A Tunable Strategy for Continuous Production of Electrolyte-Free Formic Acid and Sodium Formate in a Solid-State-Electrolyte Based Electrocatalytic CO2 Reduction System.

Electrocatalytic CO₂ reduction reaction (CO₂RR) based on solid-state-electrolyte (SSE) reactors can efficiently convert CO₂ 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 CO₂RR process at the cathode poses a challenge, constraining the performance and stability of CO₂RR 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.