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'Major discovery' from MIT primed to unleash solar revolution

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Re: 'Major discovery' from MIT primed to unleash solar revolution

#31

Post by ztravis »

ars wrote: post #28
ztravis wrote: post #24

Earlier quoted context omitted.

You are correct about your first point - the connection with photosynthesis is shaky at best. This research describes a new electrocatalyst for the production of oxygen. The source of electrical energy for driving this production could be solar cells, but that would be just one potential use. The paper does focus on photosynthesis, however, because the Nocera's lab works on "artificial photosynthesis," a field largel…

Thanks for the clarifications. >artificial photosynthesis" focuses not on carbon fixation but on the transformation of light to electrochemical energy (via electron/proton transfer). Then why call it photosynthesis? It's not, it's photovoltaics. If you want photosynthesis you have have to fix carbon, or you're making a mockery of the term. And if you are making hydrogen directly, then call it photolysing. Either way…

To be honest, I don't know why it's called artificial photosynthesis versus photovoltaics - perhaps it is because this research looks to the actual chemical systems involved in photosynthesis as models for man-made systems (as opposed to trying to develop light-converting systems ab initio). In any case, "artificial photosynthesis" is commonly used to refer to research both on hydrolysis via solar energy and carbon fixation into organic compounds, both of which are fundamental to photosynthesis as a whole.

I was wrong about the chlorine production, actually - it only occurs at high concentrations of salt. Otherwise (or with different solutes), you can produce oxygen. Still, I believe that this reaction is not efficient enough to be feasible as an energy source. Overall, you do want the hydrogen, but you also need an oxidant to, for example, run a fuel cell. I think there are hydrogen-chlorine fuel cells, but I imagine it would be easier and more practical to run a hydrogen-oxygen cell instead to avoid using chlorine gas/producing HCl. In any case, it boils down to developing catalysts to improve the rate and efficiency of this electrolysis (by lowering overpotentials).

I agree with you that your paragraph makes a lot more sense than the parent article. It's annoying how these press releases make things seem much more revolutionary than they really are.

Re: 'Major discovery' from MIT primed to unleash solar revolution

#32

Post by orib »

ars wrote: post #16
danteembermage wrote: post #6

What's not clear to me from the article is, if the cheap easy catalyst makes oxygen gas from water, what's left over before we get the platinum involved, perhaps a bunch of hydrogen ions in solution? Something like 6xH20 -> O2 + 2xH30 or 2xH20 -> O2 + 2H+

What? You can't make oxygen gas and hydrogen ions at the same time. If you make oxygen gas you also make hydrogen gas. Which is not a big deal, electrolysis is not new. Not sure what the platinum has to do with it though.

Who says you're making necessarily making oxygen gas? I don't know the details of current industrial processes, but you can easily free hydrogen by displacing it with something that binds more tightly (eg, Sodium: 2H2O + 2Na => H2 + 2NaOH) and produce free hydrogen gas with sodium hydroxide waste. I suspect that a similar sort of process is happening currently when water is hydrolyzed with a "catalyst" in current processes.

Platinum is often used in catalysts. It works by providing an alternative reaction pathway that takes less energy to fuel the reaction. An analogy is that instead of rolling a rock up a hill to get it from point A to point B, the catalyst provides access to a tunnel through the hill.

Re: 'Major discovery' from MIT primed to unleash solar revolution

#33

Post by ars »

orib wrote: post #32
ars wrote: post #16

Earlier quoted context omitted.

What? You can't make oxygen gas and hydrogen ions at the same time. If you make oxygen gas you also make hydrogen gas. Which is not a big deal, electrolysis is not new. Not sure what the platinum has to do with it though.

Who says you're making necessarily making oxygen gas? I don't know the details of current industrial processes, but you can easily free hydrogen by displacing it with something that binds more tightly (eg, Sodium: 2H2O + 2Na => H2 + 2NaOH) and produce free hydrogen gas with sodium hydroxide waste. I suspect that a similar sort of process is happening currently when water is hydrolyzed with a "catalyst" in current pro…

If you're reacting sodium to water to get hydrogen you're not exactly electrolyzing water now are you?

The same is true with current processes, if your catalyst is being used up to bind oxygen then a: it's not a catalyst it's a reactant, and b: well don't, and c: you're not electrolyzing water, you're doing some more complicated reaction.

So emitting O2 from electrolysis is not even the slightest bit new. That part of the article was basically nonsense.

Re: 'Major discovery' from MIT primed to unleash solar revolution

#35

Post by babul »

ars wrote: post #17

OK, I tried. I really tried to give them the benefit of the doubt - I mean it's mit.edu, but seriously what they wrote there and what I know of physics have little to do with one another. I fell like I'm missing a joke somewhere. First off: what does electrolysis have to do with photosynthesis? If you want to store energy it's just as important with wind, or any other. Second: photosynthesis and photovoltaics are not…

But, but, but it's on mit.edu!

I know what you're saying and had similar thoughts. I suppressed my concerns thinking "some of this seems wrong but this is on mit.edu so they must have been through many checks".

Same lesson to be learnt as http://news.ycombinator.com/item?id=263599 ?

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