Graphene is at the center of most energy storage applications. The unique carbon nanomaterial consists of a two-dimensional sheet of carbon atoms arranged in a hexagonal lattice and has many beneficial properties that can be exploited to enhance the performance, durability, and functionality of energy storage devices.
Graphene has potential in several applications, including energy storage devices. Image Credit: BONNINSTUDIO/Shutterstock.com
Graphene and Climate Change
Polluting and unsustainable fossil fuels are steadily being replaced with clean, renewable energy sources such as wind and solar power. However, the intermittent nature of these energy sources means energy storage or converting devices are needed to reap the full benefits.
These energy storage devices must be integrated into the system to make it more efficient and cost-effective. Graphene could make an important contribution by providing an alternative form of energy generation. It demonstrates high electrical and thermal conductivity, mechanical stability, and solar radiation absorptivity, making it ideal for use in fuel cells, lithium-ion batteries, supercapacitors, and dye synthesized solar cells.
Graphene Fuel Cells
Fuel cells convert the chemical energy in a fuel into electricity with high efficiency using an expensive platinum catalyst. Research is focused on replacing the metal with other non-precious metals or metal oxides. Graphene is also a strong contender because of its high conductivity and large surface area and adhesion to particles of the catalyst.
Graphene is already used in fuel cells as a support material for the anode catalyst, but it could be used to decrease the loading of the platinum/platinum alloy catalyst, improve the electrical conductivity of the catalyst, and aid dispersion of the metal to increase activity and decrease loading – or replace it altogether.
At the cathode, graphene is used to support the cathode catalyst and can increase activity when doped with boron or nitrogen. Research also suggests graphene could be used as a standalone catalyst. When mixed with carbon nanotubes it displays an increased oxygen reduction reaction (ORR), which can be further amplified by doping with nitrogen, sulfur, or boron.
Graphene could also be utilized as the electrolyte membrane of the fuel cell, the part of the cell responsible for the transfer of ions between the cathode and anode. The membrane must exhibit high ionic conductivity and high chemical, thermal and mechanical stability – graphene oxide fits the bill.
Dye-Sensitized Solar Cells (DSSC)
DSSCs are promising for directly harvesting solar energy; graphene can improve their efficiency at the photoanode, electrolyte, and counter electrode. The material enhances light collection and electronic transport at the photoanode and improves performance at the counter electrode.
Graphene was also added to a solid polymer electrolyte to prevent leakage, evaporation and corrosion, and showed promising results in terms of stability and efficiency.
Graphene-Based Batteries
Graphene-based batteries are amongst the most developed energy storage device. The material has the potential to feature in many different types of battery – usually together with graphite to form a hybrid electrode - where it can improve efficiency, stability, and cycle/discharge cycle rates.
In lithium-ion batteries, graphitic carbon is used as the anode material, where it has high crystallinity and the arrangement of graphene layers leads to LiC6 being formed. This allows for a high transfer of electrons between lithium and carbon which is stored between two sheets, and a high energy capacity.
Supercapacitors and Graphene Use
Supercapacitors are an amalgamation of a battery and capacitor and can deliver energy very rapidly and recharge almost as quickly. Graphene could be used as an alternative to the current materials for storing ions on supercapacitor electrodes because of its high surface area, stability, and conductivity.
Graphene could be used as a coating on a capacitor plate to form a double layer coating, or as an electrode to improve the electrode surface area of graphene and enhance network conductivity, leading to better ionic transport via the electrolyte. The hope is that one day, supercapacitors could offer a viable alternative to Li-ion batteries.
The Future of Graphene
Graphene has long been hailed as a revolutionary material, and it seems it could have an impact almost everywhere. Although research is still in its infancy, it is clear graphene has many roles to play in energy storage devices thanks to its high surface area, high electrical and thermal conductivity, and high stability.
References and Further Reading
Olabi, A.G et al. (2021) Application of graphene in energy storage device – A review, Renewable and Sustainable Energy Reviews, https://www.sciencedirect.com/science/article/pii/S1364032120303178. Accessed 27 July 2021.
Critchley, L. (2019) Using Graphene for Energy Storage, AZoNano - https://www.azonano.com/article.aspx?ArticleID=5276. Accessed 27 July 2021.
The Graphene Council, Graphene in Energy Storage, The Graphene Council - https://www.thegraphenecouncil.org/page/EnergyStorage15JUL. Accessed 27 July 2021.
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