Preparation And Performance Study Of Platinum Copper Oxygen Reduction Catalyst Loaded On Heteroatom Doped Carbon Carrier

Proton exchange membrane fuel cells（PEMFCs）have great advantages in the field of new energy due to their advantages of clean,pollution-free,and high energy utilization.However,their cathode oxygen reduction reaction（ORR）is slow,requiring the use of costly precious metal platinum for catalysis,resulting in high cost of fuel cells and hindering the large-scale commercialization of fuel cells.However,currently used commercial platinum carbon catalysts for fuel cell cathodes have shortcomings such as low platinum atom utilization,low activity,and poor stability,which are one of the key reasons for solving the high cost of fuel cells.Therefore,in order to promote the further commercialization of fuel cells,it is necessary to study and prepare ORR catalysts with high catalytic activity,strong stability,and high platinum atom utilization.Currently,the most commonly used carriers for platinum carbon catalysts are XC-72,Ketjen black EC-300J,and Ketjen black EC-600J.However,the inert surface of these carbon carriers leads to weak interactions with platinum based metals,which in turn makes metal nanoparticles susceptible to detachment reducing the stability of the catalyst.Studies have shown that modifying carbon carriers can enhance the interaction between metals and carbon carriers,and doping heteroatoms onto carbon carriers is one of the effective strategies for carrier modification.Based on the interaction theory between carbon carriers and metals and the guidance of electrochemical theory,this paper systematically studied the structural properties of heteroatom doped carbon carriers and the electrochemical performance of catalysts loaded with metals,starting from heteroatom doped carbon carriers.The main contents are as follows:（1）Using chitosan as a nitrogen source to coat and dope carbon carriers,physically mixing chitosan with carbon carriers,and then calcining at high temperature,coating chitosan onto carbon carriers（XC-72,Ketjen black EC-300J,Ketjen black EC-600J）to obtain three types of coated nitrogen doped carbon carriers.A metal supported catalyst was prepared by an improved Na BH₄reduction method.The nitrogen doped carrier（NEC6）prepared on the basis of Ketjen black EC-600J has a more excellent pore structure and a relatively higher content of pyridine nitrogen and graphite nitrogen.NEC6 regulates the electronic structure of Pt and disperses Pt nanoparticles.Electrochemical tests after loading the metal showed a high mass activity of 0.45 A mg _Pt^-1;after the stability test,the mass activity loss was only 16.7%,much lower than the mass activity loss of JM Pt/C（48.4%）;the membrane electrode test showed that the peak power density of Pt₃Cu/NEC6 was 608 m W cm^-2,1.25 times that of JM Pt/C.（2）In order to further enhance the activity and stability of the catalyst,increasing the nitrogen content and the relative content of pyridine and graphite nitrogen is an effective strategy.Based on this,chitosan was used as a single nitrogen source and carbon source for in situ doping to improve the nitrogen content of the carbon carrier,zinc chloride was used as an activator to optimize the pore structure,and the type and content of nitrogen in the carrier were regulated by changing the carbonization temperature（700,800,900）.The carrier（HCNC-8）prepared by carbonization at 800 has excellent pore structure and high nitrogen content,with pyridine nitrogen and graphite nitrogen occupying the main part.The interaction between HCNC-8 and Pt better disperses metal nanoparticles and regulates the nucleation of metal nanoparticles.Electrochemical testing of Pt₃Cu/HCNC-8 showed a high mass activity(0.53 A mg _Pt^-1),with only 11.8%loss of mass activity after stability testing.The maximum power density for the membrane electrode testing was681 m Wcm^-2,1.4 times that of commercial JM Pt/C.（3）Nitrogen atom doped carbon carriers have been proven to be an effective strategy for improving the activity and stability of catalysts.However,further research has shown that doping two or more heteroatoms onto carbon materials has more active sites than single doped carbon materials.Based on this,using chitosan as nitrogen source and carbon source,phosphoric acid as phosphorus source and activator,N and P double doped carbon carriers were prepared,and metal loaded catalysts were obtained.The doping amount of phosphorus atoms is controlled by adjusting the amount of phosphoric acid added.When the amount of phosphoric acid added is 10 m L,the structural characteristics（pore structure,defect degree,atomic doping amount,etc.）of NPC-10 are the most outstanding.Pt₃Cu/NPC-10 catalyst exhibits excellent comprehensive performance.After electrochemical testing,its mass activity is0.57 A mg _Pt^-1;membrane electrode test shows that Pt₃Cu/NPC-10 has a maximum power density of 715 m W cm^-2,which is 1.47 times that of commercial JM Pt/C.