New Cornell research suggests an economically viable model to scrub carbon dioxide from the atmosphere to thwart runaway, point-of-no-return global warming.
The researchers propose using a “bioenergy-biochar system” that removes carbon dioxide from the atmosphere in an environmental pinch, until other removal methods become economically feasible and in regions where other methods are impractical. Their work appeared in the Oct. 21 edition of Nature Communications.
“If we continue on current emissions trajectories, we will need to draw down excess carbon dioxide from the atmosphere if we’re going to avoid catastrophic levels of climate change. We’re offering a mitigation model that can do that. It’s not a silver bullet, but it may be among the tools we need in a portfolio of carbon dioxide mitigation strategies,” said Dominic Woolf, Cornell research associate in crop and soil sciences and lead author on “Optimal Bioenergy Power Generation for Climate Change Mitigation With or Without Carbon Sequestration.”
Among the recent ideas to cleanse the atmosphere of carbon is to plant huge regions of forests – called reforestation or afforestation. Scientists have also considered bioenergy with carbon capture and storage (BECCS), in which bioenergy power plants capture their own carbon dioxide emissions, and then store them underground or in the ocean. BECCS is very expensive and impractical now, but could become a more viable option toward the end of this century, according to this research.
The new study suggests a system using biochar, carbonized plant matter made by charring organic material – burning without using air – in a process called pyrolysis. The bioenergy-biochar system, called c, is stable and lowers sequestration losses when carbon is captured. After the organic matter is turned into carbon-sequestering biochar, it can be placed into the soil as a fertilizer substitute and improve crop production.
Although it has been omitted from major atmospheric mitigation scenarios until now, the new model shows that including biochar in a suite of options unlocks the ability to achieve cost-effective carbon dioxide removal earlier and deeper than would otherwise be possible.
Woolf sounds a hopeful note: “We need a full suite of mitigation strategies. It’s quite possible to scrub the atmosphere and remove carbon dioxide to avoid runaway climate change – where we could transition to manageable climate change,” he said. “This isn’t purely about advocating completely for biochar, but we need to recognize that we have technologies in place that can help our atmosphere, and we should create an optimal portfolio for ideas.”
In addition to Woolf, the paper’s other researchers are Johannes Lehmann, professor of soil and crop sciences; and David R. Lee, professor of applied economics from Cornell’s Charles H. Dyson School of Applied Economics and Management.
Plasma etching makes biochar activation faster
The ability to absorb and discharge energy quickly make supercapacitors an integral part of energy harvesting systems, such as the regenerative braking systems of hybrid vehicles, according to explainthatstuff.com. However, supercapacitors are expensive.
About half the materials cost comes from the use of activated carbon to coat the electrodes, according to Materials Today. Supercapacitor-grade activated carbon can cost $15 per kilogram.
Two South Dakota State University engineering researchers are using biochar, an inexpensive carbon-rich material and a new method of creating the porous surface needed to capture electricity to reduce the cost of supercapacitors.
Associate professor Qi Hua Fan of electrical engineering and computer Science uses plasma etching to active the biochar. Associate professor Zhengrong Gu of agricultural and biosystems engineering uses the activated biochar to make supercapacitors. Biochar is a byproduct of the pyrolysis process that turns plant materials into biofuel.
“Raw biochar needs activation to create the porous structure needed to trap ions,” explained Fan. Traditional chemical activation requires a high temperature, in the range of 1,700 Fahrenheit for two hours, and a chemical catalyst, followed by chemical washing and prolonged drying. This makes it an energy-intensive, time-consuming process.
The charcoal-like biochar can be made from crop residue, such as corn stover, wood or even dried distillers grain with solubles, known as DDGS. However, for this research, Fan used commercially available biochar made from yellow pine.
Several research groups had analyzed the specific capacitance and performance of this type of biochar, he explained, “so we had a baseline.” In addition, a company could supply the quantities of biochar necessary to make sure that test results were repeatable.
To do the plasma etching, oxygen was used and excited by radio frequency through a dielectric barrier discharge. Fan then gave the activated biochar to Gu, who made the supercapacitors. The research was supported by a five-month, proof-of-concept grant from the North Central Regional Sun Grant Center. Two graduate students worked on the project.
Increasing capacitance, improving efficiency
When the researchers compared capacitor performance, they found that those made using plasma treatment had 1.7 times higher specific capacitance, 171.4 Farads, compared to 99.5 Farads using chemical activation. “That’s a big improvement,” Fan pointed out.
The process took only five minutes with no external heating or chemicals needed. “It is very fast and consumes very little energy,” he noted. “The energy required to activate biochar is equivalent to what we use for a light bulb.”
In a paper published in the Journal of Power Sources, Fan, Gu and assistant physics professor Parashu Kharel explain, “oxygen plasma was capable of creating various pore sizes that would allow easy access for the electrolyte ions to the porous surface, leading to a higher capacitance than the chemically activated biochar.”
In addition, oxygen plasma-activated capacitors had lower estimated resistance, 3.3 ohms, as opposed to 14.5 ohms for chemically treated capacitors. This was attributed to the ions having easier access to the micropores and mesopores created by plasma processing.
And, Fan added, “Yellow pine is not the best biochar for supercapacitors.” He expects a similar improvement in performance using biochar derived from other types of biomass.
However, he pointed out, the process must be optimized for each type of structure. “Activation depends on what kind of plasma, what conditions are used and how long we treat the material.”
Fan has filed a patent application for the plasma activation process he developed. The next step will be to apply for funding to expand this promising processing technique for other types of biochar.
“No matter what kind of parameters we eventually end up with, this will be very efficient,” he added.