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.
Microbiologists unravel relationship among plants, mycorrhizal fungi
An ancient, mutually beneficial relationship between plants and fungi could make agriculture more sustainable by reducing the need for chemical fertilizers, according to professor Heike Bücking of the South Dakota State University Department of Biology and Microbiology.
For more than 500 million years, the majority of land plants have shared their carbohydrates with arbuscular mycorrhizal fungi that colonize their root systems, Bücking explained. In exchange, these fungi provide plants with nitrogen and phosphorous, and improve the stress resistance of their host.
These fungi are seen as living fossils and explore the soil with its hyphae in the search for nutrients, and deliver these nutrients to its host. As reward the host plant transfers anywhere from 4 to 20 percent of its photosynthetically fixed carbon to these mycorrhizal symbionts.
“We think these fungi have the potential to increase the biomass production of bioenergy crops and the yield of food crops and do so in a more sustainable and environmentally friendly way,” said Bücking. She studies these interactions in food and bioenergy crops including wheat, corn, soybeans, alfalfa, clover and perennial grasses, such as prairie cordgrass.
Her research has been supported by the National Science Foundation, South Dakota Wheat Commission, Sun Grant Initiative, Soybean Research and Promotion Council and the U.S. Department of Energy – Joint Genome Initiative.
Defining plant-fungi relationships
Supply and demand determine the amount of nutrients that plant and fungi exchange in this mutualistic relationship, according to Bücking. To unravel these complex interactions, she collaborates with researchers at the Vrije Universiteit in Amsterdam and the University of British Columbia as well as other South Dakota Agricultural Experiment Station researchers.
“Though a host plant is colonized by multiple fungi species simultaneously, the plant knows exactly where certain benefits are coming from. The host plant can distinguish between good and bad fungal behavior and allocates resources accordingly,” she said, noting that the host plant transfers anywhere from 4 to 20 percent of its photosynthetically fixed carbon to mycorrhizal fungi.
These fungi also form common mycorrhizal networks that give them access to multiple hosts. Her research showed that when host plants were shaded and thus decreased their carbohydrate allocation, fungi responded by reducing their nutrient share.
Optimizing fungi for specific crops
She and her collaborators have also found that some fungi are more beneficial than others. For example, Bücking and her collaborators evaluated the relationship between alfalfa and 31 different isolates of 10 arbuscular mycorrhizal fungal species.
They then classified the fungal isolates as high-, medium- or low-performance isolates. The researchers found that high-performance isolates increased the biomass and nutrient uptake of alfalfa by more than 170 percent, while the low-performance ones did not have any effect on growth.
However, those that benefit one crop may not provide the same nutrients or benefits to another crop species, she cautioned. “Even different isolates of one fungal species can behave differently, and it will be necessary to identify fungi that are optimally adapted to their specific environment and host plant to get the highest plant benefit.
Adapting to stressors
In addition to providing nutrients, these fungi can protect food and bioenergy crops from environmental stresses, such as drought, salinity and heavy metals, and diseases, Bücking explained. “All the stresses that a plant can potentially be exposed to are generally improved by mycorrhizal interactions.”
Increasing tolerance through conventional breeding generally targets only one specific stress factor, but crops are often subjected to multiple stresses simultaneously, she pointed out. “These fungi, if used efficiently, can provide the plant with an improved resistance against stresses that are often difficult for us to predict.”
However, she added, more research is necessary to better understand how this ancient symbiosis between land plants and fungi can be used to its full potential.
South Dakota State University is a public research university located in Brookings, South Dakota.
It is the state’s largest and second oldest university. A land-grant university and sun grant university, founded under the provisions of the 1862 Morrill Act, SDSU offers programs of study required by, or harmonious to, this Act. In step with this land-grant heritage and mission, SDSU has a special focus on academic programs in agriculture, engineering, nursing, and pharmacy, as well as the liberal arts.
The Carnegie Foundation for the Advancement of Teaching classifies SDSU as a Research University with high research activity. The graduate program is classified as Doctoral/Science, Technology, Engineering, Math dominant. SDSU is governed by the South Dakota Board of Regents, which governs the state’s six public universities and two special schools.