Research On Chemical Durability Enhancement And Application Of Perfluorinated Proton Membrane For Fuel Cells

Proton exchange membrane fuel cells（PEMFCs）converting hydrogen chemical energy into zero-pollution electricity will play an important role in developing a hydrogen-based energy economy to reduce the energy dependence on traditional fossil fuels.It has the advantages of high power density,zero emission,quiet operation,and may be widely used in transportation,power generation and other fields,and in recent years,more and more attention.Proton exchange membrane（PEM）is a medium that provides proton transport,and serves as a separation layer of anode fuel（H₂）and cathode gas（O₂）,which is a key component of determining the performance of fuel cells.At present,the commercial PEM is mainly perfluorosulfonic acid（PFSA）-based material,which has significant high proton electrical conductivity,mechanical integrity and excellent thermal and chemical stability under humidification conditions.Among them,the chemical durability of the perfluorosulfonic acid（PFSA）proton exchange membrane is crucial for its application in the proton exchange membrane fuel cell（PEMFCs）.Composite membranes have been shown to be one of the simple and effective methods used to improve the performance of fuel cell membranes.As a class of substances that can actively scavenge the free radicals,the free radical scavenger can effectively reduce the chemical attenuation of the PFSA membrane,and then improve the service life of the PEMFCs,which has been widely added to the membrane.According to different requirements,various types of free radical scavengers are synthesized and applied to PFSA membrane,which improves the chemical durability of perfluorproton membrane.The paper mainly focuses on the following aspects:（1）In view of the relatively single composition of the existing proton membrane free radical clearing system,a new free radical clearing cooperative system is developed by combining organic antioxidants with metal ion chelation ability with inorganic free radical scavengers.The different perfluorosulfonic acid（PFSA）composite membranes were prepared by single doping and codoping of alizarin（AZR）and cerium ions.AZR and cerium ion codoping not only significantly enhanced the oxidative stability of the membrane but also lessened both the migration of cerium ions from the membrane and the ionic cross-linkages of cerium ions with sulfonic acid groups.AZR/Ce codoping of the PFSA composite membrane exhibited a maximum power density of 966 m W cm^-2at 75°C under 80%RH,which was 89.45%of that of the pristine PFSA membrane,whereas only 79.37%remained for cerium ion single doping of the membrane under the same conditions.The AZR/Ce-codoped PFSA composite membrane released much less fluoride than the single-doped PFSA,AZR,or cerium ion composite membranes.The antioxidation effects of AZR/Ce codoping of the PFSA composite membrane were also studied by scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,electrochemical hydrogen crossover analysis,and cell performance analysis.Notably,the open-circuit voltage（OCV）test indicated that the AZR/Ce-codoped PFSA composite membrane was still viable after 456 h of testing,whereas the other membranes were seriously damaged.（2）In order to relieve the problem that the perfluorosulfonic acid（PFSA）membrane has to sacrifice the proton conductivity due to the enhanced chemical degradation,Ce（III）-terephthalic acid metal organic frameworks（Ce-TPA MOFs）with efficient·OH radical scavenging efficiency are designed via coordinating the organic antioxidant ligand（terephthalic acid,TPA）with inorganic radical scavenger（Ce ions）.Ce-TPA MOFs with a different weight ratio of 0.5,1.0,or 2.0%was introduced in PFSA matrix to produce composite membranes.On the one hand,the hydrophilic groups of Ce-TPA MOFs caused better water absorption,which promoted the proton conduction to some extent.Also,the presence of the redox Ce³⁺/Ce⁴⁺couple,oxygen vacancy,and TPA molecules in Ce-TPA MOFs scavenging·OH radical together via synergy effect.The optimum peak power density of the PFSA/Ce-TPA_1.0composite membrane at 75°C under 80%RH was1086?m W?cm^-1,that of pristine PFSA membrane was only 1032?m W?cm^-1.Furthermore,PFSA/Ce-TPA_1.0 composite membrane experienced the decay of only0.31 m V/h during 96 h operation under the same conditions,whereas that of pristine PFSA membrane was 2.20 mV/h.（3）An effective new bifunctional inorganic filler,tourmaline（TM）-loaded Ce O₂ core-shell micronanostructure（TM-Ce O₂）,was designed and implemented to simultaneously increase the stability and proton conductivity of perfluorosulfonic acid（PFSA）-based proton exchange membranes.Composite membranes exhibited excellent mechanical strength,chemical stability,and proton conductivity upon the introduction of TM-Ce O₂ into the PFSA matrix.The presence of TM provided excellent proton conductivity and mechanical strength to composite membranes,while the addition of Ce O₂ alleviated the chemical deterioration of composite membranes by scavenging hydroxyl radicals.The maximum power density of the PFSA/TM-Ce O₂（1 wt%）composite membrane at 80°C under 100%RH was1006?m W?cm^-1,whereas that of the pristine PFSA membrane under identical conditions was only 906?m W?cm^-1.Additionally,proton exchange membrane fuel cells（PEMFCs）containing PFSA/TM-Ce O₂ membranes show a decay of only 0.29m V/h in 168 h while operating at 80°C under 50%RH.Compared to PFSA/TM-CeO₂,PEMFCs with the pristine PFSA membrane showed a decay of 2.18 mV/h under the same conditions.