A Urine/Cr(VI) Fuel Cell: Electrical Power from Processing Heavy Metal and Human Excretion

Tuesday, October 13, 2015: 17:00
212-B (Phoenix Convention Center)
W. Xu, Z. Fan, X. Wu (Zhejiang Univerisity), and Z. Wu (Zhejiang Univerisity)
Hexavalent chromium (CrO42-, Cr2O72-, CrO3, CrF6, etc.) is seriously hazardous substance inducing various point mutations in DNA and oxidative changes in proteins due to its strong oxidational properties[1]. Notably, Cr(VI) is strongly oxidative which can oxidize most organics such as urine in wastewater. Thus, it is possible to develop a fuel cell by using hexavalent chromium and urine as fuels according to the following reaction mechanism:

Anode reaction:     CO(NH2)2+6OH-→N2+CO2+5H2O+6e     E0= -0.746 V vs. SHE

Cathode reaction:  Cr2O72-+14H++6e→2Cr3++7H2O      E0= +1.33 V vs. SHE

Overall reaction:    CO(NH2)2+Cr2O72-+8H+→N2+CO2+2Cr3++6H2O     E0= +2.076 V

This work shows a strategy of reducing Cr(VI) by human urine with self-generation electricity via a urine/Cr(VI) fuel cell (UCrFC), in which urine functions as fuel and Cr(VI) severs as electrons acceptor. Urine is electro-oxidized on carbon supported nano-Ni catalyst at anode and Cr(VI) is electro-reduced at catalyst-free cathode in acid medium[2,3]. An ion selective separator, consisting of an anion exchange membrane (AEM) and a cation exchange membrane (CEM), AEM||KClaq||CEM separator, is introduced to improve the cell performance by hindering the crossover of dichromate and ammonium.

A maximum power density of 3400 mW m-2 (159 times to microbial fuel cells[4]) was achieved with an OCV of 1.3 V (twice of that in microbial fuel cells[4]) in AEM||KClaq||CEM-UCrFC, when using 50 mg L-1 Cr(VI) in 0.25 M H2SO4 as catholyte and neat urine as anolyte. The apparent first-order kinetic constants of Cr(VI) reduction were -0.224, -0.145 and -0.118 h-1, respectively, when initial concentration of Cr(VI) were 13, 22 and 50 mg L-1. Total organic carbon and total nitrogen removal from urine were observed in 71 h in the anode chamber, with removal efficiency of 79.2% and 78.4%, respectively. At the same time, ~93% of Cr(VI) was removed in the cathode chamber. A high cathodic coulombic efficiency of more than 98% was achieved. One liter of fresh urine could reduce about 28 g of Cr(VI) via UCrFC. This fuel cell provides an alternative technology for using waste (human urine) to treat another waste (hexavalent chromium), and is potentially applicable to other waste/waste system.


1. A. D. Dayan, A. J. Paine, Hum. Exp. Toxicol. 2001, 20, 439-451.

2. W. Xu, H. Zhang, G. Li & Z. Wu, Scientific Reports, 2014, 4: 5863.

3. B. Yu, H. Zhang, W. Xu, G. Li & Z. Wu, Scientific Reports, 2014, 4: 5860..

4. L. P. Huang, X. L. Chai, S. A. Cheng, G. H. Chen, Chem. Eng. J. 2011, 166, 652-661.