Separation of ions from water and wastewater using micro-scale capacitive-faradaic fuel cells (CFFCs), powered by H2(g) and air

Abstract

A novel method for separation of ions from water and wastewater is proposed. The technique utilizes micro-scale porous conducting particles (e.g. activated carbon) loaded with bifunctional catalyst capable of hydrogen oxidation and oxygen reduction reactions. Within the proposed process of ions removal, the particles act as micro-scale adsorbing capacitive-faradaic fuel cells (CFFCs) which require air and hydrogen gas for the adsorption of ions during the water treatment step and desorption of ions in the brine production.The process was proved for the removal of perchlorate ions from NaClO4 solutions in deionized water and groundwater using two types of CFFCs prepared from Lewatit AF5 microporous carbon and a powdered activated charcoal loaded with Pt (5 wt%) catalyst. During the O2-induced adsorption of ClO4− ions, the reduction of atmospheric oxygen on Pt (faradaic electrode of the CFFC) results in depletion of electrons from the carbonaceous part (i.e. the capacitive electrode) of the micro-scale fuel cell, which leads to adsorption of anions in the electric double layer. The hydrogen oxidation reaction that occurs during the regeneration of the ClO4− - loaded CFFCs results in accumulation of electrons in the capacitive electrode and in repulsion of perchlorate ions into the regenerant solution. The principle of the novel technique was also proved for separation of Cu2+ cations from CuCl2 solution using micro-scale CFFCs made of Lewatit AF5 loaded with Pt catalyst (wt 5%). In these experiments the fuel cells were powered by H2 gas during the Cu2+ adsorption step and by air during the regeneration.