U. Maryland and Redox Power partnering to commercialize low-temperature solid oxide fuel cells for distributed generation and transportation
|Redox Power’s 25 kW “Cube” sitting outside a conference room. Click to enlarge.|
University of Maryland researchers have partnered with Redox Power Systems LLC to commercialize low-temperature solid oxide fuel cell (LT-SOFC) technology for distributed generation—and ultimately transportation—applications at about one-tenth the cost and one-tenth the size of current commercial fuel cell systems.
The fuel cells, based upon patented technology developed by professor Eric Wachsman, director of the University of Maryland Energy Research Center (UMERC) in the A. James Clark School of Engineering, are the foundation of a system being commercialized by Redox that provides safe, efficient, reliable, uninterrupted power, on–site and optionally off the grid, at a price competitive with current energy sources.
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, Wachsman noted in a 2011 paper in Science exploring LT-SOFCs.
An SOFC has three major components: two porous electrodes (cathode and anode) separated by a solid oxygen ion (O2–) conducting electrolyte. At the cathode, oxygen is reduced and the resulting O2– 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.
Among the technologies available to convert hydrocarbon-based resources (which include not only fossil fuels but also, potentially, biomass and municipal solid waste) to electricity, SOFCs are unique in their potential efficiency. For stand-alone applications, SOFC chemical to electrical efficiency is 45 to 65%, based on the lower heating value (LHV) of the fuel, which is twice that of an internal combustion (IC) engine’s ability to convert chemical energy to mechanical work. In a combined cycle, there are numerous combined heat and power (CHP) applications using SOFC systems, which have the potential to achieve efficiencies of >85% LHV.
Unfortunately, government policy, the popular press, and many scientific publications have focused on fuel cells as part of a broader hydrogen economy, thereby relegating fuel cells to a “future energy” solution due to the need for a required overhaul of our current hydrocarbon-fueling infrastructure. Although this may be true for PEMFCs, SOFCs have the advantage of fuel flexibility that allows them to be used on our existing hydrocarbon fuel infrastructure while simultaneously providing efficiency gains (and corresponding CO2 emission reductions).—Wachsman and Lee (2011)
|University of Maryland Professor Eric Wachsman describes how solid oxide fuel cells work.|
The PowerSERG 2-80, also called “The Cube”, connects to a natural gas line and electrochemically converts methane to electricity. The initial breakthrough in the PowerSERG is in the fuel cells, which Wachsman has improved to produce more power at a lower temperature. More power means fewer cells to do the work of larger power generation systems, enabling the devices to be much smaller. Also, lower operating temperatures allow for the use of conventional materials in The Cube, driving costs down significantly.
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.
Wachsman decreased the operating temperature of solid oxide fuel cells to 650 °C, with future reductions projected to be as low as 300 degrees. At these lower temperatures, the system can turn on much more rapidly and operate with greater reliability, allowing The Cube to be built with conventional stainless steel parts rather than expensive alloys.
In addition to lowering the operating temperature, Wachsman and his students and colleagues over the course of 25 years developed fuel cells that generate ten times the power at these lower temperatures than anything else on the market, cutting the system’s cost by a factor of ten. Power density is > 2W/cm2.
As part of the optimization, Wachsman developed dual-layer electrolytes using new materials and significantly improved the anode so it can withstand cycling.
Over a 25-year time period, we have achieved major advances in both the composition of fuel cell materials and the micro and nanostructure of those materials. Putting these together has resulted in a cell that has an extremely high power density, on the order of two watts per square centimeter.—Eric Wachsman
The first-generation Cube runs off natural gas, but it can generate power from a variety of fuel sources, including propane, gasoline, biofuel and hydrogen.
|Redox Chief Technology Officer Bryan Blackburn presents the PowerSERG 2-80 “Cube”.|
Redox plans to release The Cube in 2014. The first version will be configured to 25 kilowatts, which can comfortably power a gas station, moderately sized grocery store or small shopping plaza. Additional power offerings will follow. Using different-sized fuel cell stacks, the company can offer The Cube at 5 kW, to provide always-on electricity for an average American home, or up to 80 kW in one system.
In the future, Redox plans to produce fuel cell systems for automobiles, which the company claims could triple gas mileage.
Eric D. Wachsman and Kang Taek Lee (2011) Lowering the Temperature of Solid Oxide Fuel Cells. Science Vol. 334 no. 6058 pp. 935-939 doi: 10.1126/science.1204090