Automated and Continuous-Flow Platform to Analyze Semiconductor–Metal Complex Hybrid Systems for Photocatalytic CO2 Reduction

Sunlight-driven CO2 reduction is increasingly considered as a promising approach to contribute toward a carbon-neutral fuel cycle, but most photocatalyst systems are currently studied individually under batch conditions with manual, labor-intensive analytical procedures. Here, we present the advantages of a continuous-flow setup to study photocatalytic CO2 to CO reduction systems, which also benefits from aspects of automation (using programmed in-line gas quantification of multiple samples in parallel). The capabilities of the methodology are demonstrated using a state-of-the-art light absorber platform based on ZnSe quantum dots (QDs) in combination with a series of molecular co-catalysts based on Ni and Co for visible-light-driven CO2 reduction in aqueous ascorbate solution. A newly synthesized Co-tetraphenylporphyrin featuring three sulfonate groups and one amine group (Co(tppS3N1)) is identified to exhibit a benchmark photocatalytic activity (18.6 μmol of CO, 79.7 mmol of CO gZnSe–1, TONCo (CO) of 619, external quantum efficiency (EQE) >5%). The utility of our methodology is further shown by applying the setup to study the photocatalyst systems under lower light intensities, low CO2 concentration, and aerobic conditions, which impact the photocatalytic activity and selectivity. Overall, this work reports an improved methodology for studying photocatalytic CO2 reduction alongside advancing the understanding of QD molecular co-catalyst hybrids using ZnSe QDs as a versatile light absorber based on earth-abundant components that operate under fully aqueous conditions.