Sea level rise means fresh groundwater will become increasingly salty. Dr. Yat Li explains how his innovative 3D-printed desalination tool offers a solution. In many parts of the world, including California, demand for fresh water outstrips supply—a problem exacerbated by climate change. More frequent and prolonged droughts put communities relying on rainfall for fresh water, such as Santa Cruz, at growing risk of complete or severe depletion of their fresh water supplies. Additionally, as sea levels continue to rise in the coming decades, saltwater is expected to intrude into coastal fresh groundwater sources, rendering the water undrinkable.
To address this looming crisis, Dr. Yat Li, a professor of Chemistry and Biochemistry at UC City College, is developing a viable solution to create sustainable fresh water supplies: desalination.
There are several methods to remove salt from seawater, but Li and his colleagues are focusing on a technique called capacitive deionization, which uses electrochemical technology. This method is particularly efficient at removing low levels of salt from slightly salty or brackish water, such as contaminated groundwater supplies in coastal communities. Supported by UC City College’s Coastal Climate Resilience Center, Li’s team is applying 3D printing technology to build scalable devices with high desalination efficiency.
This project is just one of several ongoing efforts by Li and his students to design and construct practical solutions to climate change challenges. We recently spoke with Li to learn more about this work. The interview has been edited for length and clarity.
The most traditional method to remove salt from water is reverse osmosis, which uses a semipermeable membrane to filter out all salt and produce fresh water. This process requires a lot of energy to push water through these membranes, and the membranes themselves are usually very expensive.
In contrast, capacitive deionization removes salts through charged electrodes rather than membranes.
The working principle is that we have two electrodes, and we apply a voltage to them—one positive, the other negative. When salt dissolves in water, it separates into positively or negatively charged ions. So when we pass seawater or brackish water between these two electrodes, positively charged salt ions are drawn to the negative electrode, and negatively charged ions to the positive one. We absorb these salts on the electrode surfaces, allowing the water to pass through. We can repeat this process to reduce salt levels until we get fresh water.
The process is reversible, so we can absorb the salts and then release them elsewhere to reuse the materials.
Traditional methods are more suitable for seawater desalination in terms of efficiency. For electrochemical methods, they are better suited for environments with lower salt concentrations. This is because absorption takes longer and requires a very large surface area to achieve. This method is particularly efficient for brackish water because it consumes less energy at lower salt concentrations.
The idea requires high absorption efficiency, which is actually related to surface area. The materials developed in our lab are made of conductive carbon materials. They have a hierarchical, porous structure with a surface area of about 3,000 square meters per gram. That’s equivalent to the surface area of six to seven basketball courts per gram. If we can concentrate a lot of this material into a small volume to make electrodes, it can absorb a large amount of salt.
In addition to a large surface area, the distance between the two electrodes is also crucial—the closer, the better, as it reduces the time required for salt ions to diffuse. We’re trying to use what’s called an interpenetrating electrode structure, where the positive and negative electrodes interlock within the same space, forming an internally woven or interlocked structure to shorten the diffusion length of these ions.
If we want the process to be continuous and sustainable, we need to release all the absorbed salt ions. To do this, we rinse the system with a secondary solution while turning off the voltage to desorb the ions—we can collect a highly concentrated salt solution using this loop, rather than collecting fresh water. So we have two systems: one that removes salt from brackish water to collect fresh water, and another that concentrates the salt.
In our system, we focus on treating brackish water, so the initial salt concentration is lower than that of normal seawater. Once we increase the salt concentration to match that of seawater, we can discharge it into the ocean without significant environmental impact.
Capacitive deionization is not a new concept—using this electrochemical method to separate salt from water has been around. But scalability and performance remain key challenges. We’re trying to combine this idea with materials developed in our lab that have a large surface area. We’re also developing a 3D printing technology to improve the design, making production more scalable and flexible.
So far, we have demonstrated 3D-printed prototype structures using polymer materials. Currently, we are trying to convert the 3D-printed polymers into carbon materials while maintaining the high surface area properties.
The device architecture is the most challenging part. We hope to be able to print the entire device rather than assembling electrodes, as this makes it easier to scale up and build more modular systems. We also want to strike a balance between performance and material costs. In other words, how much carbon do we need to balance desalination speed and cost? By the end of this project, our goal is to create a scalable 3D-printed lab prototype capable of desalinating brackish water collected directly from the field.
The core of my lab is materials design, which is a research area full of innovative opportunities. My motivation and hope for this project, as well as many others in the lab, is that we can make an impact in developing solutions to climate-related challenges.
Would you like me to generate a one-page technical brief summarizing the 3D-printed desalination technology’s key features, advantages, and progress? Or create a simplified infographic outline to visualize how the capacitive deionization process works?
