In order to fight climate change, the EU is providing funds for knowledge development on water electrolysis technologies. Numerous projects have been funded so far, and an EU wide water electrolysis network has been formed, however, from an RTOs perspective, there is no overview of knowledge development and knowledge diffusion regarding the European Green hydrogen technological innovation system. In this thesis, we have used the CORDIS database to develop a social network model of all the water electrolysis projects funded by the EU, alongside we performed interviews with central European RTOs and reviewed project reports to analyze knowledge development and diffusion. We have summarized the key areas for knowledge development in PEM, SOE and Alkaline networks and we have also found certain issues related to knowledge development and diffusion within the green hydrogen network. Given these issues, we finally proposed recommendation for RTOs and the EU in order to improve knowledge development and diffusion.