Bengaluru: Researchers at the University of Colorado Boulder, along with those from Poland and the UK, have devised a way to improve supercapacitors without using batteries— a development that could increase energy storage capacity and potentially change the way we charge electronic devices today.
The findings were published in the peer-reviewed journal PNAS Friday.
Supercapacitors are devices that hold large amounts of energy to discharge in bursts, such as braking mechanisms in vehicles or turning-on devices. As next-generation energy storage devices start to become the norm in industries around the world, researchers have increasingly been delving into their nano- and micro-scales of material structure to understand how to perfect them.
The team of researchers from the US, Poland, and the UK set about trying to understand how to improve supercapacitor energy capacity and experimented with various porous materials for building one. They demonstrated that differences in chemical charges in atoms and ions can cause a flow of electricity, despite a complete lack of chemical reactions, which is what produces power in batteries today.
The researchers, under project head Ankur Gupta, note that this electrolyte transport within such porous materials used to build supercapacitors can be explained using basic electricity laws written by famed physicist Gustav Kirchhoff, which are a staple part of electricity basics studied in school and college. As a consequence, they suggest an addendum that can be applied to porous materials.
This discovery could help develop more efficient energy storage devices that could substantially reduce charging times for everything from laptops to electric vehicles.
“We modified Kirchoff’s Laws for electrolyte transport and suggested that Kirchhoff’s voltage law needs to be modified to include electrochemical potential, and not just electric potential,” Gupta, whose lab is called LIFE — Laboratory of Interfaces, Flow, and Electrokinetcis — told ThePrint.
In their paper, the authors specifically talk about the use of materials that are deemed porous at nanoscales or have nanopores. In such structures, molecules containing ions are unable to latch onto the surface, splitting up into their respective component charges and inducing an electrochemical potential difference that makes electricity flow.
Based on their model of porous materials with large surface areas, the authors conclude that their methodology offers a way to achieve a higher efficiency flow that does not rely on chemical reactions, but works only on the flow of ions. According to the paper, this opens up immediate possibilities for constructing various 3D-printed electrodes and improving supercapacitor performance. Additionally, the team shows that their findings are supported by direct numerical simulations.
Highways of charge flow
With supercapacitors and other materials that have to do with the flow of electricity, materials offer more advantages when understood at a nanometer level. Within porous materials, the large number of pores drastically increases the surface area of a material.
Thus, when a salt like sodium chloride is added to it when energy is applied, the nanopores do not allow the entire molecule to bind to the surface. Instead, the salt molecule splits into a sodium ion and a chloride ion, creating a separation of charge and inducing the flow of electrochemical current.
To understand the implications of the findings, Gupta likens the flow of electric current and the flow of electrochemical current to a map route and a dense network of highways — electricity flow in a material is like drawing a map route from point A to B, but electrochemical flow in porous material is the nitty gritty that makes up the various roads and highways and the convoluted paths vehicles take to physically get from point A to B.
And for his team to get here, they started off thinking about other porous material that allows for the flow of liquids.
“The basic idea is that there is a lot of porous material in nature, or mechanical engineering, for example. Water flows in wells, both oil and water, and it is aided by porous materials. We wanted to use some of those principles and apply them to an electrochemical system,” explained Gupta.
The flow of electrochemical charge through membranes is not fully understood yet, and understanding these dynamics in the porous material is necessary for cutting-edge energy storage devices. Supercapacitors have been in use for nearly 50 years, and today are already used heavily in not just regenerative braking in the automotive sector, but also for power backup and UPS, household alarms, even flashes for photography, and any other applications that require short bursts of large amounts of power.
Applications of findings
Gupta explains that there have been significant strides in supercapacitor research in the last 15 years or so. Batteries continue to remain the main focus for energy storage, but the destructive nature of batteries is one of the main reasons researchers today are even more interested in electrochemical flow.
The team isn’t the only one working on supercapacitors and porous material. However, they are the first to introduce a model to predict electrolyte transport in complex networks of nanopores using modified Kirchhoff’s laws.
As the next steps, the team plans to characterise such nanopore systems to standardise them and conduct further experiments using eventual 3D printing.
“Some electric buses in China are powered by supercapacitors,” said Gupta. Since buses make very frequent stops, they charge at each station for a short period and store enough energy until the next station. Public transit is a very obvious use case, he explains.
“This promises to be a good thing because supercapacitors rely less on chemical reactions, with no risk of explosions, and they can even replace batteries in some cases. There has to be a conscious effort at finding such materials for the future.”
(Edited by Uttara Ramaswamy)
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