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

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