Electrolytic Production of Hydrogen

With a few anecdotal exceptions, dihydrogen gas, commonly known as hydrogen, does not exist in its natural state. It must therefore be prepared in a variety of ways. Among these methods, electrolytic preparation is a particular way of converting electricity. Hydrogen produced in this way requires temporary storage, the technology of which depends on its subsequent use.

Hydrogen is an energy carrier, but not a natural fuel, insofar as its production requires the use of energy whose origin must be taken into account. While the combustion of hydrogen does not release any pollutants, the necessary energy still needs to be produced cleanly. Electrochemical reactions also involve the conversion of electrical energy into chemical energy (in the case of electrolysis) or vice versa (in the case of discharging cells and batteries). In theory, these conversions can achieve 100% efficiency. In practice, these efficiencies are of course limited by the existence of various losses involving the formation of heat, but the situation is far more favorable than in the case where the energy to be converted consists solely of heat. In the latter case, the second principle of thermodynamics imposes a maximum efficiency that depends on the difference between a high and a low temperature (Carnot's principle). Under these conditions, it is theoretically impossible to achieve 100% efficiency, as this would imply an infinite temperature. Electrochemical conversions are therefore promising because they offer the prospect of improving yields by implementing new technological advances.

If we consider a complete chain comprising several conversions of energy into different forms, resource conservation naturally means maximizing the product of the efficiencies of the various successive conversions. For example, in the case of transport, we could imagine electricity production in a thermal power plant (or even better, a photovoltaic or wind power plant), followed by storage of the electrical energy in chemical form (hydrogen obtained by electrolysis of water), then conversion of the chemical energy into electrical energy (fuel cells), then mechanical energy (electric motor). This type of chain allows for maximum resource conservation by maximizing conversion efficiency. If, on the other hand, we replace the last two stages in this same chain with a hydrogen-powered internal combustion engine, we once again come up against Carnot's limitation, derogating from the principle of saving resources. It should be noted that the chain can stop at the point of energy restitution, in the case of stationary applications designed to supply homes with electricity and heat on an almost autonomous basis. In addition to these considerations, electrochemical conversions have the added advantage of very often limiting...