Direct Air-Water Capture and Hydrogen Generation via Flowing Hygroscopic Solvents

Extracting water directly from the air to produce hydrogen holds significant potential for sustainable and environmentally friendly energy production. This approach eliminates the need for water resources and reduces environmental pollution associated with traditional hydrogen production methods. It is particularly well-suited for humid environments. Currently, direct hydrogen production from air involves first capturing water using hygroscopic materials, followed by regeneration processes such as light or heat to obtain high-purity water. However, commonly used solid hygroscopic gels, despite their excellent moisture absorption properties, are limited by their inherent volume and water-holding capacity, making continuous water extraction from air and subsequent hydrogen production challenging. Here, we propose a straightforward method using a continuously flowing hygroscopic solution to achieve continuous water extraction from air for hydrogen production. We used a highly concentrated LiCl solution to capture moisture from the air, resulting in a water-enriched, lower-concentration LiCl solution. This water-enriched LiCl solution was then subjected to low-temperature membrane distillation (<333K), where water was transferred through a porous polytetrafluoroethylene (PTFE) membrane to an electrolytic cell and subsequently split into hydrogen and oxygen, effectively converting moisture from the air into hydrogen energy. We demonstrated and validated the method's ability to continuously extract moisture from the air and produce hydrogen for 100 hours in both alkaline electrolytic cells and proton exchange membrane (PEM) electrolytic cells. This work offers new insights into direct hydrogen production from air. Future advancements could pave the way for greener and more efficient energy production methods.