Efficient Bicarbonate Electrolyzer with a Forward-Bias Bipolar Membrane.

Direct electrolysis of carbon dioxide (CO2)-captured bicarbonate solutions offers a promising route for CO2 valorization, as it avoids the energy-intensive regeneration and compression steps required to supply purified gaseous CO2. However, most bicarbonate electrolyzers rely on proton-driven in situ CO2 release at the cathode, which promotes hydrogen evolution, increases the cell voltage, and limits energy efficiency. Here, we demonstrate a bicarbonate electrolyzer based on a forward-bias bipolar membrane (fBPM) that decouples local CO2 release from direct proton flux. The fBPM cell delivers a carbon monoxide (CO) partial current density of 167.1 (±2.6) mA cm-2 at 4.44 (±0.03) V, with CO Faradaic efficiencies of up to 71% at 100 mA cm-2, surpassing the reverse-bias BPM and cation-exchange membrane configurations and comparing favorably with state-of-the-art bicarbonate systems. Operando Raman spectroscopy revealed that the fBPM maintains a more alkaline cathode-membrane microenvironment, increasing the availability of locally released CO2. A system-level energy analysis indicates an energy cost of 36.7 GJ per tonne of CO, highlighting fBPM-enabled bicarbonate electrolysis as a viable approach for integrated CO2 capture and electrochemical conversion.