Sulfate-intercalated cobalt-doped nickel-Iron layered double hydroxide nanosheet arrays for corrosion-resistant oxygen evolution in alkaline seawater.

Against the backdrop of rapid hydrogen economy development and growing environmental concerns, direct seawater electrolysis for hydrogen production offers a promising pathway to circumvent freshwater dependence. However, the competitive chlorine evolution reaction (CER) and electrode corrosion triggered by chloride ions (Cl-) at the anode severely hinder its industrialization. Although NiFe layered double hydroxides (LDHs) are regarded as ideal non-precious-metal candidate catalysts for alkaline seawater oxygen evolution reaction (OER), the leaching of active sites caused by chloride ions (Cl-) and insufficient long-term durability under industrial-level current densities remain significant challenges. Herein, a cation-anion synchronous co-modification strategy was proposed: SO₄2--intercalated and Co-co-doped NiFe-LDH nanosheet arrays (CFN-SO₄2-) were in situ grown on nickel foam via a one-step room-temperature corrosion co-precipitation method. SO₄2- intercalation serves as an interlayer pillar that expands the interlayer spacing and induces a β → α phase transition, suppressing Cl- access through the dual mechanisms of electrostatic repulsion and a reinforced hydrogen-bonding network, Co2+/Co3+ co-doping modulates the electronic structure of the layers, optimizing the adsorption of oxygenated intermediates and stabilizing Fe sites. Experimental results demonstrate that the catalyst exhibits superior apparent activity in seawater compared to freshwater, a phenomenon rarely reported in the literature. The catalyst exhibits an overpotential of only 249 ± 1 mV (j = 100 mA cm-2) in alkaline freshwater conditions, whereas in alkaline simulated seawater it requires merely 223 mV (j = 100 mA cm-2) and operates stably for over 1000 h at 500 mA cm-2. In naturally alkalized seawater subjected to filtration pretreatment, the overpotential further decreases to 200 mV (j = 100 mA cm-2) with stable operation exceeding 500 h at 500 mA cm-2. The counterintuitive phenomenon of superior performance in natural seawater relative to freshwater is proposed to originate from the promoting effect of selective Cl adsorption on Fe sites toward the OER and the stabilization of the LDH interlayer structure by intrinsic constituents of seawater. This work provides new insights for the cation-anion synergistic design of LDH-based catalysts toward industrial-level alkaline seawater electrolysis.