Ammonia Synthesis via Electrochemical Nitrogen Reduction Reaction on Iron Molybdate under Ambient Conditions

Optimizing oxygen vacancies through grain boundary engineering to enhance electrocatalytic nitrogen reduction

Electrocatalytic nitrogen reduction is a challenging process that requires achieving high ammonia yield rate and reasonable faradaic efficiency. To address this issue, this study developed a catalyst by in situ anchoring interfacial intergrown ultrafine MoO2 nanograins on N-doped carbon fibers. By optimizing the thermal treatment conditions, an abundant number of grain boundaries were generated between MoO2 nanograins, which led to an increased fraction of oxygen vacancies. This, in turn, improved the transfer of electrons, resulting in the creation of highly active reactive sites and efficient nitrogen trapping. The resulting optimal catalyst, MoO2/C700, outperformed commercial MoO2 and state-of-the-art N2 reduction catalysts, with NH3 yield and Faradic efficiency of 173.7 μg h-1 mg-1cat and 27.6%, respectively, under - 0.7 V vs. RHE in 1 M KOH electrolyte. In situ X-ray photoelectron spectroscopy characterization and density functional theory calculation validated the electronic structure effect and advantage of N2 adsorption over oxygen vacancy, revealing the dominant interplay of N2 and oxygen vacancy and generating electronic transfer between nitrogen and Mo(IV). The study also unveiled the origin of improved activity by correlating with the interfacial effect, demonstrating the big potential for practical N2 reduction applications as the obtained optimal catalyst exhibited appreciable catalytic stability during 60 h of continuous electrolysis. This work demonstrates the feasibility of enhancing electrocatalytic nitrogen reduction by engineering grain boundaries to promote oxygen vacancies, offering a promising avenue for efficient and sustainable ammonia production.

Electrochemical Fixation of Nitrogen by Promoting N2 Adsorption and N-N Triple Bond Cleavage on the CoS2/MoS2 Nanocomposite

An electrochemical N₂ reduction reaction (NRR), as an environmentally benign method to produce NH₃, is a suitable alternative to substitute the energy-intensive Haber-Bosch technology. Unfortunately, to date, it is obstructed by the lack of efficient electrocatalysts. Here, a CoS₂/MoS₂ nanocomposite with CoS₂ nanoparticles decorated on MoS₂ nanosheets is fabricated and adapted as a catalyst for the NRR. As unveiled by experimental and theoretical results, the strong interaction between CoS₂ and MoS₂ modulates interfacial charge distribution with electrons transferring from CoS₂ to MoS₂. Consequently, a local electrophilic region is formed near the CoS₂ side, which enables effective N₂ absorption. On the other hand, the nucleophilic area formed near the MoS₂ side is in favor of breaking stable N≡N, the potential-determining step (*N₂ → *N₂H) which brings about a much decreased energy barrier than that on pure MoS₂. As a result, this catalyst exhibits an excellent NRR performance, NH₃ yield and Faradaic efficiency of 54.7 μg·h^-1·mg^-1 and 20.8%, respectively, far better than most MoS₂-based catalysts.