PEMFC and SOFC fuel cells - description and management of the system

PEMFC and SOFC fuel cells are the subject of two articles: system description and management [BE 8 595] and heat and mass transfer [BE 8 596] .

Fuel cells, the operating principle of which was first developed by Sir William Grove in 1839, remained laboratory devices for many years. At the turn of the 1960s, they became energy generators for space applications. Their interest in more domestic and everyday applications was subsequently reinforced by growing awareness of the greenhouse effect. All fuel cells operate at the reaction stage, with hydrogen as fuel and oxygen as oxidizer, to form water, but also to provide electrical and heat energy. So, a priori, they're a perfect source for combating the greenhouse effect. However, this idyllic picture is somewhat theoretical (not to say simplistic), since dihydrogen does not occur as a molecule in nature, and its production by electrolysis of water or reforming of hydrocarbons, as well as its packaging and transport, consume energy and emit greenhouse gases. The energy approach can therefore only be global. Nevertheless, the current energy efficiency of fuel cells suggests a global gain and development in the hydrogen sector. This is undoubtedly the way of the future, although we can't yet predict a date for mass production, as the most distant horizon concerns applications in personal transport. Other fields of application are likely to develop first. These include stand-alone sources of electrical energy, or even emergency power units, or stationary applications combining the use of heat and electrical energy (cogeneration). In these cases, control is based on heat energy, while electrical energy is used on site or fed back into the grid according to consumption needs.

Of all fuel cell types, this article focuses on PEMFC (proton exchange membrane fuel cell) and SOFC (solid oxide fuel cell) high-temperature fuel cells, both of which use solid electrolytes and are therefore good candidates for both stationary and transport applications. Today, while the vast majority of vehicle prototypes use PEMFCs to power the electric drive train, the fuel cell power supply differs from one manufacturer to another. APU ("auxiliary power unit") projects, for their part, favor SOFC fuel cells, as they are likely to run more easily on gasoline or diesel.

There are, of course, other types of fuel cell, which will not be discussed here. DMFC ("direct methanol fuel cell") fuel cells are similar in nature to PEMFC fuel cells, but are difficult to use due to the toxicity of methanol and their low power density. AFC ("alkaline fuel cell") batteries operate at low temperatures, around 65°C, but the electrolyte (potassium hydroxide KOH)...