The main factor to improve the performance of CoSe2 for photocatalytic CO2 reduction: element doping or phase transformation

In this work, orthorhombic CoSe2 is fabricated by nitrogen doping into a cubic CoSe2 structure, in which the crystalline phase undergoes transformation. The doped atoms lead to the rotation of the Se22− group, and then the faults of phase change can be observed. Thus, the reverse phase transformation provides an opportunity to study the aspects of element doping and phase change on photocatalytic CO2 reduction simultaneously. The phase change material of N-doped orthorhombic CoSe2 shows high activity toward the photoconversion of CO2 to CO, and the average production rate of CO is up to 1.66 × 104 μmol h−1 g−1 in the first 3 hours, being twice as efficient as that of cubic CoSe2. Intermediate COOH* is detected by in situ infrared spectroscopy and theoretical calculations are also conducted to reveal the intrinsic impact of the doping element on the photosplitting of CO2.