Visible-light-responsive hybrid photocatalysts for quantitative conversion of CO2 to highly concentrated formate solutions

Abstract

Photocatalysts can use visible light to convert CO2 into useful products. However, to date photocatalysts for CO2 conversion are limited by insufficient long-term stability and low CO2 conversion rates. Here we report hybrid photocatalysts consisting of conjugated polymers and a ruthenium(II)–ruthenium(II) supramolecular photocatalyst which overcome these challenges. The use of conjugated polymers allows for easy fine-tuning of structural and optoelectronic properties through the choice of monomers, and after loading with silver nanoparticles and the ruthenium-based binuclear metal complex, the resulting hybrid systems displayed remarkably enhanced activity for visible light-driven CO2 conversion to formate. In particular, the hybrid photocatalyst system based on poly(dibenzo[b,d]thiophene sulfone) drove the very active, durable and selective photocatalytic CO2 conversion to formate under visible light irradiation. The turnover number was found to be very high (TON = 349 000) with a similarly high turnover frequency (TOF) of 6.5 s–1, exceeding the CO2 fixation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase in natural photosynthesis (TOF = 3.3 s–1), and an apparent quantum yield of 11.2% at 440 nm. Remarkably, quantitative conversion of CO2 (737 mmol, 16.5 mL) to formate was achieved using only 8 mg of the hybrid photocatalyst containing 80 nmol of the supramolecular photocatalyst at standard temperature and pressure. The system sustained photocatalytic activity even after further replenishment of CO2, yielding a very high concentration of formate in the reaction solution up to 0.40 M without significant photocatalyst degradation within the timeframe studied. A range of experiments together with density functional theory calculations allowed us to understand the activity in more detail.