## 1 Introduction
Moreover, years of dedicated research and innovation have placed the EU at the forefront of global hydrogen technology, spanning the entire value chain from production to storage, distribution, and a multitude of final uses across all economic sectors [8]. Therefore, the EU's focus on renewable hydrogen--produced via electrolysis powered by renewable sources--has positioned it at the forefront of global hydrogen technology, covering the entire value chain from production to end-use applications [9]. Molten salts (MSs), known for their high thermal stability and heat transfer ability, can effectively store thermal energy from renewable sources, such as CSP. This capability facilitates the wholly renewable production of hydrogen, as well as other fuels, by harnessing solar energy efficiently. Moreover, MSs can store excess renewable energy generation, allowing for the decoupling of solar energy collection from the production of renewable gases, using that energy on-demand to drive thermochemical reactions for gas production outside of sunlight hours. Therefore, the exploration of MS technology for the supply of thermal energy to thermochemical processes presents a novel and potentially transformative approach for the production of renewable hydrogen and syngas, promising to align with the EU's strategic initiatives to advance clean energy technologies and reduce greenhouse gas emissions. The primary aim of this work is to provide a comprehensive overview of three critical areas: (1) the use of MS mixtures as heat transfer fluids and storage media, including their feasible operational conditions and thermophysical properties; (2) hydrogen production processes; and (3) syngas production processes that can be integrated with MS technology. This research was conducted as part of a Joint Research Activity in the SALTOpower project, which aims to advance excellence in research by further exploiting MS technologies. The research activities specifically focus on the development of a flexible interconnection between power and gas energy distribution systems, aiming to facilitate the generation of power and/or gas using medium-to-high-temperature renewable heat sources. The insights derived from this study are intended to contribute significantly to the development of scalable and sustainable energy systems to align with the EU's long-term goals for energy security and environmental sustainability. Regarding the methodology adopted for the collection of contributions, priority was given to articles providing data useful for the practical application of molten salts. Drawing on the consolidated experience of the authors on the topics addressed, both related publications produced by the authors themselves and those considered most significant with respect to the subjects discussed were included. In cases where the topic did not fall within the direct experience of the authors, the selection of articles to be cited was carried out mainly using the Scopus platform, giving preference to contributions most relevant to the applications considered. This manuscript is organized as follows: in Section 2, the main applications for MSs are outlined, along with the most used types and their thermophysical properties. Additionally, the advantages and disadvantages of using MSs both as heat transfer fluid and as a storage medium are discussed. Section 3 details the three main types of thermo-electrochemical cycles used for hydrogen production, showcasing the system configurations and operational conditions. Section 4 provides a comprehensive description of the various layouts and processes involved in the production of syngas, detailing the specific conditions under which these processes are conducted. Section 5 presents brief assessments of the feasibility of MS-driven processes for gas production, with a focus on heat supply considerations. Finally, Section 6 presents the conclusions, further work, and future research directions.