The active role of green hydrogen in shifting to a sustainable energy regime worldwide is driven by the need to reduce climate impact and address the energy crisis, given the low-carbon and non-toxic nature of renewable energy sources. In this review, recent progress in production technologies made over the past five years (2020–2025) is critically assessed, and the efficiency and scalability of two-step thermochemical electrolysis are compared with new algal bio-hydrogen systems. In contrast to common introductions, this study identifies specific research gaps in addressing the low energy density and safety limitations of existing storage systems, including metal-organic frameworks (MOFs) and nanostructured metal hydrides, where there should be a direct association between the technical drawbacks of these systems and their economic consequences. Moreover, this study summarizes new findings on the economic viability of hydrogen-based fuels and infrastructure constraints that are not sufficiently developed for large-scale use. Finally, this study provides a roadmap for future research on improving catalyst stability and cost-reduction models to facilitate the safe and widespread adoption of a green hydrogen economy.
Farooq et al. (2026) studied this question.