Hydrogen is a promising renewable fuel and an industrially important gas, such as for the Haber-Bosch process for fertilizer production. Though hydrogen is currently produced non-renewably from methane and coal, it can be produced more cleanly in the cathodic reaction of water splitting – combining two protons and two electrons. This reaction is known as the hydrogen evolution reaction (HER). At the anodic side of water splitting, water is oxidized to dioxygen gas and protons, completing the reaction. Further developing and understanding HER with earth-abundant transition metal molecular complexes will help develop a sustainable hydrogen economy. Cobalt bis(benzenedithiolate) type catalysts are adept at catalyzing proton reduction to hydrogen. Attaching these molecular catalysts to an electrode surface combines the advantages of molecular catalysts with the advantages of heterogeneous catalysis. We have previously shown cobalt bis(benzenedithiolate) catalysts physisorbed onto graphitic electrodes; however, the activity of these systems declines over time, likely because the catalyst slowly dissociates from the surface. To solve this issue, we propose a stronger, covalent link between the catalyst and the electrode surface. Through an appended amine, the catalyst is attached to graphene oxide (GO) by reaction with the epoxide groups on the surface of GO. These GO-cat nanosheets can be cast into thin films on inert electrode surfaces and reduced to reduced graphene oxide, which restores conductivity. The synthesis of the benzenedithiol ligand with amine functionality, characterization of the resulting [Co(III)bis(benzylaminedithiolate)]<sup>-</sup> complex, and covalent attachment of this modified catalyst to graphene oxide via the epoxide ring opening reaction will be presented. The morphology and chemical identity of the thin films of reduced graphene oxide with the covalently-linked cobalt bis(benzenedithiolate) catalysts is further characterized by atomic force microscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, solid state Raman, and X-ray photoelectrocon spectroscopy. The electrocatalytic hydrogen evolution activity, efficiency, and durability over time of these thin films is finally compared with the physisorbed system.

Covalent attachment of cobalt bis(benzylaminedithiolate) to reduced graphene oxide as a thin film catalyst for hydrogen production

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ACS Fall 2022

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