Research On Low-platinum And Non-platinum Nanocrystalline Catalysts For Fuel Cells

Under the premise of serious energy shortage and environmental pollution in today’s world,fuel cells have received extensive attention because of their great advantages in energy supply and clean energy utilization.However,the commercial development and large-scale popularization of fuel cells are greatly limited due to the slow kinetics of the cathodic oxygen reduction reaction（ORR）.At present,noble metal catalysts led by platinum are mainly used to improve the oxygen reduction reaction rate of fuel cells,but they also face problems such as high cost,low reserves and weak phosphoric acid resistance.Therefore,it is necessary to develop inexpensive and excellent oxygen reduction catalysts.In response to the above problems,the mainstream research directions are divided into two types,one is to reduce the content of platinum or adjust the structure of Pt-based catalysts,and the other is to use non-platinum group metals or transition metals and prepare metal-free catalysts.In this thesis,the synthesis of a low-platinum alloy catalyst and a non-platinum alloy catalyst and their applications in cathode oxygen reduction reaction and fuel cells were investigated,respectively.In terms of low platinum catalysts,this thesis introduces Ga element and Ptfor alloying treatment,and uses inexpensive formamide as raw material to prepare Pt-Ga nanocrystalline catalysts,and explores such as calcination temperature,precursor ratio,auxiliary agent,the effect of carbon support and other conditions on the oxygen reduction activity of the catalyst.Among them,the half-wave potential of PtGa₂ supported by activated carbon（AC）in acidic medium reaches 0.89 V,which exceeds the 20 wt.%Pt/C commercial catalyst,and its mass activity and specific activity are 4.14 times that of commercial Pt/C,respectively.and 2.86 times.It was used as the cathode oxygen reduction catalyst material,and 20 wt.%Pt/C commercial catalyst was used as the anode hydrogen oxidation catalyst,which was coated on the gas diffusion layer to prepare the membrane electrode and assembled into a high temperature proton exchange membrane fuel cell at 150°C.The maximum power density reaches259 mW·cm^-2.In terms of non-platinum catalysts,starting from metal palladium,a series of different Pd-M alloy catalysts were prepared in this thesis,and the effects of reducing agent,pH value,carbon support and other conditions on the oxygen reduction activity of the catalysts were explored.With graphitized carbon（GCB）as the carrier and ethylene glycol as the reducing agent,the CeO₂-supported Pd-W alloy catalyst prepared under the condition of pH equal to 10 has the best effect,and the half-wave potential in acidic medium reaches 0.9 V,and exceeds the 20 wt.%Pt/C commercial catalyst.The XPS characterization indicates that the origin of the activity is that part of the electrons of the Pd element are transferred by the action of W,which increases its binding energy,thereby enhancing the oxygen reduction activity.In this thesis,with the purpose of reducing the content of Ptin oxygen reduction catalysts,through alloying or developing Pd-based catalysts,PtGa₂@AC alloy catalysts and Pd/W-CeO₂@C alloy catalysts with good performance were prepared by different means.The exploration of low-cost and high-performance electrocatalysts has certain reference significance.