Fuel cell degradation modes

Significant research into failure modes and advances in the understanding of the mechanisms as well as mitigation has been achieved in recent years 

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Ammonia, produced due to the coexistence of H2 and N2 at high temperatures in the presence of catalyst, was estimated to be in the concentration range of 30 to 90 ppm [37, 38], Uribe et al. [39] examined the effects of ammonia trace on PEM fuel cell anode performance and reported that a trace in the order of tens of parts per million could lead to considerable performance loss. They also used EIS in their work. By measuring the high-frequency resistance (HFR, mainly contributed by membrane resistance) with an operation mode of H2 + NH3/air (feeding the anode with hydrogen and ammonia), they obtained some information related to membrane conductivity, and found that conductivity reduction due to ammonia contamination is the major cause of fuel cell degradation. 

PEM Fuel Cell Failure Mode Analysis presents a systematic analysis of PEM fuel cell durability and failure modes. It provides readers with a fundamental understanding of insufficient fuel cell durability, identification of failure modes and failure mechanisms of PEM fuel cells, fuel cell component degradation testing, and mitigation strategies against degradation. 

For MEA designers or fuel cell stack engineers, a polarization curve is an immensely useful practical analysis tool. It allows for a comparative assessment of sources of voltage losses in the cell, fuel cell failure modes, critical or limiting current densities, as well as impacts of degradation and water management. For materials scientists, the polarization curve entails useful information on performance effects... 

Previous work includes a Failure Mode Identification (FMEA) and fault Tree Analysis (FTA) of a general PEMFC by Rama, et al. (2008). Additionally, a more recent FTA work was presented by Placca. L Kouta. R (2011), looking at the failure modes that could cause PEMFC degradation, yielding a more detailed fault tree of fuel cell degradation. 

Table 2 Fuel cell operating modes and major types of degradation...

Table 2 lists typical fuel cell operating modes under actual vehicle opaating conditions along with varions types and causes of degradation observed (liyama 2007 ... 

ESR spectroscopy, used in the direct detection or spin trapping modes, is a sensitive method for the detection of polymer fragments and for determining the degradation mechanism. Recent applications for the study of stability in ionomer membranes used as proton exchange membranes in fuel cells demonstrate the capability of ESR to detect details that cannot be obtained by other methods. 

In conclusion, it is evident that most of the degradation issues in diffusion layers are related to the hydrophobic properties of the materials. Therefore, techniques that investigate the different degradation and corrosion modes that may affect the diffusion layers inside fuel cells are vital in order to design and choose optimal diffusion layers with the goal of achieving the best reliability and performance possible. 

Much recent ongoing work has focused on the chemical degradation mechanisms and revealed that radical attack is the root cause of the membrane decomposition. However, there is still a lack of fundamental understanding of the mechanisms for the degradation of mechanical strength, which is related to the membrane failure mode responsible for the sudden death behavior of fuel cells. 

Separate Accelerated Stress Test (AST) protocols have been proposed by the US Department of Energy to assess the durability of fuel cell under conditions that promote distinct degradation modes... 

Improve performance of reversible stacks (capable of operating in both fuel cell and electrolysis modes) by reducing area specific resistance, rate of degradation, and seal leakage. 

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