Discovered in 1839 by Sir William Grove, the fuel cell is an electrochemical device that directly converts the heat of combustion of a fuel into electricity, without being limited by Carnot's principle, thus enabling high conversion efficiencies. What's more, during conversion, the fuel is electrochemically oxidized at the anode and the oxidant (oxygen from the air) is reduced at the cathode, so that the only product released is water, giving fuel cells an attractive ecological credential. However, after more than 150 years of research, large-scale commercialization of fuel cells is constantly being postponed, as we show in the lecture, for reasons of cost and unresolved technological hurdles.
Over and above the thermodynamic and kinetic aspects that govern its operation, we review the various fuel cell technologies, of which there are 6, which differ either in the chemical nature of the electrolyte, the operating temperature, or in the power generated and therefore the applications targeted, covering an installed power range from W (electronics), to kW (electric vehicle) and MW (stationary storage for network applications, hospitals). This brief overview shows the current interest in (i) low-temperature systems with proton exchange membranes, known as PEMFCs, and (ii) high-temperature systems, known as SOFCs ( Solid Oxide Fuel Cells). The major advantage of the latter is its ability to co-generate electricity and heat, so that its overall efficiency can reach 70-80%, as well as the possibility of using, in addition toH2, various other fuels such as natural gas, methanol or biogas. On the other hand, its weakness lies in the instability of the materials used, leading to premature ageing and inadequate performance despite high cost. The low-temperature PEFMC system, highly sought-after for electric vehicle applications, on the other hand, benefits from rapid start-up and good fast-power behavior, but suffers from numerous problems such as (i) the need to use expensive catalysts (Pt), (ii) CO poisoning, which requires an extremely pure fuel (H2), (iii) the absence of co-generation or (iv) membrane drying. To minimize the drawbacks of PEMFC and SOFC technologies, while retaining their advantages, current research is focusing on intermediate PCFC-type systems using a ceramic membrane like SOFCs, but protonic like PEMFCs that can operate at 180°C, or ITSOFC-type cells with lower operating temperatures (around 200°C) than SOFCs. The fact remains, however, that all these new directions, together with that of direct methanol fuel cells (DMFCs), continue to pose colossal problems for materials (electrodes, electrolytes, interconnectors) in terms of both performance and cost.
In view of this complexity, we may conclude that fuel cells are still in the R&D phase, and that 10 to 15 years are still needed before commercialization and market penetration, or that fuel cells, which have been a technology of the future for over 150 years, will remain so for several decades yet, leaving it to the audience to choose one or other of these two formulas in the light of the lecture.
