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

Abstract

The conversion of carbon dioxide (CO2) 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 CO2 reduction to CO or formic acid and active/efficient electrocatalysts with high Faradaic efficiencies (FEs) have been developed [2]. However, CO2 reduction to higher value C2+ 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 C2+ products has advantages over electrochemical CO2 conversion (CO2RR) as issues such as carbonation, and CO2 loss during CO2RR are omitted in CORR due to the stability of CO in alkaline solutions. Facing common challenges as CO2RR, 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 C2+ products with ethylene as the main product. The pristine Cu HFGDEs showed low selectivity towards C2+ 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 C2+ _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 CO2RR in a bicarbonate medium, significantly higher current densities and FEs of C2+ products (>90%) and ethylene (>65%) were achieved when the HFGDE were used for CORR. Moreover, lower partial current densities of C2+ 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 cm2- was obtained using the flow-cell reactor, indicating the promises of HFGDEs as an emerging electrode configuration for efficient CORR to C2+ products. Figure 1