According to Wikipedia, Venus's atmosphere is 96.5% CO2, 3.5% N2, and trace amounts of other stuff. Not sure what "combustible form" of energy you are talking about?
"...at 50km, the abundance [of H2SO4] works out to ~14mg/m^3 or about 7ppm. So, between sulfuric acid and water vapor, you have about half as much mass per cubic meter as water vapor in the air near the ALMA observatory in the Atacama desert in Chile. Bone dry by terrestrial standards, but sopping wet compared to say the Moon." [0]
That plus higher-than-earth solar radiation to electrolyze it into H2 and O2 and you've got yourself a floating, solar-powered rocket fuel mine.
Water is more common elsewhere in the solar system. There might be water ice on the Moon, even Mercury. Comets are largely water ice, so are C-type asteroids. Many moons of the outer planets are supposed to have liquid or water ice in their cores. Titan and Europa possibly have more water than Earth.
Which is to say, there's probably easier and (eventually at least) cheaper planetary targets for H2 and O2 factories.
Yeah sorry my sleeping through Gen Chem all those years ago really showed in that comment. I did however do some research and CO2 seems useful for storing energy, so that is interesting in it's own right, especially given the amounts of sunlight and wind present on that planet. [1]
I also want to backtrack on the "the planet is almost certainly devoid of lifeforms" comment, as it seems there has been speculation that the clouds of Venus do host life. [2]
