Study On The Structural Components Of Cathode Catalytic Layer In PEMFC And The Effect Of Degradation On The Reaction Transmission By LBM

Proton exchange membrane fuel cell(PEMFC)is a device that directly converts the chemical energy of fuel into electric energy,and is considered as an energy conversion device facing the future.The electrochemical reactions in the catalytic layer(CL)of proton exchange membrane fuel cells mainly depend on the structural parameters related to the components and their distribution in CL,and are inevitably severely affected by degradation factors.The structure change and degradation process of CL have a great impact on the performance of PEMFC,so it is urgent to carry out in-depth exploration of the structure size and degradation factors of each component in CL.In this paper,a random algorithm is used to reconstruct the micro-porous structure of the cathode CL.Subsequently,lattice Boltzmann method(LBM)was used to study the structural parameters of CL,such as the size of carbon carrier and platinum particle(Pt),the thickness of the ionomer,and the influence of single component degradation and comprehensive degradation on the oxygen reduction reaction process in the cathode of CL at different degradation rates.The research work of this paper is summarized as follows.This paper analyzes the influence of the structural components of CL on the properties of CL.The increase in carbon carrier size promotes oxygen transport through CL pores,which is due to the decrease in the curvature and porosity of oxygen transport channels in porous CL.However,this is not conducive to oxygen diffusion through the ionomer to the active site of the reaction,reducing the overall oxygen reduction reaction(ORR)rate.With the increase of Pt particle size,the number of reaction sites in CL will decrease.However,it is necessary to consider that with the increase of the diameter of Pt particles,the thickness of the ionomer on the surface decreases,which leads to the enhancement of oxygen diffusion in the ionomer.With the increase of the ionomer thickness,the oxygen diffusion resistance in the pores of CL increases.In addition,with the increase of the ionomer thickness,oxygen is more easily confined in the pore,and the process of oxygen diffusing through the ionomer to the active site of Pt becomes more difficult.The transport resistance of oxygen through the ionomer increases with the increase of the ionomer thickness,which decreases the overall ORR rate.However,too thin an ionomer thickness can lead to Pt exposure,which reduces the number of reaction sites.The results show that appropriate design of carbon carrier size,Pt particle size and ionomer thickness is the key to achieve high oxygen transport performance and high overall oxygen reduction reaction rate of CL.Meanwhile,this paper analyzes the influence of aging degradation process on the properties of CL.Based on LB model,this paper adopts ionomer’s microscopic reconstruction method that is closer to the reality.It innovatively considers the separate degradation of platinum particles,carbon carriers and ionomers,as well as the overall degradation process of three components,to analyze the degradation effects of different components in CL and the comprehensive degradation effects.In addition,the oxygen transport and electrochemical reaction process in CL under the condition of limiting current density were studied by using two sets of uniform degradation rate and exponential degradation rate.The results show that the degradation of platinum reduces the reaction sites in the catalytic layer,thus worsening the electrochemical kinetics and reducing the overall reaction rate.In contrast,the degradation of carbon and ionomer exhibits two opposite effects.On the one hand,the degradation of carbon and ionomers,especially the degradation of ionomers,improves oxygen transport and thus speeds up the overall reaction rate.On the other hand,degradation of carbon and ionomer will trigger the separation of platinum particles,resulting in a lower reaction rate.In the early stage of the multicomponent degradation process,the total reaction rate is limited due to the limitation of oxygen transport in the catalytic layer.With the increase of degradation degree,the transport of oxygen in the ionomer membrane is enhanced,and the electrochemical kinetics becomes the factor determining the degradation rate,especially the exponential degradation rate.In this study,the oxygen transport and electrochemical reactions within the catalytic layer were evaluated comprehensively under different degrees of degradation of the catalytic layer,which can provide guidance for the design of high-performance anti-degradation catalytic layers for the next generation of fuel cells.