As reported in a paper in the Journal of Power Sources, the fuel cell performance of the SOFCs with an optimized ALD YSZ surface treatment is close to that of SOFCs with porous Pt, which is known as the best performing catalyst in the low-temperature regime (250–450 °C).

Electrochemical impedance spectroscopy showed that the performance enhancement was due to improved electrode kinetics by the increase in charge transfer reaction sites between the surface of supporting silver and the ALD–YSZ particulates.

Fuel cell durability tests shows that the ALD YSZ surface treatment improves the long-term stability. X-ray photoelectron spectroscopy also confirms that the ALD YSZ capping prevents reduction of the surface silver oxide and destruction of the mesh morphology.

An SOFC has three major components: two porous electrodes (cathode and anode) separated by a solid oxygen ion (O^2–) conducting electrolyte. At the cathode, oxygen is reduced and the resulting O^2– ions are transported through the electrolyte lattice to the anode where they react with gaseous fuel, yielding heat, H₂O, and (in the case of hydrocarbon fuels) CO₂, and releasing electrons to the external circuit.

SOFCs are of great interest because of their efficiency and fuel flexibility. Proton exchange membrane fuel cells (PEMFCs) require hydrogen fueling, because they are based on proton conducting electrolytes. However, solid oxide fuel cells (SOFCs) can oxidize any fuel, because the electrolyte transports an oxygen ion.

However, conventional solid oxide fuel cells operate as high as 950 °C to run effectively. At this high temperature, the system can’t be easily turned on and off, performance degrades, and the balance of the system requires expensive, high-temperature alloys that drive up prices.

Lower temperature SOFCs thus offer a number of benefits, including lower cost and great reliability, as well as rapid startup with less energy consumption. This opens up an opportunity for portable and transportation applications with transient operation.

In June 2014, ARPA-E launched its Reliable Electricity Based on ELectrochemical Systems (REBELS) program, with a focus on low-cost Intermediate-Temperature Fuel Cells (ITFCs) emphasizing three technical approaches: the production of efficient, reliable ITFCs; the integration of ITFCs and electricity storage at the device level; and the use of ITFCs to convert methane or other gaseous hydrocarbons into liquid fuels using excess energy. (Earlier post.)

Resources

• You Kai Li, Hyung Jong Choi, Ho Keun Kim, Neoh Ke Chean, Manjin Kim, Junmo Koo, Heon Jae Jeong, Dong Young Jang, Joon Hyung Shim (2015) “Nanoporous silver cathodes surface-treated by atomic layer deposition of Y:ZrO₂ for high-performance low-temperature solid oxide fuel cells,” Journal of Power Sources, Volume 295, Pages 175-181 doi: 10.1016/j.jpowsour.2015.06.136