An anionic coordination strategy has been developed to construct a halogen-coordinated Ni-based metal-organic cage (MOC) for the photocatalytic reduction of carbon dioxide (CO₂). It is found that iodide anions significantly reduce the energy gap between the Ni d orbitals and iodide p orbitals, facilitating electron transfer from the Ni center to the adsorbed CO₂ (TEOA = triethanolamine).

Abstract

Photocatalytic reduction of carbon dioxide (CO₂) provides a promising strategy for producing high-value chemicals and fuels. However, developing high-performance photocatalysts for CO₂ reduction remains a great challenge due to the poor stability of reaction intermediates. Herein, we present an anionic coordination strategy to facilitate the stabilization of intermediates by constructing halogen-coordinated metal-organic cages (MOCs) (Ni₈L₁₂X₄, X = Cl, Br, I). Theoretical calculations show that the formation of *COOH intermediate is the rate-limiting step and halogen coordination effectively regulates the energy barrier for this reaction. Notably, iodide anions significantly reduce the energy gap between the Ni d and iodide p orbitals, enhancing electron transfer from the Ni center to adsorbed CO₂ and promoting the production of *COOH. As a result, Ni₈L₁₂I₄ demonstrates superior performance with a CO production rate of 2680.23 µmol g⁻¹ h⁻¹ and 95% selectivity, outperforming Cl- and Br-coordinated Ni MOC by 200- and 5-fold, respectively. This work opens a new coordination engineering strategy for fabricating efficient photocatalysts for CO₂ reduction.