Anionic formulation of electrolyte additive towards stable electrocatalytic oxygen evolution in seawater splitting

Highly stable oxygen evolution in alkaline seawater is demonstrated by anionic addition strategy. Phosphate ions act as a corrosion inhibitor to prevent the chloride absorption, buffer local pH and inhibit dissolution of transition metal ions. • A general screening rule is proposed to correlate anion property and Cl – repellency. • In situ spectroscopy and calculations reveal the pH-buffering effect of PO 4 3- ions. • Seawater splitting is greatly enhanced at a current density of 0.5 A cm −2 for 500 h. Hydrogen generation through seawater electrolysis provides a promising, attractive pathway towards the utilization of sustainable energy. However, the catalytic activity and stability of oxygen evolution anode are severely limited by the chloride-induced corrosion and competitive oxidation reactions. In this work, we demonstrate an anion-assisted performance improvement strategy by quick and universal screening of electrolyte additive via correlating Cl − repellency with the anionic properties. Particularly, the addition of phosphate ions is found to enable highly stable alkaline seawater splitting at industry-level current density (0.5 A cm −2 ) over 500 h using transition metal hydroxides as anodic electrocatalysts. In situ experiments and theoretical simulations further reveal that the dynamic anti-corrosion behaviors of surface-adsorbed phosphate ions are attributed to three factors including repelling Cl − ions without significantly blocking OH − diffusion, preventing transition metal dissolution and acting as a local pH buffer to compensate the fast OH − consumption under high current electrolysis.