Electrochemistry Communications (Nov 2020)
Separation and hydrogenation of nitrate ions by micro-scale capacitive-faradaic fuel cells (CFFCs)
Abstract
A new electrochemical process is proposed for a zero-discharge removal of nitrate ions from water. The process utilizes micro-scale capacitive-faradaic fuel cells (CFFC) made of activated carbon particles loaded with a Pt-Cu catalyst capable of oxygen reduction, hydrogen oxidation and nitrate hydrogenation reactions. Every CFFC comprises capacitive activated carbon electrode and faradaic Pt electrode. Oxygen reduction on Pt results in electrons’ deficiency in activated carbon which is equilibrated by an adsorption of nitrate ions from the treated water. Once the CFFCs are saturated with NO3− they must be regenerated. To repel NO3− ions into the regenerant solution the dissolved H2 is oxidized on Pt electrode of the CFFC. The accumulation of electrons in capacitive activated carbon electrode results in release of NO3− ions. Simultaneously the nitrate ions are reduced by the H2 gas on the Pt-Cu catalyst of the CFFC.Operation of CFFCs with 5%Pt-1%Cu catalyst resulted in highly effective separation and hydrogenation of nitrate ions into the N2 gas and ammonia. The adsorption density for nitrate ions was 0.175 meq/g_carbon. Selectivity for N2 gas was ≈ 55%. Further studies are required to decrease costs of CFFCs and to increase the N2 selectivity of the hydrogenation step.
