Generating Electricity Where The Rivers Meet The Sea At Penn State
Researchers from Penn State University have created a new hybrid technology which is capable of generating “unprecedented” levels of electricity by exploiting the change in salt concentrations where freshwater rivers meet saltwater oceans.
The idea of generating electricity from the point where freshwater meets seawater isn’t new in and of itself, with several technologies already existing to do just that. There are two primary methods — pressure retarded osmosis, or PRO, and reverse electrodialysis, or RED — but, according to Penn State, both have not lived up to expectations. All the way back in 2012 I (apparently) covered PRO research conducted at the Department of Chemical and Environmental Engineering at Yale University. At the time it was suggested that PRO technology could provide electricity enough to meet the needs of 520 million people. A third method, though relatively new technology, is called capacitive mixing, or CapMix, but like RED, neither ended up generating enough electricity to be viable.
However, researchers from Penn State may have come up with a solution by combining RED and CapMix into one single technology in an electrochemical flow cell. “By combining the two methods, they end up giving you a lot more energy,” said Christopher Gorski, assistant professor in environmental engineering at Penn State, who along with Bruce Logan, Evan Pugh Professor and the Stan and Flora Kappe Professor of Environmental Engineering, and Taeyoung Kim, post-doctoral scholar in environmental engineering, came up with the hybrid technology idea.
Instead of attempting to re-decipher the specifics of these technologies, we’ll quote directly from Penn State to describe the process:
“The team constructed a custom-built flow cell in which two channels were separated by an anion-exchange membrane. A copper hexacyanoferrate electrode was then placed in each channel, and graphite foil was used as a current collector. The cell was then sealed using two end plates with bolts and nuts. Once built, one channel was fed with synthetic seawater, while the other channel was fed with synthetic freshwater. Periodically switching the water’s flow paths allowed the cell to recharge and further produce power. From there, they examined how the cutoff voltage used for switching flow paths, external resistance and salt concentrations influenced peak and average power production.”
“There are two things going on here that make it work,” explained Gorski. “The first is you have the salt going to the electrodes. The second is you have the chloride transferring across the membrane. Since both of these processes generate a voltage, you end up developing a combined voltage at the electrodes and across the membrane.”
The Penn State researchers are pleased with their work so far, but are looking to do more research on the stability of the electrodes over time, and whether other seawater elements such as magnesium and sulfate may affect the performance of the cell.
“Pursuing renewable energy sources is important,” Gorski said. “If we can do carbon neutral energy, we should.”
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