Review of Sustainable Hydrogen Energy Processes: Production, Storage, Transportation, and Color-Coded Classifications

Rapid urbanization and population growth have intensified global energy demand, with fossil fuel consumption aggravating air pollution and climate change. Hydrogen, a clean energy carrier, is essential for transitioning to a low-carbon economy. This study examines the color-coded classification of hydrogen production pathways, derived from both renewable and non-renewable sources, and examines their emission profiles. Additionally, it delves into the critical aspects of hydrogen storage and transportation, highlighting the need for robust infrastructure to ensure the effective integration of hydrogen into the energy system. The study concludes that traditional hydrogen production methods, such as coal gasification and steam methane reforming (SMR), significantly contribute to air pollution due to their reliance on fossil fuels and lack of carbon capture. While blue hydrogen, utilizing carbon capture and storage (CCS), offers a reduction in greenhouse gas (GHG) emissions, turquoise and green hydrogen, produced via methane pyrolysis and water electrolysis, respectively, present cleaner alternatives with zero GHG emissions. With regard to hydrogen storage, metal and complex hydrides emerge as cost-effective options, while compressed hydrogen is suitable for large-scale storage. For applications demanding high energy density, liquefied and cryo-compressed hydrogen are viable, despite their associated costs and complexities. For hydrogen transportation, pressurized tanks, cryogenic liquid hydrogen tankers, and gas pipelines are considered. Pipelines are favored for long-distance transportation due to their cost-effectiveness, while cryogenic liquid hydrogen tankers are preferred for short distances, despite higher costs and infrastructure requirements.