A Pair-Electrosynthesis for Formate at Ultra-Low Voltage Via Coupling of CO2 Reduction and Formaldehyde Oxidation

Abstract Formate can be synthesized electrochemically by CO 2 reduction reaction (CO 2 RR) or formaldehyde oxidation reaction (FOR). The CO 2 RR approach suffers from kinetic-sluggish oxygen evolution reaction at the anode. To this end, an electrochemical system combining cathodic CO 2 RR with anodic FOR was developed, which enables the formate electrosynthesis at ultra-low voltage. Cathodic CO 2 RR employing the BiOCl electrode in H-cell exhibited formate Faradaic efficiency (FE) higher than 90% within a wide potential range from − 0.48 to − 1.32 V RHE . In flow cell, the current density of 100 mA cm −2 was achieved at − 0.67 V RHE . The anodic FOR using the Cu 2 O electrode displayed a low onset potential of − 0.13 V RHE and nearly 100% formate and H 2 selectivity from 0.05 to 0.35 V RHE . The CO 2 RR and FOR were constructed in a flow cell through membrane electrode assembly for the electrosynthesis of formate, where the CO 2 RR//FOR delivered an enhanced current density of 100 mA cm −2 at 0.86 V. This work provides a promising pair-electrosynthesis of value-added chemicals with high FE and low energy consumption.