Theoretical Study On The Supported Metal Catalysts On Mo₂C MXene

Since the first synthesis of two-dimension layered materials:MXenes?transition metal carbides,nitrides,and carbonitrides?in 2011,their unique physical and chemical properties have attracted great attention in the fields of battery,energy storage,supercapacitor,catalyst and so on.Generally,MXenes are obtained by etching MAX phase materials in strong acid or strong alkali solutions.In contrast to the traditional carbon-based catalysts,the supported metal catalysts on MXene possess better electrochemical durability and stability.Up to date,still few M₂X MXene members have been reported experimently,among which Mo₂C synthesized in 2015 has been found possessing many unique characteristics,including catalysis,thermoelectricity,superconductivity and so on.Therefore,we choose it as the substrate in this work to investigate Mo₂C-based single atom catalysts?SACs?,single cluster catalysts?SCCs?and single monolayer catalysts?SMCs?through metal decorations using density functional theory.We first calculate the electronic structure,in order to investigate the geometric stability.Then we investigate catalytic activity towards oxygen reduction reaction?ORR?and CO oxidation reaction,aiming to provide guidances for developing and fabricating MXene-based catalysts.The main researching work and results are summarized as follows:?1?The stability and catalytic reactivity of single Pd atom decorated molybdenum carbide with oxygen group?Mo₂CO₂?We choose a single Pd atom as a typical representative,aiming to explore the stability of a single Pd atom supported pristine Mo₂CO₂ and defective Mo₂CO₂ with an oxygen vacancy.The results indicate that defective Mo₂CO₂ structure with an oxygen vacancy can stably anchor a single Pd atom forming a SAC.Then,we take the CO molecule as a probe to explore the catalytic activity towards CO oxidation.It is found that the formed SAC has good catalytic activity.Our results show that the defective MXene is a good substrate material to support SACs,and the results can provide theoretical guidance to explore and fabricate MXene-based SACs.?2?The eleven SACs supported on Mo₂CO₂To provide a useful guideline to experiments,we propose three criteria to screen the stable and high-efficient SACs towards low-temperature CO oxidation.The criteria include the catalysts'stability,adsorption strength to CO and O₂,and the difference between activation barrier and absolute adsorption energy of reactants,respectively.The properties of single atom of eleven metals on Mo₂CO₂ are compared and screened.Our results indicate that the Zn atom decorated Mo₂CO₂ is a promising SAC with very high stability and has high activity towards low-temperature CO oxidation.?3?The Cu₃ SCC supported on Mo₂CO₂To solve the stability problem of SACs and the CO-poisoning problem of Pt-based catalysts,we investigate a SCC of Mo₂CO₂ supported Cu₃ cluster.The results indicate that the studied SCC has good stability and high activity toward CO oxidation reaction?Cu₃ cluster acts as an electron reservoir to store and release electrons,and mediate the whole reaction?.This results validate that MXene is a kind of advanced substrate material,which provide a guideline to investigate and fabricate MXene-based SCCs.?4?The stability,durability and ORR reactivity of Mo₂C supported monolayer metal?Cu,Pt,Pd,Ag and Au?catalystsTo reduce the usage of Pt nanoparticles and improve ORR performance simultaneously,we investigate the pristine Mo₂C supported metal monolayer catalysts.We first investigate their geometric structures,adsorption properties of ORR intermediates,and ORR performance from kinetics and thermodynamics.The results speculate that Mo₂C supported monolayer Au has many merits,including low cost,good stability,enhanced durability and enhanced ORR performance as compared with the commercial Pt/C catalysts.We hope the results can inspire more experimental and theoretical studies to design,explore and apply advanced MXene supported monolayer composite.?5?The Ag monolayer decorated Mo₂C as a catalyst for purifying hydrogenTo solve the CO-poisoning problem of anode Pt catalyst,we propose a new device for purifying hydrogen:Ag monolayer decorated Mo₂C(Ag_ML/Mo₂C).The adsorption energies of H₂,CO,O₂,H₂O and CO₂,and their electronic structure analysis,as well as Boltzmann distribution analysis of the adsorption states are analysed.It is found that Ag_ML/Mo₂C plays the role as a filter membrane,which can filter out CO in the hydrogen fuel.In order to remove CO completely from fuels,we explore the influence of the O₂supply concentrations to purify hydrogen.The calculated results indicate that low supply O₂ injects to the Ag_ML/Mo₂C can remove CO more effective,and this method can reduce the loss of H₂ as much as possible.We hope this results could promote the development of efficient catalysts for purifying hydrogen,and provide more reference values to explore and apply advanced MXene materials.Based on the abovementioned discussions,by comprehensively compare the effects of geometric structure,electronic structure and catalytic activity of the supported SACs,SCCs and SMCs on Mo₂C,we hope our theoretical results can shed light on fabricating,exploiting,and applying MXene-based catalysts.