That mystery paper that Daniel Nocera presented on at the CSC? It finally came out in Science today (doi: 10.1126/science.1162018) as a ScienceXpress [1].
It's all electrochemistry mumbo-jumbo, which uses some sort of implied Co2+ catalyst to split water. I can neither claim to understand or describe it, so here's an idea: the first person to respond in the comments with a plain English explanation of the concepts gets a prize. A prize of solid gold![2]
(Via Digg, if you can believe it or not. Science news travels quickly!)
1. Lamest name ever, seriously. The AAAS should rename it ScienceXXpress (science-double-x-press)!
2. Okay, maybe just gold nanoparticles. Okay, maybe just a mixtape and a piece of science memorabilia. Of solid gold! Actually, you can negotiate the prize after you explain the science. Prize money tops $25.
Thursday, July 31, 2008
Daniel Nocera's big secret paper
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9 comments:
the abstract is certainly tantalizing (curse my lack of access at home!)
OK, i'm a PhD student in echem/surface science (fuel cell focus). I'll take a stab at explaining, but keep in mind i don't know who my audience is.
Basically, Nocera is reporting that he has come up with a catalyst that splits water at much higher efficiencies than anyone else has achieved.
By applying a potential that is a mere 60mV above the thermodynamic value (1.29V vs. 1.23, this is the "overpotential"), he can achieve a reasonable rate of O2 formation. He uses Pt on the other side for H2 formation (reduction).
Previous attempts also use highly concentrated KOH solutions to try and bring down the overpotential for water oxidation. IF you need to know why, study up on the Nernst equation.
Furthermore, he reports that changes of a single pH unit are equivalent to 59mV changes in overpotential, which is consistent with a Nernstian process (ie: follow the Nernst equation).
And, he does a bunch of mass spec and NMR to identify the species coming out of this process...and confirm that the O comes from water etc.
The advantages to using Co in-situ is
1.)that he can continuously clean (regenerate) the surface of the catalyst due to the solubility of different oxidation state of Co -- It's robust
2.)He is using Co vs. expensive Pt
3.)His process uses "safe" environmentally friendly chemical (if you don't consider Co as a heavy metal)
4.) It avoids time-consuming and sometime harsh catalyst processing and synthesis techniques -- meaning it can be formed once the electrolyzer/fuel cell has been assembled)
However, he has very little data on what form this catalyst takes (its an amorphous mess) and he has very little data on the mechanism by which it occurs. He could also do A LOT more electrochemical characterization as well as some solid state measurements of film conductivity. I'd also like to see him change the substrate and publish a schematic of his cell setup. It's also be interesting to see how it works for O2 reduction.
Enough to get a prize?
Cheerios,
SEB
Where's the Beef?
OK it's Nernstian but that does not mean it is efficient enough for real applications.
There is no mention of current density or possible Ohmic heating causing all sorts of real world problems.
At best he describes a solution to a quarter of the problem.
There will still be Pt on three electrodes.
I'll wait for the Beef.
I don't think the Nernstian argument has anything to do with the kinetics. All it aims to suport is that there is no side reaction occurring that could explain(refute) his results(conclusions).
The current density at 60mV overpotential is greater than 1mA/cm2 at 8 hours, which is reported in the paper...along with other runs in pH=7 solution with no Co ion present. This means they can generate about 2.3e-7 L/cm2*s of O2 even with a poorly dispersed, low surface area catalyst at low overpotential <-- This is based on the data in solution containing Co ion. It is not as good for catalyst with no Co present at pH=7. Also, it does not specify a mass activity.
All in all, that is pretty decent and good enough for a lot of startup money. Also, take a look at the CV and you can get an idea of some sweet kinetics.
The CVs they published don't show signs of significant IR drop in their cell, however this is why i'd like to see conductivity data on the catalyst itself. In any case, low conductivity catalyst could perhaps be worked around by dispersing the catalyst on a good support -- much akin to LiFePO4 (insulator) as the cathode material in Li batteries.
In the end, i am still skeptical as well. But if this is true, it is a pretty big deal.
I'd really like to see them try it with a normal substrate rather than a poorly conducting doped oxide.
-SEB
hey, giving out prizes actually works!
Mr. Anonymous the first (aka Seb), I award ye full marks. Hit me up via email to provide your details and receive your tasty, tasty prize: joel dot kelly at ualberta dot da.
Looks like I'll have to dig up my electrochemistry notes.
Also, just curious: is there a specific reason you both chose to comment anonymously?
In praise of Anonymity.
Some of my co-workers jobs ultimately depend on DOE funding fuel cells. It would take someone with bigger cojones than me to hold my hand up and say "They just plain ain't gonna work".
Meanwhile keep taking the money.
You never know. Someday it might all work.
Just keep taking the money.
Check this out....
http://www.theoildrum.com/node/4378
SEB
Anonymous said:
By applying a potential that is a mere 60mV above the thermodynamic value (1.29V vs. 1.23, this is the "overpotential"), he can achieve a reasonable rate of O2 formation.
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I could be wrong, but isn't the thermodynamic potential only 1.23V vs NHE when the pH is zero? Shouldn't the potential at pH 7 be closer to 0.8 volts? Also, there is an obscure paper in the Analyst from 1994 by Efstathiou et al. which shows CVs with reduced onset potentials of water oxidation from a cobalt phthalocyanine modified carbon electrode. Their paper has similar pH conditions, and reports basically an identical overpotential, which I think is actually closer to 500 mV than merely 60. There is work dating back 25 years that demonstrates catalytic activity in various cobalt oxide species toward water oxidation. Maybe I'm ignorant, arrogant, and have a male-anatomy-derived inferiority complex, but to the best of my knowledge Professor Nocera's contribution was to modify an electrode that already existed (without really changing its properties), and use it for a new application (electrolysis of water). There is merit in this, but it does not stem from the reduced overpotential of his electrode.
By the way, I don't think Professor Nocera ever claimed to have as small an overpotential as 60 mV. 500 mV is already doing pretty good compared to most other electrodes.
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