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.

Dual-site collaboration boosts electrochemical nitrogen reduction on Ru-S-C single-atom catalyst

Electrocatalytic reduction of nitrogen into ammonia(NH_(3))is a highly attractive but challenging route for NH_(3)production.We propose to realize a synergetic work of multi reaction sites to overcome the limitation of sustainable NH_(3)production.Herein,using ruthenium-sulfur-carbon(Ru-S-C)catalyst as a prototype,we show that the Ru/S dual-site cooperates to catalyse eletrocatalytic nitrogen reduction reaction(eNRR)at ambient conditions.With the combination of theoretical calculations,in situ Raman spectroscopy,and experimental observation,we demonstrate that such Ru/S dual-site cooperation greatly facilitates the activation and first protonation of N_(2)in the rate-determining step of eNRR.As a result,Ru-S-C catalyst exhibits significantly enhanced eNRR performance compared with the routine Ru-N-C catalyst via a single-site catalytic mechanism.We anticipate that our specifically designed dual-site collaborative catalytic mechanism will open up a new way to offers new opportunities for advancing sustainable NH_(3)production.

Composition Engineering Opens an Avenue Toward Efficient and Sustainable Nitrogen Fixation

In this work,we open an avenue toward rational design of potential efficient catalysts for sustainable ammonia synthesis through composition engineering strategy by exploiting the synergistic effects among the active sites as exemplified by diatomic metals anchored graphdiyne via the combination of hierarchical high-throughput screening,first-principles calculations,and molecular dynamics simulations.Totally 43 highly efficient catalysts feature ultralow onset potentials(|U_(onset)|≤0.40 V)with Rh-Hf and Rh-Ta showing negligible onset potentials of 0 and-0.04 V,respectively.Extremely high catalytic activities of Rh-Hf and Rh-Ta can be ascribed to the synergistic effects.When forming heteronuclears,the combinations of relatively weak(such as Rh)and relatively strong(such as Hf or Ta)components usually lead to the optimal strengths of adsorption Gibbs free energies of reaction intermediates.The origin can be ascribed to the mediate d-band centers of Rh-Hf and Rh-Ta,which lead to the optimal adsorption strengths of intermediates,thereby bringing the high catalytic activities.Our work provides a new and general strategy toward the architecture of highly efficient catalysts not only for electrocatalytic nitrogen reduction reaction(eNRR)but also for other important reactions.We expect that our work will boost both experimental and theoretical efforts in this direction.

Promoting electrocatalytic nitrogen reduction to ammonia via dopant boron on two-dimensional materials

Electrocatalytic nitrogen reduction reaction(NRR)is a key process for producing energy efficient and environment friendly ammonia.Boron-doped two-dimensional materials are highly promising as NRR catalysts.However,the interaction between doped boron and matrix materials on NRR catalytic performance is still unclear,which is limiting the development of catalysts containing boron for NRR.Here,NRR on different boron-doped twodimensional(2D)materials was explored by first principle theory.It is found that adsorption energy of intermediate*NNH(E*NNH)can be used as a descriptor to characterize the catalytic activity for NRR.Boron-adsorbed black phosphorus(B-BP)is demonstrated showing excellent NRR catalytic activity and suppressing hydrogen evolution reaction.It is disclosed that the excellent catalytic performance of boron-doped structures comes from a proper quantitatively electron transfer(0.8e)between nitrogen in*NNH and the active site boron atom.This work not only established a descriptor for NRR catalytic activity on B-doped 2D materials,but also screened out a potential NRR catalyst.More importantly,the intrinsic reason and mechanism of high catalytic activity of boron-doped structures were proposed.This work provides a design principle for exploring high-performance NRR electrocatalysts containing boron.

Perspectives on electrochemical nitrogen fixation catalyzed by two-dimensional MXenes

Ammonia is the most basic raw material in industrial and agricultural production.The current industrial production of ammonia relies on the Haber-Bosch process with high energy consumption.To overcome this shortcoming,the development of electrocatalytic ammonia synthesis under moderate conditions is considered as a potential alternative technology.The two-dimensional(2D)MXenes family has been proved promising as electrocatalysts,but from the currently available literature,it is hard to find a systematic review on MXenes-catalyzed ammonia synthesis.So in the present review,we summarize the key perspectives on that topic in recent years as well as outline,from a prospective view,strategies of catalyst design.We analyze in detail the methods for preparing high performance MXenes-based catalysts and the corresponding underlying mechanisms,and also discuss the criteria and potential challenges,expecting to provide inspiration for the development of efficient MXenes-based route to electrochemical ammonia fixation.

Polyoxometalates-derived ternary metal oxides electrocatalyst for N_(2) reduction under ambient conditions

Accelerating the breaking of the nitrogen nonpolar bond(N≡N)is an important factor to improve the effi ciency of the electro-catalytic nitrogen reduction reaction(e-NRR).In this work,polyoxometalates-derived FeMo-based ternary oxide materials MoO_(2)-Mo_(4)O_(11)-FeMoO_(4)@X(abbreviated as MoFeO@X,X represents the synthesis temperature of 650,750 and 850℃)were designed and synthesized for e-NRR under ambient conditions.The scanning electron microscopy images of MoFeO@750 show an ellipsoidal-like structure(0.86×0.6μm).The relatively large specifi c surface area,formation of multiple interfaces,together with the synergistic eff ect of iron and molybdenum bimetals,would make MoFeO@X catalyst more easily absorb and activate N_(2)in the e-NRR.Expectedly,the synthesized MoFeO@750 shows an optimal NH_(3)production rate of 16.57μg·h^(−1)·mg cat.^(−1)and Faradaic effi ciency of 12.33%at−0.3 V versus reversible hydrogen electrode(νs.RHE),with outstanding electrochemical and structural stability.

Single-atom catalysts based on two-dimensional metalloporphyrin monolayers for ammonia synthesis under ambient conditions

We systematically investigated the catalytic performance of 3d,4d,and 5d transition metals anchored onto two-dimensional extended porphyrin(PP)substrates as nitrogen reduction reaction(NRR)electrocatalysts,employing density functional theory(DFT)calculations and four-step high-throughput screening.Four novel metalloporphyrin(MPP,M=Zr,Nb,Hf,and Re)single-atom catalyst candidates have been identified due to their excellent catalytic performance(low onset potential,high stability,and selectivity).Through comprehensive reaction path search,the maximum Gibbs free energy changes for NRR on the ZrPP(enzymatic-consecutive hybrid path),NbPP(consecutive path),HfPP(enzymatic-consecutive hybrid path),and RePP(distal path)catalysts are 0.38,0.41,0.53,and 0.53 eV,respectively.Band structures,projected density of states,and charge/spin distributions show that the high catalytic activity is due to significant orbital hybridizations and charge transfer between N_(2) and MPP catalysts.We hope our work will promote experimental synthesis of these NRR electrocatalysts and provide new opportunities to the electrochemical conversion of N_(2) to NH_(3) under ambient conditions.

Hydrogen-assisted activation of N_(2)molecules on atomic steps of ZnSe nanorods

Electrochemical reduction reaction of nitrogen(NRR)offers a promising pathway to produce ammonia(NH_(3))from renewable energy.However,the development of such process has been hindered by the chemical inertness of N_(2).It is recently proposed that hydrogen species formed on the surface of electrocatalysts can greatly enhance NRR.However,there is still a lack of atomiclevel connection between the hydrogenation behavior of electrocatalysts and their NRR performance.Here,we report an atomistic understanding of the hydrogenation behavior of a highly twinned ZnSe(T-ZnSe)nanorod with a large density of surface atomic steps and the activation of N_(2)molecules adsorbed on its surface.Our theoretical calculations and in situ infrared spectroscopic characterizations suggest that the atomic steps are essential for the hydrogenation of T-ZnSe,which greatly reduces its work function and efficiently activates adsorbed N_(2)molecules.Moreover,the liquid-like and free water over T-ZnSe promotes its hydrogenation.As a result,T-ZnSe nanorods exhibit significantly enhanced Faradaic efficiency and NH3 production rate compared with the pristine ZnSe nanorod.This work paves a promising way for engineering electrocatalysts for green and sustainable NH3 production.