高性能燃料电池室温条件长期存储性能下降的两个原因:膜失水与铂氧化
第二个因素如果没有表征方式作为证据,作为判断题我会判断错误,对于我算是新知识。
Fast stack activation procedure andeffective long-term storage for high-performance polymer electrolyte membranefuel cell
Seung Yong Yang
Dong-Jun Seo
Myeong-Ri Kim
Min Ho Seo
Sun-Mi Hwang
Yong-Min Jung
Beom-Jun Kim
Young-Gi Yoon
Byungchan Han
Tae-Young Kim
Abstract
Time-saving stack activation and effectivelong-term storage are one of most important issues that must be resolvedfor the commercialization of polymer electrolyte membrane fuel cell (PEMFC).Herein, we developed the cost-effective stack activation method to finish thewhole activation within 30 min and the long-term storage method by usinghumidified N2 without any significant decrease in cell's performance for 30days. Specifically, the pre-activation step with the direct injection of DIwater into the stack and storage at 65 or 80 °C for 2 h increases thedistinctive phase separation between the hydrophobic and hydrophilic regions inNafion membrane, which significantly reduces the total activation time within30 min. Additionally, the long-term storage with humidified N2 has no effecton the Pt oxidation and drying of Nafion membrane for 30 days due to itsexergonic reaction in the cell. As a result, the high water content inNafion membrane and the decrease of Pt oxidation are the critical factors that havea strong influence on the activation and long-term storage for high-performancePEMFC.
首先讲了原因
Interestingly, the both of the watercontent in polymer membrane and the Pt oxidation are the critical factors thathave a strong influence on the activation and long-term storage.
文章主要讲的是方法
膜电极The Gore PRIMEA 57membrane-electrode-assembly (MEA) with a membrane thickness of 18 mmwas used toconduct the longterm storage of the PEMFCs.
After the cell activation, the MEAs withactive areas of 1 and 25 cm2 were kept in various gases in both dry andhumidified conditions at room temperature for 30 days
Fig. 1. Polarization curves after various activations processes at 65 C.
Fig. 2. Stack performance as a function of activation temperature.
Fig. 3. X-ray photoelectron spectra (XPS) of Pt electrocatalyst in MEAs tested under
different environmental conditions.
燃料电池经过活化或者运行停机后,长时间存储过程中膜失水容易理解,通过XPS表征表明催化层中的铂空气中室温长时间存储会发生氧化。
Table 1 XPS results on oxidation states of Pt electrocatalysts in MEAs tested under different environmental conditions.
Fig. 4. Electrochemical characterizations of MEAs under humidified air (a-c) and N2 (d-f).
Fig. 5. Cyclic voltammetry of MEAs under humidified air (a) and N2 (b).
A lower oxide coverage of Pt increases theoxygen reduction reaction because the Pt surface that is uncovered by PtO andPt(OH)2 can react with oxygen molecules.
作者推测铂室温氧化过程是以水为催化剂的分子氧氧化过程。
Conclusions
The activation process is required toincrease an initial stack performance. The swelling of polymer membrane as wellas Pt reduction play pivotal role in the enhancement of stack's performance throughactivation process. The pre-activation at high temperature increases the phaseseparation between the hydrophobic and hydrophilic regions in Nafion membranein a short time, leading to reduce the activation time. Additionally, aconstant current at 0.65 V helps to decrease the Pt oxidation while minimizing thecarbon corrosion. In this work, the effect of vacuum activation step on theswelling of polymer membrane is quite insignificant.
The influence of long-term storage on theelectrochemical properties of MEA was also investigated using dry/humidifiedair and N2 gas. The drying of the polymer's membrane was not affectedsignificantly by using humidified gases due to the residual water that was leftin the cell when there was no external air flowing into the cell. However,long-term storage in air condition adversely affected the performance of thecell due to the severe the Pt oxidation. In this work, we showed that long-termstorage in N2 gas had little influence on the performance of the cells due toits endergonic reaction. Thus, we concluded that the long-term storage in N2gas provides a great advantage to the fuel cell system.