Preparation And Oxygen Reduction Reaction Performance Research Of Platinum-based Metal Catalysts

Fuel cells break through the limitations of the Carnot cycle,and have unique advantages in energy conversion efficiency,making them one of the most promising portable power sources.Moreover,fuel cells are diverse and environmentally friendly.However,problems such as the slow kinetics of the oxygen reduction reaction at the fuel cell cathode and the large reaction potential still need to be resolved.Platinum（Pt）-based noble metal catalysts have become the first choice for cathode oxygen reduction catalysts due to their highly efficient catalytic effects.Precious metals are scarce and expensive,so reducing the amount of Pt while improving catalytic activity and stability can achieve the goal of reducing fuel cell costs.Current studies have found that the introduction of other metals to adjust the morphology of the synthesis of open structure catalysts can increase the atom utilization rate,and can also reduce the amount of Pt used to achieve cost reductions.In this thesis,Pt and cobalt（Co）are alloyed,and the morphology of the catalyst is adjusted to design a catalyst that can expose more catalytic active sites;and gold（Au）,which is more stable in the catalytic reaction,is incorporated to enhance the stability of the catalyst.The specific research contents are as follows:（1）A novel self-etched engineering of Pt-Co nanodendrite in nanoframe（Pt-Co ND-NF）synthesized through a simple one-pot approach,for the first-time.The modulation mechanism of Pt-Co ND-NF formation is established by investigating critical factors of adjusting:the water amount,the ratio of mixed solvent oleylamine to oleic acid and the amount of surfactant hexadecyl trimethyl ammonium bromide.Besides,the formation process of Pt-Co ND-NF is carefully explored with reaction time progress,further confirming the state of Pt-Co nanoframe blockade on Pt-Co nanodendrite（ND）.The Pt-Co ND-NF exhibits enhanced ORR catalytic performance,in which the mass activity(0.939 A mg_Pt^-1)is higher than that of commercial Pt/C(0.187 A mg_Pt^-1).The half-wave potential shifts only 18 m V to the left after 50k cycles compared to the initial value.In the nano-frame structure,the highly open space structure exposes the efficient active site space,which can provide a promising method for improving the catalytic activity.（2）First,the Pt Co-Au ternary alloy catalysts are synthesized by solvothermal method,and then the geometric structure catalysts are changed by acetic acid etching to obtain the Pt Co-Au nano-frame（NF）catalyst.The Pt Co alloy catalysts are modified by adding a small amount of Au to reduce the degradation of catalytic performance caused by the dissolution of Co in the early stage.Immediately afterwards,the excess Co is etched away so that more active sites can be effectively exposed to maintain catalytic activity.The mass activity of the Pt Co-Au NF catalysts are 5.9 times higher than that of the commercial TKK-Pt/C,and the catalytic activity is maintained at a good level.At the same time,in terms of catalyst stability,the half-wave potential of Pt Co-Au NF only attenuates4 m V after 10,000 potential cycles,and the catalyst stability is better improved.