Hierarchical NiCo2O4 hollow nanocages for photoreduction of diluted CO2: Adsorption and active sites engineering

Abstract CO2 adsorption is a critical step for CO2 photoreduction, especially in diluted CO2, whereas an in-depth understanding of CO2 adsorption effects is still lacking. Herein, isostructural NiCo2O4 and MgCo2O4 hierarchical hollow nanocages (NiCo2O4 HCs and MgCo2O4 HCs) have been ingeniously constructed for diluted CO2 photoreduction. NiCo2O4 HCs exerts an apparent quantum yield of 1.56 % with CO selectivity of 89 %, exceeding most previous inorganic catalysts in pure CO2. Nevertheless, MgCo2O4 HCs is almost inert, even though it shows higher CO2 uptake ability. DFT calculations results indicate that CO2 molecule adsorbed on Ni sites can be readily reduced to CO, while the CO2 on Mg sites cannot participate in this reaction. Therefore, only adsorbed CO2 which can participate in reduction reactions, named active adsorption, can accelerate the whole reactions. This work unearths atomic-level insights into the relation between CO2 adsorption and reduction, providing fundamental guidance to improve photocatalytic performance.