Hydrogen and oxygen produced in this way from water could also be used as fuel on a spacecraft. Launching a rocket with water would, in fact, be a lot safer than launching it with additional rocket fuel and oxygen on board, which can be explosive. Once in space, the special technology could split the water into hydrogen and oxygen which in turn could be used to sustain life or to power electronics via fuel cells.
There are two options for doing this. One involves electrolysis as we do on Earth, using electrolytes and solar cells to capture sunlight and convert this into a current.
The alternative is to use “photocatalysts,” which work by absorbing light particles—photons—into a semiconductor material inserted into the water. The energy of a photon gets absorbed by an electron in the material which then jumps, leaving behind a hole. The free electron can react with protons (which make up the atomic nucleus along with neutrons) in water to form hydrogen. Meanwhile, the hole can absorb electrons from water to form protons and oxygen.
The process can also be reversed. Hydrogen and oxygen can be brought together or “recombined” using a fuel cell returning the solar energy taken in by the “photocatalysis”—energy which can be used to power electronics. Recombination forms only water as a product—meaning the water can also be recycled. This is key to long-distance space travel.
The process using photocatalysts is the best option for space travel as the equipment weighs much less than the one needed for electrolysis. In theory, it should work easily. This is partly because the intensity of the sunlight is far higher without the Earth’s atmosphere absorbing large amounts on its way through to the surface.