Theoretical Study On Electrocatalysis And Ion Transport Mechanism Of Anti-Perovskites

Anti-perovskites（X₃AB）have the reversed position of anions and cations as compared to perovskites.Due to the inherited compositional flexibility of perovskites and the enrichment of cations at X sites,anti-perovskites have excellent properties related to electrocatalysis or ion transport.In this thesis,using first-principles calculations,we investigate the mechanism of hydrogen/oxygen evolution reactions（HER/OER）and sodium ion transport of anti-perovskites,which provide strong support for improving the properties of the materials and understanding their structure-property relationships.The main achievements are as follows:（1）Investigation on bifunctional catalytic performance of anti-perovskite Ni₃ZnC,Co₃ZnC and Ni₃FeN for hydrogen/oxygen evolution reactions.Low-cost anti-perovskites as efficient bifunctional electrocatalysts for water splitting have been reported recently.However,its microscopic catalytic mechanism is not clear.In this work,HER and OER performance of three typical bifunctional anti-perovskite catalysts Ni₃ZnC,Co₃ZnC and Ni₃FeN were calculated for the first time.Comprehensive analysis reveals that HER catalytic performance ranking:Ni₃ZnC（100）>Ni₃FeN（111）>Co₃ZnC（100）.Combined with the OER catalytic activity,we concluded that Ni₃ZnC（100）may have the best bifunctional performance.We also calculated the transition-metal doping effect and concluded that the doping of Fe for Co₃ZnC and Cu for Ni₃FeN may further enhance the bifunctional catalytic activity.The effect of experimentally common carbon vacancies was calculated to be detrimental to the HER performance.Our work gave an atomic perspective of HER and OER catalytic mechanisms of anti-perovskites,which is helpful for the further development of water splitting electrocatalysts.（2）Investigation of doping effect on catalytic performance of hydrogen evolution reaction of anti-perovskite Ni₃InN.Anti-perovskite Ni₃InN exhibits efficient HER catalytic performance and excellent stability in alkaline solution.Cu doping can further improve the HER catalytic activity of Ni₃InN and reduce the water dissociation energy barrier.However,there is a lack of systematic theoretical studies on how transition metals modulate the electrocatalytic activity of anti-perovskite.In this work,the HER catalytic performance of Ni₃InN doped with different transition metals was calculated,and the relationship between the Fermi-abundance model related to the d electronic state of the doped atoms and the HER catalytic performance is discussed.In order to model the catalytic process more accurately,we used the implicit solvent model to deal with solvent effects during the calculation.The results show that the Bridge site between the dopant atom and the Ni atom on the surface are the main catalytic sites.In addition,V,Zr,Ir and Pt doped Ni₃InN exhibit excellent HER catalytic performance,which is attributed to the enhanced binding between hydrogen and the surface by the transition metal doping.（3）Investigation of sodium-ion transport mechanism and elastic properties of double anti-perovskite Na₃S_0.5O_0.5I.Sodium-rich anti-perovskites have unique advantages in composition tuning and electrochemical stability as solid-state electrolytes in sodium ion batteries.However,its Na⁺transport mechanism is not clear and the Na⁺conductivity needs to be improved.The utilization of sulfur ions to partially replace oxygen ions of sodium-rich anti-perovskites Na₃OI has been predicted to enhance the ionic conductivity of the material.In this work,we investigate the stability,elastic properties and ion transport mechanisms of both the double anti-perovskite Na₃S_0.5O_0.5I and anti-perovskite Na₃OI.The results indicate that the Na I Schottky defect is the most favorable intrinsic defect for Na⁺transport and due to the substitution of S^2-for O^2-,Na₃S_0.5O_0.5I has stronger ductility and higher Na⁺conductivity compared to Na₃OI,despite the electrochemical window is slightly narrowed.The divalent alkaline earth metal dopants can increase Na⁺vacancy concentration,while impeding Na⁺migration.Among the dopants,Sr²⁺and Ca²⁺are the optimal dopants for Na₃S_0.5O_0.5I and Na₃OI,respectively.Notably,the Na⁺conductivity at room temperature of the non-stoichiometric Na₃S_0.5O_0.5I is 1.2×10^-3 S/cm,indicating its great potential as the solid-state electrolyte.Moreover,strain effect calculation show that the biaxial tensile strain is beneficial for Na⁺transport.Our work reveals the sodium-ion transport mechanism and elastic properties of double anti-perovskites,which is of great significance for the development of solid-state electrolytes.