Electrochemical cells

Electrochemical cells store energy through the conversion of electrical energy into chemical energy, which can later be converted back into electrical energy when needed.

Electrochemical cells include various devices like fuel cells (e.g. containing hydrogen), supercapacitors, and batteries (Winter & Brodd, 2004).

Hydrogen fuel cells

Hydrogen energy storage involves splitting water into hydrogen and oxygen through a process called electrolysis. The produced hydrogen can be stored in either a liquid or gas state, while oxygen is vented into the atmosphere.

_{Hydrogen fuel cell from Manahan, 2023; CC BY-NC-SA 4.0}

Hydrogen fuel cells can be used as clean energy to replace fossil fuels (Götz et al., 2016).

Supercapacitors

Supercapacitors are electrochemical devices that store and deliver energy. They are composed of two conductive electrodes with an electrolyte in between, which allows ions to move while keeping the electrical charges separated.

_{Schematic of a supercapacitor (Fig. 2) from Aslani, 2012; © Marjan Aslani; author has granted permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes}

Supercapacitors are particularly useful for applications where quick bursts of energy are needed, and where charging and discharging need to happen very quickly.

Compared to batteries, supercapacitors possess high power density and a long cycle life. However, their use is limited by the degradation of the electrolyte over time and a high self-discharge rate, which means they lose energy faster when not in use (Burke et al., 2014).

Batteries

Batteries are energy storage systems that convert stored chemical energy into electrical energy to power different electric devices.

Similar to supercapacitors, batteries are electrochemical energy storage devices, consisting of a conductive electrolyte placed between two electrodes: a cathode and an anode, each made of different materials with different electrical potentials.

In batteries, the electrical energy is produced by reduction and oxidation (redox) reactions at the cathode and anode (Yang et al., 2011).

We will explore batteries some more in the next section.

Flow batteries

Flow batteries, also known as redox flow batteries, are a type of rechargeable battery where energy is stored in liquid form. These batteries work by dissolving two different chemical components into separate tanks filled with liquid electrolytes.

When the battery is being charged, electrical energy from sources like the power grid or solar panels is converted into chemical energy and stored in the tanks. During discharge, this stored chemical energy is converted back into electrical energy. The charge and discharge processes in these batteries occur by pumping the electrolytes through the system on separate sides of a membrane.

_{Scheme of a redox flow battery (Figure 1.) from Clemente et al., 2020; CC BY 4.0}

Flow batteries offer long life and scalability, making them a promising option for large-scale energy storage applications. However, their complicated structure and lower energy density limit their use in smaller devices (Alotto et al., 2014).

Research and share

Research more about the applications of flow batteries and find examples of flow battery manufacturers. Share your findings in the comments below.

References

Alotto, P., Guarnieri, M., & Moro, F. (2014). Redox flow batteries for the storage of renewable energy: A review. Renewable and sustainable energy reviews, 29, 325-335.

Aslani, M. (2012, December 14). Electrochemical Double Layer Capacitors (Supercapacitors). Stanford University.

Burke, A., Liu, Z., & Zhao, H. (2014, December). Present and future applications of supercapacitors in electric and hybrid vehicles. In 2014 IEEE International Electric Vehicle Conference (IEVC) (pp. 1-8). IEEE.

Clemente, A., Ramos, G. A., & Costa-Castelló, R. (2020). Voltage h∞ control of a vanadium redox flow battery. Electronics, 9(10), 1567.

Götz, M., Lefebvre, J., Mörs, F., Koch, A. M., Graf, F., Bajohr, S., … & Kolb, T. (2016). Renewable Power-to-Gas: A technological and economic review. Renewable energy, 85, 1371-1390.

Manahan, S. (2023, April 14). Green Chemistry and the Ten Commandments of Sustainability. University of Missouri.

Winter, M., & Brodd, R. J. (2004). What are batteries, fuel cells, and supercapacitors?. Chemical reviews, 104(10), 4245-4270.

Yang, Z., Zhang, J., Kintner-Meyer, M. C., Lu, X., Choi, D., Lemmon, J. P., & Liu, J. (2011). Electrochemical energy storage for green grid. Chemical reviews, 111(5), 3577-3613.

Electrochemical cell. Alksub; CC BY-SA 3.0