Green hydrogen pathways for a net-zero future: technologies, circular economy integration, life-cycle performance and safety dimensions

This review critically evaluates the technological, environmental, and policy dimensions of green hydrogen using an integrated framework grounded in green chemistry, the circular economy, and the sustainable development goals. Rather than treating green hydrogen as a universal energy solution, the review synthesises advances in production, storage, transport, safety, and policy instruments to assess where and under what conditions hydrogen deployment is sustainable. Conventional, biological, electrolytic, photocatalytic, and waste-derived pathways are compared in terms of efficiency, lifecycle emissions, resource intensity, material criticality, and toxicity. Storage and distribution options including compressed and liquefied hydrogen, chemical carriers, and porous materials are assessed for energy density, safety, recyclability, and infrastructure readiness. Life-cycle assessment data are integrated to identify key hotspots in global warming potential, water use, cumulative energy demand, and human toxicity. Policy frameworks, including India's National Green Hydrogen Mission, are examined with emphasis on implementation mechanisms, certification, and industrial integration. The analysis demonstrates that no single pathway satisfies all sustainability criteria, highlighting the need for targeted deployment, system integration, and regional optimisation. Embedding green chemistry principles alongside coordinated policy and infrastructure planning is essential for a resilient and equitable hydrogen economy.