Effects of trace amount of copper, nickel and bismuth on hydrogen evolution reaction of the carbon felt electrode in a hydrochloride-based flow battery

The hydrogen evolution reaction (HER) is a detrimental side reaction in most aqueous flow batteries (AFB), the activity of which is sensitive to the existence of certain metal impurities or additives in the electrolyte. In this work, the individual and combined effects of Cu, Ni and Bi on the activity of HER are explored. Specifically, when a current density on the scale of mA cm−2 is applied, the AFB operates as an electrolyzer with 3 M HCl electrolyte, making HER the primary reaction in the negative half-cell. The changes in HER activity are assessed by measuring the potential difference between the negative electrode and an Ag/AgCl reference electrode in the negolyte storage tank. The results indicates that a Cu area loading as low as 12.5 μg cm−2 reduces the HER overpotential by approximately 100 mV, which is also affected by the stoichiometry of the electrodeposition process. Cu and Ni exhibit a synergistic effect in catalyzing HER, while the electrodeposition of Bi has been shown to effectively inhibit the catalytic effects of these metals. [Display omitted] •Cu deposition load of merely 12.5 μg cm−2 exacerbates the HER of the carbon felt electrode.•Ni2+ concentration of above 25 μM exacerbates the HER without electrodepositing.•Bi is competent to inhibit the catalysis of Cu and Ni on the HER.