SO2-tolerant electrochemical CO2 capture and NaHCO3 conversion enabled by saline water electrolysis

Abstract

Electrochemical carbon capture offers a sustainable route to mitigate CO₂ emissions, but practical deployment is often limited by modest capture rates and system complexity. Here we report a saline–water electrolysis strategy that simultaneously captures CO₂ and converts it to sodium bicarbonate (NaHCO₃) without external chemical additives. Hydroxide ions (OH⁻) generated in situ at the cathode via the hydrogen-evolution reaction (HER) enable rapid CO₂ absorption and selective conversion to NaHCO₃ by maintaining the catholyte at pH 8–9, consistent with thermodynamic speciation. In simulated flue gas, the system delivers a CO₂ capture rate of 5.27 mmol_CO2 cm⁻² h⁻¹ (55.6 kg_CO2 m⁻² day⁻¹) at 300 mA cm⁻², >99.5% capture efficiency, >90% faradaic efficiency, and energy consumption as low as 87 kJ mol_CO2⁻¹ (1.98 GJ t_CO2⁻¹). The process is tolerant to sulfur dioxide (SO₂), maintaining ∼85% NaHCO₃ conversion for >240 h with 1.0% SO₂ in the feed. Using pure water as the catholyte enables direct production of high-purity NaHCO₃, enhancing operational flexibility. Techno-economic analysis indicates capture costs with US$90.3 per t_CO2 when co-located with a desalination facility and low-cost electricity, while considering the revenues from products NaHCO₃, H₂ and Cl₂ can further improve the economics. This multifunctional, impurity-resistant, and renewable-compatible approach offers a practical, scalable pathway for industrial CO₂ capture and mineralization.