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 °C improved the kinetics (jo =1 × 10−2 A cm−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 °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.