Electrolyte engineering for effective seawater splitting based on manganese iron chromium layered triple hydroxides as novel bifunctional electrocatalysts

Abstract

Seawater splitting remains far-fetched due to the interference of corrosive chlorine evolution reactions at the anode. The lowering of overpotential with the help of an effective electrocatalyst is one way to deal with it. However, to achieve hydrogen production under high current, a potential above 2.0 V needs to be applied practically, which is an electrochemical chloride oxidation–dominant region. In this study, we show that the presence of a trace amount of anionic inhibitors, especially carbonate, provides a much-needed anionic protective layer at the anode surface, selectively restricting chlorides but allowing hydroxides to reach the anode surface. The hypothesis was examined on a novel MnFeCr layered triple hydroxide as a bifunctional electrocatalyst. The developed electrocatalyst exhibits an overpotential of 242 mV for OER and 154 mV for HER at a benchmarking current density of 10 mA cm⁻². Theoretical calculations were used to establish the possible OER pathways and explain the reason for a good electrocatalytic activity of the developed electrocatalyst. Having such an electrocatalytic activity, in alkaline real seawater, the electrocatalyst in the presence of carbonate inhibitors shows an impressive stability over 500 h maintaining a cell potential of 2.2–2.3 V without showing any sign of electrode degradation. The findings thereby provide a much-needed solution to make seawater splitting feasible for sustainable hydrogen production.