Supercapacitors are electrochemical devices that store energy by accumulating charged particles on electrode surfaces rather than through chemical reactions like batteries. This surface-based storage allows them to charge and discharge incredibly quickly and endure hundreds of thousands, even millions, of charge-discharge cycles without significant degradation. They particularly excel at delivering powerful bursts of energy. For devices needing rapid charging and discharging or a long lifespan, like regenerative braking systems in electric cars, backup power for critical systems, or portable electronics requiring quick power boosts, supercapacitors are often a better fit.
But just like any technology, supercapacitors need better components, particularly the materials used in their electrodes, since they have to withstand incredible amounts of energy transfer quickly.
Scientists are constantly searching for new materials to improve the electrodes, capable of holding more charge, releasing it faster, and lasting through countless charge-discharge cycles. One material that has shown promise is Tungsten Diselenide (WSe₂), a compound with a layered structure. WSe₂ has unique electrical properties, making it a potential candidate for supercapacitor electrodes. However, when used alone, these WSe₂ layers tend to stack up too tightly, like papers in a book sticking together. This makes it hard for the charged particles (ions) from the electrolyte liquid to get in and out easily. This clumping, in turn, limits how much energy the material can store and how quickly it can work.
Now, new research led by Kyonggi University, South Korea, Chettinad Academy of Research and Education, Tamil Nadu, Maharani Cluster University, Karnataka, Saveetha Institute of Medical and Technical Sciences, Tamil Nadu and others is tackling the WSe₂ clumping problem head-on. The researchers introduced a helpful polymer, Polyvinyl Pyrrolidone (PVP), into the mix while creating the WSe₂. PVP is known for being a molecular multitasker, and it can help guide the growth of materials and improve how well they interact with other substances, like the electrolyte in a supercapacitor. The scientists hypothesised that combining WSe₂ with PVP could create a new composite material that would overcome the limitations of bare WSe₂.
To test their idea, the researchers used a method called hydrothermal synthesis. They put the ingredients for WSe₂ and PVP together in a sealed container with water and heated it up under pressure. This controlled environment allowed the WSe₂ to form tiny flakes, but crucially, the PVP was right there alongside them. The PVP acted like that chaperone, preventing the WSe₂ flakes from stacking too tightly. Instead, they formed larger, more spread-out nanoflakes, with the PVP polymer intertwined, almost like scaffolding holding the structure open.
They then used this new WSe₂@PVP composite material to make an electrode for a supercapacitor, testing its performance in a common electrolyte solution (2M KOH). They ran several tests, including Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS). CV checks the supercapacitor’s power and responsiveness and shows how much charge the material can handle and how quickly it can react. GCD measures the energy storage capacity and how long it takes to charge and discharge. EIS measures the internal resistance and how easily ions and electrons can move through the material.
The results showed that the WSe₂@PVP composite significantly outperformed the bare WSe₂. In the GCD tests, the composite showed a much longer discharge time, indicating it stored more energy. When they calculated the specific capacitance, a measure of how much charge the material can store per unit of mass, the WSe₂@PVP hit a high of 393.1 Farads per gram (Fg⁻¹) at a certain power level, while the bare WSe₂ only managed 233.3 Fg⁻¹.
But it wasn't just about holding more charge; it was also about how well it performed under pressure and how long it lasted. The WSe₂@PVP composite showed excellent "]rate capability, which could still store much energy even when charging and discharging very quickly. Its durability also significantly improved. After 5000 charge-discharge cycles, the WSe₂@PVP electrode retained an astonishing 98% of its initial capacity. The bare WSe₂ wasn't tested for this long, but other similar materials often show more significant degradation. The researchers noted a slight drop to 98% might be due to minor increases in internal resistance or some charged particles sticking to the surface over time, but retaining 98% after 5000 cycles is still considered exceptional stability in this field.
The scientists attributed this leap in performance to the unique structure created by the PVP. By preventing the WSe₂ flakes from clumping, the PVP created a more open, accessible structure. The electrolyte ions can now easily reach many more active sites on the WSe₂ flakes. This larger accessible surface area, combined with faster pathways for electrons and ions to travel through the material, significantly improved the electrochemical reactions. The PVP also seems to act as a protective layer, helping the WSe₂ nanoflakes maintain their structure and integrity even after many cycles of charging and discharging.
This research paves the way for practical applications by developing a cost-effective and relatively simple method (the hydrothermal process) to create a high-performance supercapacitor material. Better supercapacitor electrodes mean we can build energy storage devices that are more efficient, charge faster, last longer, and become cheaper to produce.
This research article was written with the help of generative AI and edited by an editor at Research Matters.