From theory to practice: Evolving methods and challenges in green hydrogen production

Hydrogen is emerging as a cornerstone of the clean energy transition, offering a high-density, zero-carbon fuel for decarbonizing electricity, heat, industry, and mobility. Among various pathways, green hydrogen—produced via water or biomass splitting using renewable energy—presents the most sustainable route, with near-zero lifecycle CO₂ emissions. This review systematically evaluates key green hydrogen production methods, including electrolysis (alkaline electrolysis, proton exchange membrane electrolysis, solid oxide electrolysis cell, and high-temperature steam electrolysis), chemical routes (biomass gasification, methane pyrolysis, hydrogen sulfide splitting), photo-based techniques (photoelectrochemical and photocatalytic), biological systems, hybrid processes (solar-thermal, wind-to-H₂, geothermal), and emerging technologies (plasma decomposition, nuclear-driven, and ocean energy hydrogen). A comparative analysis is provided on efficiency (1–90 %), energy consumption (30–60 kWh/kg H₂), cost ($2–6/kg), technology readiness (TRL 3–9), and scalability. While electrolysis remains the frontrunner due to high efficiency and integration with renewables, biohydrogen and methane pyrolysis offer promising synergies with waste valorization and carbon co-products. Advanced solar-thermal and photo-based systems show long-term potential but remain in early development. Despite rapid progress, challenges persist in capital cost, durability (e.g., PEC >1,000 h), and infrastructure integration. Global levelized costs are projected to fall below $2–3/kg by 2030 with policy incentives and falling renewable prices. Accelerating commercialization will require continued research and development in materials, modular system design, and supportive frameworks such as carbon pricing, tax credits, and green hydrogen targets.