So I recently saw this post about a recent breakthrough the Navy made in producing fuel from water make a small round on Facebook from questionable “alternative news” site Addicting Info and it kind of set off my BS detector. First, because this story is a few months old. It actually turned out the article was from April, so part of my skepticism was unfounded. But the opening claim that this wasn’t being reported much in mainstream outlets is wrong, as several sites beat them to the punch (even FOX NEWS! Which would probably make Addicting Info’s head explode.). The other thing that struck me as odd was how the Addicting Info piece seemed to think this technology is practically ready to use right now. That surprised me, because for nearly the last two years, my graduate research at UVA has been focused on developing materials that could help produce fuel from CO2.
This Vice article does a pretty good job of debunking the overzealous claims made by the Addicting Info piece and others like it. As Vice points out, you need electricity to make hydrogen from water. Water is pretty chemically stable in most of our everyday lives. The only way the average person ends up splitting water is if they have metal rusting, which would be a really slow way to generate hydrogen, or by putting a larger battery in water for one of those home electrolysis experiments.
The Naval Research Lab seems kind of unique among the groups looking at making fuel from CO2 in that they’re extracting hydrogen and CO2 from water as separate processes from the step where they are combined into hydrocarbons. Most of the other research in this area looks at having metal electrodes help this reaction in water (nearly any metal from the middle of the periodic table can split CO2 with enough of a negative charge) . Because of water’s previously mentioned stability, they often add a chemical that can more easily give up hydrogen. A lot of groups use potassium bicarbonate, a close relative of baking soda that has potassium instead of sodium, to help improve the conductivity of the water and because the bicarbonate ion really easily gives up hydrogen. In these set-ups, the goal is for the electricity to help the metal break off an oxygen from a CO2 to make CO, and when you get enough CO, start adding hydrogen to the molecules and linking them together.
Carbon atoms are initially removed from CO2 molecules on a copper surface, forming CO. When CO get close to each other, they can bond together. From Gattrell, Gupta, and Co.
But basically, no matter what reaction you do, if you want to make a hydrocarbon from CO2, you need to use electricity, either to isolate hydrogen or cause the CO2 to become chemically active. As the Vice article points out, this is still perfectly useful for the Navy, because ships with nuclear reactors continually generate large amounts of electricity, but fuel for aircraft must be replenished. If you’re on land, unless you’re part of the 30% of the US that gets electricity from renewable sources or nuclear plants, you’re kind of defeating the point. Chemical reactions and industrial processes always waste some energy, so burning a fossil fuel, which emits CO2, to make electricity that would then be used to turn CO2 back into fuel would always end up with you emitting more CO2 than you started with.
However, this process (or one like it) could actually be useful in a solar or wind-based electricity grid. Wind and solar power can be sporadic; obviously, any solar grid must somehow deal with the fact that night exists, and both wind and solar power can be interrupted by the weather. (Nuclear power doesn’t have this issue, so this set-up would be irrelevant.) However, it’s also possible for solar and wind to temporarily generate more electricity than customers are using at the time. The extra electricity can be used to power this CO2-to-fuel reaction, and the fuel can be burned to provide extra power when the solar or wind plants can’t generate enough electricity on their own. This is also where the Vice article misses something important. Jet fuel can’t have methane, but methane is basically the main component of natural gas, which is burned to provide about another 30% of electricity generated in the US today. And because methane is a small molecule (one carbon atom, four hydrogen atoms) it can be easier to make than the long hydrocarbons needed for jet fuel.
Also, one thing I’m surprised I never see come up when talking about this is using this for long-term human space exploration as a way to prevent to maintain a breathable atmosphere for astronauts and to build materials. If you can build-up the carbon chains for jet fuel, you could also make the precursors to lots of plastics. The International Space Station is entirely powered by solar panels, and solar panels are typically envisioned as being part of space colonies. Generally, electricity generation shouldn’t be a major problem in any of the manned missions we’re looking at for the near future and this could be a major way to help future astronauts or space colonists generate the raw materials they need and maintain their environment.
If you want to read more about the Naval Research Lab’s processes, here are some of the journal articles they have published lately:
http://pubs.acs.org/doi/abs/10.1021/ie301006y?prevSearch=%255BContrib%253A%2BWillauer%252C%2BH%2BD%255D&searchHistoryKey= http://pubs.acs.org/doi/abs/10.1021/ie2008136?prevSearch=%255BContrib%253A%2BWillauer%252C%2BH%2BD%255D&searchHistoryKey= http://pubs.acs.org/doi/abs/10.1021/ef4011115 http://www.nrl.navy.mil/media/news-releases/2014/scale-model-wwii-craft-takes-flight-with-fuel-from-the-sea-concept