Electrochemical Performance of Fuel Electrodes in Solid Oxide Co-Electrolysis Cells Operated Under Various Conditions
Authors: Nara Kazuma , Oshima Toshihiro , Shibata Yuki , Sakamoto Mio , Tachikawa Yuya , Sasaki Kazunari 
Published: December 2024

Introduction

Solid oxide co-electrolysis cells are electrochemical devices which can electrolyze steam and carbon dioxide at the same time into hydrogen and carbon monoxide which are components of synthesis gas. Waste heat can be recycled effectively by creating a combined system of carbon hydrate synthesizer and the cells, and along with high temperature operation, carbon dioxide can be also recycled to carbon hydrates with high efficiency. To design a co-electrolysis system, and calculate efficiency numerically, characteristics of the solid oxide co-electrolysis cells must be clarified. In this study, we aim to obtain and quantify electrochemical characteristics of fuel electrodes in solid oxide co-electrolysis cells by measuring I-V curve and calculating exchange current density in various operating conditions, to be applied in solid oxide co-electrolysis system planned as future work.

Experimental

The tested electrolyte-supported solid oxide cell consists of Ni-YSZ (8 mol%Y2O3 – 92 mol%ZrO2) cermet, a composite of Ni and YSZ, as fuel electrode, YSZ plate as electrolyte, and LSCF ((La0.6Sr0.4)(Co0.2Fe0.8)O3) as air electrode. Gas mixture of hydrogen, vapor, carbon-dioxide, and nitrogen were supplied to the fuel electrode with the total flow rate of 100 ml min-1. Some conditions to evaluate the effect of gas composition on the fuel electrode performance are shown in Figure 1 (a). On the other hand, dry air was supplied to the air electrode with the total flow rate of 150 ml min-1. I-V curve and electrochemical impedance were obtained using a Solartron electrochemical measurement system. A phenomenological exchange current density equation of the fuel electrode was obtained by regression analysis based on the experimental results [1-3].

Results and Discussion

Figure 1 (b) shows the fitted exchange current density obtained by considering hydrogen-water vapor reaction as well as carbon monoxide-carbon dioxide reaction. From the peak in the graph, the obtained exchange current density depended on the partial pressures of hydrogen and water vapor. Therefore, in the cases shown in Figure 1 (a), compared with CO2 electrolysis reaction, steam electrolysis reaction seems to be the dominant reaction at fuel electrodes in solid oxide co-electrolysis cells [4,5]. In the presentation, dependencies of operating temperature, and partial pressure of each gas component will be discussed.

Reference

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Figure 1