Cu(i) complex based on 6H-indolo[2,3-b]quinoxaline: structure and electrocatalytic properties for hydrogen evolution reaction from water

Abstract

Using a rigid ligand, 6H-indolo[2,3-b]quinoxaline (HL), a Cu(I) complex formulated as Cu₂L₂ (1) has been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. The complex is a planar Cu₂ dimer, in which two Cu(I) ions are linked by two L⁻ with a Cu⋯Cu separation of 2.637 Å. And different Cu₂ units are connected by strong π–π stacking interactions into a three-dimensional (3D) supramolecular architecture. The HL ligand can't electrocatalyze the hydrogen evolution reaction (HER) from water, whereas the Cu(I) complex can act as an electrochemically stable electrocatalyst. In the presence of the Cu(I) complex, the exchanging current density i₀ for the HER is improved. And with the increase of the temperature, the HER current density is increased, and the average activation energy E_a from 30 to 50 °C for the HER in the presence of the complex is calculated as ca. 40 kJ mol⁻¹.