Electrochemical Impedance Spectroscopy Study of Metal Hydride Electrodes Using a Porous Model: Effect of Thermal Pretrea
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https://doi.org/10.1007/s11837-020-04465-1 2020 The Minerals, Metals & Materials Society
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Electrochemical Impedance Spectroscopy Study of Metal Hydride Electrodes Using a Porous Model: Effect of Thermal Pretreatment and Titanium Incorporation MARCOS MARTI´NEZ,1 ERIKA TELIZ,1,2 CARLOS F. ZINOLA,2 ´ NICA DI´AZ1,3 and VERO 1.—Electrochemical Engineering Interdisciplinary Group, School of Engineering, Chemical Engineering Institute, University of the Republic, J.Herrera y Reissig 565, CP 11300 Montevideo, Uruguay. 2.—School of Science, Fundamental Electrochemistry Lab, Electrochemical Engineering Interdisciplinary Group, University of the Republic, Igua 4225, CP 11400 Montevideo, Uruguay. 3.—e-mail: [email protected]
The aim of this work was to study the influence of titanium and thermal pretreatments on the electrochemical performance of Zr1xTixCr0.7Mo0.3Ni alloys used as anodic active materials in Ni-MH batteries to improve their electrochemical energy storage performance. It was observed that the substitution of Zr by Ti produced new responses in electrochemical impedance spectroscopy (EIS) diagrams. EIS spectra were adjusted employing a fitting methodology through a model for a porous electrode where the physical meanings of parametric figures and time constants were emphasized. Changes in the system response with the electrode state of charge (SOC) were also studied, and new functional relations between time constant values and SOC were found. The results give new evidence supporting the fact that certain crystallographic phases (such as cubic center body phases) have a helpful influence on the diffusion process, while other phases (such as the hexagonal titanium phase) contribute negatively to it.
INTRODUCTION Metal hydride (MH) materials implemented as negative electrodes in alkaline Ni/MH rechargeable batteries remain an interesting subject of scientific research with technological applications. The increasing complexity of electrochemical systems has led to the development of a greater number of techniques to complete the understanding, and among them, electrochemical impedance spectroscopy (EIS) has become an interesting power tool. At the present time, it is used in the characterization of electrode processes and complex interfaces, since data allow us to become more informed about the structure of these interfaces and the related reactions that occur. The technique distinguishes the threads that occur in a system according to their different time constants, being able to study them separately and obtain parameter values from said threads. The use of this technique has been (Received July 26, 2020; accepted October 23, 2020)
growing considerably and actuality employed in several research topics.1–5 Similarly, its use in the study of NiMH batteries has been constantly increasing, being applied in the analysis of the reaction mechanism of the electrodes.6–14 Experimental data obtained by EIS can be mathematically modeled in two ways:
Obtaining the expression of the im
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