Exploring hydrogen energy systems: A comprehensive review of technologies, applications, prevailing trends, and associated challenges

Exploring hydrogen energy and its associated technologies is a pivotal pathway towards achieving carbon neutrality. This article comprehensively reviews hydrogen production technologies, storage technologies, and end -use applications of hydrogen, based on the input energy source, operating conditions, conversion efficiency, energy density, and unit investment cost. The review also highlights the advantages, disadvantages, and technological readiness of hydrogen production technologies, and storage methods. The selected hydrogen production methods include pyrolysis, gasification, fermentation, biophotolysis, electrolysis, thermolysis, and photolysis, while the selected hydrogen storage technologies are compressed, liquid, cryo-compressed, adsorption, and hydrides. Water electrolysis, highly efficient at 55 - 80 % and versatile, comes with a higher cost of $4.15 - $10.30/kg. In contrast, pyrolysis offers more cost-effective solutions with moderate efficiency (35 - 50 %) and a reasonable yield (25 - 65 g/kg), making it suitable for budget -sensitive projects. Compressed, liquid, and cryo-compressed hydrogen offer high efficiency with the added benefit of compact storage due to their high volumetric and gravimetric densities. Metal and chemical hydrides provide excellent safety and efficiency, with metal hydrides also delivering high volumetric density for more compact solutions. Furthermore, the review explores the applications of hydrogen energy in renewable energy systems, support to existing grid, transportation, cogeneration and tri-generation, and metallurgy along with insights from pilot projects. Moreover, the article examines the challenges and opportunities encountered in hydrogen production, storage methods, and end -use applications. Finally, the article conducts a SWOT analysis, pinpointing key aspects crucial for the successful adoption of hydrogen in the future. The conclusions indicate that ongoing efforts in performance enhancement, scaling up, and technical advancements are essential to establish a cost-effective hydrogen economy.