The global pursuit of clean, secure, and sustainable energy systems has elevated hydrogen to a central role in decarbonization strategies. As a versatile, carbon-free energy carrier, hydrogen can be produced from diverse feedstocks—including water, biomass, and fossil fuels—and its combustion emits only water, offering a transformative solution for sectors resistant to electrification, such as heavy industry, long-haul transport, and grid stabilization. Beyond its environmental advantages, hydrogen enables large-scale energy storage, mitigates intermittency of renewables, and enhances systemic flexibility. To assess its full potential, the hydrogen value chain must be examined across four interdependent domains: production, storage, transportation, and utilization. Current hydrogen production is dominated by steam methane reforming (SMR) and coal gasification, which are cost-effective but carbon-intensive. In contrast, water electrolysis powered by renewable electricity yields "green hydrogen" with near-zero emissions. Technological advancements in electrolyzers—notably proton exchange membrane (PEM), alkaline, and solid oxide systems—have improved efficiency and scalability, though challenges like high capital costs and energy inputs persist. Emerging methods, such as biomass gasification and solar-driven photoelectrochemical splitting, show promise but require further development to achieve commercial viability. Efficient storage is critical to align hydrogen’s intermittent production with demand. Compressed gas and cryogenic liquid storage are mature technologies but suffer from low energy density and boil-off losses. Solid-state alternatives, such as metal hydrides and porous adsorbents (e.g., metal-organic frameworks), offer higher volumetric efficiency and enhanced safety. However, material degradation, thermal management, and scalability issues necessitate ongoing research to optimize these systems for widespread deployment. Hydrogen’s low density and reactivity pose unique transport challenges. Pipelines are cost-effective for regional distribution but require specialized materials to prevent embrittlement. For long-distance transport, liquefied hydrogen tankers and chemical carriers (e.g., ammonia, liquid organic hydrogen carriers) are gaining traction, with recent improvements in cryogenic insulation and catalytic conversion efficiency reducing energy penalties. Hydrogen’s versatility enables deep decarbonization across multiple sectors. In transport, it powers fuel cell electric vehicles (FCEVs), heavy-duty trucks, and maritime vessels, with prototypes for aviation underscoring its potential for energy-dense applications. Industrial uses include steelmaking via direct reduced iron (DRI) processes, reducing CO₂ emissions by over 90% compared to conventional blast furnaces. Hydrogen also serves as a critical feedstock for ammonia synthesis, methanol production, and petroleum refining, while its integration into gas turbines and hybrid power plants enhances grid stability. Hydrogen’s unique attributes—clean combustion, storage capacity, and cross-sector applicability—make it indispensable for achieving net-zero emissions. Realizing its full potential demands coordinated advancements across production, storage, transport, and end-use technologies, supported by policy frameworks and infrastructure investments. As renewable energy capacity expands, hydrogen is poised to underpin resilient, low-carbon energy systems worldwide.
