Controllable Preparation Of Pt-based Nanoalloys And Their Electrocatalytic Properties

As an efficient and clean energy conversion device,fuel cells can directly convert chemical energy into electrical energy,and are widely used in various fields such as automobiles,airplanes,and mobile power sources.Pt catalyst is considered to be the best fuel cell catalyst due to its excellent catalytic activity.However,its high cost,slow kinetics,and poor stability seriously limit its commercial applications.Therefore,introducing various other metal elements（such as Ag,Cu,Ru,etc.）to construct Pt-based nano alloy electrocatalysts can effectively reduce costs and improve their electrochemical catalytic activity and stability.Given this,bimetallic,tri-metallic,and even high entropy Pt-based nanoalloys were successfully prepared by using various strategies.By regulating the morphology,structure,size,degree of alloying,and lattice defects of the nanoalloys,Pt-based nanoalloys with multiple active sites and a high degree of alloying were precisely constructed and controllably prepared.Multiple electrochemical catalytic reactions including methanol electro-oxidation reaction（MOR）,ethanol electro-oxidation reaction（EOR）,hydrogen evolution reaction（HER）of the Pt-based alloy materials were further investigated,thereby uncovering the structure-activity relationships.In addition,density functional theory（DFT）was used to conduct theoretical calculations on its catalytic performance,revealing possible catalytic mechanisms and performance improvement reasons.The main conclusions of the thesis are as follows:1.Highly porous PtAg nanoflowers（NFs）are synthesized by combining liquid reduction and chemical etching at room temperature.The atomic ratio of platinum-silver can greatly affect the composition,morphology,and particle sizes（280 nm,170 nm,and 45 nm）.The etched nanoflowers exhibit porous structures and produce diverse defects such as surface step atoms and dislocations and holes,exposing a large number of active sites.For MOR reaction,the optimized E-Pt₁Ag₂ NFs/C exhibits a larger electrochemical active area(53.1 m² g^-1)and high-quality activity(1136 mA mg _Pt^-1),which is 2.6 times that of commercial Pt/C catalysts.After 10000 seconds stability testing,the quality activity can be still maintained at 232 mA mg _Pt^-1,and the morphology and dispersity are well kept after the stability test.The CO-stripping voltammograms prove that the catalyst has excellent anti-CO poisoning ability.DFT calculations have also confirmed that the introduction of Ag accelerates charge transfer,rapidly oxidizes and removes CO,and enhances the ability to resist poisoning.2.Homogeneously alloyed and size-tunable PtM nanoparticles were firstly synthesized at room temperature by combining a high gravity liquid reduction process in a rotating packed bed（RPB）reactor with subsequent modification by taking Pt Ag as an example.The particle sizes of the RPB products generated in different feed flow rates are 30 nm,50 nm and 70nm,respectively.The effects of supergravity level,feed flow rate,feed ratio,and metal addition ratio were investigated,and the optimal preparation process conditions were determined.Compared with the traditional batch-type stirred tank reactor（STR）,the products synthesized by RPB have a smaller size,narrower distribution,and higher alloying degree.The as-synthesized RPB-Pt Ag NFs-30 nm exhibit superior catalytic performance and excellent anti-CO poisoning ability for MOR with a high mass activity of 1830 mA mg _Pt^-1,which is 3.5 and 3.3 times higher than those of STR-Pt Ag NFs and commercial Pt/C.The catalyst shows excellent anti-poisoning ability and stability in CO stripping experiment and i-t test.Density functional theory（DFT）calculations and the X-ray absorption fine structure（XAFS）measurement indicate that the homogeneous atom surface of RPB-PtAg NFs exhibits more electron transfer than the heterogeneous atom surface,and optimizes the d-band center of Pt,thus promoting CO oxidation.Furthermore,this approach can be applied to other four typical binary/ternary Pt-based nanoflowers.3.Ternary PtCuRu nanoflowers with Ru-rich edges were fabricated by using a facile one-pot solvothermal method.The effects of reaction temperature,type of modifier and the amount of modifier on the morphology and structure of nanoflowers were investigated,and the optimal preparation process conditions were determined.PtCuNPs-11 nm,PtCuRu NFs with average particle sizes of 17 and 37 nm were prepared by changing the amount of Ru added（0,2.07,and 5.18 mg）.PtCuRu nanoflowers exhibit abundant high-index crystal faces and Ru-rich edge active sites.The study on MOR and EOR electrocatalytic reactions shows that Pt_0.68Cu_0.18Ru_0.14 NFs with a high alloying degree,Ru-rich edge,and abundant high-index facets exhibit outstanding catalytic performance.The specific activity for MOR(7.65 mA cm^-2)is 4.1 and 6.0 times higher than those of commercial Pt Ru/C and commercial Pt/C.For EOR,the specific activity(7.90 mA cm^-2)is 4.0 and 7.1 times higher than those of commercial PtRu/C and commercial Pt/C,respectively.Density functional theory（DFT）calculations confirmed that the alloying effect optimizes the electronic structure of the catalyst,reduces the d-band of Pt,enhances the adsorption strength of*OH,accelerates the oxidation and removal of toxic substances CO,and improves the intrinsic activity and anti-poisoning ability of the catalyst.4.High entropy PtRuCoNiCu nano dendrites（NDs）were synthesized by the solvent thermal method.Firstly,the optimal preparation process conditions for the ternary PtRuCo NDs were determined.On this basis,quaternion PtRuCoNi and PtRuCoCu NDs,as well as high entropy nano dendrites PtRuCoNiCu,were prepared by further adding Ni and Cu.The high entropy PtRuCoNiCu NDs with uniform size expose a large number of lattice distortions and lattice defect structures on the surface.The catalytic performance of MOR and alkaline HER electrocatalytic reactions was further tested.For MOR,the optimized mass activity(4830 mA mg^-1_（Pt+Ru）)and area activity(14.9 mA cm^-2),which are 9.3 and 14.9 times higher than those of commercial Pt/C materials,respectively.For the alkaline HER reaction,the required overpotential at a current density of 10mA cm^-2 is only 10 mV,with a Tafel slope of 23.4 mV dec^-1,which is much better than other catalysts and commercial Pt/C materials,and comparable to the reported Pt-based high entropy nanoalloys.