Controllable Synthesis And Atomic Scale Regulation Of Noble Metal Catalysts

Metal nanocrystals have a wide range of applications in catalysis,medical,sensing and information storage.It is well known that the size,composition,morphology and crystal structure of metal nanocrystals can seriously affect their performance.Therefore,the preparation of metal nanocrystals with controllable crystal structure will allow us to explore their properties.Traditionally,controlling crystallographic structure for a bulk metal generally requires high temperature and pressure conditions.This method is not conducive to practical applications due to hash conditions and high cost.However,at the nanoscale,surface stress/tension plays an important role in regulating the crystal phase structure of nanocrystals.Although scientists have put a lot of efforts,modulating the crystal phase structure of metal nanocrystals with a milder method remains a huge challenge.Developing efficient,high-durability water-splitting electrolyzers can largely convert intermittent electrical energy from wind and solar energy into fuel molecules for everyday life usage.Polymer electrolyte membrane(PEM)electrolyzers can effectively avoid the problems of alkaline electrolyzers existing,such as product gas diffusion,limited current density and low operating voltage.Unfortunately,in low pH and strong oxidizing environments,slow kinetic oxygen evolution(OER)and catalysts deactivation easily prevent the practical application of this technology.Compared to Ir-based materials,Ru is cheaper due to more abundant reserves on the earth and more active for OER.However,under strong acid and oxidizing environment,RuO2 is easily oxidized to RuO4 at a high operating potential,resulting in its deactivation.One of the most important reasons for the deactivation is that,the lattice oxygen in RuO2 participates in evoluting of oxygen product during OER reaction.Therefore,developing a highly active and highly stable Ru-based material for oxygen evolution is still a challenge for scientists.The use of fossil fuels is accompanied by releasing of greenhouse gases such as carbon dioxide(CO2),nitrous oxide(N2O),hydrofluorocarbons(HFCs)and sulphur hexafluoride(SF6),which are harmful for human health and the environment.Therefore,searching for alternatives to fossil fuels and developing renewable energy are urgently required.Hydrogen(H2),as an energy carrier,is considered to be one of the cleanest energy sources in the 21st century due to its high energy density and environmental friendliness.Currently,H2 is mainly derived from methane reforming,which is accompanied by the release of green gas CO2.The cathodic reaction of water-spiltting,hydrogen evolution(HER),is considered to be one of the most effective alternative hydrogen production methods along with avoiding the release of CO2.At present,the most effective HER catalyst is platinum(Pt)or Pt-based material.Howerer,high price,limited reserves of Pt hinders its practical application.Therefore,reducing the usage in HER and further improving the HER catalytic activity of Pt is still challenging.Through epitaxial growth on the surface of PdCu3,we obtained a thermodynamically unstable face-centered-cubic(fcc)Ru dependeding on smaller lattice mismatch between PdCu3 and fcc-Ru via using a mild solvothermal method.X-ray diffraction(XRD)and spherical aberration correction microscopy confirmed the successful preparation of fcc-Ru.In addition,through the galvanic replacement between Ru and Pd-Cu alloys,a transformation from the Pd-Cu@Ru core-shell structure to the yolk-shell structure was observed during epitaxial growth process.Among them,obtaining the thermodynamically unstable crystal phase is mainly dependent on the lattice mismatch between the fcc-Ru and Pd-Cu alloys.By adjusting the Pd/Cu ratio to tune the interplanar spacing of the Pd-Cu alloy,the lattice mismatch between the fcc-Ru and Pd-Cu alloys is further moduated,and different crystallographic structure of Ru can be obtained.Due to different surface atoms arrangement,fcc-Ru and hcp-Ru shows different catalytic activities in the model reaction of styrene and nitrobenzene hydrogenation.Tuning the electronic structure of single atom Ru embedded on the metal support through compressive strain can promote the acidic water oxidation reaction and mitigate the decay of Ru-based materials.First,a series of Pt-Cu alloy supported mono-dispersed Ru catalysts were constructed by acid etching and electrochemical leaching.The successful preparation of single atom Ru was further confirmed by spherical aberration correction microscope and synchrotron radiation characterizations.During the acidic oxygen evolution reaction(OER),the Ru1-Pt3Cu catalyst requires only 220 mV overpotential to reach the current density of 10 mA/cm2 outperformed the commercial RuO2(320 mV)and the stability of the catalyst is an order of magnitude higher than that of commercial RuO2.In addition,there exists a inverse-volcano curve between the activity of Ru single atoms embedded in different Pt-Cu alloys and the Pt/Cu ratios.Density functional theory studies show that the compressive strain from the Ptsxin shell modulates the electronic structure and redox behavior of Ru1,optimizing the binding energy to oxygen intermediates,and consenquently boosting the acidic OER performance,improving resistantance to over-oxidation and dissolution.For platinum(Pt),considered to be the most effective catalyst for the HER,a Sabatier volcano exhibits pure Pt has too strong binding to H*,resulting in H2 difficult to desorption,which is detrimental to the HER activity.Due to the weaker binding energy of Pb to H*based on the Sabatier volcano curve,so we can use the electronic effect between Pb and Pt to regulate the d-band center of Pt,optimizing the binding energy to H*,and further boosts the HER performance.First,Pd3Pb nanoplates(NPs)seeds were successfully prepared,and then sub-monolayer Pt was deposited on the surface to obtain AL-Pt/Pd3Pb nanocrystals.The spherical aberration correction microscope clearly observed the sub-monolayer Pt on the surface of Pd3Pb.Impressively,in acidic HER test,the as-prepared AL-Pt/Pd3Pb NPs presents excellent activity and stability with only 13.8 mV overpotential to reach the current density of 10 mA/cm2 outperformed the commercial Pt/C(30 mV).In addition,during continuous 25h-chronoamperometry test at 10 mA/cm2,the AL-Pt/Pd3Pb NPs also shows negligible activity decay in acidic HER condition.