The solubility of CO2 decreases with temperature, so boiling would drive off most of it. However, this is unnecessary when using sodium carbonate for electrolyte and its time consuming and uses up a lot of energy.
For reducing agents, there are lots of choices include, glucose, maltose, maltodextrin, cinnamon extract, other plant extracts, corn syrup (Karo), Tate & Lyles golden syrup etc.
The silver lungs guy tries to get you to buy his expensive reducing agent, but its just a carbohydrate like one of the above.