Durable high-entropy non-noble metal anodes for neutral seawater electrolysis

Abstract

Enhancing hydrogen production is key to achieving a carbon–neutral world. Among the various technologies available, using renewable energy for water electrolysis stands out as a leading method for creating green hydrogen. However, standard water electrolysis requires substantial quantities of ultra-clean fresh water for optimal energy efficiency and operations. This poses a problem as fresh water only represents a minuscule 0.01 % of our planet’s water reserves. Seawater electrolysis is a potential solution to resolve this limitation and attain sustainable hydrogen production. Nevertheless, electrolysis of seawater in its neutral state demands stringent reaction conditions, making it imperative to thoughtfully design the electrodes, particularly the anodes. This study presents the development of highly durable, noble-metal-free, high-entropy alloy anodes suitable for neutral seawater under highly fluctuating power operation. The anode demonstrates impressive stability (up to 6,000 cycles), lasting over 100 h at 100 mA cm−2 in a 0.5 M aqueous NaCl electrolyte. Its Faradaic efficiency for O2 production is 42 %. Density functional theory calculations reveal that the oxidized surface (passivation layer) of the anode prevents Cl− adsorption, helping to protect the catalytically active sites and prevent catalyst degradation. This finding suggests that noble-metal-free anodes can serve as practical alternatives to those made from noble metals for neutral seawater electrolysis. Moreover, the utilization of seawater without acid or alkali treatment paves the way for safer and more sustainable hydrogen production. This is a significant stride toward realizing our goal of carbon neutrality.