CNF membranes served as porous carbon nano-reservoirs for MnOx and electrolyte. The CNF/MnOx composites also kept a 3D porous aerogel structure with hierarchical pores, which enabled stable transport of both electrolyte ions and electrons to the electrode surface, leading to low a charge-transfer impedance and good electrochemical kinetics. The CNF/MnOx-based symmetric supercapacitor showed a satisfied energy density and power density of 37.5 Wh kg−1 and 2.75 kW kg−1, respectively. All the above results demonstrate the feasibility of using sustainable nanocellulose as a nanoscale carbon substrate for the synthesis of hybrid composite electrodes toward renewable supercapacitor applications.

Highlights

Parallel to the growing need for renewable energy supply, there is an increasing demand for high-performance power sources with low-cost, lightweight, portable, and environmentally friendly features
Because of high aspect ratios and numerous hydroxyl groups being exposed, the nanocellulose fibers are likely to intertwine together, which facilitates the formation of the gel network, for mass concentrations above 0.8 wt.% [48]
The nanocellulose suspension was mixed with Mn(OAc)2 solutions containing different concentrations of solute, and freeze-dried into freestanding hybrid aerogels with tailored shapes and sizes

Summary

Introduction

Parallel to the growing need for renewable energy supply, there is an increasing demand for high-performance power sources with low-cost, lightweight, portable, and environmentally friendly features. Supercapacitors have emerged as a promising candidate for electrochemical energy storage because of their fast charge–discharge processes, providing a high energy density and a reasonable power density [1]. Both the materials and the structures are the cruxes in developing high-performance supercapacitors [2]. The derived supercapacitors sometimes suffer from a low energy density. Aiming at solving these problems, various categories of redox-reaction materials, including metal oxides, conductive polymers, and hybrid materials, have been employed as electrodes to dramatically improve the energy density. As the appeal of hybrid structures lies in the synergistic effects based on interfacial charge and energy transfer processes, controlling the nature of the interface and maximizing the interfacial area become critical issues

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Conclusion