Design And Simulation Of Two-dimensional Single/diatomic Electrocatalysts Based On First Principles

Developing a sustainable technology to generate fules and chemicals from renewable energy sources like wind and solar energy,plays a key role in alleviating energy shortage and reducing the emission of CO₂.To reach this goal,one promising strategy is to develop efficient electrochemical conversion processes that can synthesize high added-value products from atmospheric carbon dioxide,nitrogen and water etc.Electrocatalysts are at the heart of electrocatalytic devises since they determine the reaction rate,selectivity and efficiency.For oxygen reduction reaction?ORR?,carbon dioxide reduction reaction?CRR?and nitrogen reduction reaction?NRR?,the most widely used catalysts now are platinum,copper and gold,ruthenium and rhodium metal electrodes,respectively.However,these materials have many shortcomings to serve as ideal catalysts,such as high cost and scarcity of Pt electrode limit the large^<sub>scale commercial applications of fuel cells;the poor selectivity and prohibitively high overpotential that Cu catalyzes electroreduction of CO₂to hydrocarbons has;and the Faradic efficiency toward NRR is typically lower than 1%with a competitive hydrogen evolution reaction for Ru metal.In recent years,single atom catalysts?SACs?and dual-metal-site catalysts?DMSCs?have made great progress in many electrochemical reactions which can benefit from its unique electric structure,high surface area and efficient atomic utilization.Hence in this paper,we have performed density functional theory?DFT?and combined with micro-kinetic simulations to study the ORR,CRR and NRR performance of four types of novel SACs or DMSCs.The main research results are summarized as follows:?1?.Commercial application of fuel cell technology requires to develop cost-effective non-platinum catalyst for 4e^-ORR.By means of DFT calculations,we demonstrated that two-dimensional Fe-Pp sheet with dispersed distribution of single Fe atom is a promising ORR catalyst candidate.Pristine Fe-Pp sheet can actively catalyze ORR through 4e^-route.Specially,ligand functionality with cyan group can weaken the adsorption of ORR intermediate,which accordingly enhances the catalytic performance of Fe active site.Moreover,strain engineering was applied to optimize the electronic structure and activity of Fe-Pp-CN sheet.The limiting potential of Fe-Pp-CN monolayer reaches the theoretical upper bound under a small tension of+2%.Our studies open new possibility for designing non-platinum catalyst in experiment.?2?.Single-atom materials has made significant progress in catalyzing ORR,which accelerates the practical application of fuel cells.Experimentally synthesized Ni₃?HITP?₂?HITP=2,3,6,7,10,11-hexaiminotriphenylene?exhibits high activity toward 2e^-ORR to peroxide under alkaline conditions.For further improving the efficiency and stability of fuel cell,we need to screen out other effective metal centers with high 4e^-selectivity.We carried out DFT calculations and micro-kinetic simulations to study the ORR performance of M₃?HITP?₂with common 3d-5d elements as metal centers.Based on scaling relationships between adsorption energies of ORR intermediates,we constructed the activity volcano plot and identified remarkable performances of Fe and Mn sites that can comparable to Pt electrode.Moreover,the construction of micro-kinetic model not only directly supports high efficiency of these two materials,but also illustrates the reason why thermodynamic model fails in predicting the activity of the most active catalysts accurately.Therefore,we have screened out two effective 4e^-ORR catalysts of M₃?HITP?₂by combining DFT and kinetic simulations,which lays the theoretical foundation for experimental investigations.?3?.Electroredcution of CO₂to useful fuels can mitigate energy and environment issues.However,the performance of most catalysts are limited by robust scaling relationships between adsorption strengths of carbon-involved species.Inspired by experimental investigation on dual-metal-site catalysts?DMSCs?,we carried out DFT calculations to rationally design and screen potential 10 heteronuclear and 5 homonuclear DMSCs for CRR electrocatalysts.Firstly,using the binding free energies of OH*and COOH*as two indicators,three DMSCs,namely Ni/Fe,Ni/Mn,Cu/Mn were screen out as promising candidates.Additionally,these sites bind CO*moderately,and tend to produce CO?g?as a final product.More importantly,two-dimensional kinetic volcano uncover that they can break the scaling relationship between?G_COOH*and?G_CO*and show similar and even lower overpotentials than Au?211?surface.This work not only provides rational strategy for screening DMSCs,but also proposes the guidance for further improving CRR performance.?4?.Electrochemical reduction of N₂ has been plagued with sluggish reaction kinetics and poor Faradic efficiency.Though the novel single-atom catalysts show huge potential in NRR compared to metal electrodes,the improvement is still limited for practical application.The single-atom and dual-metal-site characters of expanded dual metal phthalocyanine?M₂-Pc?provide the possibility to adsorb N-involved intermediates flexibly and further improve the catalytic activity and selectivity of NRR.We systematically studied the NRR performance of M₂-Pc sheet by means of DFT calculations.The calculations show that the top-stable configuration of the key NH₂*intermediate on M₂-Pc surface is different from that of metal catalysts,leading to Re₂-Pc exhibits slightly higher NRR limiting potential than volcano climax of metal facets.In particular,the abnormal stain effect on catalytic performance of Re center can further alleviate the limitations of scaling law,which can be explained by bonding analysis via COHP calculations.Our work lays the theoretical foundation to break through the limitations that current electrocatalysts faced.