Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

FP7

STAYERS Streszczenie raportu

Project ID: 256721
Źródło dofinansowania: FP7-JTI
Kraj: Netherlands

Periodic Report Summary 5 - STAYERS (STAYERS Stationary PEM fuel cells with lifetimes beyond five years)


Project Context and Objectives:

Project STAYERS introduction and objective:

Economical use of PEM fuel cell power for stationary applications demands a lifetime of the fuel cells of at least 5 years, or more than 40,000 hours of continuous operation. The prospect of large scale application for automotive use has focused PEM research on low cost production techniques with practical lifetimes of the fuel cells of 5,000 hours. For the stationary use, especially in the chemical industry and in remote areas, robustness, reliability, and longevity are often more important than the cost of the initial investment. For stationary generators the yearly cost of maintenance and overhaul are expected to be much larger than for intermittent applications such as automotive- and back-up power.

To reach the high goals of the project, basic material research is given maximum attention. The durability of all components of a stack of PEM fuel cells, especially that of the Membrane Electrode Assembly (MEA), rims and seals, cell (bipolar) plates, and flow field is of paramount importance for a stationary power generator.

Project STAYERS is dedicated to the goal of obtaining 40,000 hours of PEM fuel cell lifetime employing the best technological and scientific means. Apart from materials research it also requires a detailed investigation of degradation mechanisms and their mitigation during continuous operation. Factors relevant for the balance of plant (BOP) will also be addressed. These are the operating temperature, degree of humidification of fuel and air, and the excess ratio with respect to the stoichiometry of the supplied gases. The effect of possible contaminants should be taken into account.

A lifetime of 40,000 hours, if defined as the time elapsed until 10 % of the initial voltage is lost, is equivalent with an average voltage decay rate of 1.5μV/h. To establish this lifetime within the 26,000 hours of a three years project advanced materials research and development will be combined with models and accelerated tests.

Project Results:

In the previous periods of the project, the following major achievements have been accomplished:

WP-2:

- For the baseline membrane no significant degradation was observed from post mortem analyses after 10.000 hrs of operation.
- A novel membrane process route has been developed eliminating the necessity for post-treatment, resulting in membrane IMP-1; In addition, process improvements enabled production of IMP-1 in rolls, rather than sheets (baseline membranes)
- An improved membrane (IMP-2) including radical scavengers has been supplied and is currently applied in field tests; In accelerated stress tests (AST’s) this membrane has shown extended lifetimes, indicating extrapolated lifetimes beyond 40.000 hrs

WP-3:

- Four iterations of membrane electrode assemblies (MEA’s) have been supplied and tested on lab-scale and in the power plant; Especially with the latest so-called rainbow concept (containing numerous MEA-variations within one stack) promising results and better insight in degradation mechanisms have been obtained
- Investigative tools for MEA analysis have been developed and have been applied in extensive post-mortem analyses of the first iteration (SC-0). These have indicated loss of cathode catalyst active surface area as the predominant mechanism for irreversible decay
- In addition lab-scale studies have revealed the substantial effect of various contaminants both for air and hydrogen on reversible decay

WP4:

- The coolant and anode flow field have been investigated; no potential for lifetime improvement has been found
- Seal materials have been tested and improved candidates have been selected for durability tests
- A first new stack housing has been evaluated, indicating the necessity for further improvements
- The industrial plant for durability testing has been used from the start and has been upgraded with enhanced software for performance analysis
- BOL/MOL/EOL stack analyses on 4 MEA iterations have been performed.

WP5:

- An AST mimicking the predominant (irreversible) decay has been developed
- CO and NO2 contamination studies, mimicking the reversible decay have been performed for various MEA iterations
- Membranes including scavenger formulations have been evaluated

WP6:

- Using Ansys CFD a 3D two-phase parametric model has been developed and has been validated with experimental BOL and EOL results
- The model has been refined and used to study various effects, such as the influence of contaminants

From the very start of the project, the observed voltage decay has been in part reversible, for instance upon a system stop and subsequent start and for a part irreversible. Further voltage recovery of the so-called retrievable decay has been observed, as a result of typical voltage excursions during standard test lab analyses, like IV-curve measurements. Even more voltage recovery is observed after the application of dedicated conditioning protocols.

Accelerating the identification of the dominant decay mechanism in the SC-1 MEA reference type, SC-0 type MEAs have been extensively analysed by Nedstack and Solvicore in close collaboration. This has resulted in a top-4 of most probable degradation mechanisms causing the observed voltage decay:

1) Cathode loss of active surface area; irreversible
2) Cathode loss of active surface area by poisoning; reversible
3) Cathode increase of proton resistance; irreversible
4) Anode loss of active surface area by poisoning; reversible; this effect is enhanced by anode loss of active surface area by particle growth/carbon corrosion, resulting in a decreasing hydrogen contaminant tolerance and increasing reversible decay

Potential Impact:

Summary 5th 6-month period: Jan-Jun 2013

In WP-1, as part of the FCH JU funded projects related to PEMFC degradation, STAYERS, KEEPEMALIVE, PREMIUMACT and EURECA, a workshop on degradation of PEM fuel cells was organized by SINTEF. The workshop aimed at gathering the partners within these projects to exchange experience and discuss PEM degradation issues, potentially focussing on:

• experience/results from the relevant FCH JU projects
• MEA sensitivity to gas impurities
• components and cell lifetime prediction methods/models

The workshop focus was thus to provide for enhanced insight into PEM fuel cell degradation issues and how to counteract these to ensure longer lifetime and more reliable fuel cell operation. A summary of the workshop and presentations are to be found at the project website:

http://www.sintef.no/Projectweb/STAYERS/News--Events/

WP-2 Production of IMP2 membrane in larger scale

IMP2 is an Aquivion-based, ePTFE-supported membrane developed by Solvay Specialty Polymers in the frame of Stayers Project. With the aim to increase membrane lifetime in fuel cell environment, IMP2 also contains a radical scavenger system.

IMP2 samples were produced during the fourth reporting period using a small-scale manufacturing process and then used to build Rainbow stack III. Owing to the promising results IMP2 showed, it has been decided to use IMP2 (together with scavenger-free IMP1) as membrane for the final SC4 stack.

In order to guarantee the delivery of the large amount of material request to build SC4 stack, Solvay Specialty Polymers took care of the development of a larger-scale process to produce IMP2 in roll form. To do that some technical issues have been faced and addressed during the process scale-up. Resolution of these issues was demonstrated to be crucial to ensure the preparation and delivery of membrane in good quality.

During this period in WP3, the strategy adopted to understand the MEA sensitivity in field test confirmed its success. By introducing a high number of single variations, different degradation patterns could be observed, and a first link to environmental conditions found. These environmental conditions were also tested in laboratory by introducing some basic contamination tests based on CO, NO2 or SO2.

Analysing the degradation and increasing its understanding to elaborate a reliable lifetime prediction was also an important topic. This brought also the partners to discuss about mitigation strategies on the system side, to better control the reversible and retrievable degradations to keep them to their lowest possible values.

Finally, the post-mortem analysis after the AST protocol allowed quantifying the strength of this test, as well as its acceleration factor for further evaluation of the SC-4 MEA and further improvement of lifetime predictions.

Within WP 4, the following progress has been booked regarding stack hardware:

• cell plates

Dimensional, electrical and surface properties after approx.10.000 and 18.000 hrs operation have been quantified; no dramatic changes which limit stack lifetime have been observed; some properties are further investigated

• seals

The currently applied seals do not meet the STAYERS target; in particular for the coolant channels the lifetime is limited below 20.000 hrs. Improved seals have been evaluated and are applied in SC-4 stacks that will be tested for durability in the power plant

• Housing

An improved housing design (incl a higher corrosion resistance) has been tested and is ready for application in the final iteration of SC-4 stacks

Analyses of the power plant feed streams have quantified contaminants both in hydrogen and air. Contaminants have also been determined at the catalyst surface area, causing reversible (and possibly irreversible) decay. Improved air filtration will be tested to reduce this effect.

In WP5, the effect of CO poisoning before and after AST has been compared. MEA SC2 shows a considerable decrease in CO tolerance after degradation. CO tolerance has also been investigated for one of the SC3 (CC4Aa, AC SC-2) variation and found to be similar to SC2, while SC1 has a better CO tolerance. Initial experiments with NO2 additions to the cathode air show that the effect is more or less fully reversible and not depending on the cathode humidity.

The previously developed model for PEM FC in WP6 was used to predict fuel cell lifetime by varying selected material properties that are changing during the operation and their effect was expressed by changes in the current-voltage characteristics.

The simulation of PEM fuel cell operation is achieved by extrapolating the experimentally obtained results for 6,400 hours of operation with changes in the material properties of individual cell components.

The identified parameters that were tested are: (1) electrical conductivity of bipolar plates; (2) ECSA, permeability, electrical conductivity, porosity and contact angle for the catalyst; (3) protonic conductivity; (4) electrical conductivity, porosity and contact angle for the GDL.

Experimentally, the effects responsible for performance loss are due to a combination of various mechanisms which are more or less significant depending on the region where the experimental point is situated on the I-V curve. In modeling End of Life data, in a first approach the effects were treated individually by simulation of cases were only one parameter is changing at a time. Than the material properties were split into two categories: those affecting the performance at low current densities and those affecting the performance at high current densities. Simulations were performed for each category and also a worse case scenario cumulating the effects of all parameters was made.

Among the studied parameters high impacts have ECSA, GDL properties and the protonic conductivity.

List of Websites:

www.stayers.eu


Reported by

NEDSTACK FUEL CELL TECHNOLOGY BV
Netherlands
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