Tunable electrocatalytic H2 evolution activity of nickel-dithiolene coordination polymers

Abstract

With a surge in atmospheric greenhouse gas levels, a switch to carbon-free energy sources, such as hydrogen, is imminent. Herein, the electrocatalytic activity of triphenylenehexathiolate (THT) based coordination polymers (CPs), NiTHT, was studied toward the hydrogen evolution reaction (HER) in acidic medium. Liquid–liquid interfacial synthesis was employed for film synthesis, with a controlled film thickness ranging from 212 nm to 1740 nm. The best performing film exhibited an overpotential of 501 mV vs. RHE to reach a current density of 10 mA cm⁻², with a Tafel slope of 98 mV dec⁻¹, indicating that either the Heyrovsky or the Tafel step was rate determining for the catalysis. Additionally, the influence of extrinsic factors (the identity and concentration of the supporting electrolyte and the catalyst loading) and intrinsic factors (thickness and morphology) on the hydrogen evolution activity of the materials was studied and the kinetics of the HER were rationalized. Finally, the long-term stability of the NiTHT films was evaluated and the highest selectivity (faradaic efficiency, FE) for hydrogen evolution was determined to be > 90%. Post-catalysis characterization revealed a retention of structural integrity with ∼12.5% of Ni leaching into the acidic medium employed for the HER. Solvothermally synthesized NiTHT_ST CP showed an improved catalytic overpotential of 301 mV vs. RHE in a pH 1.3 electrolyte solution, with a FE toward the HER of > 90% over 28 h, displaying a more robust phase of the framework compared to that generated via the interfacial method.