High-entropy layered hydroxide for efficient and sustainable seawater oxidation

Abstract

Developing efficient and stable electrocatalysts for high-current-density seawater oxidation remains challenging due to competitive chlorine evolution reaction at the anode. High-entropy layered hydroxides with different compositions, unique layered structures, and high mixing entropy have the potential to act as efficient as well as sustainable electrocatalysts for direct seawater splitting. Here, we report the development of a novel high-entropy NiCrCoFeMo layered hydroxide (HE-LH) material using a single-step hydrothermal method, which was found to be superior to its quaternary and ternary counterparts due to the availability of a larger number of electroactive sites and better chloride-restricting ability of interlayer anions. The HE-LH achieved a 100 mA cm⁻² current density at overpotentials of only 242, 258 and 281 mV in 1 M KOH, 1 M KOH + seawater and 6 M KOH + seawater, respectively. The robustness due to the anti-corrosion ability of HE-LH has also been explored in highly alkaline (6 M KOH) real seawater, which showed stability over 140 h at an operating current density of 500 mA cm⁻². The generation of β-NiOOH, also as active sites, during a prolonged electrooxidation process in seawater-based electrolyte was found to be beneficial to maintain such high activity. The combination of HE-LH with Pt/C in a two-electrode system also offered a high current density of 500 mA cm⁻² at a cell voltage of only 1.92 V in highly alkaline (6 M KOH) real seawater electrolyte and exhibited stability over 50 h. With these excellent performances, the developed novel HE-LH is believed to have the potential for practical exploration in seawater electrolysers.