Theoretical Study On Electrocatalytic Nitrogen Reduction Of The Metal-atom Modified Arsenene And Black Phosphorus

Synthetic ammonia is one of the essential foundations for the development of modern industry and modern agriculture.Up to now,industrial ammonia synthesis is still mainly based on the Haber-Bosch method,which was introduced at the beginning of the 20th century.During the industrial ammonia synthesis,of nearly one century,the Haber-Bosch method has been limited by the scale of the ammonia production due to its high energy consumptions and the low conversions rate.The improvement of ammonia processes is therefore one of the most pressing sustainability issues to be addressed.Catalyst,as an intermediate medium for reducing the energetic barriers of the relevant reactions,is an important entry point for the exploration of the efficient ammonia processes.In addition,electrocatalytic technology not only provides stable regulation of chemical reactions at ambient conditions,but also allows precise control of chemical reaction rates.Therefore,the combination of catalyst and electrocatalytic technology is seen as a new alternative to the Haber-Bosch method of ammonia synthesis for modern industry.However,the selectivity of the catalyst during electrocatalytic nitrogen reduction reactions is one of the difficulties of current research.Therefore,a rational design of the catalyst is desired to achieve an efficient and stable ammonia synthesis process.Based on first principles calculations of density functional theory（DFT）,we performed a theoretical study on the electrocatalytic nitrogen reduction of the metal-atom modified arsenene and the VA-group two-dimensional（2D）materials,which was summarized as follows:Initiated by the single-atom catalyst,we systematically investigated the effect of different individual transition metal atoms（V,Cr,Fe,Co,Cu,Ru,Pd,Ag,Pt and Au,etc.）doped on the surface of mono-layer arsenene on the nitrogen reduction performance.Based on a comprehensive scheme of nitrogen adsorption,free energy barrier and catalyst selectivity,four heterogeneous catalytic atoms,V,Fe,Co and Ru,were predicted to be available for surface doping.These atoms possess high loading capacity as well as stable adsorption of nitrogen molecules.In particular,the two possible N₂ adsorption configurations and the very low overpotential（0.1 V）of the V-doped arsenene system via the enzymatic pathway make this atom very competitive in its category of single-atom catalysts.The role of the electron"accept-donation"mechanism in nitrogen fixation catalysis has been elucidated in detail by combining electronic density of states（DOS）and charge density differences（CDD）analysis,and it has been found that V acts as a charge transmitter with the As atom in contact with it,allowing the transfer of as many electrons as possible to the nitrogen,which has a positive effect on its weakening of the N≡N bond.We explored the effect of phosphorus（P）atom coordination on the nitrogen reduction catalytic performance of metal dual-atoms anchored arsenene systems.The P-atom coordination of Nb atom anchored arsenene（Nb@P₃-Ars）was selected as the best candidate for further investigation of the nitrogen reduction mechanism by using a"two-step"strategy with stringent nitrogen reduction criteria.It is shown that Nb@P₃-Ars is not only thermodynamic stable at room temperature when used as a catalyst for electrocatalytic nitrogen reduction,but also dominates the competition with hydrogen precipitation reactions.In particular,when the electrocatalytic reduction process occurs via the distal pathway,Nb@P₃-Ars has a low overpotential（0.36 V）,which favors the efficient reduction of nitrogen to ammonia.Starting from the double-atoms catalyst,we designed the nitrogen（N）atoms coordinated metal double-atoms anchored black phosphorene systems（TM₂@N₄-BP or TM₁TM₂@N₄-BP）and calculated the nitrogen reduction catalytic performance of different kinds of metal double-atoms（homo-nuclear/hetero-nuclear）in this system.It was shown that the distal and mixed pathways of Co₂@N₄-BP and Ru Fe@N₄-BP were superior to the other pathways,with overpotentials of only0.30 V and 0.40 V.Furthermore,considering the influence of the electrolyte solution in real experiments,we compared the sensitivity of the catalysts to the adsorption of different species（N₂,H₂O,H and CO₂,etc.）,demonstrating that Co₂@N₄-BP with high efficiency and selectivity.Finally,molecular dynamics simulations verified that the catalyst maintains good stability of structure and catalytic performance at room temperature.Therefore,the synthesis of Co₂@N₄-BP and Ru Fe@N₄-BP in experiment are expected to be possible.This theoretical study further deepens our physical insights into the electrocatalytic mechanism in the nitrogen reduction,which is expected to guide the rational design of novel nitrogen reduction catalysts based on the metal atom modified VA-group two-dimensional materials.