Hydrogen as an energy carrier has the highest energy/weight ratio, and therefore it has been advocated as the desired fuel for automotive power, auxiliary power, stationary power generation, and also as an energy storage medium. Among various hydrogen generating methods, high temperature electrolysis (HTE) of water using solid oxide electrolysis cells (SOECs) has attracted substantial attention over the last decade due to its high efficiency of conversion and low energy consumption.

To date, extensive effort has been devoted to the development of SOECs and promising results have been shown.^1,2 However, while most of SOECs are based on an anode-supported cell (ASC) structure, only limited research on metal-supported SOECs is reported.^3,4 Compared with conventional ASC type SOECs, metal-supported solid oxide electrolysis cells (MS-SOECs) have unique advantages due to low cost of fabrication, high mechanical strength, good redox stability, and excellent thermal cycling resistance.^5,6 Because of these characteristics, MS-SOECs are considered as a promising solution for intermittent and mobile electrolysis applications.

In this work, symmetric-structure MS-SOECs with stabilized zirconia electrolyte are developed at LBNL. Nanostructured cathode and anode are fabricated by infiltrating catalysts on both steam and oxygen electrodes. The cells are tested in the temperature range of 650 to 800 ^◦C, with steam content between 3-75 vol%. Our MS-SOECs show the highest performance for the cells with zirconia-based electrolyte (Figure 1), to the best of our knowledge. At 1.3 V (thermoneutral voltage) and 50 vol% steam content, the measured current densities were 4.8 A/cm² at 800 ^◦C, 3.1 A/cm² at 750 ^◦C, 2.0 A/cm² at 700 ^◦C, and 1.2 A/cm² at 650 ^◦C. This performance was achieved by optimizing the catalyst chemistry, catalyst arrangement, and infiltration process. In order to study the effects of the cell fabrication process, the electrochemical performance at various steam contents and overpotentials is analyzed, and the corresponding microstructures are examined. The high cell performance shows a great potential of MS-SOEC technology, and the insight from these experiments will provide guidance for further research and development.

¹S.D. Ebbesen, S. H. Jensen, A. Hauch, and M. B. Mogensen, Chem. Rev., 114(21), 10697-10734 (2014).

²M. A. Laguna-Bercero, J. Power Sources, 203, 4-16 (2012).

³T. Chen, Y. Zhou, M. Liu, C. Yuan, X. Ye, Z. Zhan, and S. Wang, Electrochem. Commun., 54, 23-27 (2015).

⁴G. Schiller, A. Ansar, M. Lang, and O. Patz, J. Appl. Electrochem., 39(2), 293-301 (2009).

⁵M. C. Tucker, J. Power Sources, 195(15), 4570-4582 (2010).

⁶M. C. Tucker, Energy Technol., 5(12), 2175-2181 (2017).

Figure 1. Performance of a metal-supported solid oxide electrolysis cell (a) at 700 ^◦C with 3%, 25%, 50% and 75% steam contents in the cathode, and (b) with 50% steam content in the cathode at 650, 700, 750 and 800 ^◦C.