使用梯形电位循环考察了电压上限、相对湿度、电池温度对电极耐久性的影响。

催化层ECSA的衰减状态过程中，电压上限更高，相对湿度更大，电池温度更高，ECSA下降的更厉害。

添加了电压上限的停留时间这一因素。而且可以看出在实验中，电压上限，相对湿度，电池温度、电压上限时间影响递减，电压上限最为敏感。

无法通过简单增加铂载量提升耐久性。就必须对电堆的设计功率、功率密度、铂的利用率和电堆成本做出妥协。

Achieving 5，000－h and 8，000－h Low－PGM Electrode Durability on Automotive Drive Cycles

R． K． Ahluwalia1， X． Wang1， J－K Peng1， V． Konduru2， S． Arisetty2， N． Ramaswamy2 and S． Kumaraguru2

Abstract

Whereas total Pt loading in anode and cathode catalysts below 0．125 mg cm−2 is required to meet the stringent cost target for automotive fuel cell systems （FCS） for light duty vehicles， low－loaded cathode catalysts are susceptible to unacceptable aging－related performance losses at high current densities． A framework model， validated by accelerated stress test data， has identified cell voltage， relative humidity （RH） and temperature as the key operating variables that affect degradation of a high－activity d－PtCo／C cathode catalyst with 0．1 mg cm−2 Pt loading． Drive cycle simulations indicate that these can be controlled by properly selecting the minimum FCS power， compressor－expander module （CEM） turndown， and stack coolant temperature． The optimum system parameters are 4－kWe minimum power for an 80－kWe FCS， CEM turndown of 12．5， and 66 °C average coolant exit temperature that combine to limit the maximum cell voltage to 850 mV and outlet RH to 90％–100％． Depending on Pt loading， the mismatch between actual and allowable degradation for 10％ power loss over 5，000－h lifetime requires the stack to be oversized by 2．4％–5％， resulting in 8．4％–41％ lower Pt utilization and 7．1％–20．5％ penalty in stack cost． The corresponding results for 8，000－h lifetime are 10．3％－14％ stack oversizing， 23％–51．8％ lower Pt utilization， and 24．1％–35．4％ stack cost penalty．

使用梯形电位循环考察了电压上限、相对湿度、电池温度对电极耐久性的影响。

催化层ECSA的衰减状态，电压上限更高，相对湿度更大，电池温度更高，ECSA下降的更厉害。

另一种表现形式，极化曲线，高电流密度下的性能衰减状态。

添加了电压上限的停留时间这一因素。而且可以看出在实验中，电压上限，相对湿度，电池温度、电压上限时间影响递减，电压上限最为敏感。

为了满足8000hr耐久性，ECSA衰减到55％，需要满足的MAP图。

无法通过简单增加铂载量提升耐久性。

必须通过调变出口温度、空压机－膨胀机的TD、限制电压上限才能实现5000－8000hr耐久性的预期。

就必须对电堆的设计功率、功率密度、铂的利用率和电堆成本做出妥协。 燃料电池不是无所不能，需要客观评价现有的技术体系。需要对热火朝天的风口进行冷思考。

该类工作如果对不同的阴极催化剂体系进行考核和模拟就更有指导意义了。

评价的仅是催化层的耐久性，并不包含对电解质膜等其它材料和大面积单电池、电堆的耐久性考核。

Conclusions
We have formulated a framework for developing an electrode
durability model from experimental data obtained on a differential cell hardware． The framework was used to determine a pathway for reaching the target lifetime of a high activity d－PtCo／C alloy catalyst on LDV drive cycles． The main conclusions of this study are summarized below．
• The underlying reaction mechanism controlling ORR does not
appear to change with aging under cyclic potentials． The observed
degradation in ORR kinetics can be associated with Pt dissolution
that causes ECSA loss and with preferential Co leaching that relaxes
the lattice strain considered responsible for enhanced activity of the
alloy catalyst．
• The observed increase in O2 transport resistance with aging
may be associated with the loss in catalyst roughness， tempered by a
slight decrease in the local resistance （RO2） that may be ascribed to
ionomer conditioning or rearrangement of catalyst particles on
carbon support． In a separate study we find that RO2 is higher in
the alloy catalyst electrode than in pure Pt electrodes possibly
because of ionomer poisoning by Co that leaches out during the
electrode fabrication process．

Cell voltage， relative humidity and temperature are the key
variables that affect catalyst degradation． Drive cycle simulations
indicate that these can be controlled by properly selecting the
minimum FCS power， CEM turndown， and stack coolant temperature．
The optimum parameters on UDDS are 4－kWe minimum
power， turndown of 12．5， and 66oC average coolant temperature that
combine to limit the maximum cell voltage to 850 mV and outlet RH
to 90％． The cell degradation can be further mitigated by lowering
the CEM turndown to 10 and raising the average cell temperature to
70 °C so that the average outlet RH is 52％／78％ during UDDS／
HWFET， and the cell voltage varies between 760–825 mV． These
dry operating conditions may prove challenging to membrane
stability and require further investigation．
• There is a mismatch between the cell degradation that occurs
under the optimum conditions and that allowable for 5，000－h and
8，000－h electrode lifetime． Depending on the Pt loading， the
mismatch requires that for 5，000－h lifetime the stack be oversized
by 2．4％–5％， resulting in 8．4％–41％ lower Pt utilization and
7．1％–20．5％ penalty in stack cost． The corresponding figures for
8，000－h lifetime are 10．3％–14％ stack oversizing， 23％–51．8％
lower Pt utilization， and 24．1％–35．4％ stack cost penalty．
Further work is required to validate the conclusions of this study
on large cells and stacks operated in H2／air． Raising the cell
temperature to establish and maintain a drier environment is
beneficial for electrode stability but challenges membrane durability，
and this too needs to be investigated． Clipping cell voltage to 0．85 V，
limiting minimum power to 4 kWe， and curtailing CEM turndown to
12．5 compromise FCS efficiency． A trade－off study is needed to
understand the trade－off between electrode lifetime and fuel consumption．