Hybrid hydrogen–e-fuels systems for decarbonizing heavy transport

Heavy transport sectors such as aviation, maritime shipping, and long-haul trucking are still among the most challenging industries to decarbonize owing to high energy demands, long operational ranges, and limited fueling infrastructure for low-carbon alternatives. Although green hydrogen and synthetic e-fuels show strong potential as next-generation clean energy carriers, each still encounters notable technological, economic, and logistical limitations when deployed individually. This review examines the rapidly evolving concept of hybrid hydrogen–e-fuel systems, in which hydrogen is combined with synthetic fuels such as e-methanol, e-diesel, and e-kerosene to improve combustion efficiency, reduce carbon intensity, and overcome storage and energy-density limitations. A comprehensive analysis of production pathways, including electrolysis-based hydrogen generation, carbon capture for e-fuel synthesis, and Power-to-Liquid (PtL) workflows, is provided. The review further evaluates hybrid combustion strategies in dual-fuel engines, highlighting advancements in hydrogen-assisted ignition, flame stability, and emissions reduction. Sector-specific applications for aviation, maritime, rail, and heavy-duty road transport are assessed through techno-economic and life-cycle frameworks, with an emphasis on infrastructure readiness, fuel costs, and scalability potential. Some vital constraints, such as hydrogen storage safety, material compatibility, energy penalties in Power-to-X (PtX) conversion, and regulatory uncertainties, are critically discussed. Finally, emerging opportunities in catalyst engineering, AI-driven system optimization, and integrated renewable fuel networks are identified as pathways toward achieving large-scale deployment. This review consolidates existing knowledge and outlines a forward-looking research agenda to support the transition toward carbon-neutral heavy transport through hybrid hydrogen–e-fuel technologies.