The Green Hydrogen Production by Water Electrolysis

Hydrogen is considered a major asset in the energy transition. In terms of energy, it has a lower calorific value (LCV) almost three times higher than that of gasoline and can store large amounts of energy over long periods of time. It can therefore be used for a variety of purposes, such as industrial processes, heat production, or energy applications, both mobile and stationary, using fuel cells or direct combustion.

Hydrogen therefore appears to be a very good alternative to fossil fuels. However, before it can be used, it must be produced sustainably, i.e. using green processes and, above all, at a "reasonable" cost, i.e. competitive with the current fossil fuel market. This technical and economic issue inherent in the production and use of hydrogen is at the heart of the French Hydrogen Recovery Plan and is an integral part of the Priority Research Program and Equipment (PEPR-H2) for carbon-free hydrogen scheduled for the decade 2020-2030.

Despite all this, hydrogen production is still, for economic reasons, mainly derived from the steam reforming of fossil fuels, which leads to the production of 10 kg of carbon dioxide for every 1 kg of hydrogen produced. This steam reforming technique, although the most cost-effective, produces gray hydrogen, which at best can become blue after decarbonization. An alternative must therefore be found to produce green hydrogen at a cost that is competitive with gray hydrogen, and among the possible technologies, electrolysis appears to be a promising alternative. This technique is very interesting in that its carbon footprint is zero when the electricity fed into the electrolyzer is carbon-free. Various electrolyzer technologies, differing in their electrolyte and operating temperature, are available at various Technology Readiness Levels (TRL). However, further progress in fundamental research is still needed to better understand the potential of this technique and to consider its development for mass production.

This article presents the various low-temperature electrolysis techniques (alkaline and proton exchange membrane (PEM)) and high-temperature (HT) techniques. Their performance and operating conditions are compared within a system approach, and the technical and economic barriers are then highlighted.