Unsaturated coordination-regulated high-spin nickel sites for selective solar-driven carbon dioxide conversion in pure water

Abstract

Achieving efficient photocatalytic carbon dioxide (CO₂) reduction is crucial for sustainable energy and carbon neutrality. However, a fundamental challenge resides in the rational design and fine-tuning of catalyst active sites. Here, we construct edge-rich nickel–aluminum layered double hydroxide (E_D-NiAl-LDH) nanoflakes with abundant lattice O defects for effective and selective solar-driven CO₂ conversion in a pure water system. The E_D-NiAl-LDH exhibits an excellent carbon monoxide (CO) production rate of 773.4 µmol g⁻¹ h⁻¹ with a high selectivity of 98.5%, surpassing that of state-of-the-art photocatalysts reported in recent years. Outdoor tests also demonstrate an impressive CO₂-to-CO photo-conversion rate of 500 µmol g⁻¹ h⁻¹, with stable activity over an 80-hour period. In situ characterization methods and theoretical calculations confirm that the edge-rich structure provides abundant unsaturated coordination-regulated high-spin Ni active sites. The high-spin Ni active sites possess half-filled degenerate e_g orbitals in the octahedral field, which significantly accelerates the migration of photogenerated electrons from Ni to CO₂ molecules while inhibiting other competitive reactions, thereby enabling the observed exceptional performance. This work establishes edge engineering as a general strategy to unlock high-spin catalytic centers in LDHs, advancing the design of efficient solar fuel systems.