A comprehensive review of green hydrogen production technologies: current status, challenges, research trends and future directions

Green hydrogen (H 2 ), produced from renewable energy sources (RES), has emerged as a key-enabler for decarbonizing the energy and industrial sectors. However, reducing production costs and optimizing supporting infrastructure remain major challenges for large-scale deployment. While most of the existing research focuses on the downstream stages of the green hydrogen supply chain (GHSC), there is a lack of studies that provide a comprehensive analysis of different production technologies from different renewable sources. Moreover, limited attention has been given to the scalability potential of these technologies to meet future H 2 demand, which is an essential consideration for enabling large-scale green H 2 deployment. A clear understanding of the production stage – including available technologies, their technological maturity and their capacity to scale – is essential to address these challenges effectively. This study aims to fill that gap by critically characterizing green H 2 production technologies, contributing to a cost-effective and sustainable GHSC development, with particular emphasis on water electrolysis as the most promising and mature technology. A comprehensive review and comparative analysis between the most relevant green H 2 production technologies are presented, considering biomass- and water-based production methods, including thermochemical (gasification and pyrolysis), biological (photolysis and fermentation), and water-splitting (thermolysis, photolysis and electrolysis) processes. The review highlights the operational characteristics, industrial applicability and scalability potential of these technologies, while identifying key challenges and outlining current research priorities and emergent directions. Although biomass gasification is the most mature among biomass-based options, its application for dedicated H 2 production is hindered by low H 2 yields, feedstock variability and constrained availability, all of which hinder scalability. In contrast, water electrolysis, particularly Proton Exchange Membrane (PEM) and Alkaline Water Electrolysis (AWE), emerge as the most promising and scalable technology for near-term scale-up. PEM electrolysis offers high H 2 purity, rapid responsiveness to variable RES input, and energy efficiencies up to 65 %, with levelized costs as low as $4.2/kg, in optimistic scenarios. The focus on water electrolysis is due to its superior technological readiness, operational flexibility and alignment with renewable energy integration needs. This study identifies PEM and AWE as leading production technologies and highlights ongoing research needs in materials, catalysts, and system design. The findings also provide actionable insights for researchers, policymakers and industry stakeholders in selecting the most appropriate green H 2 production technologies and designing a cost-effective GHSC. Technical, economic, regulatory and social challenges are outlined, and strategies to support global green H 2 transition is proposed. • Comprehensive review of green hydrogen (H 2 ) production technologies from biomass- and water-based renewable sources, with emphasis on technological readiness and integration with renewable energy for effective green H 2 supply chain development. • Critical comparison of thermochemical, biological, and water-splitting methods with focus on scalability and industrial applicability. • Outlines key research priorities in materials, catalysts, and system design to improve performance and reduce costs. • Provides actionable insights for policymakers, industry, and researchers to support global green hydrogen transition, addressing technical, economic, regulatory, and social challenges.