Hydrogen production from urban reclaimed water electrolysis: A new path for synergistic development of resource recycling and carbon neutrality.

The global pursuit of carbon neutrality and the escalating urban water crisis have created an urgent need for innovative solutions that simultaneously address energy transition and water resource management. Electrolytic hydrogen production from reclaimed water has emerged as a promising strategy at this water-energy-climate nexus, yet its technical feasibility and practical viability remain inadequately explored. This review assesses the potential of reclaimed water electrolysis by examining feedwater characteristics, electrolyzer compatibility, catalyst stability, process integration, lifecycle performance, and techno-economic feasibility. Compared with freshwater-based electrolysis, the use of reclaimed water can reduce competition for high-quality water resources and support the transformation of wastewater treatment plants into integrated water-energy recovery hubs. Available evidence indicates that, when supplied with low-carbon electricity, reclaimed water electrolysis could reduce lifecycle carbon emissions by up to 67% relative to grid-powered freshwater electrolysis. However, its current hydrogen production cost remains 12-18% higher, mainly because of additional pretreatment, membrane protection, catalyst degradation, and maintenance requirements. The main technical constraints arise from chloride, dissolved organic matter, hardness ions, nutrients, and trace metals, which can promote chlorine evolution, electrode corrosion, catalyst poisoning, mineral scaling, and membrane fouling. Recent advances in contaminant-tolerant catalysts, selective membranes, hybrid pretreatment, microbial electrolysis cells, and oxygen valorization provide promising routes to improve durability and resource efficiency. Future deployment will require electrolysis-specific feedwater standards, lifecycle-based accounting of water and carbon benefits, and modular systems integrated with wastewater treatment plants and renewable electricity. Overall, reclaimed water electrolysis is a promising but still maturing pathway for coupling urban water reuse with hydrogen production.