Theoretical Prediction Of The Catalytic Performance Of Two-dimensional Material For Electrochemical Reduction Of Nitric Oxide

Nitrogen is one of the most abundant elements in the earth and can be converted to various products such as ammonia（NH3）and nitric oxide（NO）.NH3 is an essential substance for plants,animals and other life forms,while NO is a serious environmental pollutant.Therefore,reducing or converting NO is an important issue in the field of nitrogen cycle.The electrochemical method is considered to be one of the effective means to solve the energy and environmental problems because of its advantages such as being able to be performed under mild conditions,low consumption,and cleanliness.Electrocatalytic nitric oxide reduction reaction（NOER）is one of the main pathways to reduce NO pollution and convert NO into useful ammonia products.This process can occur quickly depending on the auxiliary role of the catalyst.However,the commonly used NOER catalysts are mainly based on transition metal catalysts,which faced the disadvantages of high cost,low content,and low catalytic efficiency,which greatly limits their large-scale application.Therefore,developing cheap electrocatalyst with high stability,high activity and high selectivity is a challenge for nitric oxide reduction reactions.To this end,we studied the application of boron-doped graphene（BG）and carbon-doped boron nitride nanosheet（C-doped h-BN）as non-metal catalysts in the NOER process through density functional theory.The specific results are as follows:（1）Introducing elemental boron in 2D graphene to improve its catalytic activity for NOER.On this catalyst,the optimal reaction path of NOER is:NO→NO^*→HNO^*→NH₂O^*→NH₂OH^*→NH₂^*→NH₃,and the reaction product is NH₃,in which the protonation of NO^*to HNO^*is the rate-determining step of the whole pathway,the Gibbs free energy barrier is 0.35 eV.Meanwhile,the catalyst shows favorable inhibition effect of hydrogen evolution reaction.Furthermore,HNO^*can be effectively coupled with NO molecules,after a series of protonation processes,eventually N2O is the final product,and its lowest limiting potential is still the step of forming HNO^*intermediate.The highest kinetic energy barrier for NH3 production along the lowest energy pathway is 0.70 eV,which is slightly lower than the highest kinetic energy barrier（0.76 eV）to produce N2O.Therefore,N2O is also a possible product of NOER.（2）The catalyst formed by C atom replacing N atom in the h-BN monolayer exhibits excellent catalytic activity for NOER.At low NO coverages,NH3 is formed through HNO^*intermediate with an onset potential of-0.37 V,while at high coverages,N2O is easily formed via dimer with an onset potential of only-0.15 V.Moreover,the highest energy barrier（0.36 eV）for generating N2O is less than the highest energy barrier（0.59 eV）for generating NH₃ along the lowest energy pathway.This indicates that NOER tends to form N2O through 2 electron reduction pathway on the catalyst,that is,2NO（g）+2H⁺+2e^-→N₂O+H₂O（l）,and the catalyst has a significant inhibitory effect on competitive hydrogen evolution reaction.The research results in this paper show that both boron-doped graphene and carbon-doped boron-nitrogen sheet materials are extremely promising for metal-free electrocatalyst with high catalytic activity and selectivity for NOER.