Tunable Selectivity and High Efficiency of CO₂ Electroreduction via Borate-Enhanced Molten Salt Electrolysis

Converting CO₂ into value-added chemical fuels and functional materials by CO₂ reduction reaction (CO₂RR) is conducive to achieving a carbon-neutral energy cycle. However, it is still challenging to efficiently navigate CO₂RR toward desirable products. Herein, we report a facile strategy to extend product species in borate-containing molten electrolyte at a positively shifted cathodic potential with a high current density (e.g. 100 mA/cm²), which can selectively electro-transform CO₂ into desired products (either CO or solid carbon nanofibers, respectively reaching a high selectivity of ∼90%). The borates can act as a controller of electrolyte alkalinity to buffer the concentration of sequentially generated O^2- during CO₂RR, positively shifting the reduction potential of the captured CO₂ and concurrently extending the product species. The sustainable buffering effect is available under CO₂ atmosphere. Compared with borate-free electrolyte, the CO₂ conversion efficiency is over three times higher, while the electrolysis energy consumption is decreased by over 40%.