First-principles Study Of Transition Metals And B-doped C₃N And C₉N₄ Monolayers

The environmental pollution and energy crisis are becoming more and more serious.The hydrogen evolution reaction?HER?and nitrogen reduction reaction?NRR?have shown fascinating potential in solving the global environmental pollution and energy crisis.The search for efficient catalysts to fully reduce the cost of HER and NRR has attracted more and more scientists and technicians.Moreover,fully analyzing the reaction mechanism of hydrogen and nitrogen reduction on high-efficiency catalysts can make people have a deeper understanding of them,and will also help people accelerate the search for high-efficiency catalysts that serve these two reactions.This paper mainly studies the electrocatalytic hydrogen evolution performance of transition metal doped C₃N monolayer and the electrocatalytic nitrogen reduction performance of B-doped C₉N₄ monolayer.The details are as follows:Transition metal doped or transition metal,N co-doped carbon materials have attracted increasing attention as efficient catalysts for the HER,to replace Pt or reduce the usage of Pt.This type of transition metal doped C₃N catalyst has a high catalytic performance for HER and does not require the addition of other substances in the main body of C₃N.This fact provides a significant advantage in terms of synthesis.By using first-principles calculations,the Transition metal-embedded C₃N monolayer has been theoretically investigated for HER,for which eighteen Transition metal are selected from 3d,4d,and 5d rows.These transition metals are respectively doped with C monoatomic vacancies,N monoatomic vacancies,C-N diatomic vacancies,and C-C diatomic vacancies in C₃N monolayers.The M-CC catalysts,with the Transition metal atom embedded into the C-C double atomic vacancy,are the most stable among the various.All the M-CC catalysts show the metallic conductivity and high thermal stability.And the metal conductivity of the system can greatly improve its electrocatalytic HER performance.The hydrogen binding free energy for the M-CC catalysts can be optimized to be close to 0 e V by choosing suitable Transition metal,and the kinetic barrier under the Tafel mechanism for the further gaseous hydrogen evolution can be low to 0.58 e V.These results suggest that HER catalytic activities of the M-CC catalysts are likely comparable and even higher than the well-explored Mo S2 nanostructures or Pt catalysts.Moreover,HER activities of the M-CC catalysts can be illustrated by the electronic state distribution near the Fermi level of the catalytically active sites.This study provides a new possibility for the cost-efficient HER catalyst of high activity and for the application of C₃N nanostructures.NRR is a very attractive yet challenging route for sustainable NH3 synthesis at ambient conditions,for which efficient catalysts are required due to the highly strong N?N bond.In this work,the B decorated C₉N₄ monolayer?B-C₉N₄?for NRR is studied by using first-principles calculations.It is found that the inert N₂ can be sufficiently activated through the electron “acceptance-donation” pattern between N₂ and the B dopant.Ten possible adsorption sites of B atom were found,and the most stable and stable configuration was obtained.And in the most stable configuration,there are two ways to adsorb N₂,B adsorbs one N atom and B adsorbs two N atoms at the same time.Through the calculation of the adsorption energy,the configuration with lower adsorption energy can more effectively activate the N₂ son,so the former adsorption method is selected for the following calculation.N₂ reduction has been carried out in a continuous mechanism and an alternating mechanism.The subsequent N₂ reduction prefers the alternating mechanism and the reduction of *N₂ to *N₂H is the potential-limiting step with an overpotential of 0.56 V.Furthermore,B-C₉N₄ exhibits a metallic nature,which can promote the charge transfer during the reduction process.The stability of B-C₉N₄ can be confirmed by the calculated B adsorption energies and the ab-initio molecular dynamic simulation.Consequently,owing to the high activity,good electrical conductivity,and excellent stability,B-C₉N₄ is a promising metal-free N₂ reduction catalyst.Our work not only provides an efficient electrocatalyst for NH₃ production,but also opens up a promising avenue to develop highly active and robust metal-free catalysts for other applications.