Sustainable+Energy+Materials+Laboratory
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A New Efficient Oxide Coating Technology to Improve Fuel Cells
A new efficient oxide coating technology that can be applied in less than five minutes could lead to dramatic improvements in the lifetime and performance of fuel cells. The fundamental principle behind this approach is maximizing the oxygen reduction reaction site of a platinum thin-film electrode, preventing the electrodes from aggregating at high temperatures.
Fuel cells have emerged as a clean electricity generation system that does not pollute the air. In particular, solid oxide fuel cells (SOFCs) are beginning to gain a great deal of attention due to their higher power generation efficiency compared to other fuel cells. It is also advantageous to use other power sources than expensive hydrogen fuel.
However, the high costs and insufficient lifetimes caused by high temperatures needed to operate the solid oxide fuel cells have remained significant challenges to commercialization.
Recently, attempts to lower the operating temperature (< 600°C) of these devices by introducing thin-film processes have drew attention of researchers, with the resulting products known as thin-film-based solid oxide fuel cells.
In order to create enhanced device performance at lower temperatures, the research team, led by Professor WooChul Jung in the Department of Materials Science and Engineering, applied and developed oxide coating technology to maximize the oxygen reduction reaction sites of a platinum thin-film electrode and to prevent platinum electrodes from thermal aggregating.
The team succeeded in over-coating a platinum electrode with a new coating material called praseodymium-doped ceria (Pr,Ce)O2-, which has high conductivity for both electrons and oxygen ions and excellent catalytic properties for oxygen reduction reactions. As a result, electrode resistance was reduced by more than 1000 times, creating the potential for these electrodes to be used in high-temperature electrochemical cells.
In addition, they proposed that the high performance of thin-film-based oxide fuel cells’ oxygen electrodes could be realized through the nano-structuring of (Pr,Ce)O2-δ without any platinum.
Professor Jung said, “The electrode coating technology used in this study is of great technical value because of the utilization of affordable and mass-produced electrochemical deposition.” He added, “In the future, this technology will be feasible for replacing platinum electrodes in thin-film-based oxide fuel cells, and we expect that the affordable prices of this fuel cell will eventually boost market competitiveness.”
This research was described in Advanced Energy Materials in July and was featured as the Inside Front Cover and video abstract. It was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Korea Electric Power Corporation (KEPCO) Research Institute.
Figure 1. The change of electrode activity with and without overcoated (Pr,Ce)O2-δ nanostructures.
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Lifespan of Fuel Cells Maximized Using Small Amount of Metals
(Professor Jung (far right) and his team)
Fuel cells are key future energy technology that is emerging as eco-friendly and renewable energy sources. In particular, solid oxide fuel cells composed of ceramic materials gain increasing attention for their ability to directly convert various forms of fuel such as biomass, LNG, and LPG to electric energy.
KAIST researchers described a new technique to improve chemical stability of electrode materials which can extend the lifespan by employing a very little amount of metals.
The core factor that determines the performance of solid oxide fuel cells is the cathode at which the reduction reaction of oxygen occurs. Conventionally, oxides with perovskite structure (ABO3) are used in cathodes. However, despite the high performance of perovskite oxides at initial operation, the performance decreases with time, limiting their long-term use. In particular, the condition of high temperature oxidation state required for cathode operation leads to surface segregation phenomenon, in which second phases such as strontium oxide (SrOx) accumulate on the surface of oxides, resulting in decrease in electrode performance. The detailed mechanism of this phenomenon and a way to effectively inhibit it has not been suggested.
Using computational chemistry and experimental data, Professor WooChul Jung’s team at the Department of Materials Science and Engineering observed that local compressive states around the Sr atoms in a perovskite electrode lattice weakened the Sr-O bond strength, which in turn promote strontium segregation. The team identified local changes in strain distribution in perovskite oxide as the main cause of segregation on strontium surface. Based on these findings, the team doped different sizes of metals in oxides to control the extent of lattice strain in cathode material and effectively inhibited strontium segregation.
Professor Jung said, “This technology can be implemented by adding a small amount of metal atoms during material synthesis, without any additional process.” He continued, “I hope this technology will be useful in developing high-durable perovskite oxide electrode in the future.”
The study co-led by Professor Jung and Professor Jeong Woo Han at Department of Chemical Engineering, University of Seoul was featured as the cover of Energy and Environmental Science in the first issue of 2018.
(Figure1.Correlation between the extent of lattice strain in electrode, strontium segregation, and electrode reaction.)
(Figure 2. Cathode surface of solid oxide fuel cell stabilized using the developed technology)
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