Boosting the storage capacity and the rate capability of flexible graphene film via a nondestructive thermo-chemical reduction

Abstract

Tuning the electrical conductivity, the porosity, and the surface chemistry of a flexible graphene film (FGF) without damaging its integrity is pivotal to boost its charge storage capacity and rate capability toward supercapacitor application. In this perspective, we herein propose a two-step non destructive reduction approach to adjust the physicochemical properties of the FGF; the first step involves a chemical reduction by hydroiodic acid (HI), and the second step implicates a thermal treatment under ambient air. The impact of the two-step thermo-chemical reduction on the structure, the porosity, the electrical conductivity, and the capacitive behavior of the FGF are scrutinized by a series of relevant characterizations. It is found that the chemical treatment enables a high electrical conductivity, improved thermal stability, and enhanced capacitance due to the presence of iodine/iodide ions on the FGF's surface. Moreover, thermal treatment at 450 °C increases the specific surface area, introduces oxygen functional groups into the surface, and improves the surface wettability of the FGF. Hence, the as-prepared FGF electrode delivers a remarkable specific capacitance of 350.44 F·g−1 at 0.5 A·g−1 with excellent rate capability of 219.60 F·g−1 at 10 A·g−1. The FGF based symmetric supercapacitor attains a high energy density of 12.82 W·h·kg−1 at a power density of 125 W·kg−1 and retains an energy density of 9,51 W·h·kg−1 as the power density reaches 2500 W·kg−1.