Hydrogen production from low-quality water: challenges and perspectives

The Next Generation EU plan fosters the development of a large capacity for hydrogen generation. However, water and energy resources are strictly connected to an indissoluble nexus. For that, water electrolysis may counteract the coexistence of two primary UNO Sustainable Development Goals humankind must face to achieve a prosperous and equal society, namely SDG 7 (Affordable access to renewable energy sources) and SDG 6 (clean water). To design innovative energy systems implementing hydrogen as an efficient and sustainable vector, water resources need careful management and energy use ought not to compete with freshwater delivery. Therefore, the present study reviews the technologies available for hydrogen production and their fitness to water quality standards. Among the feeding possibilities to be scrutinized, wastewaters and saline waters are worth attention. Each source of water asks for a specific design and management of the water treatment pre-process. Since these steps are energy-demanding, in some applications, the direct use of low-quality water to produce hydrogen may be envisaged. An example is the direct feeding of seawater to Solid Oxide Electrolysers (SOE). SOEs appear more promising than commercial low-temperature electrolysis systems since water steam production integrates the function of preliminary water treatment.