Preparation And Electrocatalytic Properties Of Nanoporous Materials

Proton exchange membrane fuel cells?PEMFCs?have broad application due to their use as alternative energy sources fossil fuels,especially in automotive systems and portable electronic products.However,due to the corrosion of the carbon support,the debonding between the Pt nanoparticles and the carbon support and the dissolution/aggregation/Ostwald ripening of the Pt,the mass activity and structural stability of the catalyst are still far from satisfactory.Despite efforts to develop various Pt-based catalysts in recent years,the high cost of Pt is still a major obstacle to its widespread use as a cathode electrocatalyst.In particular,in direct methanol fuel cells?DMFCs?,methanol permeating the cathode will also be oxygenated on the Pt-based catalyst.The resulting mixed potential and the efficiency of the fuel cell are attenuated.Therefore,it is of vital importance to find a catalyst showing high catalytic activity and durability.The development of catalysts that are inexpensive,simple to operate,and mass-produced has become a focus.In this thesis,the nanoporous Pt₃Si alloy and high-entropy alloy catalyst were prepared by the combination of arc melting,melt quenching and dealloying,and their electrocatalytic properties were studied as follows:1.The enhancement effect of Si doping on the electrocatalytic performance of nanoporous Pt₃Si alloyThe development of electrocatalysts with high activity and stability is the core problem of fuel cell commercialization.In this paper,a new bimetallic Pt-Si alloy with nanoporous structure is reported,which has lower initial potential and higher current density in the electrocatalytic reaction of methanol and ethanol,and is one of the ideal catalysts.It is worth noting that this alloy has better electrocatalytic performance in oxygen reduction reaction.Due to the compression strain generated by Si and nanoporous structure,nanoporous Pt₃Si?NP-Pt₃Si?alloy has a high performance of oxygen reduction reaction?ORR?.At 0.9 V,the mass activity is 0.44A mg_Pt^-1,reaching the goal of 2017 DOE.In addition,NP-Pt₃Si has high stability,due to the chemical stability of Si in acidic electrolyte and the stability of nanoporous structure.Density functional theory calculation showed that the d-band center of Pt₃Si alloy moved down relative to pure Pt,which weakened the binding with O*and HO*,thus improving the ORR activity of the catalyst.2.Preparation and electrocatalytic properties of nanoporous high-entropy alloysThe controlled combination of various immiscible metal elements into a nanostructure will bring immeasurable technical and scientific potential,but traditional bottom-up synthesis methods still face challenges.Here,we successfully synthesized six-element PtPdAuAgRuAl high-entropy alloy.In terms of electrocatalysis,the peak voltage of ethanol-catalyzed oxidation of the nanoporous high-entropy alloy Pt₄Pd₄Au₄Ag₃RuAl₃ with the same Pt load moved to 364 mV lower than that of commercial Pd/C under alkaline conditions,indicating that the alloy could improve the catalytic oxidation kinetics of ethanol.Interestingly,after 400cycles,there was almost no loss of activity of the alloy,indicating that the NP-Pt₄Pd₄Au₄Ag₃RuAl₃,a high-entropy alloy material,had a stable structure under alkaline conditions and was an ideal catalyst for ethanol fuel cells.