SOFC cathode preparation process. (Credit: University of the Basque Country)Scientists at the University of the Basque Country (UPV/EHU) have studied the effects of using lanthanum-based perovskite ceramic contact materials in solid oxide fuel cells (SOFCs).
Unlike in other fuel cells, the ion conducting electrolyte of SOFCs is solid, which offers various advantages. “The materials are relatively inexpensive, their sensitivity to impurities in the fuel is low and they are highly efficient and powerful. What is more, as the components are solid, their configuration is much more versatile as they can be manipulated,” explained Dr. Karmele Vidal, researcher in the UPV/EHU’s IMaCris/MaKrisI group. On the downside, however, the researcher highlights that “very expensive materials are used because the cells operate at high temperatures.”
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“Many pieces of research indicate that the improvement in the contact between the interconnector and the cathode is one of the significant challenges in the production of SOFCs,” Vidal pointed out. Thus, it is necessary to use new materials that will improve bonding between these components without reducing the cell’s capacity. The materials used as a contact layer between the interconnector and the cathode must have high electronic conductivity, good chemical and structural stability at the operating temperature (the cells operate at 600-800 ºC).
In order to meet all these requirements, the UPV/EHU’s research group has opted for perovskite type materials. The name comes from a relatively rare mineral in the earth’s crust, but it has been extended to a more general group of crystals that have this same structure.
In their research, they have been working with perovskites to design certain components in the parts of the fuel cell, like the cathode and the contact layer. “We saw that perovskite type materials are good electron and ion conductors; so they are suitable for the design of the contact layer and cathode, respectively,” said Vidal.
As important as the type of material used to manufacture fuel cell components is the way it is synthesized. “The priming temperature and time taken are, among other things, variables that affect the material’s microstructure, which is crucial as far as its properties are concerned,” explained the researcher. Among the synthesis methods studied, the means for priming the perovskites that has offered them the best results is combustion. Basically, this consists of a reaction between nitrates as the oxidant and glycine as the fuel. This causes self-combustion, the flame reaches a high temperature and the formation of the necessary material takes place.
Right now, there are prototypes and one or two commercial products based on these fuel cells, but the main problem they face is that, according to Dr. Karmele Vidal, they are not very cost-effective yet. As they are devices for supplying power thought up for equipment that required requiring high power levels, Vidal takes the view that they offer a way of decentralizing the dependence that currently exists on the electricity grid, apart from offering a means for producing electrical power that is not dependent on oil. “Quite honestly,” she concludes, “I believe that this technology will come into its own when the current system becomes more expensive owing to the increase in crude oil prices.”
Morán-Ruiz, A., Vidal, K., Laguna-Bercero, M., Larrañaga, A., & Arriortua, M. (2014). Effects of using (La0.8Sr0.2)0.95Fe0.6Mn0.3Co0.1O3 (LSFMC), LaNi0.6Fe0.4O3−δ (LNF) and LaNi0.6Co0.4O3−δ (LNC) as contact materials on solid oxide fuel cells Journal of Power Sources, 248, 1067-1076 DOI: 10.1016/j.jpowsour.2013.10.031
