What Are the Latest Developments in Generating Electricity?
Our society demands power on an increasing basis, and so we need to find new and creative ways to meet these callings. Scientists have gotten creative, and below are but a few of the recent advancements in making electricity in new and novel ways.
Picking Up The Leftovers
Part of the energy dream is to take small little actions and make them contribute to passive energy collecting. Zhong Lin Wang (Georgia Tech in Atlanta) hopes to do just this, with things from as small as vibrations to walking being energy generators. It involves piezoelectric crystals, which give off a charge when physically altered, and electrodes being layered together. When the crystals were pressed on the sides, Wang found the voltage was 3-5 times bigger than predicted. The reason? Amazingly, static electricity was causing further unanticipated charges to be exchanged! Further modifications to the layout resulted in the triboelectric nanogenerator or TENG. It is a sphere-based design where the left/right electrodes are on the exterior sides and the inner surface contains a rolling ball of silicone. As it rolls around, the static electricity generated is collected and the process can go on indefinitely, so long as motion is occurring (Ornes).
Salt Water Meets Graphene
Turns out, given the right conditions, your pencil tips and ocean water can be utilized to make electricity. Researchers from China found that if a drop of salt water is dragged across a graphene slice at different velocities generates a voltage at a linear rate – that is, changes in velocity are directly related to the changes in voltage. This result seems to be coming from an unbalanced charge distribution of the water as it moves, unable to acclimate to the charges both inside it and on the graphene. This means that nanogenerators can become practical – someday (Patel).
But it turns out that sheet of graphene can also do the job of generating electricity when we stretch it out. This is because it is a piezoelectric, a material formed from single-atom thickness sheets whose polarization can be changed based on the orientation of the material. By stretching the sheet, the polarization grows and causes electron flow to increase. But the number of sheets does play a role, for researchers found that even-numbered stacks produced no polarization but odd-numbered ones did, with diminishing voltages as the stacking grew (Saxena “Graphene”).
Fresh Water vs. Salt Water
It’s possible to use the differences between salt and fresh water to extract electricity from ions stored between them. The key is osmotic power, or the drive of fresh water towards salt water to create a fully heterogeneous solution. By using an atom-thin-sheet of MoS2, scientist were able to achieve nanoscaling tunnels that allowed certain ions to transverse between the two solutions because of electric surface charges limiting passages (Saxena “Single”).
One of the biggest material developments of the recent past has been carbon nanotubes, or small cylindrical structures of carbon that have many amazing properties such as high strength and symmetrical structuring. Another great property they have is electron liberation, and recent work has shown that when nanotubes were twisted around into a helical pattern and stretched, the “internal strain and friction” cause electrons to be freed. When the cord is dipped in water, it allows the charges to be collected. Over a full cycle, the cord generated as much as 40 joules of energy (Timmer “Carbon”).
Building a More Heat-Efficient Battery
Wouldn’t it be great if we were able to take the energy our devices generate as heat and somehow convert back into useable energy? After all, we are trying to fight the heat death of the Universe. But the issue is most technologies need a large temperature differential to be utilized, and its way more than that which our tech generates. Researchers from MIT and Stanford have been working on improving the technology though. They found that a specific copper reaction had a lower voltage requirement for charging than it did at a higher temperature, but the catch was a charging current was needed to be supplied. That is where reactions of different iron-potassium-cyanide compounds came into play. Temperature differentials would cause the cathodes and the anodes to switch roles, meaning that as the device heated and then cooled it would still produce a current in the opposite direction and with a new voltage. However, with all of this considered the efficiency of this setup is a measly 2%, but as with any emergent tech improvements are likely to be made (Timmer “Researchers”).
Building a More Solar-Efficient Cell
Solar panels are notorious as being the way of the future but still lacking the efficiency many desire. That may change with the invention of dye-sensitized solar cells. Scientists took a look at the photovoltaic material used to collect light for the purpose of making electricity and found a way to change the properties of it using dyes. This new material readily took in electrons, kept them easier which helped prevent their escape, and allowed for a better electron flow which also opened the door to more wavelengths to be collected. This is in part because the dyes have a ring-like structure that encourages strict electron flow. For the electrolyte, a new copper-based solution was found instead of expensive metals, helping to lower costs but increasing the weight because of the need to bond the copper to carbon in order to minimize short-circuiting. The most interesting part? This new cell is most efficient in indoor lighting, nearly 29%. The best solar cells out there currently only fair at 20% when indoors. This could open up a new door to collecting background energy sources (Timmer “New”).
How can we increase the efficiency of solar panels? After all, what holds back most photovoltaic cells from converting all the solar photons striking it into electricity is the wavelength restrictions. Light has many different wavelength components and when you couple this with the necessary restrictions to excite the solar cells and so only 20% of it becomes electricity with this system. An alternative would be solar thermal cells, which take the photons and convert them into heat, which is then converted into electricity. But even this system peaks at 30% efficiency and it requires a lot of space for it to work and needs the light to be focused to generate heat. But what if the two were combined into one? (Giller).
That is what MIT researchers looked into. They were able to develop a solar-thermophotovoltaic device which combines the best of both technologies by converting the photons into heat first and having carbon nanotubes absorbing that. They are great for this purpose and also have the added benefit of being able to absorb nearly the entire solar spectrum. As the heat is transferred through the tubes, it ends up in a photonic crystal layered with silicon and silicon dioxide which at about 1000 degrees Celsius starts to glow. This results in an emission of photons which are more suitable for stimulating electrons. However, this device is only at 3% efficiency but with growth it can likely be improved upon (Ibid).
Alternative to Lithium Ion Batteries
Remember when those phones were catching on fire? That was because of a lithium-ion issue. But what exactly is a lithium-ion battery? It is a liquid electrolyte involving an organic solvent and dissolved salts. Ions in this mix flow with ease over a membrane which then induces a current. The major catch to this system is dendrite formation, aka microscopic lithium fibers. They can build up and cause short circuits which lead to heat ups and...fire! Surely there must be an alternative to this...somewhere (Sedacces 23).
Cyrus Rustomji (University of California at San Diego) may have a solution: gas-based batteries. The solvent would be a liquefied floronethane gas instead of the organic one. The battery was charged and drained 400 times and then compared to its lithium counterpart. The charge it held was nearly the same as the initial charge but the lithium was only 20% its original capacity. Another advantage the gas had was lack of flammability. If punctured, a lithium battery will interact with the oxygen in the air and cause a reaction, but in the case of the gas it just releases into the air as it loses pressure and will not explode. And as an added bonus, the gas battery operates at -60 degrees Celsius. How heating the battery impacts its performance remains to be seen (Ibid).
Ornes, Stephen. "The Energy Scavengers." Discover Sept/Oct. 2019. Print. 40-3.
Patel, Yogi. “Flowing salt water over graphene generates electricity.” Arstechnica.com. Conte Nast., 14 Apr. 2014. Web. 06 Sept. 2018.
Saxena, Shalini. “Graphene-like substance generates electricity when stretched.” Arstechnica.com. Conte Nast., 28 Oct. 2014. Web. 07 Sept. 2018.
---. “Single-atom-thick sheets efficiently extract electricity from salt water.” Arstechnica.com. Conte Nast., 21 Jul. 2016. Web. 24 Sept. 2018.
Sedacces, Matthew. "Better Batteries." Scientific American Oct. 2017. Print. 23.
Timmer, John. “Carbon nanotube ‘yarn’ generates electricity when stretched.” Arstechnica.com. Conte Nast., 24 Aug. 2017. Web. 13 Sept. 2018.
---. “New device can harvest indoor light to power electronics.” Arstechnica.com. Conte Nast., 05 May 2017. Web. 13 Sept. 2018.
---. “Researchers craft a battery that can be recharged with waste heat.” Arstechnica.com. Conte Nast., 18 Nov. 2014. Web. 10 Sept. 2018.
© 2019 Leonard Kelley