Fibrous Pb(II)-Based Coordination Polymer Operable as a Photocatalyst and Electrocatalyst for High-Rate, Selective CO2-to-Formate Conversion

Abstract

A nonporous [Pb(tadt)]_n (tadt = 1,3,4-thiadiazole-2,5-dithiolate) coordination polymer, KGF-9, with a 2D infinite (−Pb−S−)_n structure has been previously reported as a precious-metal-free photocatalyst for selective CO₂-to-formate conversion under visible light. In the present work, a microwave (MW)-assisted solvothermal reaction is used to synthesize KGF-9 with improved physicochemical properties and catalytic activity. Compared with KGF-9 prepared by the previously reported methods, that prepared by the new synthesis route exhibited a greater specific surface area, greater crystallinity, and greater photoconductivity. These improved properties led to a drastic increase of the apparent quantum yield (AQY) for selective formate production, from 2.6 to 25% at 400 nm; this AQY represents a record-high value among reported heterogeneous photocatalysts for CO₂-to-formate conversion. Interestingly, the AQY for formate production is unchanged irrespective of the light intensity (0.04–14 mW cm⁻²), indicating little contribution of charge accumulation in the bulk during the reaction (i.e., indicating efficient charge transport to surface reactants). When composited with Ketjen Black, KGF-9 enabled the electrochemical conversion of CO₂ to formate in aqueous solution while maintaining a high selectivity. A high-rate reduction of CO₂ to formate with a total absolute current density of 200–300 mA cm⁻² is achieved, with a Faradaic efficiency (FE) of >90%.