Abstract: The present disclosure provides a moisture-swing sorbent composition comprising an ion exchange resin loaded with borate ions. The composition captures carbon dioxide from ambient air at low humidity and releases it when exposed to high humidity environments. The ion exchange resin contains quaternary ammonium functional groups that serve as cation sites for charge neutrality with anionic species. The ions may consist of carbonate and borate ions, providing synergistic effects that enhance both capacity and rate of carbon dioxide capture compared to single-anion systems. The composition demonstrates dual functionality through simultaneous carbon dioxide capture and atmospheric water harvesting capabilities. The sorbent achieves moisture-swing carbon dioxide capacities while maintaining reversible operation through humidity-controlled regeneration cycles without requiring high temperature or pressure swing regeneration methods.