ZnO Quantum Dots Coupled with Graphene toward Electrocatalytic N Reduction: Experimental and DFT Investigations.

Electrochemical reduction of N to NH is a promising method for artificial N fixation, but it requires efficient and robust electrocatalysts to boost the N reduction reaction (NRR). Herein, a combination of experimental measurements and theoretical calculations revealed that a hybrid material in which ZnO quantum dots (QDs) are supported on reduced graphene oxide (ZnO/RGO) is a highly active and stable catalyst for NRR under ambient conditions. Experimentally, ZnO/RGO was confirmed to favor N adsorption due to the largely exposed active sites of ultrafine ZnO QDs. DFT calculations disclosed that the electronic coupling of ZnO with RGO resulted in a considerably reduced activation-energy barrier for stabilization of *N H, which is the rate-limiting step of the NRR. Consequently, ZnO/RGO delivered an NH yield of 17.7 μg h  mg and a Faradaic efficiency of 6.4 % in 0.1 m Na SO at -0.65 V (vs. RHE), which compare favorably to those of most of the reported NRR catalysts and thus demonstrate the feasibility of ZnO/RGO for electrocatalytic N fixation.