Tuning Electronic Interaction Between Metal And S-doped Carbon Supports For Electrocatalytic Reactions

Supported metal nanocatalysts with the advantages of high atom utilization and recyclable use,play a vital role in the development of current chemical industry.In recent years,with the development of the research,researchers have found that the support not only acts as a carrier,but also interacts with the metal components,thereby affecting the reaction activity and selectivity of the metal catalyst.In 1978,Tauster et al.found that TiO2 supported Pt catalysts after a high temperature treatment under reducing atmosphere could weaken the adsorption of CO and H2 on Pt.They termed this phenomenon as strong metal-support interaction.After decades of research,researchers have continuously deepened and extended their understanding of the concept of metal-support interaction.So far,the metal-support interaction covers many kinds of mechanisms,including(1)the electronic interaction between metal and supports;(2)the synergistic effects between metal and supports;(3)the anchoring effect of support on metal;(4)the classic strong metal-support interaction(that is,the coating of the metal by the oxide)and so on.Among these mechanisms,the electronic interaction between metal and supports has gradually become a research hotspot in recent years due to its significant regulation on catalytic reactions and selectivity.The potential equilibrium at the contacting interface of the metal and the supports requires that the electrochemical potential as well as Fermi energy levels of metal and support tend to be equal.Since metal and support have different Fermi levels,electron transfer occurs at the contacting interface,which affects the charge density distribution of metals and supports.The change of the charge density distribution on the metal components will further influence its d-band distribution and the density of states(DOS).For catalysis,changes in the DOS of the active metal will change the adsorption energy of reactants and intermediate products,and ultimately affect the selectivity,activity,and even durability of the catalytic reaction.In recent years,with the deterioration of environment and diminishment of sources,clean energy and renewable energy technologies have developed rapidly.As an indispensable high-efficiency catalyst on the electrodes of electrolysis cells and fuel cells,carbon-supported noble metal catalysts have become a research hotspot.Early studies have found that sp2 hybridized carbon atoms will interact with the precious metal Pt,thereby affecting the oxygen reduction reaction(ORR)activity and durability.Recently,the electronic structure of the carbon support can be adjusted by further incorporating heteroatoms into the carbon support,which would tune its electronic interaction with the metal.Benefiting from the soft and hard acid-base effect between Pt and S,this thesis uses S-doped carbon material as the support to explore the electronic interaction between Pt and S-doped carbon material and its corresponding effect on the electrocatalytic hydrogen evolution reaction(HER)and ORR,aiming at constructing the structure-activity relationship between the electronic structure and the catalytic reactions and providing guidance for the design of high-performance catalysts.The main content is as follows:1.We found a new phenomenon regarding on the particle size-dependent charge transfer reversal between metal and carbon supports.We prepare Pt catalysts with different particles sizes on S-doped carbon material,including single Pt atom and Pt cluster catalysts.Accordding from the results of experimental characterization and theoretical simulation,it is found that the particle size could tune the charge transfer between Pt and S-doped carbon materials,that is,for single Pt atom,electrons transfer from single Pt atom to S-doped carbon materials;when it comes to Pt nanocluster,electrons are transferred inversely from S-doped carbon to Pt nanocluster.We speculate that it may arise from the particle size induced change of electron affinity and d band center of metal,leading to the increase of electron capture ability with the particle size.Furthermore,electrochemical results exhibited that Pt clusters have better HER performance than Pt single atom,even exceeding that of commercial Pt/C.Combining theoretical simulation with comparative experiments,we proved that the change of electron distribution density is correlated with the performance of HER activity and the increase of electron density on Pt can facilitate the kinetics of HER.2.We investigated and elucidated the roles of isolated site effect and electronic structure effect of single Pt atom catalysts with different coordination environments on the selectivity of ORR.We constructed Pt single atoms catalysts with different coordination environments on commercial carbon black,including Pt-N sites and Pt-S sites.It is found that the isolated site characteristics of Pt-N and Pt-S can naturally promote ORR to proceed in a 2-electron pathway.However,the differences of the electronic structure will induce the in-situ generated H2O2 to be further reduced to H2O when it contacts the Pt-N sites.While for the Pt-S sites,ORR can always maintain a high 2-electron selectivity.A series of characterization results indicate that the high depletion of unoccupied states of Pt-N sites can effectively activate H2O2 molecular and induce the selectivity differences.