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.