Surface Anticorrosion Engineering by Polyphosphate Oxyanions for Durable Seawater Oxidation

Abstract Electrolysis of seawater represents great potentials for sustainable hydrogen production. However, both competitive Cl⁻ adsorption and catalysts corrosion caused by chlorine oxidation reaction (ClOR) are major challenges in seawater electrolysis. Inspired by the concept of hard and soft acids and bases (HSAB), polyphosphate oxyanions (P₃O₁₀⁵⁻) on Ni(OH)₂ surface is coordinated to obtain harder acid Ni sites, which could obtain 160 times stability enhancement compared to pure Ni(OH)₂ for oxygen evolution reaction (OER) in alkaline seawater at 800 mA cm⁻². Also, the turnover frequency value on Ni(OH)₂‐P₃O₁₀⁵⁻ is 50 times that on Ni(OH)₂, implying higher intrinsic OER activity of Ni(OH)₂‐P₃O₁₀⁵⁻. Theoretical and experimental investigations show that P₃O₁₀⁵⁻ could facilitate transition of Ni³⁺ to harder acid Ni^>3+, thus preferring adsorption of hard base OH⁻ rather than soft base Cl⁻. This could enhance OER selectivity and inhibit undesirable ClOR. Furthermore, molecular dynamics simulations indicate that the Cl⁻ concentration near the electrode could be reduced by nearly half due to electrostatic repulsion of Cl⁻ by surface P₃O₁₀⁵⁻ oxyanions. When assembled into an electrolyzer for alkaline seawater splitting, it could operate at 2.2 V with large current up to 1.4 A for 240 h.