A recent study conducted by mechanical engineers has introduced a novel approach to enhance saltwater desalination. Instead of focusing on developing new materials, the researchers concentrated on fluid movement. They incorporated microchannels into battery-like electrodes composed of Prussian blue, a vivid blue pigment with unique chemical properties commonly used in art. This modification resulted in a fivefold increase in the extent of seawater desalination compared to electrodes without microchannels, effectively reducing salinity levels below the threshold for freshwater.
The research, led by Kyle Smith, a professor of mechanical engineering and science at the University of Illinois Urbana-Champaign, along with graduate student Vu Do, employed a chemical analog of Prussian blue. The findings hold great potential for various applications, including desalination, energy conversion and storage, CO2 conversion and capture, environmental remediation, and resource and nutrient recovery.
Published in the journal Energy and Environmental Science, the study not only confirmed the feasibility of desalination using this approach but also highlighted the significance of the electrode configuration in achieving optimal results.
“In previous research, we hypothesized that desalination could be achieved using this method, but nobody had experimentally demonstrated seawater-level desalination,” explained Smith. “During the course of our work, we discovered that the material used in the electrodes, along with the system’s configuration, plays a crucial role in the process.”
The researchers explained that the Prussian blue analog material functions by capturing positively charged ions, such as sodium, within its crystal structure. However, it can create a sort of trapping mechanism where the ions easily enter but get entangled within a network of tiny, charged pores present in the electrode. To ensure continuous desalination, the team employed a specialized apparatus that involved intricate valve switching and current synchronization inside the flow cell. Without these measures, the efficiency of the system would be compromised.
To maintain both a clear pathway for fluid flow and the ability to extract salt ions from water, the researchers engraved multiple channels onto the 5-centimeter-sized electrode, each measuring approximately 100 micrometers in width—comparable to the thickness of a human hair.
In the laboratory setting, the setup used in this study achieved desalination of artificially prepared seawater at a rate of milliliters over several hours. Consequently, the researchers’ next objective is to scale up the process for practical implementation.
Smith highlighted that the Navy grant supporting this study aims to achieve a desalination rate of two to four gallons per hour, using diesel fuel as the power source. The ultimate objective is to develop a portable device that can supply water to military troops in small expeditionary units. While the research group has broader applications in mind for these battery-like devices, scaling up the technology is a crucial step towards realizing those goals.
Do emphasized the significant contribution of mechanical engineering in this study. While the research community often focuses on materials and their chemistry, the team demonstrated the critical role of fluid mechanics in maximizing the potential of a high-quality material when integrated correctly.
Contributions to the study were also made by members of Smith’s research group, namely Irwin Loud and Erik Reale.