Synergistic effect of spatially isolated Ni2P and NiO redox cocatalysts on g-C3N4 for sustainably boosted CO2 photocatalytic reduction

Abstract

Severe recombination of photogenerated carriers and low reaction rates have been recognized as the main obstacles of graphitic carbon nitride (g-C₃N₄, CN) in CO₂ photocatalytic reduction. In this work, spatially isolated Ni₂P and NiO redox cocatalysts were synchronously introduced on CN via the facile one-step gas–solid phosphating reaction between Ni(OH)₂/CN and Na₂HPO₂·2H₂O, and the spatial distribution and mass ratio of Ni₂P and NiO could be optimized by adjusting the phosphating degree. Excitingly, the optimal sample Ni₂P/NiO/CN(0.25) delivered remarkably enhanced CO and CH₄ production of 12.05 and 2.32 μmol g⁻¹ under 8 h visible-light irradiation, respectively being 5 and 30 times that of CN, even superior to that of CN modified with atomically dispersed Pd. Mechanism analysis revealed that NiO could act as the hole acceptor via forming p–n heterojunctions with CN, favoring the water oxidation half-reactions, while Ni₂P could serve as the electron sink, facilitating CO₂ adsorption and activation, as well as the CO₂ reduction half-reactions. Due to the synergistic effect of Ni₂P and NiO, the separation and transfer of photogenerated carriers were greatly accelerated, and the CO₂ photocatalytic reduction rates of CN were dramatically boosted. Furthermore, the in situ formed Ni⁰ during photocatalytic reactions endowed the resulting catalyst with sustainably efficient CO₂ photocatalytic reduction activity. In sum, this work demonstrated the effectiveness and feasibility of spatially isolated redox cocatalyst-decoration in promoting CO₂ photocatalytic conversion. It is believed that the mechanism proposed here will encourage more rational construction of advanced photocatalysts for targeted reactions.