Stabilizing NiFe active sites using a high-valent Lewis acid for selective seawater oxidation

Abstract

Seawater electrolysis for hydrogen production harnesses renewable energy sources, contributing to sustainable development. However, competing anodic reactions, such as the chloride oxidation reaction (ClOR), can adversely affect the activity and stability of the oxygen evolution reaction (OER). In this study, we propose a strategy that significantly enhances the OER activity and selectivity of NiFe-layered double hydroxides (LDHs) by incorporating chromium (Cr) (Cr-NiFeLDHs). The Cr-NiFeLDH anode demonstrates an impressive overpotential of only 349 mV at a current density of 1000 mA cm⁻², outperforming RuO₂ in industrial applications and maintaining stability for over 140 h in anion exchange membrane (AEM) electrolyzer tests. Quasi in situ characterization reveals that Cr doping activates the high valence states of Ni, Fe and Cr, enhancing the electron transfer and activity of OER performance. Furthermore, the high selectivity for OH⁻ due to the hard Cr⁶⁺ Lewis acid effectively mitigates the competitive ClOR, a critical challenge in seawater electrolysis. This synergistic stabilization effect of high valence states fundamentally enhances the activity, selectivity, and stability of Cr-NiFeLDH anodes.