Researchers from the Spanish Catalonia Institute for Energy Research and Catalan Institution for Research and Advanced Studies, have used ceramic 3D printing to fabricate a new family of electrolyte-supported Solid Oxide Fuel Cells (SOFCs).
Utilizing SLA 3D printing, the research team developed a new approach to fuel cell production, which yielded a direct increase in capacity over those conventionally used to generate power. The “new generation” of green energy cells, which emit no environmentally-harmful gasses, could now be used in end-use electricity generation applications, or to create enhanced energy storage devices.
“Among others, electroceramic-based energy devices like solid oxide fuel and electrolysis cells are promising candidates to benefit from using 3D printing to develop innovative concepts that overcome shape limitations of currently existing manufacturing techniques,” stated the research team.
“3D printing of functional materials will revolutionize the energy sector by introducing complex shapes and novel functionalities never explored before. This will give rise to the next generation of enhanced devices ready for mass customization.”
Enhanced fuel cell storage and the environment
SOFCs are power generators that develop zero emissions. Powered by converting hydrogen into electricity, they display over 60 percent efficiency (LHV) across the whole range of kilowatt scales. Moreover, in combined heat and power units, their efficiency can reach up to 90 percent, making SOFCs one of the most efficient energy generation devices currently available. When operated in reverse mode, on the other hand, the devices become energy storage units, capable of producing storable hydrogen from electricity and water.
Referred to by the researchers as Solid Oxide Electrolysis Cells (SOECs), these are highly efficient energy conversion devices with 80 percent or more LHV. When SOEC’s are filled with steam and CO2, they can generate syngas (a mixture of CO and H2), which is used as a precursor for the production of synthetic hydrocarbons and liquid fuels. Utilizing SOECs as tools for converting CO2, could turn the cells into valuable products for the energy or chemical sectors.
Solid Oxide Cells (SOCs) meanwhile, are ceramic-based multilayer electrochemical cells consisting of a gas-tight oxide-ionic conductor electrolyte with electrodes on either side. The materials generally used for SOCs are yttria-stabilized zirconia (YSZ) for the electrolyte, combined with lanthanum strontium manganite (LSM-YSZ) for the oxygen electrode and Ni–YSZ for the fuel electrode. Other compounds such as scandia-stabilized zirconia (SSZ) are also used in the industry, to increase the performance of the cells at lower operation temperatures. Nonetheless, SSZ often suffers from stability issues under high densities in SOEC mode, making the conventional LSM–YSZ/YSZ/Ni–YSZ combination a competitive cell, even when operating at temperatures over 800℃.
While other researchers have attempted to develop new materials in order to increase cell performance, few have examined changing the cell’s geometry, according to the Spanish team. While a group of researchers from Stanford University, did achieve a two-fold increase of power density in silicon-based micro-SOFCs in 2008, similar strategies have not been used to enhance conventional SOFCs. Given recent advances in 3D printing technology, the Spanish researchers set out to utilize the benefits of AM, to develop planar and high-aspect ratio corrugated LSM–YSZ/YSZ/Ni–YSZ solid oxide cells.
3D printing the enhanced eco-fuel cells
The research team began by using Computer Assisted Design (CAD) software to sketch planar and corrugated membranes with a uniform 2.00 cm diameter, which would eventually determine the future active area of the cell. These membranes were summarily integrated with external annular rings, in order to enhance their mechanical stability, and ensure good sealing of the membranes during the testing.
A solvent-free UV-photocurable slurry was then created by the team, consisting of 8YSZ ceramic powder, acrylate UV curable monomer, photoinitiator and dispersant. The mixture was summarily deposited over a 30 × 30 cm2 printing platform inside a 3DCERAM CERAMAKER SLA 3D printer. Under UV exposure, the photocurable mixture, containing a monomer and a photoinitiator, solidified following a free-radical photo-polymerisation process. In addition to successfully forming fuel cells, excess uncured paste was found to be reusable by the team during future processes, further underlining the cells’ eco-friendly potential.
Microstructural characterization of the printed pieces and the full cells was then carried out using a ZEISS AURIGA Scanning Electron Microscope, in order to determine the crystal structure of the materials. The experiments yielded crack-free and homogeneous parts, and planar and corrugated membranes showed effective surface areas of 2.00 cm2 and 3.15 cm2, respectively, an increase of 57%. Overall, the 3D printed YSZ parts were considered suitable for working as electrolytes in end-use SOFC/SOEC applications.
In order to fabricate complete solid oxide cells, LSM–YSZ and Ni–YSZ electrodes were deposited on both sides of the 3D printed 8YSZ sintered membranes. Limited closed porosity was observed in the electrolyte, indicating the suitability of the 3D printing technology to reach gas-tight self-standing membranes. To study the reversibility of the printed cells, the planar and corrugated cells were evaluated in co-electrolysis mode, converting a combination of steam and CO2 into syngas. Although it was not deemed possible to determine a maximum performance (like that of SOFC cells), it was clear to the researchers that the corrugated cell significantly improved on the behaviour of the planar one.
Moreover, performance stability testing proved that in SOFC mode, the technology could be used in end-use applications. As a result, ceramic 3D printing had enabled the production of electrolyte-supported solid oxide cells with both conventional (planar) and enhanced-area (corrugated) architectures. In addition, the corrugated SOFC cells demonstrated an improvement that was directly proportional to the increase of its active area, achieved by 3D structuration, with a direct increase of 60% on conventional methods. The team concluded that the stackability and improved functionality of the cells, could lead to the development of a new generation of solid oxide cells, with enhanced storage and performance qualities.
“This enhancement by design, combined to the proved durability of the printed devices (less than 35 mV/1000 h), represents a radically new approach in the field and anticipates a strong impact in future generations of solid oxide cells and, more generally, in any solid state energy conversion or storage devices,” said the research team.
Additive manufacturing and fuel development
3D printing has been used to innovate a variety of increasingly environmentally-friendly fuels in recent years, often with applications in nuclear reactor efficiency. Scientists from the U.S. Department of Energy’s Argonne National Laboratory for instance, have used 3D printing to develop a new method of reusing nuclear waste. The novel technique could allow up to 97 percent of disposed waste to be recycled.
Polish FFF 3D printer producer and service provider Omni3D is working with The Cyprus University of Technology to develop a bio-fuel reactor. Using Omni3D’s 3D printing expertise, the project aims to create a reactor that’s capable of turning carbon dioxide into biomethane or ethanol.
In aerospace applications, companies such as metal US space technology startup Rocket Crafters, have developed 3D printed rocket fuels. The company uses pure powdered aluminum to create the fuel, a substance so volatile, that in nanoscale particle form it will spontaneously ignite on contact with the Earth’s atmosphere.
The researchers’ findings are detailed in their paper titled “3D printing the next generation of enhanced solid oxide fuel and electrolysis cells” published by the Journal of Materials Chemical A. The report was co-authored by Arianna Pesce, Aitor Hornés, Marc Núñez, Alex Morata, Marc Torrella and Albert Tarancón.
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Featured image shows the self-standing 3D printed 8YSZ membranes. Top view (a and b) and cross-section (c and d) of the planar and corrugated membranes, respectively. Images via the Journal of Materials Chemistry A.