Heterogeneous photocatalysis has been used before to siphon hydrogen from water and nullify gas-based pollutants. Rarely are the two used in combination, however. The research team has solved this with a "photoelectrochemical cell," which uses a solar cell to produce hydrogen in a similar manner to electrolysis water-splitting. It has two "rooms," according to Professor Sammy Verbruggen, separated by a membrane to isolate the two processes. Air is purified on one side with a photoanode, while the hydrogen is generated from "a part of the degradation process" with a cathode tucked behind the solid electrolyte membrane.

It's the team's choice of catalyst that makes the machine so effective, Verbruggen says. "In the past, these cells were mostly used to extract hydrogen from water. We have now discovered that this is also possible, and even more efficient, with polluted air," he added. The hydrogen can be easily stored and used later as fuel. It sounds like a wonder machine, although the team is quick to stress that it's only a "proof-of-concept" with "ample room for improvement" in its research paper. The current device, for instance, is only a few square centimeters — hardly enough to counterbalance carbon emissions or power the lights in our cities.