# Systematic Analysis of the Hydrogen Value Chain from Production to Utilization
## 7 Conclusions  
Based on this review of the current main hydrogen production technologies, it is concluded that electrolysis, powered by renewable energy resources, is the most interesting and promising approach to produce green hydrogen at a large scale. At the moment, gray hydrogen still presents lower production costs than any other type of hydrogen. To ensure a progressive transition from gray to green hydrogen while balancing the economic and environmental dimensions, technologies, like SMR-CCS and methane pyrolysis, that have lower emissions than conventional fossil fuel thermochemical processes and that are cheaper than green hydrogen processes, can be considered as bridging technologies. The low volumetric density presented by hydrogen, in comparison to natural gas, oil, and coal, makes the hydrogen storage process much more complex than the storage of other energy carriers. For this reason, it is not possible to highlight a single option to store hydrogen. Depending on the amount of hydrogen to be stored, the projected end-use of the energy carrier, and the storage period, different technologies can be recommended as the most suitable. When considering hydrogen transportation and distribution, there are three main options to transport and distribute hydrogen: by road, by pipeline, or by ship. The three cannot be seen as competitors, but rather as complementary, since depending on the distance to be covered and the amount of hydrogen, the most suitable option will be different. Currently, hydrogen value chains are mostly designed based on the use of fossil fuels as feedstock and green hydrogen projects are mainly experimental and laboratory-scale. To overcome the current challenges to the implementation of a green hydrogen economy, future efforts should focus on improving the efficiency and cost-effectiveness of production, storage, and transport technologies, while also scaling up industrial applications. Further investment in electrolyzers is needed to enhance efficiency, increase durability, and reduce production costs. In parallel, continued research into hydrogen storage and transportation is essential to address material integrity and safety concerns [72]. This must be supportedby long-term policy frameworks, investor confidence, stakeholder collaboration, and public education to enhance acceptance and foster partnerships. Conceptualization M.S.C. ; Investigation, M.S.C. ; Writing--Original Draft Preparation, M.S.C. ; Writing--Review and Editing, G.G., E.S., P.J.C. and A.F.F. ; Visualization, M.S.C. ; Supervision, P.J.C. and A.F.F. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The authors acknowledge Fundacao para a Ciencia e a Tecnologia (FCT) for its financial support via the project LAETA Base Funding (DOI: 10.54499/UIDB/50022/2020). The authors acknowledge IRENA [82] as the source and copyright holder from which Figure 14 was adapted. Figure 3 is adapted from Progress in Energy and Combustion Science, Volume 90, [PERSON] and [PERSON], \"Green, Turquoise, Blue, or Grey? Environmentally Friendly Hydrogen Production in Transforming Energy Systems,\" p. 100996, (c) 2022, with permission from Elsevier. Figures 4-6 are adapted from Process Safety and Environmental Protection, [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON], \"A critical review of the hydrogen production from biomass-based feedstocks: Challenge, solution, and future prospect, solutions, and future prospect\", p. 384-407, (c) 2022, with permission from Elsevier. HyLab's authors acknowledge the Base Funding Project of Collaborative Laboratory, managed by ANI--Agencia Nacional de Inovacao and funded by the call RE-C05-i02--Missao Interface N.\" 01/C05-i02/2022 of the Portuguese Recovery and Resilience Plan (PRR), and the Agenda H2 Green Valley (reference02/C05-i01.02/2022.PC645551860-0000064) project, managed by IAPMEI and funded by the call Aviso Convire n.\" 02/C05-i01/2022 of the Portuguese Recovery and Resilience Plan.