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102. EIS applications

Author

Yuan, Xiao-Zi, Song, Chaojie, Wang, Hijiang, and Zhang, Jiujun

Abstract

As described in Chapter 1, there are several types of fuel cells. Of these various types, the PEMFC has captured the most attention among fuel cell researchers. The main features of the PEMFC are: • Low operating temperature (70–100°C) • High power density (~1.4 kW/kg) • High electrical efficiency (40–60%) • Quiet operation • Zero emissions These characteristics explain why the PEMFC has become such a promising fuel cell candidate for powering vehicles, and for both stationary and portable power generation [1]. 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.

Published
2010

103. Electrical fundamentals

Author

Yuan, Xiao-Zi, Song, Chaojie, Wang, Haijiang, and Zhang, Jiujun

Abstract

In order to understand electrochemical impedance spectroscopy (EIS), we first need to learn and understand the principles of electronics. In this chapter, we will introduce the basic electric circuit theories, including the behaviours of circuit elements in direct current (DC) and alternating current (AC) circuits, complex algebra, electrical impedance, as well as network analysis. These electric circuit theories lay a solid foundation for understanding and practising EIS measurements and data analysis.

Published
2010

113. Regulation of the discharge reservoir of negative electrodes in Ni-MH batteries by using Ni(OH)x (x 2.10) and y-CoOOH.

Author

Shangguan, Enbo, Chang, Zhaorong, Tang, Hongwei, Yuan, Xiao-Zi, Wang, Haijiang, Shangguan, Enbo, Chang, Zhaorong, Tang, Hongwei, Yuan, Xiao-Zi, and Wang, Haijiang

Abstract

In this paper, a novel strategy to regulate the discharge reservoir of negative electrodes in Ni-MH batteries is introduced by using Ni(OH)x (x = 2.10) and r-CoOOH. The electrochemical measurements of these batteries demonstrate that the use of Ni(OH)x (x = 2.10) and r-CoOOH can not only successfully regulate the discharge reservoir of negative electrodes in Ni-MH batteries to an adequate quantity, but also effectively improve the electrochemical performance of the batteries. Compared with normal batteries, the in-house prepared batteries with a lower discharge reservoir exhibit an enhanced discharge capacity, improved high-rate discharge ability, higher discharge potential plateau and superior cycle stability. The effect of Ni(OH)x (x = 2.10) and r-CoOOH on the electrochemical performance of nickel electrode is also investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results suggest that the new method is simple and effective for cost reduction of Ni-MH batteries with improved electrochemical performance., Peer reviewed: yes, NRC Pub: yes

Published
2011
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149. Degradation of a PEM fuel cell stack with Nafion® membranes of different thicknesses. Part II: Ex situ diagnosis

Author

Yuan, Xiao-Zi, Zhang, Shengsheng, Ban, Shuai, Huang, Cheng, Wang, Haijiang, Singara, Vengatesan, Fowler, Michael, Schulze, Mathias, Haug, Andrea, Andreas Friedrich, K., and Hiesgen, Renate

Subjects
*ELECTRODES, *HYDROGEN, *SCANNING electron microscopy, *ION exchange chromatography, *ARTIFICIAL membranes
Abstract

Abstract: Part I of this study carried out membrane electrode assembly degradation of a four-cell stack with Nafion membranes of different thicknesses, including N117, N115, NR212, and NR211, for 1000h under idle conditions. Through on-line electrochemical measurements it was found that as degradation advanced, cells with thinner membranes experienced much more rapid performance degradation than those with thicker membranes, especially after 800h of operation, due to a dramatic increase in hydrogen crossover. In the present work we investigate the degradation mechanisms of this four-cell stack using several ex situ diagnostic tools, including scanning electron microscopy (SEM), infrared (IR) imaging, ion chromatography (IC), gas permeability measurement, contact angle measurement, and simulation. The results indicate that the drastic increase in hydrogen crossover is due to membrane thickness loss and pinhole formation. [Copyright &y& Elsevier]

Published
2012
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150. Effect of open circuit voltage on degradation of a short proton exchange membrane fuel cell stack with bilayer membrane configurations

Author

Zhang, Shengsheng, Yuan, Xiao-Zi, Hiesgen, Renate, Friedrich, K. Andreas, Wang, Haijiang, Schulze, Mathias, Haug, Andrea, and Li, Hui

Subjects
*ELECTRODES, *SCANNING electron microscopy, *CATALYSTS, *ELECTRIC circuits, *ELECTRIC potential, *PROTON exchange membrane fuel cells
Abstract

Abstract: In the present work, membrane electrode assembly degradation of a 4-cell stack with specially designed twin catalyst coated membranes (twin-CCMs) was carried out for 1600h under open circuit voltage (OCV) conditions. Four types of membrane with various thicknesses were employed in the experiment. Each twin-CCM was composed of two membranes of the same type with a catalyst layer coated only on one side. The purpose of this special configuration was to facilitate postmortem analysis of the membrane after degradation due to the detachable membrane structure. By means of several in situ electrochemical measurements, the performance of the individual cells was analysed every 200h during the degradation process. Postmortem analyses such as scanning electron microscopy, atomic force microscopy, and infrared imaging were also conducted to identify the membrane degradation mechanisms after exposure to OCV. The results indicate that membrane degradation, which correlates with electrode degradation, is the most direct reason for the failure of the whole cell/stack during OCV operation, especially for cells with thinner membranes. [Copyright &y& Elsevier]

Published
2012
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