Researchers have created a new hybrid technology. Produces unmatched amounts of electrical power where seawater and freshwater combine at the coast.
The study organized by Penn state researchers reveal the difference in salt concentration has the potential to generate enough energy to meet up to 40 percent of global electricity demands. Though two methods currently exist to capture this energy. The two most successful methods, pressure retarded osmosis (PRO) and reverse electrodialysis (RED), have inadequate expectations.
New CapMix (capacitive mixing) technology
A third technology, capacitive mixing (CapMix), is a relatively new method also being explored. CapMix is an electrode-based technology that captures energy from the voltage that develops when two identical electrodes are sequentially exposed to two different kinds of water with varying salt concentrations, such as freshwater and seawater. The problem with CapMix is that it’s not able to yield enough power to be viable.
The researchers have combined both the RED and CapMix technologies in an electrochemical flow cell. RED, uses an electrochemical gradient to develop voltages across ion-exchange membranes. Ion exchange membranes only allow either positively charged ions to move through them or negatively charged ions,
Model used in Generating Power
The team constructed custom-built flow cell in two channels separated by an anion-exchange membrane. The copper hexa cyanoferrate electrode placed in each channel, and graphite foil used as current collector. The cell 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. Examined how the cutoff voltage used for switching flow paths. External resistance and salt concentrations influenced peak and average power production.
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.
To determine the gained voltage of the flow cell depending on the type of membrane used and salinity difference, the team recorded open-circuit cell voltages while feeding two solutions at 15 milliliters per minute. Through this method, they identified that stacking multiple cells did influence electricity production. At 12.6 watts per square meter, this technology leads to peak power densities that are unprecedentedly high. Compared to previously reported RED 2.9 watts per square meter. The maximum calculated values for PRO 9.2 watts per square meter but without the fouling problems.
Though the results are promising, the researchers want to do more research on the stability of the electrodes over time and want to know how other elements in seawater like magnesium and sulfate might affect the performance of the cell.