Seawater-to-Resource Technology

Abstract

Seawater that contains water and dissolved salt (35 kg in 1 m3), represents a vast feedstock for producing high-value resources such as freshwater, sodium hydroxide (NaOH), chlorine (Cl2), and hydrogen (H2). These resources are essential across a wide range of industries including agriculture, power generation, paper and pulp, polyvinyl chloride (PVC), steel, and energy. However, conventional technologies for freshwater extraction and brine treatment rely on pressure- or heat- driven processes, requiring as much as 75.9 kWh m-3 of energy. Moreover, in the electrolysis of salt for NaOH, Cl2, and H2 production, the net NaOH yield is limited to only about 7 kg per 10 kAh, corresponding to 47 % of the theoretical value, due to NaOH consumption during impurity removal. In this study, a new electrochemical platform—referred to as the seawater-to-resource technology—was developed by integrating and adapting electrochemical processes with conventional systems. The first approach, an ion-exchange desalination battery integrated with conventional freshwater extraction, utilizes the 1 wt% brackish water generated during charge–discharge cycling as RO feedwater, reducing the desalination energy from 2.98 kWh m⁻³ to 0.96 kWh m⁻³. Although the conventional system suffered from poor Cl⁻ capture reversibility (<30 %), this study introduced an ion-exchange-based method that enhanced reversibility to 99.9 %, achieving stable cyclic performance. The second approach, electrodialysis (ED) integrated with conventional brine treatment, addressed the high energy burden of evaporation-based salt recovery (≈73 kWh m⁻³). By selectively removing ions rather than evaporating the entire brine, the ED process successfully reduced the total energy requirement to 36.8 kWh m⁻³, while maintaining effective salt concentration and reducing the subsequent evaporation load. Finally, in the electrolysis with a solid electrolyte, a Na⁺-conductive ceramic (NASICON) membrane was introduced in place of conventional polymeric Nafion to enable selective sodium transport without brine purification. This design increased Na⁺ utilization and enabled the production of approximately 14.9 kg of NaOH per 10 kAh, corresponding to 99.6 % of the theoretical yield. These results demonstrate that the seawater-to-resource technology, based on integrative and adaptive electrochemical processes, provides a highly efficient and sustainable pathway for simultaneous freshwater generation and chemical resource production from seawater.