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As the world slowly transitions away from energy based on burning hydrocarbons, from coal and oil to natural gas, the main problem after start-up costs that have hobbled a further acceptance of renewable energy sources has been their erratic power output – the sun doesn't always shine, the wind doesn't always blow.
This shortcoming in turn has driven major research worldwide into battery technology to store electrical output when renewable power sources are functioning, to be released back into the grid when needed.
Now a research team of scientists at Harvard seem to have surmounted this bottleneck by developing a flow storage battery, based on organic materials rather than traditional metals.
The novel battery technology is reported in a paper published in Nature on January 10. Under the OPEN 2012 program, the Harvard team received funding from the U.S. Department of Energy's Advanced Research Projects Agency–Energy (ARPA-E) to develop the innovative grid-scale battery and plans to work with ARPA-E to catalyze further technological and market breakthroughs over the next several years.
Harvard researchers and engineers Brian Huskinson, Michael P. Marshak, Changwon Suh, Süleyman Er, Michael R. Gerhardt, Cooper J. Galvin, Xudong Chen, Alán Aspuru-Guzik, Roy G. Gordon, and Michael J. Aziz lay out their concepts in their "A metal-free organic–inorganic aqueous flow battery" article, published on 10 January in the journal Nature.
The scientists describe their breakthrough thusly:
Solid-electrode batteries maintain discharge at peak power for far too short a time to fully regulate wind or solar power output. In contrast, flow batteries can independently scale the power (electrode area) and energy (arbitrarily large storage volume) components of the system by maintaining all of the electro-active species in fluid form. Wide-scale utilization of flow batteries is, however, limited by the abundance and cost of these materials, particularly those using redox-active metals and precious-metal electrocatalysts. Here we describe a class of energy storage materials that exploits the favourable chemical and electrochemical properties of a family of molecules known as quinones. The example we demonstrate is a metal-free flow battery based on the redox chemistry of 9,10-anthraquinone-2,7-disulphonic acid (AQDS). AQDS undergoes extremely rapid and reversible two-electron two-proton reduction on a glassy carbon electrode in sulphuric acid.
In layman's terms, the researchers have gone beyond traditional metal based free flow batteries, which have been around for more than three decades. Vanadium is used in the most commercially advanced flow battery technology now under development, but vanadium batteries typically cost about $80 per kilowatt hour. Other flow batteries contain precious metal electrocatalysts such as the platinum used in fuel cells, which is even more expensive.
In contrast, the Harvard free flow battery relies on the electrochemistry of naturally abundant, inexpensive, small, organic carbon-based "quinone" molecules, which are similar to those that store energy in plants and animals.
Dr. Roy G. Gordon, the Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science, who led the work on the synthesis and chemical screening of molecules said, "The whole world of electricity storage has been using metal ions in various charge states but there is a limited number that you can put into solution and use to store energy, and none of them can economically store massive amounts of renewable energy. With organic molecules, we introduce a vast new set of possibilities. Some of them will be terrible and some will be really good. With these quinones we have the first ones that look really good." Professor of Chemistry and Chemical Biology Alán Aspuru-Guzik used his pioneering high-throughput molecular screening methods to calculate the properties of more than 10,000 quinone molecules in search of the best candidates for the battery.
What scale are we talking about? Team member Chemistry and Chemical Biology postdoctoral fellow Michael Marshak said that if you had a whole field of turbines or large solar farm, you could utilize the technology with a few very large storage tanks, adding, "Imagine a device the size of a home heating oil tank sitting in your basement. It would store a day's worth of sunshine from the solar panels on the roof of your house, potentially providing enough to power your household from late afternoon, through the night, into the next morning, without burning any fossil fuels."
The Harvard researchers believe that their new battery could prove economical in storing energy for up to two days on a large scale and claim that the quinone battery already performs as well as vanadium batteries. In contrast to metal-based flow batteries, Professor Michael Aziz believes that quinone-based systems could cut the energy storage costs down to just $27 per kWh. In the prototype battery that the team has developed, only the negative side of the battery uses quinones, with the positive side using bromine, but the team is now working on a new version that solely uses quinones.
One thing is certain – once the Harvard team's research leads to patents, they will hardly be starved for funding from the investor community.
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