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

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 Cu-2 dimer, in which two Cu(I) ions are linked by two L- with a Cu center dot center dot center dot Cu separation of 2.637 angstrom. And different Cu-2 units are connected by strong pi-pi 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 i(0) for the HER is improved. And with the increase of the temperature, the HER current density is increased, and the average activation energy Ea from 30 to 50 degrees C for the HER in the presence of the complex is calculated as ca. 40 kJ mol(-1).