Activating inert copper hydroxide by coordination effect of stoichiometric nitrate for efficient hydrogen evolution reaction

The hydrogen evolution reaction (HER) process of metal hydroxides is significantly limited by weak hydrogen adsorption and requires a large overpotential. This study presents coordination engineering strategy to activate inert copper hydroxide through the introduction of stoichiometric nitrate ligands (CuHN). Nitrate and Cu are coordinated in an atomic ratio of 1 to 2, leading to expanded lattice space compared to conventional Cu hydroxide. This modification facilitated the successful doping of numerous Co atoms to synthesize the Co-CuHN sample, which works synergistically with nitrate to enhance HER activity. Experimental and theoretical analyses demonstrate that nitrate and Co provide electrons to Cu, thereby modulating the d-band center and surface adsorption capability. Compared to Cu(OH)₂, Co-CuHN exhibits a reduced water dissociation energy barrier of 0.54 eV, supplying abundant protons for hydrogen generation. Notably, the Gibbs free energy of hydrogen adsorption is optimized to approach zero. Consequently, Co-CuHN demonstrates a small Tafel slope of 40.0 mV dec⁻¹ and requires a low overpotential of 18 mV (10 mA cm⁻²), which is 99 mV lower than control Cu(OH)₂. This work is expected to provide a deeper understanding of anion coordination regulation of copper hydroxide.