I am by no means a chemist (beyond a secondary school level), but burning CO2 doesn’t seem possible. Doesn’t burning through application of some energy split the bonds of complicated stable molecules into less complicated, but stable molecules (by adding oxygen), thus releasing energy.

In this case; how do they recombine the CO2 into more complicated hydrocarbons? And if it’s energy negative, is it better to do this, or to use it to capture carbon?