by Brian Clegg
However, the industry has plenty of experience at making circuitry that will gradually release a capacitor’s charge – it just takes more than the capacitor alone. The other problem, capacity, has proved more intractable. Until recently, the amount of charge a capacitor can hold has not been sufficient to make them a useful replacement for a battery.
Supercapacitors, which (as the name suggests) store far more energy than conventional capacitors, are already in use, for example in electric cars using regenerative braking where the electrical energy produced during braking has to be rapidly stored. However, they are relatively bulky and limited by the ability of their electrodes to handle electrical currents. Graphene has the potential to facilitate improvement on existing designs.
At the moment, a supercapacitor that would fit into a mobile phone could only hold around 10 per cent of the charge of an equivalent-sized battery. But by giving the supercapacitor ultra-high-capacity electrodes, its storage can be significantly increased. The Waterloo team have made their prototype supercapacitors from multiple layers of graphene sheets, separated by an oily liquid salt. This medium prevents the graphene sheets from directly interacting and losing their two-dimensional properties – resulting in a multi-layer electrode that can handle far more electrons. The role is not just structural, though – the oily liquid salt provides the dielectric medium for the supercapacitor – so the whole component becomes far smaller in size and weight than with conventional materials.
Although with current designs it’s unlikely that supercapacitors will entirely replace batteries, it’s certainly a possibility for the future, as we are still very much at the start of developing ultrathin technology. Think how long it has taken us to get to our current battery capability – yet graphene has only been in practical use a handful of years. Within a relatively short timescale, graphene-based supercapacitors could give us phones that charge in seconds, and the ability to top up an electric vehicle’s power in less time than it takes to fill a tank with petrol. If that were to happen, what is arguably the biggest drawback of electric cars will be removed and we can look forward to far greener transport.
At the other extreme of scale to supercapacitors, tiny graphene capacitors have already been used as a way of detecting previously undetectably small changes in pressure.
Under pressure
In an ultrathin pressure sensor, graphene sheets on a thin polymer substrate are arranged across shallow depressions in a silicon chip. Any change in pressure on the graphene membrane changes the distance between the graphene and the silicon, closing the gap. In combination, the graphene and the air gap act as a capacitor: as the distance between the two substances changes minutely, the capacitance of the device changes too, which can be measured in a circuit.
As well as providing an alternative approach to the Sussex touch screen mentioned above, this type of sensor could be used in future to monitor engines, heating, ventilation, air conditioning and more, with remarkable sensitivity.
Before we leave the topic of energy, graphene has one more surprise to reveal. It isn’t just able to store energy, it can generate it too.
The smallest generator
We have already seen (page 86 ) that before Geim and Novoselov’s work, it had been expected that graphene would be unstable, ripping itself into blobs of carbon under the influence of the natural movements of its atoms. However, a combination of its unexpectedly large tensile strength and the restraining van der Waals forces when it is based on a substrate have tended to keep it in check. But a team at the University of Arkansas have not only spotted some residual action in the graphene atoms; they also believe that they can harness the energy of movement to produce a tiny electrical generator.
It all started when they were observing graphene under an electron microscope on a copper substrate. The image they got initially was confusingly unclear. It was only when they managed to break down what was happening in time and space that they realised they were seeing the carbon atoms fluctuating up and down in a random rippling. This was made up of a particular type of random distribution that has occasional much larger jumps, known as a Lévy flight. The rippling was the result of the heat in the room providing energy to keep the carbon atoms in energetic motion.
All the molecules in a liquid or gas are also in random motion, of course, moving far faster than the atoms in a solid. We see this in Brownian motion – the way that tiny particles of matter, if suspended in water, are bounced around by the constant barrage of moving water molecules. But the big difference is that the usual random motion can’t be harnessed because all the different motions in different directions cancel each other out. The motion of those particles is a truly random walk. Things are different, though, with graphene.
Because all the atoms are in a single lattice in a sheet, they are constrained to move more together, and rather than producing a self-cancelling collection of tiny movements, the movements occur in similar directions causing relatively large-scale ripples in the graphene, which is where it is hoped energy can be produced.
There is still some concern here that what works in theory might not work in practice. While a prototype nano-generator has been designed, it has yet to be constructed and tested. However, in principle this could mean that devices requiring small amounts of power could be kept running indefinitely by a tiny power source that never needs replacing.
Note, by the way, that this not yet another perpetual motion fantasy or a variant on Maxwell’s demon. § The energy is not being produced from nowhere. Using the device would slightly cool its surroundings as it is the thermal energy of the graphene’s surroundings, ultimately originating from sunlight, that drives it. It is, in effect, an indirect solar engine making use of ambient heat.
The only thing that makes this unlikely behaviour possible is the remarkable strength of graphene, which prevents the thermal fluctuations from tearing it apart. But clearly there are other benefits to be gained from the super strength.
Super strength in action
As we’ve already seen, graphene is by far the strongest substance as far as tensile strength goes. This means that it is almost certain to have a role in applications where strength is key, and materials are being developed with multiple strips of graphene embedded in different kinds of polymer. Wherever, for example, carbon fibres have been used to date, if even they aren’t strong enough, graphene is likely to take over.
Of course, some strength-related applications are liable to be more spin than substance. Being able to say that you have the strongest material ever discovered in your product could easily give it an apparent edge that thin slivers of graphene may not realistically deliver. For example, running shoe manufacturer Inov-8 has designed a new ‘G-series’ running shoe in collaboration with the Graphene Institute. Due out in 2018, the G-series will have graphene included in their rubber soles. The sportswear manufacturer claims that it will ‘make the shoes stronger, stretchier and more durable’. It might seem this is a running shoe equivalent of cosmetic magic ingredients such as Pro-Retinol A, and we are certainly likely to see graphene turning up in quite a few products where its presence is more about the name than anything else. However, the contribution of the Institute team does make the running shoe claims seem more likely, and indeed Manchester researcher Aravind Vijayaraghavan claims that ‘The graphene-enhanced rubber can flex and grip to all surfaces more effectively, without wearing down quickly, providing reliably strong, long-lasting grip.’
Even though a certain amount of flummery may well be in store, though, it’s worth remembering that graphene is not a brand name or just a bit of ‘science stuff’ to make trainers seem more impressive. It is, without doubt, a true wonder material.
Pinch me
The previous section on graphene’s strength was going to be my last example of graphene applications, but this is a topic where everywhere you turn something new is being tried – and one of the latest announcements at the time of writing was yet another totally diff
erent way to use graphene. Researchers working at the University of Minnesota’s College of Science and Engineering have found a way to produce graphene tweezers so small that they can grab hold of individual biological molecules floating in water.
What’s happening here has been done for some while, using a process called dielectrophoresis – but it was incapable of working at the scale of single molecules. The mechanism works by holding the item to be trapped in an intense electrical field. Because graphene is so thin, coupled with its superb conductivity, using its edge to produce this pinpoint localised field is far more precise that has otherwise been possible.
Because the graphene electrodes are so narrow, the voltage required to set up the field is small. In conventional dielectrophoresis, high voltages that are only usable under controlled laboratory conditions are required. But the graphene electrodes could grab, for example, a molecule of DNA with only 1 volt needed. Not only does this make the procedure much safer, it also means in principle that it’s possible to imagine medical diagnostics devices linked to a smartphone that could use this technique to isolate biological molecules and analyse them for diagnosis of diseases.
The analysis part does not even require a separate device. The tweezers can not only be used to grab a molecule but to act as extremely sensitive biological sensors which could enable the same tiny piece of kit to provide the data for a range of diagnostics. The Graphene Express goes on and on.
And there’s more
All of the above might seem more than enough – far more than anyone could have imagined when graphene was first discovered. From our experience with carbon fibres, it’s possible that graphene’s tensile strength could have been predicted. And there was already a suspicion that its electronic capabilities might have been interesting. But no one could have guessed just how massive a change graphene and the other two-dimensional substances would bring. And those discoveries keep coming. Look at one of the online resources at the back of the book and you will likely find a whole string of new graphene discoveries – often all made in recent months. This is not a single breakthrough but a massive chain of events.
In a sense, graphene has ushered in a whole new type of materials science dealing with these ultrathin materials. When researching this book, I could have filled a whole chapter with just the innovations discovered in one year. With their flexibility, transparency, strength and small scale, ultrathin materials are appealing to thousands of researchers across the world. It’s almost as if we had been given a whole new set of elements – certainly of structural building blocks – and were able to start manufacturing devices that were previously inconceivable.
All this started with those Friday night experiments in Manchester. And just as the capabilities of ultrathin materials have blossomed, so have the facilities and staff involved in this work.
From backroom to mainstream
Beginning with those initial small, spare-time experiments in Manchester, work on graphene and other ultrathin materials has seen a worldwide boom, with activities under way in all the major research countries, recognising the technological promise of these materials. A decade on from the publication of Geim and Novoselov’s discovery in 2004 – a very short time in terms of such a major technological breakthrough – activity had become intense, and it only continues to grow. To see how much has been made possible by graphene, we only have to look again at developments at Manchester University.
In Manchester, Geim and Novoselov originally worked in a small clean room in a corner of an old building on the campus. As interest grew, the university found that the expansion of work on graphene and other two-dimensional structures was taking off at a far faster rate than their available capacity could cope with. Within a few years of the pair winning their Nobel Prizes in 2010, there were 30 professors and around 200 students working in Manchester, all dedicated to this field. With accommodation in existing buildings stretched at best, the university got grants to build a new National Graphene Institute on a spare plot of land on the Manchester campus.
The specification was, to say the least, challenging. Konstantin Novoselov has described the Institute as ‘a building of probably unrivalled complexity’. Not only did it require large numbers of clean rooms for working in a totally dust- and contamination-free environment, ¶ it was being built for equipment that was as yet not even designed and for purposes that would not become clear until research moved further on. One thing that is certain with graphene research is that it will always feature surprises.
Construction began on the Institute in 2013, based on a complex architectural specification. Not only would the clean rooms have to be protected from air pollution, it was also essential that vibration was kept to a minimum, as sensitive devices such as scanning tunnelling microscopes, and the whole business of manipulating materials at the nanoscale, were easy to disrupt. The Institute building was to be located on a main road, a constant source of vibration, so the main clean room was pushed five metres below ground level, enabling it to be anchored directly to the bedrock below. Similarly, the section of the Institute containing heating and air conditioning units, which inevitably cause some vibration themselves, was given a clear 50-millimetre insulating gap to separate it from the rest of the building.
In a way, Geim and Novoselov’s Friday night thinking approach proved both a bonus and a challenge for the builders of the Institute. Novoselov, who was the more involved of the two in the design, made it clear that the optical, electronic, chemical and general laboratories needed to be easily adaptable for future unknown experiments and wanted offices that were interspersed with the labs, so there was easier sharing of information and ability to take in different viewpoints, rather than taking the architecturally simpler approach of putting all the offices together, separated from the lab work. The building was also designed to have a biodiverse roof garden with grasses and wildflowers to attract bees and other pollinators.
The National Graphene Institute building was fully opened in 2015 and is to be followed by two further developments. At the time of writing, construction is nearly complete on the institute’s sister Graphene Engineering Innovation Centre, which is due to open in mid-2018. This is designed to provide the next step for the original research that emerges from the Institute, putting many of the concepts mentioned in the previous pages into prototyping for production, ironing out the engineering challenges that always arise when going from the lab to the factory.
The Innovation Centre will be followed a year later by the significantly larger-scale Sir Henry Royce Institute for Advanced Materials Research, providing a centre for work on ultrathin materials as well as a range of other specialist material science developments. With its hub sited across the road from the Graphene Institute, the Royce Institute is a joint partnership between the universities of Manchester, Sheffield, Leeds, Liverpool, Cambridge, Oxford and Imperial College London, cementing Manchester’s position as the world’s leading location for ultrathin development – all because of Geim and Novoselov’s original way of thinking.
Patents and Flagships
Although the work in Manchester is world-leading, the scope and potential benefits of graphene and the other ultrathin materials are so wide-reaching that large sums are being invested across the world to advance research and bring products to market. This is reflected in the graphene-based patents issued. In 2007, 161 patents were issued. By 2009/10 the rate was up to around 1,000 a year. This rise continued to a peak of nearly 7,000 patents in 2015 – this dropped in 2016, but at the time of writing it’s too early to know if this was just a short-term deviation.
The business of patenting here is a complex one. Graphene itself couldn’t be patented – it’s a natural phenomenon – and European companies and universities and businesses have been slow to take out patents. By far the most prolific collectors of patents are China and Korea, with the US next. Many of the patents will never result in practical outputs, and some are regarded as cynical business ploys in a p
rocess known as patent trolling, where companies issue as widespread patents as they can in the hope of catching some future development in their net.
It’s also the case that around 98 per cent of the Chinese patents, for example, only cover China and seem to be due to a quota system that drives a large number of dead-end patent applications. What is interesting is that when the number of graphene-producing organisations is compared, while China still comes top, the US is next, followed by the UK. More interesting still, we have to bear in mind how the sheer size of the Chinese and US economies distorts absolute figures. When the graphene producers are taken as a proportion of GDP, Spain tops the table with the UK in second place, then India, pushing China into fourth. Countries such as Spain and the UK seem to be performing better than might be expected because there has been a conscious funding bias towards graphene developments.
There is no doubt that there will be significant product development from the patent-hungry countries – but as we have seen, a big investment is being made in research in the UK, and this is matched by a wider push in Europe through a collaboration known as the Graphene Flagship. This pulls together input from over 150 academic and industrial research groups in 23 mostly – though not uniquely – European Union countries. Although the Graphene Flagship is inevitably more bureaucratic in operation than a single institute, it has the ability to pull together information on an unprecedented scale.
