Indium modified graphite electrodes on highly zinc containing methanesulfonate electrolyte for zinc-cerium redox flow battery

The zinc deposition and dissolution reaction in methanesulfonic acid (2.5 mol L (1) Zn(II) in 6.5 mol L (1) MSA) on indium modified graphite electrodes aiming to suppress the competing hydrogen evolution reaction (HER), was studied on the negative electrode reaction in the zinc-cerium redox flow battery. Cyclic voltammetry, Tafel extrapolation and electrochemical impedance spectroscopy found that elevated temperatures 40 degrees C improved the kinetics (j(o) = 1 x 10 (2)Acm (2)) of the zinc reaction and shifted the nucleation potential positively by 65 mV. The modified graphite electrodes exhibited higher coulombic efficiencies (81%) than the as received electrode due to the reduction of HER. Higher voltage efficiencies (84%) were found at elevated temperatures irrespective of charging time or the modification method. The highest energy efficiency was 65% at 40 degrees C and 600 rpm for the modified electrode treated with the highest concentration of indium (0.2 mol L (1)) and longest dipping period (5 h). Scanning electron microscopy showed no signs of dendritic growth but confirmed the formation of spikes and clusters. Energy dispersive X-ray spectroscopy of the modified graphite electrodes after 340 galvanic cycles showed that indium was still present at the surface of the electrode suggesting good durability. (C) 2015 Elsevier Ltd. All rights reserved.