Novel coumarin substituted N–heterocyclic carbene Ag(I), Au(I) and Ni(II) complexes as electrocatalysts in hydrogen evolution reactions from water

Abstract

An organized strategy with an analogy in controlling steric and electronic parameters of N-heterocyclic carbene (NHC) Ag (5–10), Au (11/12) and Ni (13/14) complexes as molecular electrocatalysts for engineering hydrogen evolution reaction (HER) from water is revealed. The films of 10, 13 and 14 displayed much improved activity with low overpotential −298 to −355 mV vs. RHE to drive a current density of 10 mA/cm2 (Tafel slope = 70–78 mV/dec) with exchange current density of 18–49 μA/cm2. Latter observation authenticates that the HER proceeds by the electrochemical desorption of molecular hydrogen through Volmer–Heyrovsky step. Further, the durability test suggests much lower decay rate of 11.4 and 23.1% for complexes 10 and 14 after 200 cycles, respectively. Finally, Cdl and Rct were calculated using electrochemical impedance spectroscopy. The superior activity of former complexes was manifested by the NHC design and their microcrystalline porous morphology.