Graphene may be a wonder material, poised to revolutionise the electronics industry; with applications far beyond the humble CPU. But it isn’t magic. And as much as we are all used to extraordinary claims being made about the material, there is one law which all physicists hold above all others: the second law of thermodynamics.
Don't mess with the second law, people. Eyes start twitching.
According to a blog post over at Nature.com, a recent publication in Cornell University’s arXiv e-print service has kicked off a lively debate on just these terms: can there ever be such a thing as a free lunch?
The paper describes six cell battery, each cell being composed of silver and gold electrode on a graphene sheet, all suspended in a copper chloride solution. According to the paper, each cell generates 0.35 Volts, and six cells connected in series were used to power a light emitting diode.
The question is: where is the energy coming from. The paper’s author, Zihan Xu of the Hong Kong Polytechnic University interpret the voltage as evidence that the thermal energy, or movement of ions within the solution, is enough to knock electrons in the graphene sheet free. Graphene has such high electron mobility, the researchers argue, that the thermal energy is converted into electric potential.
Guess what? Not everyone agrees with this interpretation. Some scientists argue that any electrons freed by such collisions would be reabsorbed quickly into holes in the graphene, and that the energy is more likely dissipated as heat. A chemical reaction has been put forward as the most likely explanation.
The post on Nature.com concludes with a quite attributed to Yury Gogotsi of Drexel University in Philadelphia, Pennsylvania. He is sceptical of the claim, but argues: "The device described by Xu’s group is very simple and numerous labs can easily repeat this experiment to check the validity of the results."
So a lively debate, but probably not a long running one.