Activiation Of 2D Molybdenum Disulphide Surface And The Electrocatalytic Activity

Energy and environment crisis have been threatening the survival of human beings.Electrocatalysis is an artificial photosynthesis strategy,which can push the energy and mass cycles sustainably by directly or in-directly utilizing the solar energy and natural H2O,CO2 and N2.Whilst the key challenge for artificial photosynthesis is to develope cost-effective caltalysts to replace the earth scarce noble metal catalysts.With peculiar structure and tunable physical and chemical surface property,two dimentional(2D)transitional metals disulfides(TMDs)such as MoS2 has been one of the most potential future non-noble metal-based catalysts.Meanwhile,the notable improvement of the catalysts’ intrinsic activity,atom utilization and charge transfering by activiation of basal planes and inter-surface design become the focus topics.However,the lack of preparation strategies and in-deep understanding of structure-performance mechanism still hinder the design and development of cost-effective catalysts severly.In this dissertation,by comprehensive research the three aspects of preparation strategy,structure characterization and theoretical calculation,the relationship between the catalytic activity,selectivity with the structure of catalysts is studied,to reveal the basic principles behind the catalysis mechanism and lay a foundation for the optimum design of catalysts.In our research,the 2D basal planes of catalysts have been activiated by creating S vacancies to improve the number of active sites;by doping metal atoms on the 2D basal planes,sulfur vacancy formation is promoted and intrinsic catalytic activity is enhanced;by constructing heterojunction structure,the interfacial charge transmission and water adsorption and decomposition are promoted;by preparing a peculiar "sub-monolayer" MoS2 structure,the biomimic mode of the polymetallic active center in catalyst in electrocatalytic nitrogen reduction synthesis ammonia reaction(NRR)was studied.The main research in this paper are as follows:(1)A scalable solid phase reduction(SPR)method was developed to prepare MoS2 and WS2 nanosheets containing S vacancies.In our study,it was found that the reducing substance under SPR condition reduced the TMDs basal planes to produce S vacancy through intercalation reaction.At the same time,the concentration of S vacancy can be effectively adjusted by adjusting the addition of the reductant equivalent,and then its activity as a catalyst for electrolytic water hydrogen evolution can be regulated.Theoretical simulation shows that MoS2 substrate activated by SPR has higher catalytic activity of HER.(2)A controllable method of activation of 2D MoS2 via zinc in was developed to prepare Zn@MoS2 with Zn doping,sulfur vacancy and small size.In our study,we found that the content of Zn doping and S vacancy can be effectively regulated,and the obtained MoS2 nanoparticle has a lateral size of about 25nm,with good electrical conductivity,and the electrochemical catalyst’s HER catalytic performance is significantly improved compared with that of 2D MoS2.Theoretical simulation studies found that doping Zn greatly reduced the formation energy of S vacancy and made it easier to produce S vacancy.In addition,compared to not doping S vacancy,the ΔGH*value of doped zinc atom neighbered S vacancy is closer to zero.(3)An in-situ oxidation method for preparing amorphous MoO3-x/MoS2 heterojunctions with S vacancy on the rich substrate surface as the precursor was developed.Through the study,it is found that the special structure of non-crystalline MoO3-x in heterogeneous junction can significantly promote the adsorption and decomposition of water,and greatly increase the hydrogen supply required in Volmer and Hyrovsky steps in HER reaction under alkaline conditions.In addition,the difference of MoS2 and MoO3-x Fermi levels causes special interfacial field effect,which promotes the transfer of interfacial charge during electrocatalysis.Therefore,the electrocatalytic HER activity under alkaline condition is much higher than that of the precursor Sv-MoS2.(4)Sv-MoS2 nanosheets containing a peculiar "sub-monolayer" MoS2 structure(MO-S cluster)were prepared by SPR method,and its catalytic role in room temperature electrocatalytic nitrogen reduction synthesis ammonia reaction(NRR)was studied.We found that Mo-S Cluster significantly improved the catalytic activity and selectivity of MoS2 electrocatalyzed NRR(Faraday efficiency>20%).Theoretical simulation shows that the adsorption of nitrogen and nitrogen intermediates by the active center of polymetallic atoms in Mo-S Cluster follows the"side-on" mode of biological nitrogenase,which makes the overall energy barrier of NRR reaction as low as 0.51 eV,effectively avoiding the restriction of nitrogen scaling relations.In addition,the activation energy of proton coupled transfer reaction(PECT)in each step of the reaction is low,which inhibits the occurrence of competitive HER.The results of this study provide a new idea for the development of non-noble metal electrocatalysts for room temperature NRR for ammonia synthesis.