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.