Highly efficient photoelectrochemical catalytic CO2 into formate with 2D indium-based metal-organic frameworks

Developing a universal and effective strategy to synthesize two-dimensional freestanding photosensitized metal–organic framework (MOF) still remains a challenge. In this study, we successfully synthesize a series of 2D porphyrin­based MOF through a simple and effictive solvothermal method. Owing to the special π-π conjugated structure of porphyrin rings, the as-synthesized indium-tetrakis(4-carboxyphenyl)-porphyrin (In-TCPP) is sensitive to visible light. The presence of light field effect plays an important role in enhanceing electrocatalytic carbon dioxide reduction reaction (CO2RR), resulting a impressive maximum formate Farady efficiency of 92 % at −1.0 V vs.RHE, which is 100 mV positive than 84 % of under dark condition. In addition, both current density and FEHCOOH obviously increases across the entire testing potential range when exposed to visible light irradiation. The decreased Tafel slope and electrochemical impedance under visible light indicate that the porphyrin macrocycles not only serve as the ligand but also as the light-switch to facilitate the electron transfer and decrease the energy barrier of electrochemical CO2RR. This work opens up a valuable guidance for photo-coupled electrochemical reduction of CO2 to HCOOH with low overpotential.