A Tunable Strategy for Continuous Production of Electrolyte‐Free Formic Acid and Sodium Formate in a Solid‐State‐Electrolyte Based Electrocatalytic CO ₂ Reduction System

Abstract Electrocatalytic CO ₂ reduction reaction (CO ₂ RR) based on solid‐state‐electrolyte (SSE) reactors can efficiently convert CO ₂ to electrolyte‐free formic acid (HCOOH) solution, thereby circumventing energy‐intensive downstream separation processes and further fostering the advancement of carbon‐neutral technologies. However, the absence of alkali metal cations in the SSE‐based CO ₂ RR process at the cathode poses a challenge, constraining the performance and stability of CO ₂ RR and exacerbating the hydrogen evolution side reaction. Herein, a novel strategy for the tunable production of both electrolyte‐free HCOOH and sodium formate (HCOONa) solution through the regulation of anolyte composition in an SSE‐based cell is reported. Employing this strategy, the continuous generation of a ≈0.27 m electrolyte‐free HCOONa solution and ≈0.22 m electrolyte‐free HCOOH solution with extended stabilities of 300 and 200 h, respectively is achieved. More importantly, the introduction of sodium ions resulted in a reduction of cell voltage by ≈1000 mV and further enhances the stability of the cell. In situ infrared spectroscopy and density functional theory calculations reveal that GB‐Bi requires a lower applied potential for formate production, owing to its stronger binding energy to the key intermediate OCHO* compared to Bi. Finally, a techno‐economic analysis indicates that this strategy for HCOONa solution production possesses excellent economic viability.