Construction of Six-Oxygen-Coordinated Single Ni Sites on g-C3N4 with Boron-Oxo Species for Photocatalytic Water-Activation-Induced CO2 Reduction

The configuration regulation of single-atom photocatalysts (SAPCs) can significantly influence the interfacial charge transfer and subsequent catalytic process. The construction of conventional SAPCs for aqueous CO2 reduction is mainly devoted toward favorable activation and photoreduction of CO2, however, the role of water is frequently neglected. In this work, single Ni atoms are successfully anchored by boron-oxo species on g-C3N4 nanosheets through a facile ion-exchange method. The dative interaction between the B atom and the sp(2) N atom of g-C3N4 guarantees the high dispersion of boron-oxo species, where O atoms coordinate with single Ni (II) sites to obtain a unique six-oxygen-coordinated configuration. The optimized single-atom Ni photocatalyst, rivaling Pt-modified g-C3N4 nanosheets, provides excellent CO2 reduction rate with CO and CH4 as products. Quasi-in-situ X-ray photoelectron spectra, transient absorption spectra, isotopic labeling, and in situ Fourier transform infrared spectra reveal that as-fabricated six-oxygen-coordinated single Ni (II) sites can effectively capture the photoelectrons of CN along the B-O bridges and preferentially activate adsorbed water to produce H atoms to eventually induce a hydrogen-assisted CO2 reduction. This work diversifies the synthetic strategies for single-atom catalysts and provides insight on correlation between the single-atom configuration and reaction pathway.

Automated summary

The configuration regulation of single-atom photocatalysts plays a crucial role in the interfacial charge transfer and catalytic process for CO2 reduction. This study successfully anchored single Ni atoms onto g-C3N4 nanosheets, providing a highly efficient photocatalyst for aqueous CO2 reduction. Various experimental techniques revealed that the six-oxygen-coordinated single Ni (II) sites can efficiently capture photoelectrons and activate water molecules to induce a hydrogen-assisted CO2 reduction.