Synthesis Of Ordered PtFe Alloy Catalyst And Its Performance Toward Oxygen Reduction Reaction

Fuel cells are considered to be one of the most promising new energy technologies since the 21st century.However,the oxygen reduction reaction process of fuel cell cathodes is very slow and highly dependent on Pt precious metal catalysts.Due to the unknown Pt precious metal reserves and low annual production,this has seriously hindered the large-scale commercial application of fuel cells.Nowadays,the Pt-M alloy system has become a hot spot in the research of fuel cell catalysts.The Pt-M alloy system can not only effectively reduce the Pt loading of the electrode and significantly reduce the cost of the fuel cell.In the process,the binding energy of the catalyst and oxygen leads to higher oxygen reduction activity.However,Pt-M alloy catalyst materials have poor physical and chemical stability,and are often oxidized,dissolved,or separated from the carrier,agglomerate into larger particles,and lose electrochemical catalytic activity during the cycle.Therefore,the key to the study of alloy catalysts is how to further improve the stability of the catalyst while ensuring the activity of the catalyst.In this paper,we use high-temperature heat treatment to generate ordered PtFe alloy nanoparticles in situ to prepare ordered PtFe catalyst,while improving the activity and life of the alloy catalyst,mainly carried out the following work:（1）This article proposes a simple and highly repeatable method for the synthesis of ordered PtFe nanoparticles.First,the coordination of the N precursor protoporphyrin and the metal salt,and then the coordination of the nitrogen-containing metal by rotary evaporation The precursor is evenly coated on the carrier,and then the metal particles undergo a carbothermal reduction reaction during the high-temperature heat treatment process,and Pt and Fe are assembled into an ordered alloy structure in situ.In order to understand the influence of each process link in the preparation process on the catalyst’s oxygen reduction activity,we conducted in-depth exploration and optimization of the experimental process and conditions including heat treatment conditions,the amount of metal precursor added,carrier particle size,carrier selection,etc.After various parameters,the PtFe TMPP-EC600 catalyst with high oxygen reduction activity and excellent stability was reached.（2）The electrochemical results show that the prepared PtFe TMPP-EC600 exhibits excellent oxygen reduction activity under acidic medium,and the half-wave potential reaches 0.910 V（vs.RHE）;The mass specific activity reached 0.645 A/mg_（Pt）,about3.4 times that of JM 20%Pt/C,exceeding the DOE 2020 target.At the same time,the stability of the material is also greatly enhanced.The samples before and after the stability test of 30,000 cycles have basically no loss of activity,and the morphology before and after the stability test remains almost unchanged.Rotating ring disk electrode test shows that the hydrogen peroxide yield of the material during oxygen reduction is very low,mainly four-electron reaction.The formation of ordered alloys adjusts the electronic structure of Pt,and the large specific surface area of the material is also conducive to the exposure of active sites and optimizes the mass transfer,which is conducive to the improvement of the oxygen reduction activity of the material.After coordination,the N atoms in the precursor form a restricted protection around the metal atoms,which blocks the metal atoms during high-temperature heat treatment and effectively prevents the reunion of the metal particles.In addition,the resulting catalyst has a Pt-rich core.The shell structure prevents corrosion of the transition metal under acidic conditions,all of which have a positive effect on the improvement of stability.