The Oretical Study Of Two-Dimensional Transition Metal Chalcogenide Based Singleatom Oxygen Electrode Catalysts

Rapid Energy is a necessary condition for the development and progress of human society.With the development and progress of human society,the consumption of energy has doubled.The global energy mainly comes from fossil energy,which has limited reserves and belongs to non-renewable resources.More importantly,the burning of fossil energy has caused serious environmental pollution and climate problems.In recent years,scientists are committed to developing new energy technologies suitable for application to solve the problem of energy shortage and carbon emission growth.Renewable wind,solar and tidal energy have attracted the attention of researchers.How to better store and transform these energies has become the focus of research.The researchers began to pay attention to electrochemical energy technology with the advantages of cleanness,environmental protection and secondary utilization.fuel cells and metal air cells stand out among many electrochemical energy technologies due to their advantages of low environmental pollution and high conversion rate.However,the kinetic rates of these two devices are mainly limited by the oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）on the electrode.Therefore,the development of efficient and stable ORR/OER catalysts can improve the efficiency of fuel cells and metal air cells,thereby alleviating energy shortage and environmental pollution.In recent years,monoatomic catalysts have been widely used as ORR/OER electrocatalysts.Because monolayer transition metal chalcogenides（TMDs）are easy to synthesize,low production cost and good stability,they are considered as a good monoatomic catalyst carrier by researchers.Therefore,this paper uses the density functional theory to design a series of monatomic catalysts.By studying their properties and the reaction mechanism of ORR/OER,and predicting their feasibility as ORR/OER electrocatalysts,this paper puts forward theoretical guidance for experimental synthesis,which to some extent promotes the development of new clean energy technologies.The research contents are as follows:（1）We proposed a new class of ORR catalysts by doping Cr S₂ monolayer with non-metal atoms,by means of density functional theory computations.Our results revealed that most of X@Cr S₂ candidates exhibit negative formation energy and large binding energy,thus ensuring their high stability and offering great promises for experimental synthesis.Moreover,N@Cr S₂ exhibits the best ORR catalytic activity among all considered candidates due to its lowest overpotential（0.41 V）by computing free energy profiles,which is even lower than that of the Pt catalyst（0.45 V）.Remarkably,the excellent catalytic performance of N@Cr S₂ for ORR can be ascribed to its optimal binding strength with the oxygenated intermediates according to the computed linear scaling relationships and volcano plot,which can be well verified by the analysis of p-band center as well as charge transfer between oxygenated species and catalysts.Therefore,by carefully modulating the incorporated non-metal dopants,the TMDs-substrate monolayer can be utilized as a promising ORR catalyst.（2）We examined the possibility of a series of single transition metal atoms anchored on the Mo Se₂ nanosheet as electrocatalysts for both ORR/OER,using density functional theory computations.Our results revealed that TM atoms can be more stably anchored on1T-Mo Se₂ than those of on 2H-Mo Se₂.Based on the computed free energy profiles for ORR/OER,the Ni@1T-Mo Se₂ exhibits high catalytic activity toward the OER(η^OER=0.47 V),suggesting that Ni@1T-Mo Se₂ could be employed as a highly-efficient OER electrocatalyst,while Pd@1T-Mo Se₂ nanosheet is identified as an ideal bifunctional electrocatalyst for both ORR/OER due to its low overpotentials(η^ORR=0.32 V、η^OER=0.49 V).Therefore,by carefully modulating the single transition metal atoms adsorbates,the TMDs-substrate monolayer can be utilized as a promising ORR/OER bifunctional catalysts.（3）We examined the possibility of a series of single transition metal atoms anchored on the VS₂ nanosheet as electrocatalysts for ORR/OER,using density functional theory computations.We studied the effect of N coordination on catalyst activity.Our results revealed that Ni@VS₂ exhibits low overpotentials for both ORR（0.45 V）and OER（0.31V）,suggesting its great potential as a bifunctional catalyst.More interestingly,its ORR/OER catalytic activity can be effectively tuned by introducing a certain number of N dopants into Ni@VS₂.The main reason of the excellent catalytic activity of Ni@VS₂,Ni N₂@VS₂ and Ni N₃@VS₂ is that it has suitable interaction with oxygen-containing intermediates.Therefore,by carefully modulating the incorporated non-metal dopants and the single transition metal atoms adsorbates,the TMDs-substrate monolayer can be utilized as a promising ORR/OER bifunctional catalysts.