The potential of graphene for renewable energy systems
The structure of graphene [Image: UCL Mathematical and Physical Science, Flickr]
Earlier this year, in late January, Manchester and Abu Dhabi Universities announced their intention to collaborate on a project to produce foam containing graphene, a material consisting of a single layer of carbon atoms arranged in a honeycomb lattice which is 10 times stronger than steel but 1000 times lighter than a sheet of paper per unit area.
Graphene was first discovered in a lab at Manchester University in 2004 following years of attempts by scientists to produce a single layer of carbon and much theorizing, being observed through an electron microscope in 1962. Professors Andre Geim and Konstantin Novoselov used a process called the ‘scotch tape technique’ in which scotch tape was repeatedly used to peel off layers of graphene from a piece of graphite until only a single layer of atoms remained. This earned the two scientists a Nobel prize in 2010.
In the near future, graphene could potentially be used for electrical components and other items such as sensors, batteries, composites, ion-exchange membranes and other products. The research team will be focusing on three projects involving graphene and two-dimensional materials which could be used in a range of applications. One of the projects will develop a low-cost inkjet printing technique for building micro-sensors. These could then be used in the energy sector and for military applications. Another project will look at the potential for using graphene in water desalination.
Professor Brian Derby of Manchester University, speaking to The Engineer, explained that the advantage of using graphene in battery electrodes, to cite just one example, is that it has a very high surface area and yet is only one atom thick. However, in order for the material to be useful, the atom-thick layers have to be packaged in a 3D object. This is why the researchers will be attempting to produce foam from graphene in order to develop ways of packaging the material so that they can be assembled in space but hold their surface area as much as possible. The team are also hoping to develop composites in which graphene flakes are dispersed within a polymer matrix, thus creating a strong but still workable composite.
Graphene research at the University of Exeter, UK [Image: University of Exeter, Flickr]
How could graphene benefit the renewable energy sector?
In 2011, engineers at Northwestern University found that graphene anodes hold energy better than graphite, thereby enabling ten times better battery charging, with potential applications including use in electric vehicles (EVs). In 2013, researchers at Rice University in Texas, predicted that graphene, with the addition of some boron atoms, could be used to produce an ultrathin flexible anode for lithium ion batteries. The boron helps the lithium ions to stick to the graphene, thereby helping to deliver fast charging, which is why the Rice University research was conducted in association with Honda, just one of many vehicle manufacturers currently producing new EV models. Other companies, such as Kia and Hyundai have shown interest in the material, both companies filing patents for the use of graphene in fuel cells.
The Rice University researchers also found that graphene mixed with vanadium oxide can be used to develop high performance, cost-effective cathodes that can be recharged in 20 seconds and retain more than 90 percent of their capacity after extensive use. Graphene can also be used for supercapacitors and UCLA researchers have discovered that it can be coated onto a DVD. A DVD burner can then be used to inscribe millions of supercapacitor circuits into the graphene layer which can be subsequently peeled off and used by anyone requiring a super powered battery. Scientists in Sweden have also discovered that maghemite, a type of iron oxide similar to red ore, can be added to graphene causing it to roll up into a nanoscroll. These can then be used as electrodes in lithium ion batteries.
Professor Forsyth of Manchester University’s School of Electrical and Electronic Engineering believes that graphene can help to boost the efficiency of EVs by reducing the weight of batteries which currently can weigh around 200 kilograms. This would also help to extend the range of EVs beyond 100 kilometers, range anxiety currently being the major factor delaying their uptake. However, graphene’s use in batteries could also boost the energy storage sector, with Manchester University itself having trialed a grid-scale battery and converter system on its campus.
Mercedes SLS AMG E-cell at Geneva Motor Show [Image: Cedric Ramirez, Flickr]
With regard to solar PV, graphene can be used to develop anti-reflection coatings for solar cells, researchers in India having found that the material can reduce reflectance near the ultraviolet part of the solar spectrum from 35 percent to just 15 percent. Silvija Gradečak of Massachusetts Institute of Technology (MIT) has also found that graphene in PV cells can deliver higher power conversion efficiency while other researchers at Michigan Technological University have found that graphene can replace platinum in solar cell electrodes with no loss of efficiency.
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Another potential use for the material is replacing Indium Tin Oxide (ITO) in solar cells. This is a material that is rare and expensive. It is currently used for transparent electrodes but it is also very brittle. MIT scientists are hoping to develop a new solar cell made from graphene and molybdenum disulphide, resulting in a solar cell that is thin and light with 1000 times greater efficiency than conventional silicon panels.
In fuel cell electric vehicles (FCEVs), graphene could help to reduce the cost of renewable hydrogen fuel which in turn would mean more hydrogen fuel stations due to lower costs for processing. Graphene doped with nitrogen and augmented with cobalt has been shown by Rice University scientists to be an effective and durable catalyst for hydrogen production from water, replacing expensive platinum.
Thus far then, the two major renewable energy applications of graphene therefore appear to be solar cells and batteries for EVs, although the overall market for the material is now worth in excess of $9 million across semiconductors, electronics, batteries and composites.
Manchester University's planned new Graphene Engineering Innovation Centre (GEIC) [Image: Manchester University]
The UK is now racing ahead with this, Manchester University now being on track towards building a second specialist graphene research centre which has just been granted planning permission on 15th February. The Graphene Engineering Innovation Centre (GEIC) will focus on industry-led development and application of graphene products, co-operating with the National Graphene Institute (NGI) and the proposed Sir Henry Royce Institute for Advanced Material Research in order to enable graphene development from initial research to end products, thereby establishing Manchester as a leading global hub for graphene research. The emphasis will be on the improvement of currently existing materials and opening up new markets with funding for the GEIC largely provided by Abu Dhabi renewable energy company Masdar and the Higher Education Funding Council for England’s UK Research Partnership Investment Fund (UKRPIF). The centre is due to be completed by the end of 2017.