Reformed Fuel Cells (Indirect Fuel Cells)

Reformed fuel cells are hybrid systems in which a hydrocarbon fuel is first reformed or processed to remove hydrogen, which is then injected into the fuel cell. This is in contrast to direct fuel cells where the hydrocarbon fuel is injected directly in to the fuel cell.

Function and Reactions of Reformed Fuel Cells

RFCs work much the same as other fuel cells, except that hydrogen is produce in a separate location, called a reformer, and then injected into the fuel cell. At the anode, the hydrogen is broken down into a proton and an electron, which are then reformed at the cathode to produce water. It is useful to think of these as direct fuel cells in which the steps of reforming and electricity generation have been separated out. The apparatus involved in creating hydrogen from hydrocarbons is called the fuel processing system or FPS.

Another way to view RFCs is as regular hydrogen fuel cells that simply receive hydrogen through the reformation of a hydrocarbon (usually methanol or ethanol) directly on site rather than from pure hydrogen stored separately. Hydrogen is created on demand by these systems and then fed into the fuel cell.

While any hydrocarbon can be reformed to produce hydrogen, methanol and ethanol are most commonly used. These fuels provide better hydrogen to carbon ratios than other hydrocarbons, providing more energy for the same amount of carbon dioxide released.

Benefits of Reformed Fuel Cells

Compared to hydrogen fuel cells, RFCs benefit from the easy transport of fossil fuels and the fact that an infrastructure is in place, particularly for ethanol. These systems have neither the danger nor the expense of transporting hydrogen in its pure form.

Compared to direct fuel cells, there are several advantages. First, the fuel cell component of an RFC is more efficient. They do not have problems with catalyst poisoning as direct fuel cells do because only hydrogen is being injected with no source of carbon. Also, because water is not being injected into the fuel cell with the hydrocarbon, they do not require an active water management system, which makes them more efficient than direct fuel cells.

Second, RFCs can operate better at lower temperatures than direct fuel cells because the reforming process is separately controlled. Because methanol is still liquid at very cold temps (near -100 C), fuel cells that run on it are also excellent for cold weather applications.

Drawbacks of Reformed Fuel Cells

Due to the extra components, RFCs are more complex and more difficult to maintain. They are also less reliable than direct fuel cells.

RFCs require higher operating temperatures than direct fuel cells, which may seem contradictory to the previous statement that they are more efficient at lower temperatures. The disparity arises from the fact that higher temperatures must be generated in the reformer to produce hydrogen, but the fuel cell itself can run at a much lower temperature. Thus, the fuel cell is more efficient, even though the reformer is less efficient. The net outcome is better efficiency overall.

RFCs require active and advanced heat management systems. Often, the heat generated by the reformer can be harnessed to do additional work, which can greatly improve the efficiency of these fuel cells.