SOFC Technology
What is a solid oxide fuel cell (SOFC)?
A solid oxide fuel cell is an electrochemical conversion device that produces electricity directly from fuel. In an SOFC, the electrolyte is a ceramic material, and the cells operate at temperatures from 650 to 1,000°C. System design ensures that the user sees only cool surfaces, just like on a home toaster.
In a solid oxide fuel cell, the oxygen ions cross the electrolyte, unlike in a PEM stack where the hydrogen ions cross the membrane. This expands the list of possible fuels beyond pure hydrogen. SOFCs operate well on hydrogen and mixtures of hydrogen and carbon monoxide, among other fuels. With a very simple, small and efficient reformer integrated into our systems, we are able to produce mixtures of hydrogen and carbon monoxide from common fuels, including:
- Propane
- Gasoline
- Diesel fuel
- Kerosene (or JP-8 military fuel)
- Ethanol and other biofuels
- Hydrogen
The ability to operate on commonly available fuels such as these simplifies the introduction of SOFCs. For different applications, the system can be optimized to operate on the optimal fuels for that application. For example, in truck auxiliary power applications, diesel fuel which is already on-board can be used, while many recreational vehicles have diesel fuel or propane available.
SOFC Systems
Protonex is developing solid oxide fuel cell portable power sources. These systems rely on a very tightly integrated hot zone, incorporating all of the elements in the system that operated at elevated temperatures. This tight integration serves several purposes:
- Compact system for portability
- Minimizes insulation requirements, but still keeps the case cool to the touch
Protonex’ SOFC systems are based on tubular fuel cells. While SOFCs can use planar or tubular cells, tubular cells have several advantages for portable systems. The most important feature is that tubular cells are inherently stronger and more robust than most planar approaches. The tubular cells, when properly integrated into a bundle and hot zone, tolerate mechanical stresses well, a critical feature for portable systems. In addition, the tubular cells are tolerant of thermal stresses, supporting rapid startup of the systems.
Portable SOFCs can be used in applications where small generators or large batteries are currently used. Typical applications range from 100 to 1,000 watts. Relative to batteries, SOFCs and their fuel have much higher energy density than batteries, so for the same volume, the SOFC will run much longer than batteries. The SOFCs also have significantly higher efficiencies than most generators, leading to lower fuel consumption, lower emissions and longer operation on a given size fuel tank.