3D Nanoarrays Induced Compression Strain on Ultra‐Thin NiOOH Optimizes H ₂ O Adsorption for Efficient Hydrogen and Oxygen Evolution Reactions

Abstract The adsorption strength of H 2 O on the catalyst surface is a key factor in electrocatalytic hydrogen/oxygen evolution reactions (HER/OER). Excessive adsorption increases the energy barrier for intermediate formation, hindering HER/OER activity and stability. Here, a strategy is proposed for modulating lattice strain in 2D materials via 3D substrates. NiOOH/NiCu, a electrocatalyst with 2D film loaded on 3D branches, is synthesized on copper oxide nanowire arrays, and NiOOH compression strain is tuned within 0%–8.6% by controlling array diameter. In situ characterization and density functional theory calculations show that compressing NiOOH interlayer spacing weakens the adsorption of H 2 O and intermediates (*H/*O), lowers the Tafel step energy barrier and Gibbs free energy of *OOH formation, thus improving HER/OER activity. The 5.9% strained NiOOH/NiCu achieves HER and OER overpotentials of 18 and 197 mV at 10 mA cm −2 with Tafel slopes of 30.6 and 35.6 mV dec −1 , respectively, and operates stably at 1 A cm −2 for 1200 h in an alkaline anion‐exchange‐membrane electrolyzer.