Enhanced desalination performance of nitrogen-doped porous carbon electrode in redox-mediated deionization

Abstract

Recently, redox-mediated deionization (Redox-DI) has emerged as a promising ion separation process owing to its sustainable ion removal performance and feasibility. The characteristic cell configuration of Redox-DI involves two independent channels for treating water and supporting electrolytes containing redox couples in a multichannel system. This leads to continuous desalination mediated by a sustainable redox reaction on porous carbon electrodes, which is the preferred material in Redox-DI since it governs energy efficiency and ion removal performance. In particular, the activated carbon cloth (ACC) is a promising electrode due to its attractive features including simple shaping as a binder-free electrode and a large inter-fiber space assisting active mass transfer. However, very few studies have reported on the advancement of redox reactions on ACC electrodes, including electrocatalytic activity and rate capability. Therefore, this study aimed to produce a simple nitrogen-doped porous carbon cloth (N-ACC) electrode to improve the electrocatalytic activity for redox reactions, resulting in enhanced desalination performance of Redox-DI. The nitrogen content in N-ACC increased to approximately 3 at.% and was uniformly distributed on the surface of ACC using urea as a nitrogen source at mild temperature of 300 °C. N-ACC showed remarkable desalination performance with a salt removal rate (SRR) of 69.1 mg/g-h, a charge efficiency of 95.3%, and energy consumption of 122.0 kJ/mol. This is a 58.3% improvement in the SRR compared to ACC. In addition, through a parametric investigation with different cell voltages and flow rates, a high SRR (70–80 mg/g-h) and charge efficiency (90–100%) of N-ACC was demonstrated. N-doped ACC enhances the electrocatalytic activity, including fast reaction kinetics and low charge transfer resistance to redox couple reactions.