Graphene And Its Applications In The Renewable Energy Sector
By: Hemanth Kumar J
Tags: Materials Science, Graphene, Nanotechnology, Renewable Energy, Mechanical Engineering

The demand for renewable energy has been increasing by leaps and bounds. The world has been gearing up to embrace a sustainable way of life by reducing the carbon emissions to zero in all aspects. The serious steps are being undertaken by the governments all across the globe to increase the percentage of power generated by renewable sources of energy in the respective countries. In this blog, I would be highlighting the importance of Graphene in the renewable energy sector.

Graphene (The Miracle Material)

Graphene

Introduction to Graphene

Graphene is a monolayer of carbon atoms tightly bound together in a hexagonal honeycomb lattice. It is an allotrope of carbon in the form of a plane of sp2 with a molecular bond-length of 0.142 nanometers. Layers of graphene when stacked on top of each other forms Graphite, with a with an interplanar spacing of 0.335 nanometres. The separate layers of graphene in graphite are held together by van der Waals forces, which can be overcome during exfoliation of graphene from graphite.

Discovery Of Graphene

In diamond, each carbon atom is connected to four other carbons. This is a very strong arrangement that makes diamond one of the hardest known materials. In graphite, each atom is linked to three others in layers of hexagonal (six-sided) shapes. The bonds within the hexagonal sheets are strong, but each layer is only weakly attracted to the next, which allows the layers to slip by one another.

Graphene being discovered by Andre Geim and Konstantin Novoselov In 2004(Credits: The official LinkedIn Page of The Nobel Prize)

In the year of 2004, two chemists Andre Geim and Konstantin Novoselov of the University of Manchester, United Kingdom used the bonding nature and bond strength of the graphite to obtain graphene. Sticky tapes were used to obtain graphite flakes from the graphite. Then the sticky tape itself was pressed and pulled apart. This process was done repeatedly till they could obtain a single atom thick layer which is graphene.

Sticky tape is used to peel off powdered graphite, leaving a single layer of graphene (Credits: American Chemistry Society)

The initial samples of Graphene that were obtained were of few square millimetres in size which were good enough to be tested. Graphene being single atom thick was considered to be the first of its kind two-dimensional material ever discovered by the mankind.

Andre Geim and Konstantin Novoselov were awarded the Nobel Prize in Physics in the year of 2010 for the discovery of the graphene.

Key Properties of Graphene

Graphene is one of the thinnest material ever known to mankind as it’s just one atom thick and its thickness is measured to be 0.34 nanometres. It is one of the toughest materials as well. It is approximately 100–300 times stronger than steel and has a tensile strength of 130 gigapascals and Young’s Modulus of 1 terapascal. It’s one of the best conductors of electricity at the room temperature measured between (4.84±0.44) × 10³ to (5.30±0.48) × 10³ W·m−1·K−1. The electron scatter is the least in Graphene as compared to other materials. The electron mobility in graphene is found out to be more than 200,000 cm2·V−1·s−1. The uniform absorption of light across the visible and near-infrared parts of the spectrum is one of the key properties exhibited by graphene. Noting with appreciation the graphene is very well suited for spin transport.

Potential Applications Of Graphene In The Renewable Energy Sector

Battery Technology

While the development of electronic components has been progressing at a very rapid over the last 20 years. Power storage solutions such as batteries and capacitors have been the primary limiting factor due to size, power capacity and efficiency (most types of batteries are very inefficient, and capacitors are even less so). Currently, while such materials as lithium can store large amounts of energy, that potential amount diminishes on every charge or recharge due to electrode wear. For example,lithium-ion batteries face a trade-off between energy density and power density.

The laser-scribed graphene (LSG) supercapacitors demonstrated power density comparable to that of high-power lithium-ion batteries that are in use today. Not only that, but also LSG supercapacitors are highly flexible, light, quick to charge, thin, and comparably very inexpensive to produce.

Graphene LSG supercapacitor created with a DVD burner

Graphene is also being used to boost not only the capacity and charge rate of batteries but also the longevity. With graphene tin oxide as an anode in lithium-ion batteries, for example, batteries last much longer between charges (potential capacity has increased by a factor of 10), and with almost no reduction in storage capacity between charges, effectively making technology such as electronically powered vehicles a much more viable transport solution in the future. This means that batteries (or capacitors) can be developed to last much longer and at higher capacities than previously realized. Also, it means that electronic devices may be charged within seconds, rather than minutes or hours and have hugely improved longevity.

In 2011, engineers at Northwestern University discovered that graphene anodes could hold up to 10 times more power than graphite ones, charged 10 times faster and lasted longer(click on the link below for more details).

In the year of 2013, researchers from the Rice University found that graphene laced with boron could be used to produce an ultrathin flexible anode for lithium-ion batteries. The boron which can replace a quarter of the carbon atoms that would help the lithium ions stick to the graphene, which results in faster charging (click the link below for more details).

The University of Manchester, the home of graphene, has already worked on developing a grid-scale battery and converter system on campus. The aim is to develop high capacity electrical storage capable of supplying the National Grid (click the link below for more details).

Photovoltaic Cells

Eight thousand times more solar energy is produced each year than is consumed worldwide; while some of the power reaching the Earth is harvested and utilized, a massive percentage is not. As energy needs increase, solar power is becoming an attractive alternative, but its efficiency is still lagging. Furthermore, commercially available silicon-based photovoltaic cells are expensive to produce and install.

Graphene-Enabled Solar Farm in Crete, Greece

The improvement of perovskite solar cells (PSCs) has been highly promising next-generation solar power sources with very high efficiency. Flagship researchers made excellent progress in improving the lifetime and performance of PSCs, while reducing the production cost of PSCs. Adding a reduced graphene oxide spacer layer to a PSC resulted in low-cost production of PSCs with 20% efficiency, retained up to 95% after 1000h of operation. A pilot production line and a 1 kW graphene-perovskite solar farm are in the pipeline for the next period.

Graphene could have an important role to play in anti-reflection coatings for solar cells. Researchers in India found that such cells lower reflectance near the ultraviolet part of the spectrum from 35% to 15%.

According to a team at the Massachusetts Institute of Technology, Graphene incorporated photovoltaic cells have a greater power conversion efficiency as compared to the conventional photovoltaic cells (click the link below for more details).

Hybrid cells based on graphene are less expensive and more effective as a conducting electrode than the traditionally used indium tin oxide. It also provided flexibility, is lightweight, and imparts mechanical strength and a chemical robustness to the cell.

Renewable Fuels

Researchers at the University of Manchester have discovered that graphene membranes possess the ability to be illuminated with sunlight and conduct protons at an increased rate. The photo proton effect can be used to mimic the photosynthesis process and directly harvest solar energy to produce hydrogen gas (click on the link below for more details).

This gas could then be used in fuel cells in electric vehicles. Such a move would help lower the cost of renewable hydrogen fuel and make hydrogen fuel stations a more common sight along the roads as the cost of processing drops.

Conclusion

As a concluding remark, I would like to say

Graphene is truly a miracle material. Graphene would help mankind to embrace the sustainable way of living in the long run. It’s going to help mankind in the ever-growing domain of renewable energy by creating products with a better efficiency than the existing ones.

This blog is an ode to the discoverers of graphene, Andre Geim and Konstantin Novoselov.