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

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.