Microtubular Electrodes for Efficient Electrochemical CO2/CO Reduction to Value-Added Products

The conversion of carbon dioxide (CO 2) or carbon monoxide (CO) to commodity fuels and chemicals, empowered by low-carbon electricity, has attracted much attention as an alternative to conventional routes of chemical production 1. Numerous studies have focused on CO 2 reduction to CO or formic acid and active/efficient electrocatalysts with high Faradaic efficiencies (FEs) have been developed 2. However, CO 2 reduction to higher value C 2+ products needs the critical C-C coupling step, and to date, Cu has been the main electrocatalyst for this conversion 3. Electrochemical carbon monoxide reduction (CORR) to C 2+ products has advantages over electrochemical CO 2 conversion (CO 2 RR) as issues such as carbonation, and CO 2 loss during CO 2 RR are omitted in CORR due to the stability of CO in alkaline solutions. Facing common challenges as CO 2 RR, CORR suffers more from mass transport resistance and intrinsically lower aqueous CO solubility. Therefore gas-diffusion electrodes (GDEs) are desired to boost the formation of triple phases and active sites to obtain higher reaction rates. Herein for the first time we design Cu-based HFGDEs for efficient CORR to C 2+ products with ethylene as the main product. The pristine Cu HFGDEs showed low selectivity towards C 2+ products. Therefore, we tuned the Cu catalyst shape morphology and orientated growth of nanocubes on the outer surface of HFGDEs by electrodeposition. Due to the efficient C-C coupling and high C 2+ _ selectivity of copper nanocubes with dominant Cu (100), the HFGDEs showed exceptionally high current densities in the 1. 0 M KOH electrolyte, outperforming conventional GDEs tested for CORR under similar conditions. Compared with CO 2 RR in a bicarbonate medium, significantly higher current densities and FEs of C 2+ products (>90%) and ethylene (>65%) were achieved when the HFGDE were used for CORR. Moreover, lower partial current densities of C 2+ were obtained when using the hollow fibers in the non-GDE mode, confirming the significant performance of HFGDEs for achieving high-rate and selective CO reduction through maximizing triple-phase interfaces and local CO concentration. By increasing the concentration of KOH, an ethylene partial current density of 472 mA cm 2- was obtained using the flow-cell reactor, indicating the promises of HFGDEs as an emerging electrode configuration for efficient CORR to C 2+ products. Figure 1