Fuel cell diagnosis

EIS has played an important role in fuel cell technology development, as one of the most important research tools for fuel cell diagnosis. EIS can help to identify the contributions from different components or processes to the total impedance of a PEM fuel cell. Such information is very helpful for understanding the fundamental processes within the fuel cell, the performance-structure relationships, and the contributions of various components to performance loss, as well as the associated failure modes and mechanisms EIS thus assists with fuel cell design optimization and selection of the most appropriate fuel cell operating conditions. In this chapter, we will present some typical examples of the applications of EIS in PEM fuel cell research, and an overview of EIS spectra analysis. 

In recent years, EIS has been widely used in studies of electrochemical systems, including batteries and materials corrosion, and is also being increasingly employed by researchers in PEM fuel cell studies. During the last few decades this technique has emerged as a primary tool in PEM fuel cell diagnosis. 

Yuan X, Wang H, Colinsun J, Zhang J. AC impedance technique in PEM fuel cell diagnosis - a review. Int J Hydrogen Energy 2007 32(17) 4365-4380. 

Yuan, X., H. Wang, J.C. Sun, and J. Zhang. 2009. AC impedance technique in PEM fuel cell diagnosis—A review. Int.. Hydrogen Energy 32 4365M380. 

During the research and development of PEM fuel cells, many techniques have been used to diagnose or characterize cells in situ or ex situ. The following sections will discuss the techniques widely used for PEM fuel cell diagnosis. This chapter will not provide in-depth coverage of the principles and instrumentation of well-known techniques, but it will mainly focus on their applications in PEM fuel cell testing and diagnosis. 

The CV technique has been widely used in fuel cell research. The following sections wiU address in detail its applications in PEM fuel cell diagnosis. 

Thus, the measurement of hydrogen crossover plays an important role in PEM fuel cell diagnosis and the development of new membrane materials. 

Electrochemical impedance spectroscopy (EIS), also known as AC impedance spectroscopy, is a very powerful technique for characterizing the behaviors of electrode-electrolyte interfaces. Initially, EIS was used to determine doublelayer capacity subsequently, it has been used for more complicated processes, such as metal corrosion [21-24] and electrodeposition [25-27], and to characterize the electrical properties of materials and interfaces. With the developments in PEM fuel cells during recent years, EIS has been widely used for PEM fuel cell diagnosis and the electrochemical characterization of PEM fuel cell materials and components [17,28-35]. 

In PEM fuel cell diagnosis, XRD is often used to characterize the catalyst or catalyst layer after fuel cell operation, to determine the Pt particle size and compare it with the size before fuel cell operation [98]. 

In Chapter 3, electrochemical impedance spectroscopy (EIS) was introduced as a powerful technique for PEM fuel cell diagnosis. EIS measurement can be conducted at OCV and under load. The AECD of the ORR (fo ) can be calculated using Eqn (3.8), based on the simulated /f° (charge transfer resistance at the OCV for the ORR) from the Nyquist plot obtained by EIS that is shown in Fig. 3.12. The values of the membrane resistance (/fm), charge transfer resistance (/ t) and mass transfer resistance (/fmt) in a PEM fuel cell at different current densities can also be simulated using measured EIS, based on... 

Two types of EIS diagnosis exist for PEM fuel cells material/component evaluation before assembly into a fuel cell and material/component evaluation after assembly into a fuel cell. Normally, the former is evaluated using a half-cell (or an electrochemical cell), while the latter is evaluated in a fuel cell or stack. We define the former as an ex situ diagnosis, and the latter as an in situ diagnosis. In the following sections, we will describe them separately. 

Figure 5.49. Experimental schematic for EIS measurement of a 500 W fuel cell stack [55], (Reprinted from Journal of Power Sources, 161, Yuan XZ, Sun C, Wang H, Zhang J. AC impedance diagnosis of a 500 W PEM fuel cell stack part II individual cell impedance, 929-37, 2006, with permission from Elsevier.)...

This chapter has provided the basic knowledge applied in EIS diagnosis for PEM fuel cell systems, including in situ and ex situ techniques. Various gas-feeding... 

Hydrogen sensors are particularly interesting for the emerging fuel cell vehicle market. There are also applications for detection of combustion gases for fuel leak detection in spacecraft, automobiles and aircraft, fire detectors, exhaust diagnosis and emissions from industrial processes (Baranzahi... 

Zhang J, Wu J, Zhang H, Zhang J. Pern fuel cell testing and diagnosis, chapter I. Elsevier 2013. 

Rubio M A, Urquia A and Dormido S (2010), Diagnosis of f>erformance degradation phenomena in PEM fuel cells. International Journal of Hydrogen Energy, 35,2586-2590. 

Wu J, Yuan X Z, Martin J J, Wang H, Yu D, Qiao J and Merida J (2010b), Proton exchange membrane fuel cell degradation under close to open-circuit conditions Part I In situ diagnosis,/onma/ of Power Sources, 195,1171-1176. 

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