Researchers create self charging "ambient" battery w/ graphene (Maxwell's demon)

reply to post by Aim64C

Well, lets start with graphene www.youtube.com...

To get a bit more serious. Ideally you would want to have access to a semiconductor lab to replicate the experiment I think. Not sure if one could pull this off with a home chemistry kit.

Monolayer graphene samples were fabricated by chemical vapor deposition (CVD)...
A typical graphene sample of size 7 mm × 7 mm was then transferred onto SiO2 (300 nm)/Si
substrate. Au and Ag electrodes were deposited on either side of graphene by thermal
evaporation. All the electrodes, graphene edges and substrates were sealed from exposing to
the electrolyte solution.

reply to post by moebius


. . .

I think we may have answered our polarity question inadvertently.

I believe we have been presuming a piece of graphene 'flapping' between two electrodes (not really, since it would be pulled relatively taught... but you get what I mean).

However, the source says that it was affixed to a silicon-oxide substrate... this would provide some additional rigidity and durability while also limiting the incidence angle of the high-energy ions.... so that they would never have opposite angles of incidence relative to the plane.

reply to post by Aim64C


I don't see anything about a SiO2 substrate in the paper, so I don't think they use that. But interestingly, it seems the paper was updated with part of the supplement. There is now more discussion added and a small passage that speaks about the direction of the current.

The current direction can be determined for the device with Au-Ag as asymmetric electrodes (Supplementary ,red, Figure 11a).This is because work function of gold (5.0 eV) is larger than that of graphene (4.6 eV), while work function (4.26 eV) of silver is smaller than that of graphene. Therefore, we present a work-function tuning mechanism based on the overall experimental results (Figure 11b).

There is also an image that shows the voltage when electrodes of the same material is used and it is pretty much random. To me that is enough evidence that the material of the electrodes is the answer. I don't really see why any additional mechanism is required to determine the direction of the current.

reply to post by Aim64C


I don't see anything about a SiO2 substrate in the paper, so I don't think they use that. But interestingly, it seems the paper was updated with part of the supplement. There is now more discussion added and a small passage that speaks about the direction of the current.

The current direction can be determined for the device with Au-Ag as asymmetric electrodes (Supplementary ,red, Figure 11a).This is because work function of gold (5.0 eV) is larger than that of graphene (4.6 eV), while work function (4.26 eV) of silver is smaller than that of graphene. Therefore, we present a work-function tuning mechanism based on the overall experimental results (Figure 11b).

There is also an image that shows the voltage when electrodes of the same material is used and it is pretty much random. To me that is enough evidence that the material of the electrodes is the answer. I don't really see why any additional mechanism is required to determine the direction of the current.

reply to post by Aim64C


I don't see anything about a SiO2 substrate in the paper, so I don't think they use that. But interestingly, it seems the paper was updated with part of the supplement. There is now more discussion added and a small passage that speaks about the direction of the current.

The current direction can be determined for the device with Au-Ag as asymmetric electrodes (Supplementary ,red, Figure 11a).This is because work function of gold (5.0 eV) is larger than that of graphene (4.6 eV), while work function (4.26 eV) of silver is smaller than that of graphene. Therefore, we present a work-function tuning mechanism based on the overall experimental results (Figure 11b).

There is also an image that shows the voltage when electrodes of the same material is used and it is pretty much random. To me that is enough evidence that the material of the electrodes is the answer. I don't really see why any additional mechanism is required to determine the direction of the current.

reply to post by Aim64C


I don't see anything about a SiO2 substrate in the paper, so I don't think they use that. But interestingly, it seems the paper was updated with part of the supplement. There is now more discussion added and a small passage that speaks about the direction of the current.

The current direction can be determined for the device with Au-Ag as asymmetric electrodes (Supplementary ,red, Figure 11a).This is because work function of gold (5.0 eV) is larger than that of graphene (4.6 eV), while work function (4.26 eV) of silver is smaller than that of graphene. Therefore, we present a work-function tuning mechanism based on the overall experimental results (Figure 11b).

There is also an image that shows the voltage when electrodes of the same material is used and it is pretty much random. To me that is enough evidence that the material of the electrodes is the answer. I don't really see why any additional mechanism is required to determine the direction of the current.

reply to post by -PLB-

SiO2 comes up in the Methods Summary. That is where I've copied it from.

What I find strange in the revised paper is that they are not mentioning/explaining the rapid voltage decline after 20 days. Please compare Figure 1.c of v1 which only goes from 0-20 days with v2 going 0-35 days.

This makes it look very much like a battery, even if they claim to have excluded to possibility of electrochemical reactions by control experiments.

Here a typical battery discharge curve: www.ebme.co.uk...

Originally posted by moebius
reply to post by buddhasystem

 

As Aim64 said. The electrode potential would be canceled. Graphene is a conductor(think of Faraday cage). There would be a potential at the contact of the electrodes with graphene, but no potential in the graphene.

The researcher mentions that peak output power is through a 22kR resistor, which hints the internal impedance of the system is also 22kR. As the electrodes are silver and gold, this could only be because of the graphene.

Electrode potentials aside, there could also be a semiconductor junction effect between one or both of the electrodes and the graphene, effectively making it function like a diode, giving a preferred direction for the received electrons.

reply to post by moebius


Ah yes, I used the wrong search parameter. After reading the paper again I found it. They seem to imply that the voltage dropped because:

"But it was found that graphene grains had falled off from SiO2 (300 nm)/Si substrate after immersed in the solution for 33 days, which was confirmed by Raman spectrum.".

So the graphene layer was pretty much destroyed after 33 days. Of course that event could coincide with the chemical energy being depleted, but for now I am willing to give them the benefit of the doubt, as experiments without the graphene layer resulted in no potential at all.

Although this of course generates a major problem. If the graphene layer is so fragile, even if the device works as proposed, I can't see how this can ever be used in a useful application.

reply to post by -PLB-

Thanks -PLB-. I must have overlooked it while comparing both versions, will reread the new paper. The destruction of the surface is indeed an issue. So there might be galvanic corrosion of the graphene. But then it must have been reproducible with graphite. Interesting.

Figure 1.b in supplementary material is most interesting imho, showing voltage with graphite electrodes(same material at contacts). No idea how to explain this. I wish they would have run all control cells for the same period of 33 days to have some more data.

Update:

I discovered that the thesis advisor of one of the authors has tried without success to reproduce the experiment and he believes that the seals around the electrodes are not good so they are just making a weak conventional battery.

www.technologyreview.com...

I haven't been able to find more info on this, but it sounds plausible.