High temperature induced S vacancies in natural molybdenite for robust electrocatalytic nitrogen reduction

Oxygen-Bridged Vanadium Single-Atom Dimer Catalysts Promoting High Faradaic Efficiency of Ammonia Electrosynthesis

Single-atom catalysts have already been widely investigated for the nitrogen reduction reaction (NRR). However, the simplicity of a single atom as an active center encounters the challenge of modulating the multiple reaction intermediates during the NRR process. Moving toward the single-atom-dimer (SAD) structures can not only buffer the multiple reaction intermediates but also provide a strategy to modify the electronic structure and environment of the catalysts. Here, a structure of a vanadium SAD (V-O-V) catalyst on N-doped carbon (O-V₂-NC) is proposed for the electrochemical nitrogen reduction reaction, in which the vanadium dimer is coordinated with nitrogen and simultaneously bridged by one oxygen. The oxygen-bridged metal atom dimer that has more electron deficiency is perceived to be the active center for nitrogen reduction. A loop evolution of the intermediate structure was found during the theoretical process simulated by density functional theory (DFT) calculation. The active center V-O-V breaks down to V-O and V during the protonation process and regenerates to the original V-O-V structure after releasing all the nitrogen species. Thus, the O-V₂-NC structure presents excellent activity toward the electrochemical NRR, achieving an outstanding faradaic efficiency (77%) along with the yield of 9.97 μg h^-1 mg^-1 at 0 V (vs RHE) and comparably high ammonia yield (26 μg h^-1 mg^-1) with the FE of 4.6% at -0.4 V (vs RHE). This report synthesizes and proves the peculiar V-O-V dimer structure experimentally, which also contributes to the library of SAD catalysts with superior performance.

Efficient organic contaminant and Cr (VI) synchronous removing by one-step modified molybdenite cathode microbial fuel cells

As a novel technique with a wide range of applications, microbial fuel cell (MFC) could simultaneously remove organic contaminants and heavy metals in complex wastewater, despite striking differences in physicochemical properties of these contaminant. But its wastewater treatment efficiency is restricted by its lower generation performance. However, approaches for the modification of MFCs' cathode with appropriate catalyst could effectively overcome this limitation. Herein, a new-type efficient cathode catalyst was invented through modifying natural molybdenite via one-step oxidation method. In this case, molybdenite had many changes in morphology (wave-shaped bending, fragmentation and decrescent diameter) during oxidation modification process, and oxidation-modified molybdenite could provide much more active sites for the cathode. After applying this novel cathode catalyst, the electric generation capacity of MFC system increased by 5.08 times, and its simultaneous degradation efficiency of methyl blue (MB) and Cr (VI) increased by 3.35 times (compared with graphite cathode MFC). This study provides a novel low-carbon and environmentally friendly way to prepare high efficiency cathode catalyst materials and provides a new idea of simultaneous purification for organic and metallic pollutants from complex wastewater.

Recent Advances in Electrochemical Nitrogen Reduction Reaction to Ammonia from the Catalyst to the System

As energy-related issues increase significantly, interest in ammonia (NH3) and its potential as a new eco-friendly fuel is increasing substantially. Accordingly, many studies have been conducted on electrochemical nitrogen reduction reaction (ENRR), which can produce ammonia in an environmentally friendly manner using nitrogen molecule (N2) and water (H2O) in mild conditions. However, research is still at a standstill, showing low performances in faradaic efficiency (FE) and NH3 production rate due to the competitive reaction and insufficient three-phase boundary (TPB) of N2(g)-catalyst(s)-H2O(l). Therefore, this review comprehensively describes the main challenges related to the ENRR and examines the strategies of catalyst design and TPB engineering that affect performances. Finally, a direction to further develop ENRR through perspective is provided.

Electron coupled FeS2/MoS2 heterostructure for efficient electrocatalytic ammonia synthesis under ambient conditions

Developing efficient ammonia synthesis technology under ambient conditions is of vital importance. In this work, an FeS₂ coupled MoS₂ heterostructure with ultrathin features was designed by a one-step hydrothermal process for the electrochemical nitrogen reduction reaction. Density functional theory calculations reveal that the electronic structure of MoS₂ greatly changes with the introduction of FeS₂. The modulated electronic structure of MoS₂ not only exhibits enhanced conductivity but also facilitates the activation of N₂ molecules due to its abundant electronic region. The optimized FeS₂/MoS₂ nanosheet heterostructure achieves a high NH₃ yield rate of 2.59 μmol h^-1 mg^-1 and a FE of 4.63% at -0.3 V vs. RHE. Besides, the well-designed nanocomposite also shows excellent selectivity without N₂H₄ by-products and exhibits good stability after electrocatalysis for 48 hours.

Frenkel-defected monolayer MoS2 catalysts for efficient hydrogen evolution

Defect engineering is an effective strategy to improve the activity of two-dimensional molybdenum disulfide base planes toward electrocatalytic hydrogen evolution reaction. Here, we report a Frenkel-defected monolayer MoS₂ catalyst, in which a fraction of Mo atoms in MoS₂ spontaneously leave their places in the lattice, creating vacancies and becoming interstitials by lodging in nearby locations. Unique charge distributions are introduced in the MoS₂ surface planes, and those interstitial Mo atoms are more conducive to H adsorption, thus greatly promoting the HER activity of monolayer MoS₂ base planes. At the current density of 10 mA cm⁻², the optimal Frenkel-defected monolayer MoS₂ exhibits a lower overpotential (164 mV) than either pristine monolayer MoS₂ surface plane (358 mV) or Pt-single-atom doped MoS₂ (211 mV). This work provides insights into the structure-property relationship of point-defected MoS₂ and highlights the advantages of Frenkel defects in tuning the catalytic performance of MoS₂ materials.

While material defect sites are active for chemical reactions, it is important to understand how different defect types impact reactivity. Here, authors prepare Frenkel-defected MoS₂ monolayers and demonstrate improved performances for H₂ evolution electrocatalysis than pristine or doped MoS₂.

Efficient Electrocatalytic Nitrogen Reduction to Ammonia on Ultrafine Sn Nanoparticles

Electrocatalytic nitrogen reduction reaction (NRR) at ambient conditions is a promising route for ammonia (NH₃) synthesis but still suffers from low activity and selectivity. Here, ultrafine Sn nanoparticles (NPs) grown on carbon blacks (Sn_SC/C) have been synthesized through a wet-chemical method using sodium citrate dehydrate as a stabilizing agent. Benefiting from the small sizes of Sn NPs, the Sn_SC/C catalyst exhibits excellent electrocatalytic performance for NRR with a high Faradaic efficiency of 22.76% and an NH₃ yield rate of 17.28 μg h^-1 mg^-1 in the 0.1 M Na₂SO₄ electrolyte, outperforming many reported electrocatalysts for NRR under similar conditions. Density functional theory calculation results reveal that the potential-determining step on Sn NPs is the generation of NHNH* through simultaneous hydrogenation of N₂^* by a H* and a H⁺/e^- pair via Langmuir-Hinshelwood plus Eley-Rideal mechanisms.

Nanomaterials for the electrochemical nitrogen reduction reaction under ambient conditions

As an important chemical product and carbon-free energy carrier, ammonia has a wide range of daily applications in several related fields. Although the industrial synthesis method using the Haber-Bosch process could meet production demands, its huge energy consumption and gas emission limit its long-time development. Therefore, the clean and sustainable electrocatalytic N2 reduction reaction (NRR) operating under conditions have attracted great attention in recent years. However, the chemical inertness of N2 molecules makes it difficult for this reaction to proceed. Therefore, rationally designed catalysts need to be introduced to activate N2 molecules. Here, we summarize the recent progress in low-dimensional nanocatalyst development, including the relationship between the structure and NRR performance from both the theoretical and experimental perspectives. Some insights into the development of NRR electrocatalysts from electronic control aspects are provided. In addition, the theoretical mechanisms, reaction pathways and credibility studies of the NRR are discussed. Some challenges and future prospects of the NRR are also pointed out.