The performance of Cu2+ as dissolved cathodic electron-shuttle mediator for Cr6+ reduction in the microbial fuel cell

Abstract

The study investigates the performance of Cu 2+ as dissolved cathodic electron-shuttle mediator (dcESM) for simultaneous Cr 6+ reduction and electricity generation in a microbial fuel cell (MFC) at pH 2 and 4 conditions. The dcESM behavior of Cu 2+ on carbon cloth (CC) catalyzes the reduction of Cr 6+ into Cr 3+ at pH 2 by undergoing redox reactions. However, at pH 4, a simultaneous reduction of Cu 2+ and Cr 6+ was observed. Cyclic voltammetry (CV) studies were performed at pH 2 and 4 to probe the dcESM behavior of Cu 2+ for Cr 6+ reduction on CC electrode. Also, at pH 2, increasing the concentration of Cu 2+ from 50 mg L -1 to 500 mg L -1 favors the Cr 6+ reduction by reducing the reaction time from 108 h to 48 h and improving the current production from 3.94 mA m -2 to 6.24 mA m -2 , respectively. Nevertheless, at pH 4, the efficacy of Cr 6+ reduction and electricity generation from MFC is decreased from 62.91% to 18.21% and 4.42 mA m -2 to 1.10 mA m -2 , respectively, by increasing the Cu 2+ concentration from 50 mg L -1 to 500 mg L -1 . Furthermore, the performance of dcESM behavior of Cu 2+ was explored on carbon felt (CF) and platinum (Pt) electrodes, and compare the results with CC. In MFC, at pH 2, with an initial concentration of 100 mg L -1 , the reduction of Cr 6+ in 60 h is 9.63 mg L -1 for CC, 0.17 mg L -1 for CF, and 51.32 mg L -1 for Pt cathodes. The reduction of Cr 6+ (initial concentration of 100 mg L -1 ) at pH 4 in 120 h is 44.72 mg L -1 for CC, 32.13 mg L -1 for CF, and 70.85 mg L -1 for Pt cathodes. Maximum power densities of 1659 mW m -2 , 1509 mW/m -2 , and 1284 mW/m -2 were achieved when CF, CC, and Pt, respectively were employed as cathodes in the MFC.