Hydrogen in the Energy Transition: A System-Level Review of Production Pathways, Infrastructure, and Deployment Challenges

Hydrogen is increasingly recognized as a strategic energy carrier in global decarbonization pathways, particularly for hard-to-abate sectors such as steel production, chemicals, long-distance transport, and seasonal energy storage. However, its climate benefits depend strongly on the production pathway, infrastructure development, and system-level integration. To address this complexity, this review develops a systematic quantitative comparison framework that is applied consistently across major hydrogen production pathways. Each pathway is evaluated using five criteria: carbon intensity (kg CO2/kg H2), Technology Readiness Level (TRL, 1–10), process efficiency (% on an LHV basis), scalability potential, and compatibility with existing infrastructure. The resulting cross-pathway matrix enables evidence-based assessment of trade-offs rather than a purely sequential description of technologies. Four broad production categories are considered: fossil-based hydrogen, fossil-based hydrogen with carbon mitigation, nuclear-derived hydrogen, and renewable-based hydrogen. The review further examines the integration of hydrogen storage, transport, and end-use applications to identify key system constraints and infrastructure bottlenecks. Emerging approaches, including digital optimization and machine learning, are also discussed for enhancing the operation and control of hydrogen systems. The analysis indicates that while low-carbon hydrogen is essential for decarbonizing hard-to-abate sectors, its large-scale deployment remains constrained by technological, infrastructural, and investment-related challenges.