Hydrogen could be interesting as energy storage in this configuration. And hydrogen-based kerosene would make airplanes carbon-neutral but is really energy intensive
- safety: lithium-ion batteries explode if you look at them funny, and are full of poisons, while kerosene can put out a lit match and can be safely imbibed;
- materials availability: carbon is about ten times as abundant in earth's crust as lithium, and there are readily available ways to concentrate carbon from the air such as planting forests, while concentrating lithium from seawater is somewhat trickier;
- specific energy: Li-ion batteries can store 0.5 MJ/kg, and kerosene is 43 MJ/kg, which is a huge advantage for things like trucking and aviation;
- energy density: Li-ion batteries store 1 MJ/liter, kerosene is 35 MJ/liter, which is also important for things like aviation; and
- capital cost of storage facilities: you can store 200 liters of kerosene in a US$10 barrel, while 200 liters of lithium-ion batteries would be about 12,000 18650s, which costs on the order of US$50,000.
Gasoline does indeed share most of these advantages and can also be used in cheaper engines that can rev faster. Other fuels that might be reasonable to synthesize in the same way include hydrogen itself, methane, LP gas (propane/butane), and ammonia (!!).
The ideal solution would be efficient solar bioreactors where bioengineered algea converted solar energy into fats as a bioproduct of a photosynthetic process sequester CO2 that could be esterfied into alkanes or that directly produced alkanes. Long chain alkanes, my understanding is, are not toxic to life. It is the short chain stuff and aromatic ring based stuff like benzene that is hazardous.
https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/175...
Algae have very low capital costs but also fairly low photonic efficiency; it's reasonable to expect non-algae-based designs to be superior. (BTW, you can't esterify things into alkanes; alkanes aren't esters.) You're right about the toxicity profiles, although even things like hexane and octane are relatively low toxicity; hexane's oral LD50 is like tens of grams per kilogram, but they have higher toxicities if you breathe or inject them.
I was using Li as shorthand for Litium Ion batteries which I assume contain salts or oxides or hydrides of lithium. I know it is not elemental lithium. My point was that H-C bonds contain more energy than whatever is in Li batteries in the charged state per mol.
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* Kerosene is C10-C16, and diesel fuel is C9-C25, so kerosene can be thought of as a particular grade of diesel.
The only purpose of hydrogen is to make energy in one point in space & time and then use it in another point of your choice without CO2 emissions. Solar is to convert sunlight to electrical energy, but you don't get to control when the sun is shining. The technology to generate hydrogen is also completely mature and has been since before I was born, whether we are talking steam methane reforming or electrolysis. It's just not very cheap.
Long term storage of hydrogen is quite easy so. It can be stored in thermal oil, rendering it inert. In thay form it isn't even considered dangerous goods for transportation anymore.
Source: I consulted a green hydrogen project on logistics a while ago.
It's only explosive when mixed with air in confined places, as is gasoline, LPG, CNG, steel, wood and flour. Unlike most others, confinement is a requirement, otherwise it escapes too quickly. See [1] for comparison.
> hard to store safely, damages its own holding vessels
For these reasons I suggest we should produce and store methane, though hydrogen issues aren't a showstopper and hydrogen fuel cells are more efficient.
[1] https://hydrogen.wsu.edu/2017/03/17/so-just-how-dangerous-is...
As an example, many garages ban LPG cars, but don't care about CNG, AFAICT, because LPG can pool around on the bottom, but methane is light and easily escapes. Hydrogen is even lighter and harder to contain.
The link [1] has compelling arguments.
It's far easier to store it (underground, as compressed gas; this is a demonstrated technology) than it is to store energy in batteries. The cost/energy capacity can be extremely low, ~ $1/kWh equivalent.
For many industrial processes, ammonia is a well-established common feedstock, having none of the issues of hydrogen you mention.
Here in Japan, some Combined Cycle Gas Turbine plants are already running with 10% ammonia blend.
I think you are right about pure hydrogen, but I can see green-hydrogen-into-ammonia as viable for many applications including heavy transportation (train, ship, truck).
We just need much more economic electrolysis, because hydrogen is almost always produced from fossil fuels today.
Plus you could easily replace it with solar produced methanol overtime.
EV however killed the need for that for the most part.
Today I don't really think synfuels have much of a application. Batteries and storing energy electrically will win. It will not be so long until you can basically do Iron-Silicon battery for a very cheap price. Or if we finally figure Sulfer we could have amazing batteries for super cheap.
You also have the problem that most hydrogen today is made from petroleum!
Hydrogen, with all it's downsides, is awesome for long term storage because it scales sublinearly with capacity.
That depends on what metric you are looking at. Efficiency? Perhaps. Cost/kW of the electrolyzer? Not true at all.
Also, the use case for electrolyzers has changed: from converting relatively pricy baseload power to hydrogen to converting cheap intermittent power to hydrogen. For the latter you want to trade efficiency for lower capital cost.
OP started a though experiment where we think of a new technology chain where energy is abundant and irregular. In this setup hydrogen might make sense because its energy intensive process is no longer an issue.