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+) InIII-Ni (C2S2 (C6H4COO) 2) 2·3DMF·1. 5H2O (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+) InIII- (TTFTB) ·0. 7C2H5OH·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, jHCOO- = 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.