Hacker News Reader

Comment by jpfed | Hacker News Reader

Maybe this is a dumb thing to ask, but would these microdroplets also evolve H2 gas then?

I agree, the news article shows that when they accidentally stumbled on this property they did the extra effort to further investigate (for example size of droplets). I have not yet read the actual paper, but I would at the very least expect the hydrogen to be traced to rule out other hypothetical explanations.

For example suppose the sprayer was a metal through which hydrogen can diffuse, perhaps sucked in osmotically, with the OH somehow stuck at that point on the metal surface, then over time all the surface "pores" would be clogged, but the bulk metal still osmotically sucks hydrogen, so perhaps the OH's on the surface are forced to recombine into H2O2 to make space. (I think their explanation is much more likely than mine, but it illustrates the importance of tracing all the chemical end products, to make sure the reaction is happening where one thinks it is happening. essentially: perform the experiment again in a continuous mode, in a closed recipient while monitoring hydrogen concentration. Continuous mode to prevent hydrogen gas diffused in metal components to be outgassed by say temperature effects of thermal cycling)

I think their explanation is very likely though. That the concentrations were higher in smaller droplets is a strong indicator that this is a surface effect (since volume of a droplet scales down with the third power in radius, while surface area scales down only with a second power in radius). Then remember that water is a polar molecule, and if they are anything like magnets, they don't like being parallel, so I would expect the electric dipole of a water molecule to try to lay in the plane of the surface on average, but as we all know, you cant comb a hairy ball!

That... seems to me to depend on whether the process is internal (within the droplet) or external (between the droplet and the external environment, which presumably contains oxygen). If it'd internal, the hydrogen has to go somewhere, so probably; if it's external, it could just be capturing extra Oxygen somehow, so maybe not.

But I am not a chemist.

I'd be interested to see whether the effect increases in a pure oxygen atmosphere, or goes away in pure nitrogen. Really, just try a bunch of different nitrogen/oxygen mixes. Maybe you can just oxygenate the shit out of bulk water and get the same effect.

The O2 test is mentioned in the abstract: "Changing the spray gas to O2 or bubbling O2 decreased the yield of H2O2 in microdroplets"

I think you must be right, the hydrogen doesn't vanish. So this could be a way to produce H2 has without electrolysis.

I guess you'd get little H2 out of it while pumping the water all the time, it would be less energy-efficient than electrolysis.

I suspect you'd be right, but thats not for granted.

Who need pump when the rain does that for you.

For the record, I'm wrong. Hydrogen peroxide is H2O2, so it's just adding an extra oxygen from the air to the water molecule. I was thinking about Hydroxyl which is OH and would cause excess hydrogen gas.

The H ions would likely dissolve and lower the pH of the water

You need H+ to raise the pH, like when you split water in HO- and H+. [1]

In this case they get H2O2 (neutral) so the H must be neutral, so they must combine to form H2 (neutral). (Perhaps the H radical can survive some time in water until it combine with other H and form the H2.)

[1] A small technical detail is that the reaction is 2 * H2O --> H3O+ + HO-, not H2O --> H+ + HO- , but H+ is the usual shorthand.

Reply on news.ycombinator.com