The future of clean transportation: Hydrogen, batteries, ammonia, and green methane in perspective

Amid growing efforts to decarbonize the transport sector, this review examines portable energy solutions for clean mobility, focusing on hydrogen, batteries, ammonia, green methane, methanol, biodiesel, and sustainable aviation fuel (SAF). We discuss the fundamentals, production routes, storage requirements, and application feasibility of each carrier, alongside recent advancements and persisting challenges. Ammonia, while valued for its favorable storage and carbon-free combustion, faces constraints such as toxicity, indirect carbon emissions, and ammonia slip, though emerging approaches like direct air capture offer promising mitigation pathways. Green methane, ethanol, biodiesel, and SAF are identified as complementary fuels suited for sector-specific deployment, whereas batteries and hydrogen show long-term promise. Cradle-to-Grave emission analyses indicate that battery technologies deliver the lowest overall greenhouse gas footprint among the cleaner energy options, while hydrogen and methanol–gasoline blends also demonstrate notably competitive performance. Cost-per-kilometer analysis indicates the lowest value for methane (0.029 $/km), followed by hydrogen fuel cells integrated with a hydrogen storage material, MgH₂ (0.05–0.055 $/km). Lithium-ion batteries, despite high efficiency, yield moderate cost benefits (0.058 $/km) under our 100 kg energy storage system model, though high-capacity batteries could improve real-world economics. Drawing on literature data and our own assessments, we underscore that the future of clean mobility will not hinge on a single technology, but on a synergistic, multi-fuel strategy integrating the strengths of diverse energy carriers to meet the evolving demands of sustainable transport.