Defect engineering of NiCo-layered double hydroxide hollow nanocages for highly selective photoreduction of CO2 to CH4 with suppressing H2 evolution

Layered double hydroxides (LDHs) have emerged as a class of promising low-cost catalysts for photocatalytic CO2 reduction; however, an in-depth understanding of the relationship between their specific hollow morphology and enhanced catalytic performance is still lacking. In this work, from the perspective of defect engineering and morphology regulation, we found that abundant defects could be created in the NiCo-LDH by applying a novel template method to construct a hollow nanocage morphology. The rich defects in the hollow cage NiCo-LDH (HC-NiCo-LDH) were demonstrated by X-ray absorption fine structure (XAFS) experiments to be oxygen and metal vacancies. Remarkably, the HC-NiCo-LDH showed excellent CO2 photoreduction performance; the CH4 selectivity was increased from 8.92% to 62.66%, while the side reaction of H-2 evolution was suppressed from 44.92% to barely 1.77%, as compared with the defect-free bulk counterparts. The DFT + U calculations and experimental results simultaneously revealed that these defects caused a decreased bandgap to improve the photoinduced electron-hole pair separation efficiency and to facilitate charge transfer processes. This work provides defect-level insights into the NiCo-LDH hollow morphology, providing fundamental guidance to improve the activity and selectivity of photocatalytic CO2 reduction.