控制催化剂碳载体表面氧含量调变燃料电池碳载体和离聚物相互作用、水管理、氧透过离聚物层扩散阻力提升燃料电池性能与耐久性［设计三十三］
Tailoring a Three－Phase Microenvironmentfor High－Performance Oxygen Reduction Reaction in Proton Exchange Membrane FuelCells
Zipeng ZhaoMd Delowar HossainChunchuan XuZijie LuYi－Sheng LiuShang－Hsien HsiehIlkeun LeeWenpei GaoJun YangBoris V． MerinovWang XueZeyan LiuJingxuan ZhouZhengtang LuoXiaoqing PanFrancisco ZaeraJinghua GuoXiangfeng DuanWilliam A． Goddard IIIYu Huang
Summary
Despite tremendous progress in catalystdevelopment for rate－limiting cathodic oxygen reduction reaction （ORR），reducing Pt usage while meeting performance requirements in practical protonexchange membrane fuel cells （PEMFCs） remains a challenge． The ORR in PEMFCsoccurs at a catalyst–electrolyte–gas three－phase interface． A desirableinterface should exhibit highly active and available catalytic sites， as wellas allow efficient oxygen and proton feeding to the catalytic sites and timelyremoval of water to avoid interface flooding． Here， we report the design of athree－phase microenvironment in PEFMCs， showing that carbon surface chemistry can be tuned to modulate its interaction withthe ionomers and create favorable transport paths for rapid delivery of bothreactants and products． With such an elaborate interfacial design， for thefirst time we have demonstrated PEMFCs with all key ORR catalyst performancemetrics， including mass activity， rated power， and durability， surpassing theUS Department of Energy targets．
相关文献：调控催化活性中心与离聚物的界面实现高性能长耐久燃料电池
Figure 1． Characterization of CarbonMaterials （A and B） Synchrotron－based NEXAFS spectra for carbon K－edge （A） andfor oxygen K－edge （B）． The intensity is normalized by sample loading． （C）ATR－FTIR spectra． （D and E） Synchrotron－based XPS spectra for carbon 1s （D） andoxygen 1s （E）． （F） The surface oxygen to carbon ratio for three carbon samplesevaluated； C1， C2， and C3．
Preparation of Carbon Materials （C1， C2，C3， and C4）
C1 was prepared by annealing KetjenblackEC－300J in air at 400 C to achieve an increased oxygen ratio on the carbonsurface． C2 was the original Ketjenblack EC－300J． C3 and C4 were prepared byannealing Ketjenblack EC－300J in a gasmixture of argon （Ar） and hydrogen （H2） at 800 C–1，000 C to achieve a reduced surface oxygen ratio．
Figure 2． MEA Test （A） Comparison of massactivities obtained in the H2／O2 test at the beginning of test （BOT； before ADT）and end of test （EOT； after ADT）． （B–E） H2／air test． （B） Polarization plots atBOT． （C） Power density plots at BOT． （D） Polarization plots at EOT． （E） Powerdensities plots at EOT． （F） Comparison of peak power densities． The MEA testwas performed at 80 C and 150 kPaabs pressure unless specifically noted． Thisfigure shows the average results of at least two MEAs．
Figure 3． Rated Power of RepresentativeMEAs and EDS Map Analysis of Cathode Catalysts （A） H2／air polarization plotsobtained at the temperature of 94 C and pressure of 250 KPaabs for rated powerevaluation． （B） Comparison of rated power densities at BOT and EOT in forPtNi／C3， PtCo／C3． （C） Voltage loss from BOT to EOT at a fixed current densityof 0．80 A／cm2． （D–G） STEM image and EDS elemental analysis of representativePt－based nanoparticles． PtNi／C3 samples before the MEA test （D）， and at EOT（E）． PtCo／C3 samples before the MEA test （F）， and at EOT （G）． Each panelconsists of the STEM image， mapping images of individual elements， and combinedmapping of both elements．
Figure 4． The Interfacial Interactions between the Carbon Surface and HydratedPFSA Ionomers （A） An image of the ionomer and water distribution on carbonsurfaces after MD simulations． The bottom caption shows the interface energybetween the ionomers and the carbon surface with different oxygen contents （0％，2．5％， 4．0％， and 12．0％）． （B） The number of atoms refers to the ionomerdistributed within 0．3 nm distance above the carbon surfaces in simulationmodels （model size： 3．4 nm in width， 3．4 nm in depth）． （C） The average distanceof water molecules within 0．3 nm above the carbon surfaces． （D） Pressureindependent parts of oxygen transport resistance measured at 80 C， RH 65％（details are given in the Experimental Procedures）． The error bars representstandard error．
Table 1． Summary of DOE Technical Targetsand the Performance Achieved in Our MEAs with a Tailored Three－PhaseMicroenvironment
