Mechanism Study On The Effects Of Typical Cations In Marine Environment On The Output Performance Of Proton Exchange Membrane Fuel Cells

Since the 21st century,global warming has gradually intensified,and environmental issues have attracted more and more attentions.In the context,IMO has also put forward the emission reduction target of shipping industry.Low-carbon,zero carbon emission clean energy has gradually become the strategic development direction of shipping industry in the world,instead of traditional fossil energy.Fuel cell has the advantages of zero emission,high energy conversion efficiency,low noise,etc.,and it has been identified as one of the promising clean energy sources to realize the decarbonization of shipping industry.However,the degradation of fuel cells caused by the sea salt aerosol may limit the application of fuel cells in the marine field.In this study,the effects of cations in sea salt aerosol on the performance of the proton exchange membrane fuel cell（PEMFC）are investigated by experiment,and the effect mechanism is analyzed using molecular dynamics simulation.The research results are of great scientific significance for exploring the migration and diffusion law of sea salt aerosol components in the fuel cell,and enriching the mechanism of sea salt aerosol’s effect on the key parts of the fuel cell.More specifically,the following works are carried out in present study:To reveal the degradation law of PEMFC due to the cations in sea salt aerosol,a sea salt aerosol generator is designed.The degradation law of the fuel cell performance is analyzed,focusing on the cation species,cation concentration and contamination time.The four kinds of typical cations have obvious degradation effects on the output performance of PEMFC.Cations affect the fuel cell in the order of Ca²⁺>Mg²⁺>Na⁺>K⁺.The maximum power density of the fuel cell decreases by 0.064 W/cm²,0.076 W/cm²,0.099 W/cm²,and 0.125 W/cm²,respectively,after 6 h of operation in the sea salt aerosol containing four kinds of cations,namely,K⁺,Na⁺,Mg²⁺and Ca²⁺.SEM-EDS characterization of the cross-section of the contaminated MEA shows that the proton exchange membrane had a strong adsorption of cations,while only a small amount of cation is observed in the catalyst layer.To systematically investigate the influence of water content and temperature on the transport properties of proton exchange membranes,all-atom models of Nafion membranes with water contents of 3.5,7,10,13 and 16 are established.The transport properties of water molecules and hydronium ions are investigated with the combined effects of water content and temperature.The results show that with the increase of water content from 3.5 to 16,the size of water clusters in the membrane is gradually increased,and eventually connect with each other,this process is conducive to the transport of water molecules and hydronium ions in the water channel.Benefit from the establishment of water channel in the membrane caused by increased water content,the diffusion of water molecules and hydronium ions in the membrane is strengthened.Increasing the temperature can also enhance the movement of water molecules and hydronium ions in the membrane.For the effects of cations in sea salt aerosol on the performance of proton exchange membranes,all-atom models of Nafion membranes containing four types of cations,namely,K⁺,Na⁺,Mg²⁺,and Ca²⁺,respectively,are established.The changes in the microstructure of the proton exchange membrane and the mass and heat transfer properties in the membrane are analyzed in depth from the perspectives of cation type and cation hydration,and the mechanism of the influence of cations on the performance of the proton exchange membrane is revealed.The simulation results show that the cations in the proton exchange membrane decreased the diffusion coefficient of hydronium ions.The analysis of RDFs shows that cations have strong interaction with both water molecules and sulfonic acid groups.When the temperature is increased,the interaction between sulfonic acid groups and the cations changes in different way:the cations with strong interactions(Ca²⁺,Na⁺)become stronger,and the cations with weak interactions(K⁺,Mg²⁺)become weaker.What’s more,the effects of cations on the hydronium ions transport ability in the proton exchange membrane is mainly due to the destructive effects on the connectivity of the water channels in the membrane.Regarding the effects of cations on the catalyst layer,all-atom models of the cathodic catalyst layer containing four kinds of cations,namely,K⁺,Na⁺,Mg²⁺,and Ca²⁺,are established.The diffusion and penetration of oxygen molecules in the catalyst layer and the change of the relative active surface area of the catalyst layer under the action of cations are investigated.The results of the study on oxygen diffusion in the polymer film on the surface of Pt particles show that with the increase of water content,the interactions between the oxygen molecules and the polymer are weakened,ultimately leads to an enhancement of the diffusion of oxygen.The presence of cations leads to a slight decrease in the size of the water channels in the catalyst layer,and at the same time makes the distance between the water channels and the Pt particles larger,resulting in a decrease in the relative active surface area in the catalyst layer.At higher temperatures,the water channel size is further reduced,the interaction between the water channel and the Pt particles is weakened,and a substantial decay of the relative active surface area occurred.The study of the oxygen permeation process in the catalyst layer shows that the degree of influence of cations on the oxygen permeation flux is in the order of Ca²⁺>Mg²⁺>Na⁺>K⁺.