[DavidPBL]

I would describe hydrogen as an energy carrier rather than an energy source. Hydrogen is always made from something else, and the energy is either provided by that something else, or indirectly from another source, or a combination of both.

If you use an electrolyser to make hydrogen from water, your energy source is actually the electricity used to drive that reaction. The energy is stored as hydrogen gas.

Large bodies of water are great passive systems to capture CO2. For the outdoors, and if using sunlight is the energy source, algae and seaweed are definitely great candidates for capturing CO2.

Unfortunately your idea wouldn't work for our microorganisms as it is anaerobic, so it would die if exposed to air. But I like your idea for using sunlight to improve the growing conditions of algae + using automation for harvesting!