In(III) Metal-Organic Framework Incorporated with Enzyme-Mimicking Nickel Bis(dithiolene) Ligand for Highly Selective CO2 Electroreduction

Inspired by the exciting physical/chemical properties in metal-organic frameworks (MOFs) of the redox-active tetrathiafulvalene (TTF) ligands, nickel bis(dithiolene-dibenzoic acid), [Ni(C2S2(C6H4COOH)(2))(2)], has been designed and developed as an inorganic analogue of the corresponding TTF-type donors (such as tetrathiafulvalene-tetrabenzoate, TTFTB), where a metal site (Ni) replaces the central C=C bond. In this work, [Ni(C2S2(C6H4COOH)(2))(2)] and In3+ have been successfully assembled into a three-dimensional MOF, (Me2NH2+){In-III-[Ni(C2S2(C6H4COO)(2))(2)]}center dot 3DMF center dot 1.5H(2)O (1, DMF = N, N-dimethylformamide), with satisfying chemical and thermal stabilities. With the combination of reversible redox activity and unsaturated metal sites originated from [Ni(C2S2(C6H4COOH)(2))(2)], 1 showed a significantly enhanced performance in electrocatalytic CO2 reduction compared with the isomorphic MOF, (Me2NH2+)[In-III-(TTFTB)]center dot 0.7C(2)H(5)OH center dot DMF (2, with TTFTB ligand). More importantly, by mimicking the active [NiS4] sites of formate dehydrogenase and CO-dehydrogenase, a prominently higher conversion rate and Faradaic efficiency (FE), with FEHCOO- increasing from 54.7% to 89.6% (at -1.3 V vs RHE, j(HCOO)- = 36.0 mA cm(-2)), were achieved in 1. Mechanistic investigations further confirm that [NiS4] can serve as a CO2 binding site and efficient catalytic center. This unprecedented effect of redox-active nickel dithiolene-based MOF catalysts on the performance of electroreduction of CO2 provides an important strategy for designing stable and efficient crystalline enzyme-mimicking catalysts for the conversion of CO2 into high-value chemical stocks.

Automated summary

A redox-active nickel dithiolene-based MOF catalyst was designed and developed to enhance the electroreduction performance of CO2 by mimicking the active sites of biological catalysts, leading to improved conversion rates and Faradaic efficiencies for the transformation of CO2 into high-value chemical stocks.