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Tüzelő or szerelem?

Recently there has been some confusion concerning the correct translation of "fuel cell" into Hungarian. Many are using the word "üzemanyagcella". This refers to the power source of vehicles, and it is not justified to use it in a broader sense. The official Hungarian chemical name is tüzelőanyag-elem, which just as well expresses the other, e.g., industrial applications. Earlier, the word "tüzelőszer-elem" was used, which allows interesting associations, especially when written as one word as "tüzelőszerelem", where the word "szerelem" (i.e., love) can be recognized.

How does it work?

Fuel cells, just like alkaline batteries, directly produce electric energy during chemical reactions. The major difference is that batteries become unusable when they have run out, whereas fuel cells operate while they are filled with fuel.

Fuel cells usually consist of two electrodes (the anode and the cathode) and the electrolyte between them. During the process, the hydrogen molecules are split into protons and electrons with the help of a catalyst (usually platinum). The protons go through the electrolyte, while the electrons are utilized in the form of electric current. The electrons that arrive at the cathode combine with the protons and the oxygen to form water.

An important benefit of fuel cells in comparison with inner combustion engines is the fact that while the efficiency of fuel cells is not limited by theoretical thermodynamic bounds, the efficiency of inner combustion engines is limited by the thermodynamic bounds defined by the Carnot cycle.

Porous electrodes

The porous electrode

Which was the technology that was able to multiply the power of the Grove cell and made it an energy source that can be used in today’s practice? The answer is of course complex, however, one of the major power-boosters was the application of porous electrodes. The electro-chemical reaction takes place on the boundary of two phases. This means that the surface of the electrode and the rate of the reaction determine the amount of material that reacts in unit time and the power of the cell. Catalysts enhance the efficiency by decreasing the activation energy of the reaction, while porous electrodes enhance the active surface by several orders of magnitude. Such electrodes are like sponge, they have plenty of inner cavities, and so an enormous active surface, where the oxidation of hydrogen and the reduction of oxygen can take place. There is electron flow in the sponge matrix, and ion flow in the electrolyte phase. On the boundary of the two phases the electro-chemical reaction takes place, while the charge neutrality is macroscopically preserved.

The types of fuel cells

Several types of fuel cells have been developed, which can all be classified into the two broad categories of fuel cells operating at room temperature and fuel cells operating at high temperature. The previous ones can better tolerate switching them on and off successively, which is advantageous in cars, while the latter ones can be better utilized during continuous operation, e.g., in power plants. Concerning the type of fuel, the quality of the electrolyte and other components, and the structure of the cell, several different types of fuel cells are in use. Fuel cells are mostly categorized on the base of their three main properties: operational temperature, type of fuel, type of electrolyte.

The most popular fuel cell types, their temperatures of operation and efficiencies

Regenerative fuel cells

A Regenerative Fuel Cell (RFC) is a fuel cell system which can operate continuously due to closed feedback mechanisms. Many hope that such systems will form the fundaments of hydrogen economy based on renewable energy sources. Fuel cells that are able to produce energy, heat and water from oxygen and hydrogen are widely applicable. The most obvious way of producing hydrogen and oxygen is the dissociation of water with the help of renewable energy sources (wind, solar and geothermal energy). Such a system does not require special fuel cells, however, its operation demands an infrastructure that would convey the hydrogen to the place where it is used.

Summary

Why fuel cells?

Why not fuel cells?