Efficient photocatalytic CO2 reduction mediated by transitional metal borides: metal site-dependent activity and selectivity

Abstract

The search for novel and low-cost cocatalysts that can achieve high efficiency, while maintaining high selectivity in photocatalytic CO₂ reduction is highly desirable, yet challenging. Herein, we demonstrate that transitional metal borides (TMBs) Ni₃B, Co₃B and Fe₂B can serve as effective and low-cost cocatalysts to enhance the performance of photocatalytic CO₂ reduction under visible light, while other TMBs (TaB₂, NbB₂ and MoB) are almost ineffective. The performance of photocatalytic CO₂ reduction depends on the metal site in TMBs, among which Ni₃B exhibits the highest selectivity and activity compared to those of other TMBs. Specifically, Ni₃B exhibits a CO evolution rate of 157.7 μmol h⁻¹ with selectivity of 93.0% in the presence of [Ru(bpy)₃]Cl₂ as a light absorber under visible light, representing state-of-the-art cocatalyst. The excellent activity of Ni₃B can be ascribed to its metallic feature that can efficiently transport photogenerated electrons from the light absorber, as well as the unique Ni–B bond that acts as an electron accumulator to provide abundant long-lived electrons to be injected into Ni⁰ active sites for the activation of CO₂. These findings may provide the principle guidance for the search and design of efficient cocatalytic materials and systems for solar energy conversion.