Vacancy modulation on NiTi-layered double hydroxides towards highly selective CO2 photoreduction

Photoreduction of carbon dioxide (CO2) is a promising way to achieve sustainable energy production and alleviate environmental problems. Herein, we report a NiTi-layered double hydroxides photocatalyst with bivalent and trivalent metal vacancies (denoted as NiVTiV-LDHs) via alkali-etching amphoteric metal cations (Zn and Al) from NiZnTiAl-LDHs precursor. The NiVTiV-LDHs attains a CH4 selectivity of 94% with a production rate of 2398 µmol g−1 h−1, which is preponderant to the state-of-the-art photocatalysts. Operando X-ray absorption fine structure (XAFS) and Fourier-transform infrared spectroscopy (FT-IR) characterizations combined with density functional theory (DFT) calculations corroborate that Ni2+δ−O(H)−Ti3+ζ sites modulated by adjacent vacancies exhibits a declined 3d-orbital occupancy, accelerating the charge transfer for boosting CH4 formation. Moreover, the unique adsorption configuration (Ni2+δ/Ti3+ζ−CO) not only stabilizes the key intermediate *CO for further protonation, but also induces a decreased energy barrier of the rate-determining step (hydrogenation of *OCH3), accounting for the robust photocatalytic CO2 reduction towards CH4.