Year: 2025
Type: conference-abstract
Abstract: Introduction The society is undergoing a transition from carbon-based polluting non-renewable energy sources to greener ones based on electricity. While important advancements have been made, some issues related with intermittent supply must be solved [1]. Hydrogen serves as possible solution for this problem as energy carrier, although its production costs must be reduced. Solid Oxide Cell (SOC) technology offers an efficient method for hydrogen generation from water electrolysis if it is operating in Solid Oxide Electrolysis Cell (SOEC) mode, and for its transformation to electricity afterwards, when working as Solid Oxide Fuel Cell (SOFC) [2]. SOC technology presents several advantages, including the absence of precious materials, lower electricity consumption for hydrogen production and lower hydrogen consumption for electricity production or higher efficiency in both modes. SOCs can be classified as function or their architectures, with the most significant types being planar and tubular [3]. Additionally, they can be classified by their support type, being the most important configurations fuel electrode-supported and electrolyte-supported [4]. Since some of the objectives of SOC technology are reducing operating temperatures and manufacturing cost without compromising performance, planar fuel electrode-supported configurations are particularly attractive thanks to thinner electrolytes [5] compared to electrolyte-supported and more economic cost production than tubular [6]. Objectives Planar fuel electrode-supported SOCs of 5x5 cm 2 were manufactured and characterized at Instituto de Nanociencia y Materiales de Aragon (INMA) focusing on optimizing the production process with conventional techniques such as tape casting and screen printing. Standard materials widely studied were employed, such as the cermet Ni-yttrium stabilized zirconia (YSZ), YSZ as electrolyte and (La 0.8 Sr 0.2 ) 0.95 MnO 3-x (LSM)-YSZ or (La 0.60 Sr 0.40 ) 0.95 Co 0.20 Fe 0.80 O 3-x (LSCF) - Gd 0.1 Ce 0.9 O 1.95 (GDC) composites [7], including in this latter case a GDC barrier layer. Button cells around 1 cm 2 were also manufactured and characterized with accelerated degradation studies in order to understand Ni migration on fuel electrode and cell components degradation. Results Tape casting was employed for the fabrication of the fuel electrode and the electrolyte. Electrolyte slurry was made from 8%mol Y 2 O 3 -stabilized ZrO 2 (8YSZ). Two different slurries were prepared for fuel electrode. The first type consists of NiO, 8YSZ powders and corn starch, which helps to decrease polarization associated with hydrogen and steam diffusion [8]. This slurry was used for making fuel-electrode support layers, resulting in a composition of 40%vol Ni, 30%vol 8YSZ and 30% porosity after reduction. The second slurry, composed by NiO and 8YSZ powders, forms the functional layer, with a final composition of 26%vol porosity, 37%vol Ni and 37% YSZ after reduction. It was tape casted on top of the electrolyte tape. Tape photographs and schemas can be seen on Figure 1a) for fuel electrode support (top) and functional layer with electrolyte (down). Then, three NiO-YSZ layers of porous substrate and one NiO-YSZ functional layer with electrolyte were roll calendered on a hot rolling press as can be seen on Figure 1b). Finally, they were sintered at 1500ºC for 2 hours, resulting in a half-SOCs which can be seen on Figure 1c). For the two types of air electrodes (LSM-YSZ and LSCF-GDC), different inks were prepared with two different compositions: 50-50%vol and 80-20%vol. Inks were homogenized using a three-roll milling process before deposition. For 5x5 cm 2 SOCs, when LSM-YSZ was used, four layers of 4x4 cm 2 were screen printed over the electrolyte as can be seen on Figure 1d): the first two with a 50-50%vol composition, while the last two with 80-20%vol composition. For LSCF-GDC air electrode, same procedure was followed, but a 4x4 cm 2 GDC barrier layer was screen printed beforehand and sintered at 1400ºC during three hours in order to minimize strontium diffusion and the formation of ionic insulating secondary phases such as strontium zirconate (SrZrO 3 ). Air electrodes were sintered at 1150ºC for two hours. Resulting SOCs can be observed on Figure 1e). After sintering, reproducible SOCs were obtained with 300 µm fuel electrode support and 50 µm functional fuel electrode (Figure 2a)), 10 µm electrolyte (Figure 2b)), 3 µm GDC barrier layer and 40 µm air electrode in both air electrodes (Figure 2c)). While thinner electrolytes could be obtained in order to reduce ohmic loses and improve performance, they may result in a decrease of the long-term performance due to electrolyte delamination and degradation in SOEC applications. SOCs were reduced at 800ºC with humidified hydrogen (~3% H 2 O) before electrochemical characterization. Characterization of 5x5 cm 2 SOCs was conducted using an Open-Flanges set-up from Fiaxell, employing Electrochemical Impedance Spectroscopy (EIS) and current density-voltage curves ( j- V curves) at different temperatures with several atmosphere conditions in both electrodes. Temperatures measured were 750, 800 and 850ºC. On fuel electrode, humidified hydrogen (~3% H 2 O and 97% H 2 ), and 50% H 2 O-H 2 were measured while atmospheric air (~20% O 2 ) and pure oxygen were used on air electrode. EIS measurements were made at Open Circuit Voltage (OCV) in the range compressed between 100 kHz to 100 mHz with an amplitude of 50 mV, while j- V curves were measured in SOFC mode (from OCV to 0.5V) and SOEC mode (from OCV to 1.5 V) using a potentiostast SP-300 from Biologic with a 30A booster. Button cells were cut with laser from 5x5 cm 2 half-SOCs (see Figure 1f)). LSM-YSZ air electrodes of 1 cm 2 were deposited on button cells following the same protocol as for squared SOCs. Resulting button cells can be seen on Figure 1g). Experiments lasted around 100h in chronoamperometry in SOEC mode (1.3 V) at temperatures comprising the range between 750 and 850ºC with high steam concentrations (at least 50% H 2 O). Characterization took place on both Fiaxell and Probostat set-ups focusing on the use of different glass, ceramic and compressive sealings, such as GO18-311 and 354, Ceramabond 571 and mica, respectively. Moreover, EIS and j- V measurements were made at different intervals in order to understand SOCs evolution. For square 5x5cm 2 SOCs, an inverse relationship was observed between Area Specific Resistance (ASR) values obtained from EIS measurements and steam and oxygen concentrations. The higher these concentrations, the lower was ASR. Arrhenius dependency was followed with temperature. Some electrochemical results can be seen on table from Figure 2 f). For example, at 750ºC, 50% H 2 O and atmospheric air (typical SOEC operation conditions
Source: ECS Meeting Abstracts
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W4416613162
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