四种燃料电池的活化方法、活化速度、9000次0．6V－OCV循环的差异对比

Cathode starvation as an acceleratedconditioning procedure for perfluorosulfonic acid ionomer fuel cells

Emmanuel Balogun

Alejandro Oyarce Barnett

Steven Holdcroft

Abstract

Freshly assembled proton exchange fuelcells （PEMFC） require conditioning to reach maximum power density． This processmay last up to tens of hours and adds to the cost of commercial fuel celltechnology． We present an acceleratedconditioning procedure involving starving the cathode of oxidant． In singlecells， this procedure conditions a membrane electrode assembly （MEA） within 40 min， without compromising durability．The performance and durability of MEAs conditioned using this technique arecompared with US Department of Energy （DOE） and European Union （EU） harmonizedprotocols， and to an amperometric conditioning protocol． The time to reach peak power density using cathode starvationconditioning is ＜10％ of the time required for DOE， EU， and amperometricprotocols． Conditioned MEAs were subjected to accelerated degradation by cycling the cell voltage between 0．6 V andopen－circuit voltage under low relative humidity． Degradation was found tobe caused by loss of electrochemicalsurface area of the cathode， which in turn increases the charge transfer resistance of the MEA． MEAsconditioned using cathode starvation experienced only a 15％ loss inperformance； in contrast to 19， 17 and 17％ losses in performance caused by theDOE， EU， and amperometric protocols， respectively．

at 80 C， and 100％ RH and 30％ RH at the  anode and cathode， respectively， the aging process is accelerated via the  following steps： （i）maintain the cell at OCV for 8sec； （ii） perform a voltage  scan in the range OCV → 0．6V → OCV， at a scan rate of 50mV／s．

Fig． 1． Plots showing the current and power  density response as a function of conditioning time with current （black dotted  line） and power density （red） response for MEAs consisting of Nafion®

NR－211， Nafion® D520 ionomer in the catalyst  layer and Pt loadings of 0．4mg Pt／cm 2 for cathode and anode：（a） Cathode  starvation conditioning （b）DOE conditioning， （c） EU conditioning， （d）  amperometric conditioning．

Fig． 2． Time for the fuel cell to reach  maximum power density using various conditioning protocols． Error bars  represent the upper and lower boundaries of three separate measurements．

Fig． 3． Polarization （black） and power  density plots （red） of MEAs subjected to the four conditioning procedures：  （a） immediately following conditioning， （b） after 9000 degradation cycles． FC  polarization data were obtained at 80 C， H 2 anode and O 2 cathode， 100％ RH，  1atm pressure．

Table 1

Maximum power density， and current  density at 0．6V， for MEAs conditioned under different procedures and after  accelerated degradation cycles． Std． Devs． provided in Table S5．

Fig． 4． Degradation data comparing the  performance loss observed as a function of percentage loss in maximum power  density after various accelerated degradation cycles for MEAs conditioned by  the different procedures．

Table 2 MEA resistance data immediately  after conditioning and after 9000 degradation cycles for MEAs conditioned  using different procedures

Fig． 5． Plot showing （a） Electrochemical  Surface Area （ECSA） for MEA cathodes conditioned with different procedures  and subjected to increasing accelerated degradation cycles． （b） An inverse  relationship between the ECSA （m 2 ／g pt） and the MEA charge transfer  resistance （mΩ cm2） for MEAs conditioned using four different conditioning  procedures． （A） Data obtained immediately after conditioning， （B） after 3000  degradation cycles， （C） after 6000 degradation cycles， and （D） after 9000  degradation cycles． Conditions for ECSA measurement：80C， H2 anode and N2  cathode， 100％ RH， 1atm pressure．

Conclusion

The performance and durability of MEAs  subjected to a new accelerated conditioning procedure， involving cathode  starvation， was investigated and compared with the standardized DOE and EU  harmonized conditioning procedures and against an in－house－adapted amperometric  procedure． The time required to condition MEAs using the cathode starvation  procedure， as determined by the time to reach peak power density is 40min． Greater than 90％ of the maximum current （density）  is achieved after 12min． However， unlike other accelerated conditioning  procedures reported in the literature that are purported to condition MEAs in  under an hour， our cathode starvation procedure was found to lead to MEAs  that were more durable under an accelerated degradation test． The cathode starvation procedure results  in a significant reduction in ionic resistance of the catalyst layer，  increased ECSA and decreased charge transfer resistance． This is attributed to the low cathode potential  and H2 crossover from anode to cathode during the conditioning that promotes  proton transport within the CL and provides reducing conditions at the  cathode to promote sufficiently strong reducing conditions at the cathode electrode  to reduce Pt oxides and hydroxide to bare Pt． Future work should be  undertaken to address the validity of these processes．

For the MEAs conditioned by cathode  starvation， the smallest percentage change in CL ionic resistance and ECSA  was found during accelerated degradation， with no significant difference in  ionic resistance and smallest percentage loss of active sites before and  after degradation， compared to the other conditioning procedures examined． It  can be concluded that the new cathode starvation conditioning procedure has proven  to yield MEAs exhibiting high performance and durability while taking 90％  less amount of time compared to other standardized conditioning protocols． The positive attributes of this  conditioning protocol warrant further investigation to determine if the same  attributes apply to larger MEAs， fuel cell stacks， and state－of－the－art MEAs  used in the industry which operate with stabilized materials， thinner  membranes， antioxidant additives， lower Pt loadings， and． multi－component  catalysts．

最后一句作者说得很中肯，电堆估计够呛，大面积电极是否会有问题留了一个口子。