Abstract: A polymer composite includes a polymer substrate, activated carbon, and a carbonate salt. The activated carbon is infused with the carbonate salt. A hybrid composite includes a fibrous mat with activated carbon and potassium carbonate crystals adhered to the fibrous mat. Making a polymer composite includes combining activated carbon with a polymer to yield a mixture, and electrospinning the mixture to yield nanofibers, wherein the carbonate salt is adhered to or embedded in the nanofibers. Capturing carbon dioxide from a quantity of air includes contacting the polymer composite with the quantity of air in the presence of water vapor to yield potassium bicarbonate sorbed on the polymer composite.