The internet is ablaze with the new nano particle based extraction method of converting water to hydrogen. In 2002/2003 when I was 16 there was a similar craze about a lawn mower motor which supposedly ran on water. Indeed there were even conversion kits on the internet for vehicles. They didn't work because of a fundamental inefficiency of the conversion. Will this new nanotechnology improve the process so that cars can run on converted water or does there still exist a limit?

  • $\begingroup$ Is your question one of economic feasibility? $\endgroup$ – BMS Aug 26 '14 at 16:01
  • $\begingroup$ No physical like does a theory so limit the reality of the presentation $\endgroup$ – user16438 Aug 26 '14 at 16:01

The article you refer to is about the electrolytic splitting of water.

A 100% efficient electrolytic cell would require a voltage of about 1.23V to split water, but for various reasons a simple electrolytic cell requires about 1.48V. The difference between the voltages is called the overpotential, and it increases the amount of power needed to split the water because the power required per unit of hydrogen produced is proportional to the cell voltage. The excess power goes into heating the hydrogen and oxygen produced, and in this case it means that simple cells are about 83% efficient at converting electricity into hydrogen.

Catalysts can be used to increase the efficiency, and indeed platinum based catalysts can be used to reduce the overpotential and make cells with near 100% efficiency. The problem is that platinum is expensive. The result from the Stanford team is that a much cheaper nickel based catalyst can achieve the same efficiency as platinum. The paper is here, but note that it is behind a paywall.

If the catalyst proves to be stable enough then it will be useful for electrolytic production of hydrogen, but the improvement in efficiency isn't going to change the world overnight. It still takes a lot of power to electrolyse water so it's only feasible when cheap electricity is available.

  • $\begingroup$ @caseyr547: I've amended my answer to respond to your edits. $\endgroup$ – John Rennie Aug 26 '14 at 16:17
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    $\begingroup$ Let's add, just for completeness, that no improvements in water electrolysis will make hydrogen a good transportation fuel. This is linked to a number of issues, like the storage problem, the low energy density, and the missing oxygen (the fact that the atmosphere only has 20% oxygen limits the thermodynamic efficiency of fuel cells, again, which compounds the electrolysis efficiency problem). $\endgroup$ – CuriousOne Aug 26 '14 at 17:51
  • $\begingroup$ @CuriousOne For what it is worth, hydrocarbon and other fuels also share the inefficiency handicap posed by the less than 20% oxygen content of the atmosphere. $\endgroup$ – 0tyranny 0poverty Feb 17 '18 at 6:11

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