Enhanced photocatalytic N2 fixation by promoting N2 adsorption with a co-catalyst

Abstract

Photocatalytic N2 fixation involves a nitrogen reduction reaction on the surface of the photocatalyst to convert N2 into ammonia. Currently, the adsorption of N2 is the limiting step for the N2 reduction reaction on the surface of the catalyst. Based on the concept of photocatalytic water splitting, the photocatalytic efficiency can be greatly enhanced by introducing a co-catalyst. In this report, we proposed a new strategy, namely, the loading of a NiS co-catalyst on CdS nanorods for photocatalytic N2 fixation. Theoretical calculation results indicated that N2 was effectively adsorbed onto the NiS/CdS surface. Temperature programmed desorption studies confirmed that the N2 molecules preferred to adsorb onto the NiS/CdS surface. Linear sweep voltammetry results revealed that the overpotential of the N2 reduction reaction was reduced by loading NiS. Furthermore, transient photocurrent and electrochemical impedance spectroscopy indicated that the charge separation was enhanced by introducing NiS. Photocatalytic N2 fixation was carried out in the presence of the catalyst dispersed in water without any sacrificial agent. As a result, 1.0 wt% NiS/CdS achieved an ammonia production rate of 2.8 and 1.7 mg L−1 for the first hour under full spectrum and visible light (λ > 420 nm), respectively. The catalyst demonstrated apparent quantum efficiencies of 0.76%, 0.39% and 0.09% at 420, 475 and 520 nm, respectively. This study provides a new method to promote the photocatalytic efficiency of N2 fixation.