Single-atom Catalysts Based On Curvature Modulation Simulation And Design

With the end of the second industrial revolution,human consumption of fossil fuels such as coal,oil and natural gas has been increasing.The combustion of these fossil fuels has seriously disrupted the balance of the carbon cycle in the ecosystem.This has led to the greenhouse effect and a serious energy crisis.The Haber-Bosch method is the most widely used artificial nitrogen fixation synthesis technology for ammonia industrial production.However,the reaction needs to be carried out at high temperature and pressure,which requires a large amount of energy consumption and is extremely unfriendly to the environment.The electrochemical reduction method has received a lot of attention because of its relatively high product selectivity,low experimental requirements and environmental friendliness.However,CO₂and N₂molecules have extremely stable chemical properties,which pose a great challenge for the development of this technology.Designing new catalytic materials with high activity,selectivity and stability is the key to improve the reaction efficiency.Among the many catalysts,single-atom catalysts（SACs）based on two-dimensional substrates have been widely studied.In order to give SACs more tunable space,this research work focuses on the effect of curvature effect through density flooding theory,and the studied substrates include BC₃N₂nanotubes and carbon nanotubes.The details are divided into the following aspects:（1）BC₃N₂is a structurally stable two-dimensional material.Using the density general function theory（DFT）calculation method of spin polarization,SACs of V@2D-BC₃N₂with different curvature were designed by choosing to dope BC₃N₂with metal V at the N vacancies,and the CRR activities and electronic structures of SACs with different curvature chirality were calculated..The results show that the curvature can affect the CRR and the curvature effect exhibits two different regulatory mechanisms,where the unoccupied d-state increases with increasing curvature for low curvature states.For the high curvature state,the occupied states,on the other hand,increase with increasing curvature,which facilitates the transfer of electrons from theV-site to the adsorbate and ultimately promotes the adsorption of CO Meanwhile,the curvature effect can also modulate the different deviation distances of theV@2D-BC₃N₂system based on the linear relationship between transition metals and E_ad[CO]～E_ad[COOH].The results show that the binding ability of CRR intermediates can be enhanced in the high curvature state,thus increasing the reactivity of hydrocarbons and inhibiting the hydrogen precipitation reaction（HER）.It provides the possibility to prepare single-atom catalysts with good catalytic performance.（2）Carbon materials have unique microstructures and are often used as catalyst carriers,and the modulation of curvature effect can effectively improve the catalytic activity of carbon materials.Armchair-type（4-4,5-5,7-7 and 11-11）and sawtooth-type（7-0,19-0）carbon nanotubes with different curvature were constructed using spin-polarized DFT calculation method.A SACs with TM atoms doped with double vacancy carbon nanotubes were designed.and the structures of transition metal doped carbon nanotubes with different curvatures were calculated as CRR electrocatalysts.The results show that the d-band theory still holds for the SACs based on armchair CNTs and the curvature effect can effectively modulate the electronic properties.The SACs have similar CO adsorption energy to bulk Cu and lower hydrogen precipitation activity to reduce CO₂to various products including CH₄,CH₃OH,CO and HCOOH,while the limiting potential for HCOOH generation is lower than that of hydrocarbons..（3）A SACs was designed and named as Fe@CNTs by the spin-polarized DFT calculation method with a theoretical model of Fe single-atom catalysts loaded with CNTs of different curvature chirality.and investigated the factors of curvature and magnetic moment on the catalytic activity and selectivity of the catalyst NRR,analyzed the effect of metal spin polarization on N₂adsorption,and calculated the possible reaction paths of NRR and its free energy of the side reactions.The results show that the curvature in the armchair-type system has a large effect on the magnetic moment.The results show that the curvature has a stronger effect on the magnetic moment in the armchair system,so that the N₂molecule binding energy is stronger and the free energy of N₂protonation reaction is lower than that in the sawtooth system.The SACs are more inclined to the Alternating mechanism for the Fe@4-4CNT system with a critical potential of 0.74 eV and to the Distal mechanism for the Fe@7-7CNT system with a critical potential of 0.68 eV.The SACs selected in this paper showed good inhibition of HER compared to other metal-based catalysts.exhibited higher selectivity for NRR.The research content of this paper not only contributes to a thorough understanding of the mechanism of CO₂electroreduction and N₂electroreduction,but also provides a reasonable design of catalytic materials for experimental research work.