Bio-Inspired histidine-based copper complex: An efficient and robust electrocatalyst for electrochemical hydrogen evolution

The quest for an efficient and sustainable electrocatalyst for hydrogen evolution reaction (HER) using earth-abundant elements is crucial for cost-effective and environmentally friendly hydrogen production. While many catalysts show good activity and stability in strongly basic conditions, fewer materials are effective under neutral conditions, which are more practical for electrolyzer operations. This study introduces a dinuclear copper catalyst, [Cu₂(μ-OH) (μ-NO₃) (L)₂], where L is the Schiff base ligand derived from salicylaldehyde and histidine amino acid (Complex 1), for HER in both aqueous and non-aqueous environments. In non-aqueous conditions, with acetic acid as a proton source, the catalyst exhibits outstanding HER performance, achieving an overpotential of 170 mV. At an acid concentration of 0.086 M, it achieves a catalytic current of ∼17.5 mA cm⁻² at an overpotential of 0.52 V. Remarkably, in fully aqueous neutral conditions, Complex 1 reaches a significant current density with an i_c/i_p ratio of ∼82 at a scan rate of 1.0 V s⁻¹, and an apparent rate constant (k_obs) for electrocatalytic HER of ∼13,200 s⁻¹. The catalyst also shows excellent activity in 0.1 M H₃PO₄, with low overpotentials of ∼150 mV at 2.0 mA cm⁻² and 270 mV at 10.0 mA cm⁻². In controlled potential electrolysis (CPE), the catalyst maintains stable catalytic currents of 25 mA cm⁻² and 75 mA cm⁻² for 18–28 h at a potential of 0.590 V vs. RHE in neutral and acidic conditions, respectively, without noticeable decrease in catalytic current. Detailed characterizations confirm the molecular integrity of the catalyst and its predominantly homogeneous catalytic mechanism.