Are there solutions for CO2 scrubbing that use electricity and can run indefinitely, rather than chemical substrates that get used up and require replenishing?
One method if you have enough electricity is to capture some amount of air from the room, compress and/or refrigerate it until the various gasses liquefy (they each liquefy at a different temperature/pressure), and drain off each liquefied gas that you want to separate into its own container.
At least, that's how the CO2-filtering device described in The Martian worked. I'm not sure if anyone uses that system in real life. Apparently on the ISS they use filters made of zeolite[1]. From that article though it didn't say if the filters were reusable. If they are, maybe just using filters is good enough for quite a long time.
Remember the talks about DIY Oxygen concentrators during COVID emergency days, using two pipes filled with zeolite beads alternatingly pressurized from pumps and valves so to separate Nitrogen in the air and leaving Oxygen in the gas? Apparently the same Pressure Swing Adsorption principle is used to extract couple other gases as well, and CO2 is one of them.
The zeolite filters are regenerated by heating them, which causes them to release the captured CO2. This is obviously done in a sealed chamber so that the CO2 can be captured or vented overboard.
Sure. The trick is that there are regenerative chemical substrates. The material absorbes co2, gets saturated, cycled to a different part where it is heated and releases the co2 and can be used to capture again. If you use electricity to do the heating and cycling you have exactly what you asked for.
And plants are not viable as CO2 scrubbers on small scales. It takes a lot of plants to scrub the CO2 exhaled by a single human - somewhere on the order of 10 full-size trees!
Plants are generally net neutral in CO2 consumption. They consume CO2 during the day, but when not producing energy through photosynthesis, they consume O2 and produce CO2 for their cellular respiration.
The net effect is generally, plants release similar amounts of CO2 at night as they consume during the day. The exception here would be plants that use Crassulacean acid metabolism for photosynthesis, which would be a lot of your arid native plants.
I would expect plants to be CO2 negative while growing since they're using the carbon to add to their dry mass. Once fully grown I'd expect the plants to be roughly neutral.
