Porous Biomass Carbon Coated with SiO2 as High Performance Electrodes for Capacitive Deionization

Abstract

The electrosorption capacity of an electrode strongly depends on the surface properties of the electrode material, such as the surface area, pore microstructure, and pore size distribution. Carbon-based electrode materials for capacitive deionization (CDI) or electrosorption processes suffer from problems with high manufacturing costs, poor electrical conductivity, and poor wettability. The thin-film coating of SiO2 on porous biomass carbon may provide an alternative electrode material for double-layer applications. In this paper, the activated porous biomass carbon (AWSC) was first obtained through a simple potassium hydroxide (KOH) activation of wheat straw carbon (WSC) as the precursor, and then thin-film SiO2 coated AWSC (SiO2@AWSC) was prepared by a sol-gel coating process. Scanning electron microscope (SEM) imaging of SiO2@AWSC demonstrated that a SiO2 thin-film was deposited on the surface of AWSC without changing the opening structure. Compared to WSC, the Brunauer-Emmett-Teller (BET) surface area of SiO2@AWSC was greatly increased, and presented obvious micropore and mesopore distributions. Further electrochemical analyses were performed via cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance. The electrochemical results showed that SiO2@AWSC electrodes showed increased electrosorption capacitance, which were attributed to a large specific surface area, a porous structure, and enhanced wettability.