Assessing hypochlorite selectivity of corrosion resistance catalysts for alkaline seawater splitting

Using seawater for hydrogen production via electrolysis is increasingly attractive for cost savings. The main challenge is the competition at the anode between hydroxide oxidation and chloride oxidation, which must be minimised in both acidic and alkaline environments. Strategies such as electrostatic repulsion and ion selectivity have been used to reduce chloride oxidation in seawater, but no direct comparison has determined which is more effective. Here, we show two strategies using a rotating ring disc electrode setup to detect hypochlorite formation at the disc in an alkaline saline solution with different catalysts. We show that adding chromium to an oxygen evolution reaction catalyst reduces hypochlorite formation from 2.362 mM to 0.670 mM over 5 minutes. The electrostatic repulsion strategy (using sulphide doping) lowers the concentration to 0.966 mM under the same conditions, indicating that the ion selectivity strategy is more effective at reducing hypochlorite in alkaline seawater. However, the electrostatic repulsion strategy causes only a minor loss in electrochemical performance but improves selectivity by reducing hypochlorite formation. This research could offer insights into streamlining the design of oxygen evolution reaction catalysts and enhancing the efficiency of seawater electrolysis.