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 CO 2 reduction can open appealing access to boost the CO 2 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 NiCO 3 nanoparticles embedded in sponge‐like high‐magnesium calcite is disclosed. In the photocatalytic CO 2 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 H 2 evolution, a performance that surpasses many other state‐of‐the‐art nickel‐based catalysts. Experiments and theoretical calculations reveal that the carbonate vacancy of NiCO 3 strengthens the adsorption and activation of CO 2 more significantly than the corresponding oxygen vacancy of NiO. The inert CO 2 molecule becomes highly deformed on the surface of NiCO 3 which can be readily activated to the key intermediate CO 2 ·− 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.