Diiron Disulfide Methacrylate Metallopolymers as Sustainable Electrocatalysts for Water-Splitting and Molecular Hydrogen Production.

We review in this Viewpoint recent progress on the development of a new sustainable electrocatalytic system for water-splitting and molecular hydrogen generation using [diiron-disulfur] ([2Fe-2S]) active site methacrylate metallopolymers. To date, noble metal catalysts (e.g, platinum) remain the best electrocatalysts for molecular hydrogen generation using water as the chemical feedstock and proton donor. However, there remains a need for the synthesis of efficient electrocatalytic systems using low cost, earth abundant materials for sustainable H2 generation. We focus on our recent work in this area using well-defined single site [2Fe-2S]-metallopolymer catalysts. Thus, far, these systems have demonstrated rates of hydrogen production >25 times faster than [FeFe]-hydrogenase enzymes and match the current densities of platinum with only 0.2 V higher potential when operating in water at neutral pH with tris(hydroxymethyl)aminoethane (TRIS) buffer (Faradaic yields 100 ± 3%). The molecular design and synthesis of [2Fe-2S]-metallopolymers are reviewed along with mechanistic studies unraveling the causality of efficient H2 production from this catalytic system. The overall current output and overpotential are improved by the reversible electrostatic adsorption of the metallopolymer on the carbon electrode surface that enhances the proton and electron transfer rates and the use of protic buffer electrolytes (PBEs) that enhance the availability of protons. The schemes summarized here to improve the performance of [2Fe-2S] catalysts by incorporation into metallopolymers may be used to enhance the performance of other molecular electrocatalysts at the electrode surface.