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

Abstract

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 durabilityOperation conditonPressureAmbientCell temperature80 °CGasAirFlow rate2 L/minR.H.Between 0%(Dry) & 150%(90°C)Period of R.H.4min(Dry:2min ⇔Wet:2min)Number of testN=2CriterionCrossover (Leak current)10 times of initial currentTarget201510,000 cyclesFinal20,000 cycles Table2 DU(NEDO) protocol for membrane chemical durability Cell configurationCell size15cm2 (3cm×5cm)Cell holderWith gas channelWidth of gas channel / rib1mm / 1mmFlow fieldStraight folwGas flow directionCo-flowOperation conditionNumber of testN=2Cell temperature90°CPressureAmbientGasH2 / AirFlow rate5% at 0.2 A/cm2 R.H. (Humidifying)30% (61°C)DiagnosisFrequency of LSVEvery 50 hr or 100 hrCriterionCrossover(Leak current)10times of initialDurable target500 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 configurationCell size15cm2 (3cm×5cm)Cell holderWith gas channelWidth of gas channel / ribu1mm /1mmFlow fieldStraight flowGas flow directionCo-flowOperation conditionNumber of testN=2Cell temperature90°CPressureAmbientGasH2 / AirFlow rate5% at 0.2 A/cm2 R.H. (Humidifying)30% (61°C)Test time45 hrDiagnosis methodPressureAmbient(Dry/Wet cycle)gasN2 or AirFlow rate200,1000,1500 mL/minR.H.Between 0%(Dry) & 150%(90°C)Cycle number10 or 100 cycleDiagnosisFrequency of LSVEvery 50hr or 100hrCriterionCrossover (Leak current)10 times of initialDurable target500 hour Acknowledgement This research was performed under a grant from the Cell Evaluation Project from the New Energy and Industrial Technology Development Organization (NEDO) .