Preparation of zinc-doped bagasse-based activated carbon multilayer composite and its electrochemical performance as a supercapacitor

Abstract

The improvement of pseudo-capacitance is the most important factor affecting performance of supercapacitor. MnO 2 is an ideal material for the development of pseudo-capacitance, but its increased load amount while reducing its load thickness still is puzzled. In this study, a two-step method of loading MnO 2 on the surface of activated carbon (ZAC) prepared by ZnCl 2 activation bagasse was conducted to devote problem. A series of AMCM-X composites (ZAC@α-MnO 2 /CNTs/δ-MnO 2 ) with layered structures were obtained by sequentially loading linear nano-α-MnO 2 , CNTs, and sheet nano-δ-MnO 2 on ZAC using hydrothermal, freeze-drying, and electrochemical deposition methods, respectively. The loading of CNTs extended external space of substrate and facilitated further loading of δ-MnO 2 . Further, the AMCM-4 material had a mass specific capacitance of 450 F/g at 1 A/g and the asymmetric supercapacitor of AMCM-4//ZAC still had 92.3% capacitance retention rate after 5000 cycles. Moreover, XPS results showed the thickness of δ-MnO 2 (0.35 wt%) was relatively thinner than α-MnO 2 (1.93 wt%). The mechanism by which composites improved the electrochemical performance of the supercapacitor was attributed to the ability of building and covering pores of CNTs on substrate. These results will increase the re-negotiation of bagasse and improve the pseudo-capacitance of MnO 2 in supercapacitors. • A two-step method was conducted to increase MnO 2 amount while reduce thickness. • Layered composites are gained to enhance ZAC electrochemical properties. • CNTs loading affect pores structure and electrochemical properties of composites. • Composite electrode has excellent mass specific capacitance of 450 F/g at 1 A/g. • The supercapacitor has 92.3% specific capacitance retention after 5000 cycles.