Hydrogen in transport: a review of opportunities, challenges, and sustainability concerns.

This review provides a comprehensive and interdisciplinary assessment of the expanding role of hydrogen in enabling sustainable energy transitions within the transportation sector. Distinct from previous reviews, this study contributes original insights into advanced hydrogen storage technologies, integration across energy systems, and evolving policy frameworks. The review investigates the application of hydrogen in internal combustion engines, gas turbine propulsion, and fuel cell electric vehicles, with emphasis on recent progress in physical and chemical storage methods such as compressed gas, cryogenic liquid, metal hydrides, and sorbent based systems. It highlights innovations in material science and combined storage strategies that aim to improve safety, increase energy density, and reduce operational costs. Furthermore, the review explores the integration of hydrogen with renewable electricity and industrial systems, identifying its role in smart grid support, energy balancing, and flexible energy storage. The policy analysis highlights strategic national and international efforts that promote hydrogen deployment, including financial incentives, infrastructure development, and regulatory standards. The review also examines lifecycle assessment findings, comparing environmental impacts across hydrogen production routes and end use applications. Special attention is given to the role of alternative hydrogen carriers such as ammonia and liquid organic hydrogen compounds, which offer promising solutions for long distance transport and international trade. Finally, the study identifies current challenges related to technology standardization, safety regulations, and global market alignment, while outlining key research and innovation priorities essential to realizing a sustainable and inclusive hydrogen future for transportation.