Theoretical Studies Of The Regulation Of Photo/Electrocatalytic Performance Of Two-dimensional Materials

Rapid urbanisation and continuous industrialisation have greatly intensified the use of non-renewable fossil resources(e.g.coal,oil,natural gas,etc.).Energy depletion and the pollution caused by fossil fuels have a serious impact on the survival and development of human society,triggering a serious energy crisis and environmental problems.In the global energy transition and "decarbonisation" process,developing clean energy to replace traditional fossil fuels while reducing emissions such as CO2 is an important way to solve the above problems.In this field,energy conversion technologies such as photo/electrolysis of water,photo/electrochemical nitrogen fixation,carbon dioxide conversion and metal air batteries have attracted widespread attention.Hydrogen can be produced by direct electrolysis of water and the product of combustion is also water,and is therefore considered as a green and non-polluting energy source.Furthermore,ammonia is considered to be a clean alternative to fossil fuels.To this end,efforts need to be stepped up to improve the efficiency and thus reduce the cost of producing green hydrogen and ammonia.The electrochemical reactions involved in energy conversion include hydrogen precipitation reactions(HER),oxygen precipitation reactions(OER),oxygen reduction reactions(ORR),nitrogen reduction reactions(NRR)and carbon dioxide reduction(CO2RR).Catalysts play a key role in the conversion of energy.It reduces the energy barrier in the reaction process and increases the reaction rate.Noble metals such as Pt/Ir are known to have high catalytic activity,however,scarcity and cost have prevented industrialisation.Therefore,searching and developing efficient,green,reliable and sustainable clean energy sources as well as low-cost.high-efficiency catalysts has become an urgent task.In this dissertation,based on the density functional theory and excited state non-adiabatic molecular dynamics methods,we investigated a series 2D structures,such as two-dimensional(2D)metal-organic frameworks,2D covalent organic frameworks(COFs)and intrinsically polaried heterostructures.Focusing on the catalytic reactions in the energy conversion.including the potentials in photo/electrocatalystic overall splitting,oxygen reduction reactions in metal fuel cells,nitrogen reduction reactions in photo/electrochemical nitrogen fixation.We reveal the linear relationship between the catalytic activity and the intrinsic properties of the catalyst,construct efficient descriptors to describe catalytic activity,the construction of Z-Scheme van der Waals heterostructures photocatalytic system,the migration and compounding mechanism of photogenerated carriers and the effect of built-in electric field on carrier lifetime and catalytic performance,which provide a strong theoretical basis and frontier guidance for subsequent experimental research.The main contents of this paper include:1、The integrated metal-air cell and electrolyzer is one of the most effective ways to solve the energy crisis and environmental pollution.In the above energy conversion process,hydrogen precipitation reaction(HER),oxygen precipitation reaction(OER)and oxygen reduction reaction(ORR)are involved.Therefore,it is essential to design and synthesize efficient HER/OER/ORR multifunctional catalysts to improve energy conversion efficiency.In this paper,a series of single-atom catalysts were designed based on an experimentally synthesised metal-organic framework(TM-PTC,TM=V,Cr,Mn,Fe,Co,Ni).Calculations show that Fe-PTC can act as highly efficient multifunctional catalysts with efficient HER/OER/ORR catalytic activity,and its excellent catalytic performance is derived from the unique electronic structure.In addition,covalent organic frameworks(COFs)are also candidates that can be stably anchored to single atoms.Based on the experimental synthesis of MPc-pz(M=Zn or Cu)materials,the influence of 3d transit ion metal atoms on the catalytic performance was investigated and excellent multifunctional catalysts were screened..The linear relationship between intermediate adsorption energy and catalytic overpotential;the linear relationship between active site electron transfer(Δδ)and catalytic activity;and the linear relationship between non-metallic atomic p-orbital(εp)and catalytic activity were constructed.The screening and regulation laws of single-atom catalysts are revealed to provide a new scheme for the combined design of new generation multifunctional catalysts.2、Photocatalytic water splitting to produce hydrogen and oxygen for industrial production is of significant economic value.For a single photocatalyst,there are challenges in using solar energy alone for watersplitting without the use of sacrificial agents and doping or defect modulation.Using first-principles calculations in combination with nonadiabatic molecular dynamics(NAMD),we propose novel heterostructures of carbon nitride(C7N6)and the Janus GaSnPS monolayer as promising direct Z-Scheme photocatalysts for solar-driven overall water splitting.The out-of-plane electric field due to the electric polarization which is dependent on the stacking pattern alters the band alignment and catalytic activity of the heterostructures.The relatively strong interfacial nonadiabatic coupling and long quantum coherence time accelerate the interlayer carrier recombination,enabling a direct Z-Scheme photocatalytic mechanism.More importantly,the redox ability of the remanent photogenerated carriers in the Z-Scheme is strong enough to trigger both the hydrogen evolution reaction(HER)and oxygen reduction reaction(OER)simultaneously without the help of sacrificial agents.Our work reveals a fundamental understanding of ultrafast charge carrier dynamics at vdW heterointerfaces as well as new design prospects for highly efficient direct Z-Scheme photocatalysts.This result provides a theoretical reference for the design of efficient Z-Scheme catalysts and the evaluation mechanism.3、Photo/electrocatalytic nitrogen fixation is considered as one of the ideal alternatives to the conventional Haber-Bosch process due to the ability to carry out under mild conditions and achieve zero carbon emissions.The chemical inertness of nitrogen molecules(N2)and the complex pathway of nitrogen reduction reaction(NRR)are important issues faced during the design of photo/electrocatalytic nitrogen fixation catalysts.In this work,we proposed a Mo atom anchored covalent organic framework(MoPcTFPN)for photo-assisted electrocatalysis of the N2 reduction reaction using first-principles calculations.Our theoretical results demonstrated that this MoPc-TFPN catalyst has a considerably low onset potential.MoPcTFPN has a unique electronic structure with a narrower band gap for excellent electrical conductivity and a wider band gap for photocatalysis.The MoPc-TFPN exhibits remarkable absorption in the visible light region and extends to infrared light,and the unique COF configuration allows its carriers to be spatially separated,which is conducive to improving the lifetime of photogenerated carriers and enhancing catalytic ability.In addition,motivated by the experimental progress,we consider 26 TM atoms(TM=3d,4d and 5d)embedded in the Pc-TFPN framework.Through a "five-step" screening strategy,Mo,W and Re-COF catalysts are highlighted from 26 TMPc-TFPNs as the high-effective SACs for nitrogen reduction reaction(NRR)with a low limiting potential.Meanwhile,multiple-level descriptors are developed to uncover the origins of NRR activity,among which a simple descriptor φ that involves the electronegativity and number of d electrons of TM atoms shows volcano plot trends of charge transfer,N2 bond length and limiting potential of NRR.The design and screening strategy of NRR catalysts proposed in this thesis provides an important theoretical basis for the study of related experiments.