Ultrasound-induced cavitation and dispersed photocatalysts synergistically decompose water into hydrogen, offering higher efficiency. Reasons and future research avenues are explored.

Hydrogen is in the spotlight in the energy world, and it will remain so. In Europe, the necessity to integrate ever-growing amounts of Renewable Energy Sources (RES) in order to implement the ambitious European decarbonization policy (package Fit-for-55) and to preserve the security of energy supply (package Repower-EU) are feeding the interest in hydrogen. This paper will provide a thorough analysis of prospects and criticalities for the development of hydrogen both as a carrier and as a feedstock and, definitively, as a key element for the implementation of the European decarbonization policies. First, the present regulatory framework will be highlighted, taking the European Union as a main reference, since it presently has one of the most advanced hydrogen legislations in the world. Then, both hydrogen offer (technologies) and demand (both as a feedstock and as an energy carrier) will be dealt with in detail. Two additional sections will take care to illustrate, respectively, the interactions between hydrogen and the electricity grid and the issues related to the creation of a liquid hydrogen market. Finally, a conclusion section will wrap up and summarize the most urgent issues to be tackled to create a well-functioning hydrogen economy.