Covalent Attachment of Cobalt Bis(Benzylaminedithiolate) to Reduced Graphene Oxide as a Thin-Film Electrocatalyst for Hydrogen Production with Remarkable Dioxygen Tolerance

Hydrogen (H-2) can be produced in the water splitting reaction, specifically on the cathodic side through the hydrogen evolution reaction (HER), where two protons and two electrons are combined to make H-2. Herein, we report a molecular catalyst, [cobalt bis(benzylammoniumdithiolate)](+), covalently attached to graphene oxide (GO) as a thin-film catalyst for HER. A member of the acclaimed cobalt dithiolene family of HER catalysts, this complex was characterized by UV-vis and paramagnetic H-1 NMR spectroscopy, cyclic voltammetry, and mass spectrometry, showing properties similar to those of known cobalt bis(benzenedithiolate)-type complexes. The amine-modified complex is then covalently attached to GO through reaction with epoxide groups, and the resulting GO-Co suspension is drop-cast onto glassy carbon electrodes to give thin films. These films were characterized by atomic force and scanning electron microscopy, which show wrinkled films with a thickness of 330 +/- 120 nm. When reduced, the reduced graphene oxide (RGO)-[cobalt bis(benzylammoniumdithiolate)](+) films (RGO-1) show high activity for electrocatalytic hydrogen production in acidic aqueous conditions with turnover frequencies of up to 1000 s(-1) at pH 0, an overpotential of 273 +/- 5 mV at pH 3, and a Faradaic efficiency (FE) of 97 +/- 4%. Excitingly, with atmospheric levels of dioxygen, RGO-1 remains completely stable and delivers a 79 +/- 3% FE for the HER. Kinetic and thermodynamic electrocatalysis parameters are further provided, including analysis of the onset potentials, foot-of-the-wave analysis, Tafel slopes, and plateau currents. The latter gives a rate constant of 1.5 x 10(4) M-1 s(-1) for HER for RGO-1. Controlled potential electrolysis for multiple hours shows improved activity and durability over those of the analogous physisorbed systems. This study of a HER molecular catalyst immobilized in thin RGO films continues to develop our understanding of thin-film electrocatalysis for the advancement of both clean hydrogen production and other electrocatalytic reactions related to clean energy and chemical syntheses.