A research team from The Hong Kong University of Science and Technology (HKUST), in collaboration with Arizona State University (ASU) and The Hong Kong Polytechnic University (PolyU), has developed a sustainable integrated seawater-to-hydrogen system that can produce hydrogen directly from seawater while converting waste heat from electrolysis into a resource for producing the purified water required for hydrogen production. By integrating hydrogen production, water generation, and thermal management into a single system, the technology could help reduce the reliance of green hydrogen production on freshwater resources and offer a new approach for sustainable hydrogen development in water-scarce regions.
The study was led by Prof. SHANG Chii, Professor of the Department of Civil and Environmental Engineering at HKUST, and Dr. Gabriela Scheibel CASSOL, a postdoctoral fellow in the same department and an HKUST PhD graduate in Environmental Engineering. The research team also included Prof. Paul WESTERHOFF of Arizona State University and corresponding author Dr. SONG Yinghao, a postdoctoral fellow at PolyU and HKUST PhD graduate in Civil Engineering. The research was published in Nature Communications, titled "Thermally symbiotic integration of osmotic membrane distillation and electrolysis for direct seawater hydrogen production."
Innovative Thermal Symbiosis Design Enhances Resource Efficiency
Renewable hydrogen could play an important role in the transition to a low-carbon energy system. However, conventional water electrolysis relies on high-quality purified water, creating an additional challenge with respect to limited freshwater resources. Although seawater offers an abundant alternative, its salts and other constituents can cause unwanted reactions and accelerate membrane and catalyst degradation, limiting the practicality of direct seawater electrolysis.
To address these challenges, the research team integrated osmotic membrane distillation (OMD) with alkaline water electrolysis (AWE). The OMD process separates purified water from seawater while preventing major seawater constituents from reaching the electrolyzer. This enables the system to leverage mature alkaline electrolysis technology while avoiding direct exposure of critical components to seawater contaminants.
The system's key innovation lies in its thermal symbiosis design. During electrolysis, part of the electrical energy is inevitably converted into heat. Instead of simply removing this heat through conventional cooling, the researchers recover it and use it to drive OMD for water production. At the same time, the OMD process helps dissipate heat from the electrolyzer, allowing water production and thermal management to support one another in a mutually beneficial cycle that improves overall resource utilization.
More Than 99% Rejection of Major Seawater Constituents
Using real seawater, the system achieved more than 99% rejection of major seawater constituents and maintained stable performance over 500 hours of continuous operation, with Faradaic efficiency, as well as hydrogen and oxygen purity, all exceeding 99%. The researchers also developed a thermal-water-hydrogen model demonstrating that thermal circulation can be sustained within the efficiency range of commercial alkaline electrolyzers, supporting the feasibility of long-term continuous operation.
Prof. SHANG Chii, co-author of the study, said: "Developing hydrogen energy requires not only renewable electricity but also a sustainable water supply. Our research demonstrates a new approach that uses heat generated by the electrolysis process itself to produce the purified water needed by the system, transforming what would otherwise be waste heat into a valuable resource. This thermal symbiosis design not only improves the utilization of both energy and water resources but also demonstrates the feasibility of integrating seawater hydrogen production, desalination, and thermal management within a single platform. We hope this research can provide valuable insights for the future development of green hydrogen technologies in coastal and water-stressed regions."
The research team believes this innovation demonstrates the potential of integrating seawater purification, hydrogen production, and thermal management into a single platform. Future work will focus on expanding the system's application scope and further evaluating its performance under practical operating conditions to assess its potential for large-scale hydrogen production. Based on the reported results, the technology remains at the laboratory validation stage, and further scale-up and long-term durability studies will be needed before commercial deployment.
The work was supported by the Theme-based Research Scheme of the Hong Kong Research Grants Council (project no. T21-604/19-R), the HKUST 30 for 30 Research Initiative Scheme, and the PolyU Distinguished Postdoctoral Fellowship Scheme.
