Evaluation of the H 2 Evolving Activity of Benzenehexathiolate Coordination Frameworks and the Effect of Film Thickness on H 2 Production.

The design of earth-abundant catalysts for the electrochemical production of H2 from water is important for the realization of a sustainable energy future. Incorporation of molecular catalysts into extended frameworks has emerged as a viable strategy for improving catalytic performance and durability while maintaining a high degree of control over the structure and properties of the catalytic active site. Here, we investigate benzenehexathiolate (BHT) coordination frameworks as electrocatalysts for the hydrogen evolution reaction (HER) in pH 1.3 aqueous solutions. The electrocatalytic HER activity of BHT based coordination frameworks follows the order of CoBHT > NiBHT > FeBHT. CoBHT operates at an overpotential of 185 mV, the lowest observed overpotential of the reported metal dithiolene-based metal organic frameworks and coordination polymers to date. To further understand the properties that dictate electrocatalytic activity, the effect of film thickness on the HER performance of CoBHT, a parameter that has not been extensively explored for electrocatalytic coordination frameworks, was examined. As the thickness was increased to ~1 µm, charge and proton transfer through CoBHT was hindered, the number of electrochemically accessible active sites decreased, and the mechanical robustness of the modified electrode was diminished. The observed thickness-dependent HER activity of CoBHT highlights the importance of practical electrode construction and offers insight into how to optimize proton and electron transfer properties and active site densities within coordination frameworks without reducing the mechanical robustness of the immobilized catalysts.