Supercapacitors occupy a critical position among energy storage systems thanks to their advantages such as high power density, fast charge-discharge characteristics, and long cycle life. Positioned between traditional capacitors and batteries, these devices offer ideal solutions for many industrial and portable applications due to their ability to meet sudden energy demands (Figure 1). The role of supercapacitors is growing day by day, especially in areas such as electric vehicles, renewable energy systems, and wearable technologies.

Figure 1. Comparison of the characteristics of capacitors, supercapacitors, and batteries.

Types of Supercapacitors

Supercapacitors are primarily divided into three classes:

• Electric Double Layer Capacitors (EDLCs): These operate using carbon-based electrodes, and energy storage occurs through physical adsorption. These non-Faradaic systems have a high cycle life.
• PsödokPseudocapacitors: These contain metal oxides, conductive polymers, and sulfur-based electrodes. They operate based on Faradaic processes involving redox reactions. They have high specific capacitance but their cycle stability is limited compared to EDLCs.
• Hybrid Supercapacitors: These systems aim to combine the advantages of EDLCs and pseudocapacitors. With their asymmetric designs, they offer a wide potential window and high energy density.

Table 1 provides a comparison of supercapacitors according to their types.

Supercapacitors Work Principle

Depending on the type of supercapacitor, the energy storage mechanisms vary significantly (Figure 2). In electric double-layer capacitors (EDLCs), the energy storage process relies on ionic charge accumulation at the electrode-electrolyte interface. Under the influence of an external electric field, cations and anions in the electrolyte are attracted to the electrode surface by electrostatic forces, forming a double layer. Since this process is limited to physical adsorption, no chemical changes occur in the electrode structure. As a result, EDLCs offer a high cycle life and long service life. However, since energy storage occurs solely through surface interactions, their capacitance is relatively low.

In contrast, pseudocapacitors store energy through reversible redox reactions and ion adsorption/desorption processes that occur on the electrode surface. This mechanism allows for higher specific capacitances to be achieved. Active materials such as transition metal oxides, hydroxides, and sulfides are commonly used in such capacitors. However, the ion influx/efflux accompanying redox reactions can cause volumetric expansion and structural degradation in the electrode materials. This leads to capacity loss and reduced cycle stability over time.

Hybrid supercapacitors aim to combine the advantages of EDLC and pseudocapacitive structures to offer both high energy density and long cycle life. In these structures, one electrode is typically responsible for fast and stable physical processes (EDLC), while the other electrode is responsible for high-capacity chemical processes (pseudocapacitor). This expands the device’s operating voltage range and increases energy density. However, if the reaction kinetics and ion transport speeds of the two different electrode materials are incompatible, the device’s overall performance may be limited.

Figure 2. Energy storage mechanisms of different types of supercapacitors

Applications of Supercapacitors

In line with the increasing energy demand and sustainability goals of today, the effective use of renewable energy sources and the efficient storage of this energy are of great importance. Supercapacitors, which can operate in conjunction with environmentally friendly energy sources such as wind, solar, hydroelectric, ocean, biomass, and geothermal, are one of the leading technologies in energy storage due to their high power density and long cycle life. Supercapacitors are not only used to support renewable energy systems but also find applications in various fields such as mobile electronic devices, robotic systems, fast-charging electric vehicles, wearable biosensors, and power supply applications in buildings (Figure 3).

With the rapid advancement of technology and global economic developments, demand for artificial intelligence-powered equipment is growing in many industries. Examples of these areas include smart robots, smart sensors, and innovative energy storage systems. For example, robots are used in many fields such as medicine, industry, the military, and space research. Therefore, the development of an intelligent power control system that can efficiently and reliably handle various workloads over long periods of time is of great importance. Figure 4 shows examples of supercapacitors being used in different devices, as well as an example of an intelligent robot with a prosthetic hand powered by a supercapacitor.

This versatile usability makes supercapacitors a key component in future energy systems.

Figure 3. Renewable energies and supercapacitor applications.

Figure 4. Supercapacitor applications in different portable devices.

CUNAM Projects

The role of electrode material is decisive in supercapacitor performance. Materials with high surface area, chemical stability, and high conductivity are preferred. An example of this is manganese dioxide (MnO₂), which stands out due to its environmentally friendly structure, low cost, and high theoretical capacitance (~1370 F g⁻¹).
In the TÜBİTAK 3501-funded project titled “Development of High-Performance Asymmetric Supercapacitors Using Mo and V-Doped MnO₂ Electrodes” conducted within CÜNAM, the supercapacitor to be developed will feature: The molybdenum (Mo) addition enhances the redox capacity of MnO₂, thereby improving the performance of the positive electrode, while the vanadium (V) addition accelerates ion transport, enabling the negative electrode to operate stably over a wider potential range.

Production and Characterization Approach

Supercapacitor electrodes can be produced using the reactive RF/DC magnetron sputtering method with the NVTS-500 Sputter/Thermal Thin Film Coating System located at our center. This method offers more homogeneous, controlled, and repeatable film growth processes compared to solution-based methods.

The produced films are characterized using techniques such as XRD, AFM, Raman, SEM, and EDX; electrochemical performance analyses are conducted using CV, GCD, and EIS methods.

Future Perspective and Research Areas

Research on supercapacitor technologies is conducted at the intersection of materials engineering, electrochemistry, and nanotechnology disciplines, thereby strengthening our center’s interdisciplinary research capacity. The developed electrodes and devices are evaluated not only at the laboratory scale but also as scalable energy storage solutions for the future.

Our center’s supercapacitor research aims to contribute to the development of next-generation energy storage systems that meet criteria such as high energy density, long cycle life, and environmental sustainability.

References

1. Öztürk, O. Nikel Sülfür Tabanlı Hibrit Süperkapasitör Aygıt Geliştirilmesi, Doktora Tezi, 2024.
2. Conway, B. E. Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications. Springer, 1999.
3. Zhi, M., Xiang, C., Li, J., Li, M. ve Wu, N. Nanostructured carbon–metal oxide composite electrodes for supercapacitors: a review. Nanoscale, 5(1), 72-88, 2013.
4. Zhang, J., Gu, M., Chen, X. Supercapacitors for renewable energy applications: A review. Micro and Nano Engineering, 100229, 2023.
5. https://www.ntchip.com/electronics-news/what-is-a-supercapacitor