rexresearch
Zihan XU
 Graphene Battery
http://arxiv.org/abs/1203.0161
Self-Charged Graphene Battery Harvests Electricity from Thermal Energy of the Environment
 Zihan Xu, Guoan Tai, Yungang Zhou, Fei Gao, Kin Hung Wong
 [ PDF ]
12 Mar 2012




The energy of ionic thermal motion presents universally, which is as high as 4 kJ\bullet kg-1\bullet K-1 in aqueous solution, where thermal velocity of ions is in the order of hundreds of meters per second at room temperature1,2. Moreover, the thermal velocity of ions can be maintained by the external environment, which means it is unlimited. However, little study has been reported on converting the ionic thermal energy into electricity. Here we present a graphene device with asymmetric electrodes configuration to capture such ionic thermal energy and convert it into electricity. An output voltage around 0.35 V was generated when the device was dipped into saturated CuCl2 solution, in which this value lasted over twenty days. A positive correlation between the open-circuit voltage and the temperature, as well as the cation concentration, was observed. Furthermore, we demonstrated that this finding is of practical value by lighting a commercial light-emitting diode up with six of such graphene devices connected in series. This finding provides a new way to understand the behavior of graphene at molecular scale and represents a huge breakthrough for the research of self-powered technology. Moreover, the finding will benefit quite a few applications, such as artificial organs, clean renewable energy and portable electronics.
    

http://physicsworld.com/cws/article/news/2012/mar/08/graphene-in-new-battery-breakthrough
Graphene in new ‘battery’ breakthrough?

Mar 8, 2012
Researchers at Hong Kong Polytechnic University claim to have invented a new kind of graphene-based "battery" that runs solely on ambient heat. The device is said to capture the thermal energy of ions in a solution and convert it into electricity. The results are in the process of being peer reviewed, but if confirmed, such a device might find use in a range of applications, including powering artificial organs from body heat, generating renewable energy and powering electronics.
Diagram showing the experimental set-up of the battery.

 Another triumph for graphene?

Ions in aqueous solution move at speeds of hundreds of metres per second at room temperature and pressure. The thermal energy of these ions can thus reach several kilojoules per kilogram per degree. However, until now, little work had been done on finding out how to tap into this energy and produce power from it.
Zihan Xu and colleagues made their battery by attaching silver and gold electrodes to a strip of graphene – which is a film of carbon just one atom thick. In their experiments, the researchers showed that six of these devices in series placed in a solution of copper-chloride ions could produce a voltage of more than 2 V. This is enough to drive a commercial red light-emitting diode.
The technology is quite different to conventional lithium-ion batteries, for example, which convert chemical energy into electricity. "The output of our device is also continuous and it works solely by harvesting the thermal energy of the surrounding copper-chloride ions, which, in theory, is limitless," says Xu.
According to the researchers, the battery works rather like a solar cell. The copper ions (Cu2+) continually collide with the graphene strip in the battery. This collision is energetic enough to displace an electron from the graphene. This electron can then either combine with the copper ion or travel through the graphene strip and into the circuit.
Since electrons move through graphene at extremely high speeds (thanks to the fact that they behave like relativistic particles with no rest mass), they travel much faster in the carbon-based material than in the ionic solution. The released electron therefore naturally prefers to travel through the graphene circuit rather than through the solution. This is how the voltage is produced by the device, explains Xu.
Boosting voltage output

The researchers also found that the voltage produced by the device could be increased by heating the ionic solution and accelerating the Cu2+ ions with ultrasound. Both of these methods work because they increase the kinetic energy of the ions. The voltage also increases if the copper-chloride solution is more concentrated with Cu2+ ions, because the density of Cu2+ on the graphene is then greater. Other cationic solutions can be employed too, such as Na+, K+, Co2+ and Ni2+, although these produce lower voltage outputs.
The unique atomic-layer nature of graphene is crucial for this battery, say the researchers, who also experimented with graphite and carbon-nanotube thin films. They discovered that these materials only produced low voltages of around microvolts, which could be regarded as noise.
Bor Jang of Nanotek Instruments in Dayton, Ohio, who has worked on making supercapacitors from graphene, says that the concept described looks "very interesting" but that "more work will be needed to assess whether the approach could provide sufficient energy or power density for practical uses".
For its part, the Hong Kong team now plans to improve the power output of its graphene-based device and further investigate how it works.

http://www.technologyreview.com
March 5, 2012
Graphene Battery Turns Ambient Heat Into Electric Current

Physicists have built a graphene battery that harvests energy from the thermal movement of ions in solution.
Here’s an interesting idea for a battery. The thermal velocity of ions in aqueous solution is huge–hundreds of metres per second at room
temperature. And yet few people have studied this process or its potential to generate current.
Step forward Zihan Xu at The Hong Kong Polytechnic University and a few buddies who have not only studied this process but seemingly mastered it
too.
These guys have created a circuit consisting of an LED connected to a strip of graphene by some wire. They simply placed the graphene in a solution of copper chloride and watched. Sure enough, the LED lights up. (Actually, they needed six of these graphene circuits in series to generate the 2V needed to make the LED light up but you get the picture.)
Here’s what’s going on, according to Zihan and co. The copper ions, which have a double positive charge, move through the solution at a rate of about 300 metres per second thanks to the thermal energy of the solution at room temperature.
When an ion smashes into the graphene strip, the collision generates enough energy to kick a delocalised electron out of the graphene.

The electron then has two options: it can either leave the graphene strip and combine with the copper ion or it can travel through the graphene strip and into the circuit.
It turns out that the mobility of electrons is much higher in graphene than it is through the solution, so the electron naturally chooses the route through the circuit. It is this that lights up the LED.

“The released electrons prefer to travel across the graphene surface…instead of going into the  electrolyte solution. That is how the voltage was produced by our device,” say Zihan and co.

So the energy generated by this device comes from ambient heat. These guys say there were able to increase the current by heating the solution and also by accelerating the copper ions with ultrasound. They even claim to have kept their graphene battery running for 20 days on nothing but ambient heat.
But there’s an important question mark. One alternative hypothesis is that some kind of chemical reaction is generating the current, just as in an ordinary battery.

However, Zihan and co say they ruled this out with a couple of control experiments. However, these are described in some supplementary material that they do not appear to have put on the arXiv. They’ll need to make this available before others will take the claim seriously, of course. 

Taken at face value, however, this looks to be a hugely important result. Others have generated current in graphene simply by passing moving water over it, so it’s not really a surprise that moving ions can do the job as well.

It raises the prospect of clean, green batteries powered by nothing but ambient heat. As  Zihan and co modestly put it: “it represents a  huge breakthrough for the research of self-powered technology”.
Let’s hope they’re right. But for the moment at least, the jury must remain undecided.
Ref: arxiv.org/abs/1203.0161 <http://arxiv.org/abs/1203.0161>: Self-Charged Graphene Battery Harvests Electricity from Thermal Energy of the Environment

Graphene battery
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A graphene battery comprises a container housing, ion salt solution in the container housing, a substrate, a graphene film, a first electrode, a second electrode, two metal leads and a glue sealing layer. The graphene film is bonded to one surface of the substrate; the first electrode is prepared from a conductive material with a higher work function than graphene and is deposited at one end of the graphene film; the second electrode is prepared from a conductive material with a work function lower than or similar to the graphene and is deposited at the other end of the graphene film; the two metal leads are respectively connected with the first electrode and the second electrode; the glue sealing layer is cladding out of the first electrode and the second electrode; and the substrate, the graphene film, the first electrode, the second electrode, the two metal leads and the glue sealing layer are integrated as a whole to be immersed in the ion salt solution, and the two metal leads are led out to the exterior of the container. According to the utility model, the graphene battery is safe and reliable, no power or charging is required, the usage life is long, and no harm is caused to the human body and the environment.

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[ PDF ]

The invention discloses a power generating method adopting an ionic thermal motion principle. The power generating method comprises the following steps of: firstly, transferring graphene to a substrate and bonding a graphene film on the substrate; secondly, depositing a conducting material with a work function higher than that of the graphene at one end of the graphene film to obtain a first electrode and depositing a conducting material with a work function lower than that of the graphene at the other end of the graphene film to obtain a second electrode; thirdly, leading out the first electrode and the second electrode at two ends of the graphene film by using two metal wires; and fourthly, holding an ionic salt solution in a container casing, integrally immersing the substrate, the graphene film, the first electrode, the second electrode and the two metal wires in the ionic salt solution and leading the metal wires to the outside of the container casing. The invention also provides a graphene battery manufactured by using the power generating method. The power generating method adopting the ionic thermal motion principle and the graphene battery manufactured by the power generation method have the advantages of safety, reliability, no need of using power for charging, long service life of the graphene battery and no harm to a human body and environment.

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[ PDF ]




A graphene power-generation device comprises a container shell, ion salt solution, a substrate, a graphene film, a first electrode, a second electrode and two metal wires, wherein the graphene film is bonded on the substrate, and the graphene film is a one-layer film, a two-layer film, a three-layer film or a four-layer film and is a mixed film containing the above-mentioned one film, the above-mentioned two films or the above-mentioned more films; the first electrode is made of conducting materials, is deposited at one end of the graphene film and is in contact with the graphene film; the second electrode is made of conducting materials, is arranged at the other end of the graphene film and is not in contact with the graphene film which is in contact with the first electrode; the two metal wires are respectively connected with the first electrode and the second electrode; and the substrate, the graphene film, the first electrode, the second electrode and the two metal wires are packaged into a whole and are soaked into the ion salt solution, and the two metal wires are led to the outer part of the container shell. The graphene power-generation device is good in safety and reliability, long in service life and non-harmful to human and environment.

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