Separation and hydrogenation of nitrate ions by micro-scale capacitive-faradaic fuel cells (CFFCs).

• The microscale hybrid fuel cells for NO 3 − separation and hydrogenation are reported. • Microscale fuel cell comprises carbon-made capacitive and Pt-Cu faradaic electrodes. • Oxygen reduction reaction induces adsorption of NO 3 − ions by carbon. • Hydrogen oxidation reaction induces desorption of NO 3 − ions from carbon. • Released NO 3 − ions are simultaneously reduced by the H 2 gas on Pt-Cu catalyst. 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 NO 3 − they must be regenerated. To repel NO 3 − ions into the regenerant solution the dissolved H 2 is oxidized on Pt electrode of the CFFC. The accumulation of electrons in capacitive activated carbon electrode results in release of NO 3 − ions. Simultaneously the nitrate ions are reduced by the H 2 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 N 2 gas and ammonia. The adsorption density for nitrate ions was 0.175 meq/g_carbon. Selectivity for N 2 gas was ≈ 55%. Further studies are required to decrease costs of CFFCs and to increase the N 2 selectivity of the hydrogenation step. [ABSTRACT FROM AUTHOR]