Green hydrogen from water electrolysis: supply chain emissions assessment and net-zero pathways

Abstract

Green hydrogen produced via renewable-powered water electrolysis is widely regarded as environmentally sustainable, yet existing life cycle assessments often differ in their treatment of upstream supply chain processes. This study evaluates four major electrolysis technologies—alkaline, proton exchange membrane, solid oxide electrolysis cell, and anion exchange membrane —using a harmonized cradle-to-gate framework that systematically incorporates all relevant upstream emission categories. Across all technologies, upstream supply chain emissions (scope 3) contribute 15–49% of total greenhouse gas burdens, underscoring their substantial influence on life cycle outcomes. Environmental performance is shaped by material requirements, operational efficiency, and component manufacturing intensity, with critical raw materials such as platinum, nickel, and high-temperature alloys emerging as major upstream drivers. Under a net-zero mitigation scenario in which conventional grid electricity is replaced with renewable electricity, total life cycle emissions decrease by 79–90% across all electrolysis technologies. Nevertheless, upstream supply chain processes remain significant contributors, indicating that electricity decarbonization alone is insufficient. Material efficiency, low-carbon manufacturing routes, durability improvements, and recycling strategies are essential to meaningfully reduce the carbon footprint of green hydrogen. Emerging technologies such as AEM demonstrate promising environmental potential owing to their balanced material profiles and reduced dependence on supply-constrained critical materials. This study provides a harmonized methodological foundation for evaluating the environmental performance of water electrolysis systems and highlights that achieving truly sustainable green hydrogen requires coordinated advances in supply chain decarbonization, technological efficiency, and renewable electricity integration.