Portrait of Kyoung-Shin Choi in a lab.
Professor Kyoung-Shin Choi Photo: Andy Manis

Kyoung-Shin Choi’s approach to science is both simple and straightforward. When she sees an environmental problem, she just wants to fix it. Even when it’s not in her direct field of expertise.

The professor of chemistry, who was just inducted into the American Association for the Advancement of Science this year, is uniquely positioned to make good on that drive to improve. Choi’s specialty is electrochemistry, a scientific technique that uses electricity generated from sustainable sources to power chemical reactions.

Choi began her work with producing clean fuels (hydrogen) and chemicals using renewable sources like sunlight, water and biomass (plant and wood waste). She turned her attention to water in 2015, and in just a few short years has developed groundbreaking methods for desalinating seawater — potentially providing an important source of freshwater for areas of the world that desperately need it — and reducing the chloride levels in wastewater discharge.

“I wanted to come up with an electrochemical process that can do desalination, where energy, water and ions are managed in a completely different manner,” says Choi, who joined the Department of Chemistry in 2012. “That’s how we can provide a new solution for problems that cannot be solved by conventional technologies and potentially create a unique market.”

Water is typically desalinated through distillation, a process in which the water is boiled away from the salt, or reverse osmosis, in which water is squeezed through a porous membrane that separates out the salt. Both methods remove all matters in water non-selectively.

Choi initially developed a device to desalinate seawater, but then she had another idea. Wisconsin’s hard water and cold weather require the use of salt for water softening and road de-icing. Also, the state’s food industry uses a tremendous amount of salt and generates salty wastewater. All of these can increase chloride levels in municipal wastewater above the safe level determined by the U.S. Environmental Protection Agency.

“The conventional methods cannot be used to remove just chloride to make your wastewater environmentally safe,” says Choi. “So, what if we come up with an electrochemical way to remove just sodium and chloride to the level you want?”

The conventional methods cannot be used to remove just chloride to make your wastewater environmentally safe. So, what if we come up with an electrochemical way to remove just sodium and chloride to the level you want?

Kyoung-Shin Choi

The desalination battery Choi’s team developed is based on the same science that powers your smartphone through its lithium-ion battery. However, instead of using Li-ion storage electrodes, the desalination battery uses one electrode that can store and release sodium ions and another one that can do the same for chloride. Seawater or wastewater can be injected through the device, and sodium and chloride ions are removed by these electrodes.

“After this process, you are going to end up with water that contains less sodium, less chloride,” she explains. “The removed ions can be recovered as sodium- or chloride-containing useful chemicals by a follow-up process.”

The key to realizing this device was finding an inexpensive material that could electrochemically store and release chloride with a high chloride-removal capacity while being stable in salty water. Choi’s team discovered that bismuth (Bi), whose ion form is a major ingredient in Pepto-Bismol, could handle the task.

Some scientists might have stopped at the discovery point. Choi, a devout believer in the Wisconsin Idea, decided to further develop the concept to make a practical impact.

“Not all new ideas can make a practical impact,” says Choi. “Making something work in real life requires a different type of creativity and considerable efforts for scaling-up and de-risking … We want to build a new concept and we want to have a good atomic-level understanding of what’s going on. But we don’t want to stop there.”

As if the potential to effectively treat seawater and wastewater wasn’t enough, Choi’s electrochemistry method could also hold the key to an even bigger issue: transforming the way we manage phosphate, one of the most important ingredients in fertilizer.

Currently, phosphate is a destructive, double-edged sword. In phosphorous-based fertilizer, it stimulates the growth of nearly every major crop in the world. But its production and disposal create many environmental problems. For example, the conversion of phosphate rock to phosphoric acid (the chemical used to make phosphate-containing fertilizers) using sulfuric acid generates waste that accumulates radioactive elements from phosphate rock.

Choi’s team has developed a new electrochemical process that can remove phosphate from industrial and municipal wastewater and recover it as phosphoric acid without needing additional acid or generating any dangerous byproducts.

Choi is keenly aware that her research has many hurdles to overcome before it’s commercialized. Still, her work continues to turn heads. Earlier this year, she was named the 2023 Samsung Ho-Am Prize Laureate in the category of Chemistry and Life Sciences, an award that also carried a $228,400 stipend to fuel further research.

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