Fuel cells have generated so much talk lately that they have acquired an almost mythical status as a zero emissions energy source. In this newsletter, we will take a look at how these devices function and take some guesses as to what their potential might be in commercial vehicles.

A fuel cell is an electrochemical device in which the energy of a chemical reaction is converted into electricity. They do nothing more than produce electricity. If a vehicle is to be powered by a fuel cell, the fuel cell simply produces electricity and electric motors are used to drive the vehicle. The energy equation is that of a battery in reverse. Fuel cells are not new, having been invented by Sir William Grove in 1839. After that not a whole lot was done with fuel cells until NASA used them to provide some of the electrical requirements of their spacecraft in the 1960s.

Fuel cells are definitely not 'free' energy because they require hydrogen to function. This creates problems. Commercial hydrogen is usually produced electrolytically from water, a process that requires large amounts of electricity. Next, safe storage of highly explosive hydrogen on a vehicle is not easy. The option is to use fuel reforming to extract the hydrogen from HC fuels such as gasoline, natural gas or alcohols. The fuel cells themselves do not discharge like a battery: they will run so long as supplied with hydrogen fuel. The claim that fuel cells are zero emission energy producers is only true when the fuel provided is pure hydrogen. Most current fuel cells used in small vehicles require a hydrocarbon fuel such as gasoline as the hydrogen source, using a reforming process. Reforming is the separating of H2 from the HC fraction molecule in the gasoline or other HC fuel. When a fuel cell is fueled with reformed hydrogen, the results are not as environmentally friendly as some might claim because the carbon biproduct of the process has to be considered.

How a Fuel Cell works

A fuel cell functions on the principle of the thermodynamic reversibility of the electrolysis of water. For many years we have produced hydrogen and oxygen by the electrolysis of water, yes as we have mentioned before, it does take lots of electricity. When supplying hydrogen and oxygen to the two electrodes of an electrolytic cell a potential difference is created and electric current begins to flow. Join several cells together and you create a multi-cell, fuel cell. The electrochemical reaction looks like this:
2H₂ + 0₂ produces 2H₂0 + electricity

Types of Fuel Cell

There are a number of different types of fuel cell each distinguished by the electrolyte material used. We'll take a look at one that is currently being tested in city buses, and may perhaps have a future as a short range, small truck powerplant. Proton exchange membrane (PEM) fuel cells have created some excitement in the automotive industry because they are the most viable mobile fuel cell technology. The PEM fuel cell has been used a primary power source in some vehicles and Freightliner chose this technology for their optional APU unit. A PEM fuel cell uses solid polymer membrane (a thin plastic film) as the electrolyte. If the fuel cell can be supplied with pure hydrogen (as opposed to reforming it from a fossil fuel) then the only emissions that have to be considered are those used to produce the pure hydrogen. The Ballard fuel cell being used to power city buses uses a PEM principle.

Ballard power systems have led the way in developing fuel cells for automotive use and have partnership liaisons with several OEMs. The Ballard Mark 900 fuel cell is being used in trial applications in city buses in Chicago, Vancouver and Palm Springs. More recently, Ballard have agreed to supply fuel cells to Daimler-Chrysler for European trials in a number of cities including Paris, Barcelona, Reykjavik and Hamburg beginning in 2005. These types of research and development trials are laying the groundwork for the fuel cell to become a viable technology within 10 years or so. However, its use may be confined to city buses. Don't hold your breath waiting for the day we see fuel cells in a linehaul transport truck!