Reduced State of the Graphene Oxide@Polyoxometalate Nanocatalyst Achieving High-Efficiency Nitrogen Fixation under Light Driving Conditions

The nitrogen (N₂) reduction to generate ammonia (NH₃) is a prerequisite for inputting fixed nitrogen (N) into a global biogeochemical cycle. Developing highly efficient photocatalysts for N₂ fixation under mild conditions is still a challenge. Herein, we first report three kinds of reduction states of graphene oxide (GO)@polyoxometalate (POM) composite nanomaterials, which have outstanding photocatalytic N₂ fixation activities in pure water without any other electronic sacrificial agents and cocatalysts at atmospheric pressure and room temperature. A lot of experiments show that the remarkable photocatalytic N₂ fixation performance of these three nanocatalysts is due to three factors that doping the reduced POMs (also called heteropoly blues) into the reduce GO (rGO) reduces the aggregation state of rGO (from 5 to 2 nm), resulting in rGO exposing many active sites to enhance the N₂ adsorption amount, these three nanocatalysts possess a wide absorption spectrum and strong reducibility, which facilitate absorb light energy exciting abundant photoelectrons to activate N₂, and rGO can effectively suppress the electrons recombination and rapidly transfer electrons to the absorbed N₂ to accelerate NH₃ production. Among them, r-GO@H₅[PMo₁₀V₂O₄₀] (PMo₁₀V₂) exhibits the highest NH₃ generation efficiency of 130.3 μmol L^-1 h^-1, which is improved by 65.9 and 97.3% compared to the reduced PMo₁₀V₂ (rPMo₁₀V₂) and PMo₁₀V₂. Introduction of POMs provides a new perspective in the design of high-performance photocatalytic N₂ fixation nanomaterials.