Study on Protocols for Evaluating Chemical Durability of Pemfc's Electorolyte Membranes

Introduction

The Fuel Cell Commercialization Conference of Japan (FCCJ), which includes Japanese automobile and ENE-FORM companies, proposed a steady state OCV test and a dry-wet cycle test as the protocols for evaluating the respective chemical and mechanical durability of low-temperature PEFC electrolyte membranes.Under the NEDO Project called Cell Evaluation Project, Daido University(DU) decided the evaluation protocol of membrane chemical and mechanical durability based on the protocol recommended by FCCJ and DOE. Table1 and Table 2 shows the OCV and Dry-wet cycle test protocols  were decided by DU. Using these protocols, chemical durability and mechanical durability of  fluorine based and hydrocarbon membranes from all over the world have been evaluated with single cells.Regarding to OCV test protocol, the criterion of this test is set which quantity of cross leak current reached at 10 times of the initial current. As the OCV test is going, chemical degradation of membranes are caused by hydrogen peroxide is produced, and then membranes are gradually broken and finally hydrogen leak current larger increase.The results that the OCV tests were conducted on the shingle cells with those membranes shows the trends that most of fluorine-based membrane were gradually broken and hydrogen leak current increase by OCV tests. But most of hydrocarbon-based membranes  were not broken and its hydrogen leak current were not increase, in spite of cell voltages were dropped  and cell internal resistance  were increase. By the criterion of  this OCV test which the hydrogen leak current reached at 10 times of initial current, the most of hydrocarbon-based membranes were reached the target, but it is not to clarify whether the membrane’s chemical degradation were occurred in OCV tests or not. Most of fluorine-based and hydrocarbon-based membranes have a characteristic which membranes were caused chemical degradation become fragile mechanically. Recently, using such a characteristic, the protocol that combined a OCV test and a Dry-wet cycle test has been suggested by ENE-FORM companies to evaluate and accelerate membranes   chemical and mechanical durability of membranes.In this study, to clarify the degree of the chemical degradation of hydrocarbon-based membranes in the OCV test, DU examine a newly protocol of evaluating for membrane’s chemical durability by OCV test with the new diagnosis method to use dry-wet cycle test.

Table1 DU(NEDO)protocol for membrane mechanical durability

Operation conditon	Pressure	Ambient
	Cell temperature	80 °C
	Gas	Air
	Flow rate	2 L/min
	R.H.	Between 0%(Dry) & 150%(90°C)
	Period of R.H.	4min(Dry:2min ⇔Wet:2min)
	Number of test	N=2
Criterion	Crossover (Leak current)	10 times of initial current
Target	2015	10,000 cycles
	Final	20,000 cycles

Table2 DU(NEDO) protocol for membrane chemical durability

Cell configuration	Cell size	15cm2 (3cm×5cm)
	Cell holder	With gas channel
	Width of gas channel / rib	1mm / 1mm
	Flow field	Straight folw
	Gas flow direction	Co-flow
Operation condition	Number of test	N=2
	Cell temperature	90°C
	Pressure	Ambient
	Gas	H2 / Air
	Flow rate	5% at 0.2 A/cm2
	R.H. (Humidifying)	30% (61°C)
Diagnosis	Frequency of LSV	Every 50 hr or 100 hr
Criterion	Crossover(Leak current)	10times of initial
Durable target		500 hour

Experimental

Table3 shows DU newly protocol for membrane chemical durability based on the protocol recommended by ENE-FORM companies. As seen this table, OCV tests with diagnosis method of membrane’s chemical durability were conducted on single cells with Nafion HP membrane and hydrocarbon-based membranes. Dry-wet cycle test was conducted for diagnosis method to evaluate degree of   membrane chemical durability.

Table3 DU newly protocol for membrane chamical durability

Cell configuration	Cell size	15cm2 (3cm×5cm)
	Cell holder	With gas channel
	Width of gas channel / ribu	1mm /1mm
	Flow field	Straight flow
	Gas flow direction	Co-flow
Operation condition	Number of test	N=2
	Cell temperature	90°C
	Pressure	Ambient
	Gas	H2 / Air
	Flow rate	5% at 0.2 A/cm2
	R.H. (Humidifying)	30% (61°C)
	Test time	45 hr
Diagnosis method	Pressure	Ambient
(Dry/Wet cycle)	gas	N2 or Air
	Flow rate	200,1000,1500 mL/min
	R.H.	Between 0%(Dry) & 150%(90°C)
	Cycle number	10 or 100 cycle
Diagnosis	Frequency of LSV	Every 50hr or 100hr
Criterion	Crossover (Leak current)	10 times of initial
Durable target		500 hour

 Acknowledgement

This research was performed under a grant from the Cell Evaluation Project from the New Energy and Industrial Technology Development Organization (NEDO) .