A pdc-pinched copper complex for sustainable hydrogen production through ligand supported-metal centric proton-coupled electron transfer

Abstract

A water-stable [Cu(pdc)(H₂O)₂] complex, promising functional mimics of hydrogenase active sites and promoting sustainable hydrogen production in acidic water, was designed and synthesised using an ONO-type pincer ligand, 2,6-pyridine dicarboxylic acid (pdc), and copper(II) nitrate. X-ray crystallographic analysis reveals that [Cu(pdc)(H₂O)₂] crystallizes in a triclinic crystal system with square pyramidal geometry. The complex shows an excellent faradaic efficiency of 91% with remarkable stability up to 60 equivalents of acetic acid (AcOH), relative to [Cu(pdc)(H₂O)₂]. Moreover, comprehensive spectroscopic, analytical, electrochemical, and computational analyses were performed to validate the proton-coupled electron transfer reaction. pdc coordinated with the Cu centre offers a delicate balance in shuttling syn-conformational proton coupling (H_pdc^δ+⋯H_Cu^δ−, 2.1 Å), promoting sustainable hydrogen production in water. Further, the scope of the electrocatalytic fate of [Cu(pdc)(H₂O)₂] towards industrial prospects was ensured by examining the electrocatalytic capacity of [Cu(pdc)(H₂O)₂] in 0.5 M H₂SO₄. The complex exhibits a significant elevation in cathodic current with H₂SO₄ in water collected from the Relli river (27.066668° N, 88.466667° E), Kalimpong, West Bengal, envisioning its true-catalytic capacity in pilot-scale application and real prospect for industrial use.