Sponge‐Like Nickel Carbonate of High Porosity and Carbonate Vacancy for High‐Performance CO2 Photoreduction.

As most of the fossil carbon on earth is stored in an oxidized state as carbonate minerals, exploration of metal carbonate catalyst for selective CO2 reduction can open appealing access to boost the CO2 capture and storage. However, carbonate is commonly regarded as a poor matrix to host photocatalytic active species, and current literature has few reports of carbonate‐based photocatalytic material. Herein, a hierarchically porous catalyst that features ≈5 nm deficient NiCO3 nanoparticles embedded in sponge‐like high‐magnesium calcite is disclosed. In the photocatalytic CO2 reduction reaction, the as‐prepared catalyst of low Ni content attains a high CO production rate of 10 565 µmol g−1 h−1 and a high selectivity of 94% relative to H2 evolution, a performance that surpasses many other state‐of‐the‐art nickel‐based catalysts. Experiments and theoretical calculations reveal that the carbonate vacancy of NiCO3 strengthens the adsorption and activation of CO2 more significantly than the corresponding oxygen vacancy of NiO. The inert CO2 molecule becomes highly deformed on the surface of NiCO3 which can be readily activated to the key intermediate CO2·− for the photoreduction reaction. The present findings add to the existing knowledge of advanced catalysis using defect materials and demonstrate an intriguing and rare case of highly performing carbonate‐based catalyst. [ABSTRACT FROM AUTHOR]