Photocatalytic nitrogen fixation is considered as a very promising technology to solve the high-energy consumption problem in industrial ammonia synthesis. Because of the mildness of reaction conditions, its development is still limited by the low reaction efficiency and unknown reaction mechanism. Inspired by the mechanism of biological nitrogen fixation in nature, Zn 3 In 2 S 6 with different sulfur sources is prepared to study the effects of cation defects on the adsorption, activation, and reaction in photocatalytic nitrogen fixation. Because of the electron-rich property of zinc vacancies in Zn 3 In 2 S 6 nanosheets, it can effectively activate the NN triple bond, thereby increasing the rate of kinetic reduction. With the activation of N 2 molecules on zinc vacancies, the existing protons obtained from methanol (solvent) will greatly accelerate the electron transfer between interfaces during the nitrogen reduction reaction. Notably, Zn 3 In 2 S 6 with rich Zn vacancies exhibits higher activity (355.2 mg L −1 g cat −1 , 15 times) than Zn 3 In 2 S 6 with poor vacancies in nitrogen fixation. This work describes the contribution of zinc vacancies to the fixation and activation of nitrogen molecules, which is very important to establish a highly effective system of photocatalytic nitrogen fixation.

No abstract

Defect engineering is considered as an efficient method for improving the photocatalytic activity of semiconductor photocatalysis because defects can not only serve as trapping centers for electrons and holes but also work as active sites for reaction. Herein, we synthesized a series of MoS2/CdS heterojunctions with abundant sulfur vacancies and used for photocatalytic N2 reduction. The sulfur vacancies at MoS2/CdS heterojunctions were confirmed by UV–vis diffuse-reflectance spectroscopy (UV-DRS) and electron paramagnetic resonance. The charge transfer behaviors of the photocatalysts were characterized by X-ray photoelectron spectroscopy, transient photocurrent, steady and transient photoluminescence spectroscopy, and so forth. Under visible light irradiation for 4 h, the production of NH3 at 3% MoS2/CdS heterojunctions (249.7 mg L–1 g–1) was about 5.4 and 3.9 times higher than that of pure MoS2 (45.9 mg L–1 g–1) and pristine CdS (64.5 mg L–1 g–1), respectively. The reaction mechanisms and pathways were further studied by in situ diffuse reflection infrared Fourier transform spectroscopy.

One-step electrocatalytic N 2 fixation is of emerging interest but is retarded due to the tough dissociation of the N 2 triple bond and low NH 3 selectivity. Here, a plasma-electrocatalytic integrated strategy is reported to be effective to circumvent this dilemma and realize high-performance N 2 fixation via decoupling the reaction to two steps with NO x − serving as an intermediary: (i) non-thermal plasma (NTP) drives air activation into highly active NO x − intermediates, and (ii) subsequent electroreduction of the resultant NO x − into NH 3 . A gliding arc−microwave conjunction plasma mode was found to be preferred to achieve an optimal NO 2 − -N concentration of 2844.31 μg mL −1 , adopting 0.5 M KOH as the absorption solution in the first step. For the next ENO 2 − RR step, plasma-treated 0.5 M KOH was directly used as electrolyte, with well-designed Cu 2 Pd nanodots anchored on carbonized bacterial cellulose (Cu 2 Pd/CBC) as electrocatalyst. An exceptional ENO 2 − RR performance, including a superior R NHd 3 of 1956.65 μg h −1 mg −1 , highest FE of 93.79%, and long time stability of 30 h, was attained for Cu 2 Pd/CBC, outperforming the counterparts Cu/CBC and Pd/CBC. The synergism of CuPd bifunctional catalytic sites is the key to the greatly enhanced electrocatalytic activity via improving the adsorption of NO 2 − and the related intermediates while simultaneously supplying sufficient protons. This work provides an alternative strategy toward sustainable and distributed on-site ammonia synthesis.