Penn State U. – New ‘Flow-Cell’ Battery Recharged with Carbon Dioxide – Capturing CO2 Emissions for an Untapped Source of Energy


co2flowcell
The pH-gradient flow cell has two channels: one containing an aqueous solution sparged with carbon dioxide (low pH) and the other containing an aqueous solution sparged with ambient air (high pH). The pH gradient causes ions to flow across …more

Researchers have developed a type of rechargeable battery called a flow cell that can be recharged with a water-based solution containing dissolved carbon dioxide (CO2) emitted from fossil fuel power plants. The device works by taking advantage of the CO2 concentration difference between CO2 emissions and ambient air, which can ultimately be used to generate electricity.

The new flow cell produces an average power density of 0.82 W/m2, which is almost 200 times higher than values obtained using previous similar methods. Although it is not yet clear whether the process could be economically viable on a large scale, the early results appear promising and could be further improved with future research.

The scientists, Taeyong Kim, Bruce E. Logan, and Christopher A. Gorski at The Pennsylvania State University, have published a paper on the new method of CO2-to-electricity conversion in a recent issue of Environmental Science & Technology Letters.

“This work offers an alternative, simpler means to capturing energy from CO2 emissions compared to existing technologies that require expensive catalyst materials and very high temperatures to convert CO2 into useful fuels,” said Gorski.

While the contrast of gray-white smoke against a blue sky illustrates the adverse environmental impact of burning , the large difference in CO2 concentration between the two gases is also what provides an untapped energy source for generating electricity.fossil-fuels-co2-to-green-images

In order to harness the potential energy in this concentration difference, the researchers first dissolved CO2 gas and in separate containers of an aqueous solution, in a process called sparging. At the end of this process, the CO2-sparged solution forms bicarbonate ions, which give it a lower pH of 7.7 compared to the air-sparged solution, which has a pH of 9.4.

After sparging, the researchers injected each solution into one of two channels in a flow cell, creating a pH gradient in the cell. The flow cell has electrodes on opposite sides of the two channels, along with a semi-porous membrane between the two channels that prevents instant mixing while still allowing ions to pass through. Due to the pH difference between the two solutions, various ions pass through the membrane, creating a voltage difference between the two electrodes and causing electrons to flow along a wire connecting the electrodes.

After the flow cell is discharged, it can be recharged again by switching the channels that the solutions flow through. By switching the solution that flows over each electrode, the charging mechanism is reversed so that the electrons flow in the opposite direction. Tests showed that the cell maintains its performance over 50 cycles of alternating solutions.

The results also showed that, the higher the pH difference between the two channels, the higher the average power density. Although the pH-gradient flow cell achieves a power density that is high compared to similar cells that convert waste CO2 to electricity, it is still much lower than the power densities of fuel cell systems that combine CO2 with other fuels, such as H2.

However, the new flow cell has certain advantages over these other devices, such as its use of inexpensive materials and room-temperature operation. These features make the flow cell attractive for practical applications at existing .

“A system containing numerous identical flow cells would be installed at power plants that combust fossil fuels,” Gorski said. “The flue gas emitted from fossil fuel combustion would need to be pre-cooled, then bubbled through a reservoir of water that can be pumped through the flow cells.”

In the future, the researchers plan to further improve the flow cell performance.

“We are currently looking to see how the solution conditions can be optimized to maximize the amount of energy produced,” Gorski said. “We are also investigating if we can dissolve chemicals in the water that exhibit pH-dependent redox properties, thus allowing us to increase the amount of energy that can be recovered. The latter approach would be analogous to a flow battery, which reduces and oxidizes dissolved chemicals in aqueous solutions, except we are causing them to be reduced and oxidized here by changing the solution pH with CO2.”

Explore further: Chemists present an innovative redox-flow battery based on organic polymers and water

More information: Taeyoung Kim et al. “A pH-Gradient Flow Cell for Converting Waste CO2 into Electricity.” Environmental Science & Technology Letters. DOI: 10.1021/acs.estlett.6b00467

 

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Bill Gates: We will have a clean-energy ‘miracle’ within 15 years


 

Green nature landscape with planet Earth

A ‘Green-er’ Clean Energy Earth?

 

In the latest edition of their annual letter published today, Bill and Melinda Gates argue that the world needs “an energy miracle,” and are willing to bet that such a breakthrough will arrive within 15 years.

 

Bill Gates cites scientists’ estimates that to avoid the worst effects of climate change the biggest carbon-emitting countries must reduce greenhouse gas emissions by 80% by 2050, and the world must more or less stop such emissions entirely by 2100. And that’s not going to happen if we continue on our current trajectory.

 

You can see Gates explain the equation in the Quartz video above.

Gates says he was stunned to discover how little research and development money is going toward breakthroughs in cheaper, scaleable clean-energy sources.Gates announced last year that he was committing $1 billion of his own money over five years to invest in clean-energy technology, and has been pushing governments to increase their funding.

To explain the need for a breakthrough in energy technology, he uses an equation (similar to the Kaya identity equation) that represents the factors determining how much carbon dioxide the world emits every year.

“Within the next 15 years, I expect the world will discover a clean-energy breakthrough that will save our planet and power our world.” Gates believes that cleaner options such as electric cars and LED lighting won’t bring down energy consumption enough to hit those climate-change goals. In fact, he doesn’t see any current clean-energy technology that will enable the world to eliminate carbon dioxide emissions by 2100, partly because it’s not consistent or inexpensive enough.

 

Gates has personally invested in next-generation nuclear power technology, which he describes as “a very promising path.” He is also backing efforts to improve battery technology, so that energy from intermittent clean sources such as solar and wind can be stored affordably at large scale for use over time. “I think we need to pursue many different paths,” says Gates in an interview with Quartz.

 

And he’s betting on relatively fast progress. “Within the next 15 years,” Gates predicts in his letter, “I expect the world will discover a clean-energy breakthrough that will save our planet and power our world.”

** Re-Posted from the World Economic Forum

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