1. Hydrogen combustion engine: an essential vector in the energy transition

Hydrogen is now seen as one of the solutions to help reduce greenhouse gas emissions and transition to a low-carbon economy, in line with the objectives of the 2015 Paris Agreement. To be considered a sustainable solution and play its part in the energy transition, hydrogen must itself be decarbonized. It can be renewable, i.e. produced by electrolysis of water using electricity from renewable sources, or low-carbon, produced using electricity from nuclear sources. The term "low-carbon" also refers to hydrogen produced by thermochemical processes with CO ₂ capture: the "low-carbon" threshold today set by the European taxonomy regulation is 100 gCO ₂ · MJ ^–1 , or around 3 kgCO ₂ · kgH _2...