Reliable Lab-Scale Evaluation of Solid Oxide Fuel Cells Electrode Performance – the Effect of Electrode Thickness and Current Collecting Spacing
Authors: Kim Jae Jin , Ingram Brian J. 
Published: July 2021

Understanding and optimizing electrochemically active zone for oxygen reduction reaction in solid

oxide fuel cells (SOFCs) cathodes are indispensable to maximize device’s performance. For mixed ionic

and electronic conductors, the range of this zone depends on the oxygen surface exchange and solid-state

oxygen/electron transport properties of materials [1]. This aspect is also critical to realize valid

characterization of the electrode’s electrochemical activities. For instance, when a material’s electronic

conductivity is low or the electrical contact points are spaced beyond a critical distance, the electrode

polarization resistance measured by electrochemical impedance spectroscopy will be controlled by the sheet

resistance not the oxygen exchange resistance [2]. The situation becomes more complicated as the electrical

conductivity of porous layer, which is an advantageous structure with large surface area and facile gas phase

transport, considerably deviates from the material’s intrinsic property. It is expected that porosity,

connectivity, and impurity contents can have significant impact on porous electrode’s electronic conduction

[3].

In this context, we have studied effective in-plane electronic conductivity of lanthanum strontium

cobalt ferrite (LSCF) porous layers. The in-plane conductivity was measured by four-line probe

configuration [4], modified from the widely used four-point probe technique to be applied for a porous

layer. We have confirmed that the in-plane electrical conductivity of screen-printed LSCF porous layers is

one or two orders of magnitude lower than the material’s bulk property in ambient air, depending on

temperatures. This electronic conductivity deviation was taken into account to rationally design

combination of electrode thickness and current collector spacing and, in turn, to guarantee a valid

assessment of electrode performance. In addition, we found that electrical conductivity of LSCF porous

layers decreases by 20~30 %, within relatively short period of time (250~400 hours) upon repeated thermal

cycles (500 ℃ to 700 ℃). Furthermore, we found that in-plane conductivity of thin (<10 µm) electrodes is

strongly dependent on the measurement time and the local atmospheric environment relative to thicker

electrodes. Special attention is required to use a thin electrode to evaluate electrode performance.

This work was supported by the US Department of Energy (DOE), Office of Fossil Energy, (Office

of Clean Coal & Carbon Management), “Solid Oxide Fuel Cell Manufacturing in Support of Office of

Fossil Energy” program through Argonne National Laboratory under FWP No. 27327.1.

[1] S.B. Adler et al. J. Electrochem. Soc. 143 (1996) 3554-3564; S.B. Alder Solid State Ionics 111 (1998)

125-134.

[2] B.A. Boukamp et al. Solid State Ionics 192 (2011) 404-408; B.A. Boukamp et al. Solid State Ionics 283

(2015) 81-90.

[3] L. Holzer et al. J. Mater. Sci. 48 (2013) 2934-2952.

[4] S.W. Peterson et al. J. Electrochem. Soc. 161 (2014) A2175-A2181.