Modular assembly of electron transfer pathways in bimetallic MOFs for photocatalytic ammonia synthesis

Abstract

It is a long-term pursuit to implement the green and sustainable photocatalytic production of ammonia via the conversion of water and nitrogen under mild conditions. Due to the rapid recombination of photoexcited carriers and competitive reaction of hydrogen evolution, how to effectively utilize the electrons in the photocatalytic procedure becomes a key issue to achieve high photocatalytic N₂ reduction. In this study, electron pathway engineering (EPE) is proposed to regulate the electron transfer and utilization by using the stable amino-functionalized UiO-66 with bimetallic Ce–Hf nodes (NU6(Ce–Hf)) as the photocatalysts. The photocatalytic results confirm that the sample with the Ce : Hf molar ratio exhibits optimal performance (158.4 μmol g⁻¹ h⁻¹), which is ascribed to the electron transfer efficiency promoted by the electron buffering effect of Ce species and the selective adsorption ability of Hf species for nitrogen molecules. In addition, the selectivity of the nitrogen fixation reaction is approximately up to 100%, which is attributed to the inhibition of hydrogen evolution reaction by Hf species. This study may offer some inspirations to realize the effective transfer and utilization of electrons for photocatalytic materials.