Recent progress in research and design concepts for the characterization,testing,and photocatalysts for nitrogen reduction reaction

The reduction of molecular nitrogen(N_(2))to ammonia(NH_(3))under mild conditions is one of the most promising studies in the energy field due to the important role of NH_(3)in modern industry,production,and life.The photocatalytic reduction of N_(2)is expected to achieve clean and sustainable NH_(3)production by using clean solar energy.To date,the new photocatalysts for photocatalytic reduction of N_(2)to NH_(3)at room temperature and atmospheric pressure have not been fully developed.The major challenge is to achieve high light-absorption efficiency,conversion efficiency,and stability of photocatalysts.Herein,the methods for measuring produced NH_(3)are compared,and the problems related to possible NH_(3)pollution in photocatalytic systems are mentioned to provide accurate ideas for measuring photocatalytic efficiency.The recent progress of nitrogen reduction reaction(NRR)photocatalysts at ambient temperature and pressure is summarized by introducing charge transfer,migration,and separation in photocatalytic NRR,which provides a guidance for the selection of future photocatalyst.More importantly,we introduce the latest research strategies of photocatalysts in detail,which can guide the preparation and design of photocatalysts with high NRR activity.

Mechanistic Insights into Electrocatalytic Nitrogen Reduction Reaction on the Pd-W Heteronuclear Diatom Supported on C_(2)N Monolayer:Role of H Pre-Adsorption

The electrocatalytic N_(2) reduction reaction(eNRR)is a potential alternative to the Haber-Bosch process for ammonia(NH3)production.Tremendous efforts have been made in eNRR catalyst research to promote the practical application of eNRR.In this work,by means of density functional theory calculations and the computational hydrogen electrode model,we evaluated the eNRR performance of 30 single metal atoms supported on a C_(2)N monolayer(M@C_(2)N),and we designed a new thermodynamically stable Pd-W hetero-metal diatomic catalyst supported on the C_(2)N monolayer(PdW@C_(2)N).We found that PdW@C_(2)N prefers to adsorb H over N_(2),and then,the pre-generated hydrogen-terminated PdW@C_(2)N selectively adsorbing N_(2) behaves as the actual functioning“catalyst”to catalyze the eNRR process,exhibiting excellent performance with a low overpotential(0.31 V),an ultralow NH3 desorption free energy(0.05 eV),and a high selectivity toward eNRR over hydrogen evolution reaction(HER).Moreover,PdW@C_(2)N shows a superior eNRR performance to its monomer(W@C_(2)N)and homonuclear diatom(W_(2)@C_(2)N)counterparts.The revealed mechanism indicates that the preferential H adsorption over N_(2) on the active site may not always hamper the eNRR process,especially for heteronuclear diatom catalysts.This work encourages deeper exploration on the competition of eNRR and HER on catalyst surfaces.

Oxygen vacancy enhancing mechanism of nitrogen reduction reaction property in Ru/TiO2

To search the new effective nitrogen reduction reaction(NRR)electrocatalyst is very important for the ammonia-based industry.Herein,we reported the design of a novel NRR electrocatalyst with Ru NPs loaded on oxygen-vacancy TiO2(Ru/TiO2-Vo).Structural characterizations revealed that oxygen vacancy was loaded in the matrix of Ru/TiO2-Vo.Electrocatalytic results indicated that Ru/TiO2-Vo showed good NRR performance(2.11μg h^-1 cm^-2).Contrast tests showed that NRR property of Ru/TiO2-Vo was much better than those of Ru/TiO-12(B)(0.53μg hcm^-2)and Ru/P25(0.42μg h^-1 cm^-2).Furthermore,density functional theory calculation results indicated catalytic mechanism of NRR and rate-determining step(*N2+1/2 H2→*N+*NH)was the potential-determining step with the overpotential requirement of 0.21 V.A combination of electronic structure analysis and catalytic measurement shed light on the synergistic effect of Ru and oxygen vacancy on the NRR performance.

Insights into electrochemical nitrogen reduction reaction mechanisms:Combined effect of single transition-metal and boron atom

Developing single-atom catalysts(SACs) for electrochemical devices is a frontier in energy conversion.The comparison of stability,activity and selectivity between various single atoms is one of the main research focuses in SACs.However,the in-depth understanding of the role that the coordination atoms of single atom play in the catalytic process is lacking.Herein,we proposed a graphene-like boroncarbon-nitride(BCN) monolayer as the support of single metal atom.The electrocatalytic nitrogen reduction reaction(eNRR) performances of 3 d,4 d transition metal(TM) atoms embedded in defective BCN were systematically investigated by means of density functional theory(DFT) computations.Our study shows that the TM-to-N and B-to-N π-back bonding can contribute to the activation of N_(2).Importantly,a combined effect is revealed between single TM atom and boron atom on eNRR:TM atom enhances the nitrogen reduction process especially in facilitating the N_(2) adsorption and the NH3 desorption,while boron atom modulates the bonding strength of key intermediates by balancing the charged species.Furthermore,Nb@BN3 possesses the highest electrocata lytic activity with limiting potential of-0.49 V,and exhibits a high selectivity for nitrogen reduction reaction(NRR) to ammonia compared with hydrogen evolution reaction(HER).As such,this work can stimulate a research doorway for designing multi-active sites of the anchored single atoms and the innate atoms of substrate based on the mechanistic insights to guide future eNRR research.

Bi-Atom Electrocatalyst for Electrochemical Nitrogen Reduction Reactions

The electrochemical nitrogen reduction reaction(NRR)to directly produce NH3 from N_(2) and H_(2)O under ambient conditions has attracted significant attention due to its ecofriendliness.Nevertheless,the electrochemical NRR presents several practical challenges,including sluggish reaction and low selectivity.Here,bi-atom catalysts have been proposed to achieve excellent activity and high selectivity toward the electrochemical NRR by Ma and his co-workers.It could accelerate the kinetics of N_(2)-to-NH_(3) electrochemical conversion and possess better electrochemical NRR selectivity.This work sheds light on the introduction of bi-atom catalysts to enhance the performance of the electrochemical NRR.

Chromium phosphide nanoparticles embedded in porous nitrogen-/phosphorus-doped carbon as efficient electrocatalysts for a nitrogen reduction reaction

The resource recovery of heavy metals from effluent has significant environmental implications and potential commercial value.Chromium phosphide nanoparticles embedded in a nitrogen-/phosphorus-doped porous carbon matrix(CrP/NPC)are synthesized via a consecutive Cr^(6+)leachate treatment and resource recovery process.Electrochemical testing shows that CrP/NPC shows excellent nitrogen reduction reaction(NRR)performance,which yields the highest NH_(3) production rate of 22.56μg h^(−1) mg^(−1)_(cat).and Faradaic efficiency(16.37%)at−0.5 V versus the reversible hydrogen electrode in a 0.05M Na_(2)SO_(4) aqueous solution,as well as robust catalytic stability.The isotopic experiments using ^(15)N^(2) as a nitrogen source confirm that the detected NH_(3) is derived from the NRR process.Finally,density functional theory(DFT)calculations show that the electron deficiency environment of the Cr site can significantly reduce the barrier of the NRR process and promote the formation of intermediate species.

Mo_(3)(C_(6)X_(6))_(2)(X=NH,S,O)monolayers:two-dimensional conductive metal-organic frameworks as effective electrocatalysts for the nitrogen reduction reaction

As a constituent element of amino acids,nitrogen plays an important role in nourishing plants,animals and other forms of life.Although the atmosphere is rich in nitrogen gas(N_(2)),the highly inert N≡N bond makes it difficult for most organisms to directly utilize N_(2).The supply of nitrogen in the biological chain mainly depends on the slow conversion of N_(2) to ammonia(NH3)by biological nitrogen fixation[1].

Computational Design of Single Mo Atom Anchored Defective Boron Phosphide Monolayer as a High-performance Electrocatalyst for the Nitrogen Reduction Reaction

Catalytic reduction of molecular dinitrogen(N_(2))to ammonia(NH_(3))is one of the most important and challenging industrial reactions.Electrochemical reduction is considered as an energy-saving technology for artificial ambient nitrogen fixation,which is emerging as an optimal potential sustainable strategy to substitute for the Haber–Bosch process.However,this process demands efficient catalysts for the N_(2)reduction reaction(NRR).Here,by means of first-principles calculations,we systematically explored the potential electrocatalytic performance of single transition metal atoms(Pd,Ag,Rh,Cu,Ti,Mo,Mn,Zn,Fe,Co,Ru,and Pt)embedded in monolayer defective boron phosphide(TMs/BP)monolayer with a phosphorus monovacancy for ambient NH_(3)production.Among them,the Mo/BP exhibits the best catalytic performance for ambient reduction of N_(2)through the typical enzymatic and consecutive reaction pathways with an activation barrier of 0.68 e V,indicating that Mo/BP is an efficient catalyst for N_(2)fixation.We believe that this work could provide a new avenue of ambient NH_(3)synthesis by using the designed single-atom electrocatalysts.

Theoretical study on the application of the largest aluminum-pyrazole ring in electrochemical nitrogen reduction reaction

Electrochemical nitrogen reduction reaction(NRR)is a mild and sustainable method for ammonia synthesis.Therefore,developing high activity,selectivity,and economic efficiency catalysts with considering the synergistic effects between catalysts and carriers to design novel structural models is very important.Considering the non-noble metal NRR catalyst,Mo3,we tried to find a suitable carrier which is stable and economical.Herein,we used the largest atomically precise aluminum-pyrazole ring(AlOC-69)to date(diameter up to 2.3 nm).The larger ring cavities and the presence of abundant hydroxy groups make AlOC-69 an ideal molecular carrier model and provide a basis for studying its structure-activity relationship.The formation energy(-0.76eV)and stable Mo-0 bonds indicate that Mo_(3)can be stabilized on the Al_(10)O_(10)surface.Additionally,N_(2)has fully activated due to the strong interaction between the p-orbital of N and the d-orbital of Mo.The low limiting potential(-0.28V)emerges that Mo_(3)@Al_(10)O_(10)has ideal catalytic activity and selectivity.This research provides a promising catalyst model and an understanding of its catalytic process at the atomic level,providing a new approach for the co-design of catalyst and carrierin NRR.

Coupling Fe and Mo single atoms on hierarchical N-doped carbon nanotubes enhances electrochemical nitrogen reduction reaction performance

Electrochemical nitrogen reduction reaction(NRR)paves a new way to cost-efficient production of ammonia,but is still challenging in the sluggish kinetics caused by hydrogen evolution reaction competition and chemical inertness of N≡N bond.Herein,we report a“dual-site”strategy for boosting NRR performance.A high-performance catalyst is successfully constructed by anchoring isolated Fe and Mo atoms on hierarchical N doped carbon nanotubes through a facile self-sacrificing template route,which exhibits a remarkably improved NH3 yield rate of 26.8μg·h^(−1)·mg with 11.8%Faradaic efficiency,which is 2.5 and 1.6 times larger than those of Fe/NC and Mo/NC.The enhancement can be attributed to the unique hierarchical structure that profits from the contact of electrode and electrolyte,thus improving the mass and electron transport.More importantly,the in situ Fourier transform infrared spectroscopy(in situ FTIR)result firmly demonstrates the crucial role of the coupling of Fe and Mo atoms,which can efficiently boost the generation and transmission of*N2Hy intermediates,leading to an accelerated reaction rate.

Rational catalyst design and mechanistic evaluation for electrochemical nitrogen reduction at ambient conditions

Ammonia(NH3), a carbon-free hydrogen carrier, is an important commodity for the food supply chain owing to its high energy capacity and ease of storage and transport. The Haber-Bosch process is currently the favored industrial method for large-scale ammonia production but requires energy-intensive and sophisticated infrastructure which hampers its utilization in a sustainable and decentralized system of manufacture.The electrochemical nitrogen reduction reaction(eNRR) at ambient conditions holds great potential for sustainable production of ammonia using electricity generated from renewable energy sources such as solar and wind. However, this approach is limited by a low rate of ammonia production with high overpotential and the competing hydrogen evolution reaction(HER). For a better understanding and utilization of eNRR as a sustainable process, insight into rational catalyst design and mechanistic evaluations by a theoretically-directed experimental approach is imperative. Herein, recent insights into rational catalyst design and mechanisms, based on intrinsic and extrinsic catalytic activity are articulated.Following the elucidation of basic principles and mechanisms, a framework supplied by theoretical studies that lead to the optimal selection and development of eNRR catalysts is presented. Following a discussion of recently developed electrocatalysts for eNRR, we outline various recently-used theoretical and experimental methodologies to improve the intrinsic and extrinsic catalytic activity of advanced electrocatalysts.This review is anticipated to contribute to the development of active, selective, and efficient catalysts for nitrogen reduction.

Iron-group electrocatalysts for ambient nitrogen reduction reaction in aqueous media

Electrochemical nitrogen reduction reaction(NRR)is considered as an alternative to the industrial Haber-Bosch process for NH3 production due to both low energy consumption and environment friendliness.However,the major problem of electrochemical NRR is the unsatisfied efficiency and selectivity of electrocatalyst.As one group of the cheapest and most abundant transition metals,iron-group(Fe,Co,Ni and Cu)electrocatalysts show promising potential on cost and performance advantages as ideal substitute for traditional noble-metal catalysts.In this minireview,we summarize recent advances of iron-group-based materials(including their oxides,hydroxides,nitrides,sulfides and phosphides,etc.)as non-noble metal electrocatalysts towards ambient N2-to-NH3 conversion in aqueous media.Strategies to boost NRR performances and perspectives for future developments are discussed to provide guidance for the field of NRR studies.

1+1>2: Learning from the interfacial modulation on single-atom electrocatalysts to design dual-atom electrocatalysts for dinitrogen reduction

Developing efficient electrocatalysts for converting dinitrogen to ammonia through electrocatalysis is of significance to the decentralized ammonia production. Here, through high-throughput density functional theory calculations, we demonstrated that the interfacial modulation of hexagonal boron nitride/graphene(hBN-graphene) could sufficiently improve the catalytic activity of the single transition metal atom catalysts for nitrogen reduction reaction(NRR). It was revealed that Re@hBN-graphene and Os@hBN-graphene possessed remarkable NRR catalytic activity with low limiting potentials of 0.29 V and 0.33 V, respectively. Furthermore, the mechanism of the enhanced catalytic activity was investigated based on various descriptors of the adsorption energies of intermediates, where the synergistic effect of hBN and graphene in the hybrid substrate was found to play a key role. Motivated by the synergistic effect of hybrid substrate in single-atom catalysts, a novel strategy was proposed to efficiently design dual-atom catalysts by integrating the merits of both metal components. The as-designed dual-atom catalyst Fe-Mo@hBN exhibited more excellent NRR catalytic performance with a limiting potential of 0.17 V, manifesting the solidity of the design strategy. Our findings open new avenues for the search of heterostructure substrates for single-atom catalysts and the efficient design of dualatom catalysts for NRR.

Surface modification of CeO_(2-x) nanorods with Sn doping for enhanced nitrogen electroreduction

While the electrochemical nitrogen reduction reaction(NRR) represents a prospective blueprint for environmentally renewable ammonia generation,it has yet to overcome the limitations of weak activity and inferior selectivity.In this regard,surface modification tactic was constructed to markedly enhance the activity and selectivity via introducing Sn atoms into the surface of defective cerium oxide(denoted as Sn-CeO_(2-x)) as the active and robust electrocatalyst for NRR under benign environment.The introduction of Sn atoms in CeO_(2-x)can not only inhibit the HER activity of the catalyst but also modulate the electronic structure of ceria and optimize N-Ce interaction,thus enhancing NRR activity and selectivity.Outperforming all previous CeO_(2)-based NRR catalysts,this catalyst has demonstrated an ammonia yield rate of 41.1 μg mg_(cat)^(-1) h^(-1) and an exceptional Faradic efficiency of 35.3%.This work presents a viable approach for the development of advanced NRR electrocatalysts.

Enhancing ammonia production rates from electrochemical nitrogen reduction by engineering three-phase boundary with phosphorus-activated Cu catalysts

Electrochemical N_(2) reduction reaction(eNRR) over Cu-based catalysts suffers from an intrinsically low activity of Cu for activation of stable N_(2) molecules and the limited supply of N_(2) to the catalyst due to its low solubility in aqueous electrolytes.Herein,we propose phosphorus-activated Cu electrocatalysts to generate electron-deficient Cu sites on the catalyst surface to promote the adsorption of N_(2) molecules.The eNRR system is further modified using a gas diffusion electrode(GDE) coated with polytetrafluoroethylene(PTFE) to form an effective three-phase boundary of liquid water-gas N_(2)-solid catalyst to facilitate easy access of N_(2) to the catalytic sites.As a result,the new catalyst in the flow-type cell records a Faradaic efficiency of 13.15% and an NH_(3) production rate of 7.69 μg h^(-1) cm^(-2) at-0.2 V_(RHE),which represent 3.56 and 59.2 times increases from those obtained with a pristine Cu electrode in a typical electrolytic cell.This work represents a successful demonstration of dual modification strategies;catalyst modification and N_(2) supplying system engineering,and the results would provide a useful platform for further developments of electrocatalysts and reaction systems.

Recent advances of MXene as promising catalysts for electrochemical nitrogen reduction reaction

Electrochemical reduction of N2,as an eco-friendly alternative,not only allows the use of protons in water as a source of hydrogen under mild conditions but also can be driven by renewable electric energy.The major challenge is to identify high-efficiency electrocatalysts.MXene is a new class of 2D transition metal carbides,nitrides,and carbonitrides that have received significant attention in electrocatalysis.The investigations on MXene in electrocatalytic nitrogen fixation are rapidly proceeding,and some breakthroughs have emerged ve ry recently due to MXenes’satisfacto ry catalytic activity.Here,the recent progress concerning the MXene-based catalysts for electrochemical N2 reduction reaction(NRR)is highlighted.In regards to giving guidelines for exploring more efficient MXene-based catalysts for the NRR,the fabrication and surface modification of MXene are discussed.Besides,the shortcomings and challenges of current research are summarized and the future research directions are prospected.

Surface hydrophobic modification enhanced catalytic performance of electrochemical nitrogen reduction reaction

Electrocatalytic nitrogen reduction reaction(NRR)is a sustainable approach for NH_(3)production with low energy consumption.However,competing hydrogen reduction reaction(HER)in aqueous solution results in low NH_(3)production and Faraday efficiency(FE).Here,MoS_(2)nanostructures with a hydrophobic surface are synthesized by alkyl thiols modification.Aerophilic and hydrophobic surface facilitates an efficient three-phase contact of N_(2),H_(2)O,and catalyst.Thus,localized concentrated N_(2)molecules can overcome the mass transfer limitation of N2 and depress the HER due to lowering the proton contacts.Although the active-sites decrease with the increase of the alkyl chain since the thiol may cover the active site,the optimized electrocatalyst achieves NH_(3)yield of 12.86×10^(-11)mol·cm^(-2)·s^(-1)at-0.25 V and 22.23%FE,which are 4.3 and 24 times higher than those of MoS2-CP electrocatalyst,respectively.The increased catalytic performance is attributed to the high N_(2)adsorption and depressed HER.

First-principles study on Fe_(2)B_(2)as efficient catalyst for nitrogen reduction reaction

[18_(T)D$IF]Ammonia(NH_(3))is considered an attractive candidate as a clean,highly efficient energy carrier.The electrocatalytic nitrogen reduction reaction(NRR)can reduce energy input and carbon footprint;therefore,rational design of effective electrocatalysts is essential for achieving high-efficiency electrocatalytic NH_(3)synthesis.Herein,we report that the enzymatic mechanism is the more favourable pathway for NRR,due to lower limiting potential(-0.44 V),lower free energy(only 0.02 eV)of the first hydrogenation step(*N–N to*NH–N),and more electron transfer from Fe_(2)B_(2)to the reaction species.In addition,both vacancies and dopants can be helpful in reducing the reaction energy barrier of the potential-determining step.Therefore,we have demonstrated that Fe_(2)B_(2)is a potential new candidate for effective NRR and highlighted its potential for applications in electrocatalytic NH_(3)synthesis.

Tuning Double Layer Structure of WO3 Nanobelt for Promoting the Electrochemical Nitrogen Reduction Reaction in Water

Electrochemical fixation of nitrogen to ammonia with highly active,highly selective and low cost electrocatalysts is a sustainable alternative to the extremely energy-and capital-intensive Haber-Bosch process.Herein,we demonstrate a near electroneutral WO3 nanobelt catalyst to be a promising electrocatalyst for selective and efficient nitrogen reduction.The concept of near electroneutral interface is demonstrated by fabricating WO3 nanobelts with small zeta potential value on carbon fiber paper,which ensures a loose double layer structure of the electrode/electrolyte interface and allows nitrogen molecules access the active sites more easily and regulates proton transfer to increase the catalytic selectivity.The WO3/CFP electrode with optimal surface charge achieves a NH3 yield rate of 4.3μg·h-1·mg-1 and a faradaic efficiency of 37.3%at-0.3 V vs.RHE,rivalling the performance of the state-of-the-art nitrogen reduction reaction electrocatalysts.The result reveals that an unobstructed gas-diffusion pathway for continually supplying enough nitrogen to the active catalytic sites is of great importance to the overall catalytic performance.

Fe-doped SnO_(2) nanosheet for ambient electrocatalytic nitrogen reduction reaction

Ammonia plays a vital role in the development of modern agriculture and industry.Compared to the conventional Haber–Bosch ammonia synthesis in industry,electrocatalytic nitrogen reduction reaction(NRR)is considered as a promising and environmental friendly strategy to synthesize ammonia.Here,inspired by biological nitrogenase,we designed iron doped tin oxide(Fe-doped SnO_(2))for nitrogen reduction.In this work,iron can optimize the interface electron transfer and improve the poor conductivity of the pure SnO_(2),meanwhile,the synergistic effect between iron and Sn ions improves the catalyst activity.In the electrocatalytic NRR test,Fe-doped SnO_(2) exhibits a NH_(3) yield of 28.45μg·h^(−1)·mgcat^(−1),which is 2.1 times that of pure SnO_(2),and Faradaic efficiency of 6.54%at−0.8 V vs.RHE in 0.1 M Na_(2)SO_(4).It also shows good stability during a 12-h long-term stability test.Density functional theory calculations show that doped Fe atoms in SnO_(2) enhance catalysis performance of some Sn sites by strengthening N–Sn interaction and lowering the energy barrier of the rate-limiting step of NRR.The transient photovoltage test reveals that electrons in the low-frequency region are the key to determining the electron transfer ability of Fe-doped SnO_(2).