The demand

The beginning of this 21st century is marked by a demand for more mobile and flexible energy sources. Professional (electrical equipment power sources), structural (due to lack of infrastructure) and leisure needs have less lot such a demand. An independent energy source, free of networks, is wanted by all of us no matter what environment or professional activity we find ourselves in. Until today this energy independence for high power needs was provided by thermal generators and for low power deeds by classical and rechargeable batteries.

The Fuel Cells Solution

Fuel cells are the ideal candidates for replacing these types of energy sources regardless of the type of application considered. The advantages of PEMFC technology vary according to the power range considered :

High Power : Above 1 kilowatt
The main advantage of fuel cells is the fact that they work silently and also that there are no pollution, no greenhouse effect gases. However, even in this type of energy source is very competitive when it comes to its performances or to its size (weight and volume) it is severely hindered by its price when compared to its thermal competitors. This handicap should be overcome in the near future thanks to the use of fuel cells in some very specific applications such as satellite launcher, submarines, fleets of public or private transport vehicles or the electrical supply for isolated buildings. These first applications mean that not only will a preliminary phase of maintenance of fuel cells be put in place but also that the mass production manufacturing processes will be perfected. Also, a significant decrease in the price difference between fuel cells and generators should be seen in the next 10 years due to the important research and development work that is being carried out by the PEMFC manufacturers that are more and more numerous on the market today. Theses manufacturers generally come from mechanical industries or from thermal and hydraulic system management backgrounds and specialise in the assembly of the fuel cell components and their integration in the energy source.

Low Power : From a few watts to a few hundreds of watts
Fuel cells are already very competitive when considering both their price and their performances. One of the main advantages of the fuel cell energy sources is to be able to increase the range and the power according to you needs. Fuel cells are also very interesting, especially for portable applications, as they provide a way of separating the part that is the electrical power and the part that is the stocked energy. A PEMFC trasnform chemical energy into electrical energy, the size and form of the fuel cell will depend on the voltage or on the power needed for a certain application. However the energy required is kept in a reservoir outside the fuel cell, just like an automobile where the motorprovides the power to the wheels while the energy is provided by the fuel in the tank. The lifetime of a polymer electrolyte membrane fuel cell (PEMFC) is a least equal to the lifetime of the portable applications considered for these energy sources and the PEMFCs could be integrated into these appliances during manufacturing assembly or production stages. From then on, these appliances only need a fuel replacement or refill to keep working. This technology thus offers the advantage for the end-user to invest in the power part of the energy source when buying the electric appliance and to refill the fuel tank only when there is a need "to charge the portable appliance".

How a fuel cell works

Principle of fuel cell

A fuel cell is made up of 2 electrodes (one positive and one negative) separated by an ionic-conducting electrolyte (and electrical insulator). Contrary to a battery where both the energy and power is contained in the electrodes, the principle of a fuel cell is to have the reaction catalysts only in the electrodes and to generate electricity when the fuel cell is supplied with an oxidant and a fuel (reducer) from an outside reservoir. The oxidant is generally oxygen from the surrounding air while the fuel is stocked, as a gas, solid or liquid depending on the application.

Advantages and drawbacks

The advantages of fuel cells follow from the fact the energy is directly (and only) linked to the size of the fuel reservoir, while the power depends on the dimensions of the cell (which are adjustable). The only product of the global fuel cell reaction is water which is evacuated in the surrounding atmosphere in vapour form.

The main disadvantages of fuel cells include the very high cost of the components and the every low working cell voltage (less than 1 volt) which leads to various technological problems. This limiting low voltage impose a stacking up of many elements until a satisfactory electrical power level is achieved. This configuration called "filter-press" complicates the distribution of the reactants from element to element and requires the use of bipolar separating plates, which are very expensive due to their geometries and the restrictions on the materials that can be used, they need to be high electrical conductors, gas-tight and chemically resistant (hydrogen, oxygen, water).

The complexity of these systems is acceptable for high power systems that also require hydraulic, thermal and electrical management. However this "filter-press" architecture is very disadvantageous for energy sources for portable applications, which should be small, light and easily integrated into the final appliance.

PaxiTech............in the beginning

The company PaxiTech came from research and development performed in a laboratory at the CEA-Grenoble working on fuel cell components (membrane electrode assemblies) and on a specific type of fuel cell. These particular energy sources are result of architectural evolutions of low temperature fuel cells, they use very simple technology and are very easily adaptable to portable applications. Their good electrical performances and high working voltages as well as the nature of the constituent components make them unique on the fuel cell market today. They are designed for the market of energy sources for portable electric equipment that have "low power" needs, for example the portable multimedia sector and cordless tools.