Enhancing electrochemical carbon dioxide reduction efficiency through heat-induced metamorphosis of copper nanowires into copper oxide/copper nanotubes with tunable surface

Electrochemical CO2 reduction reaction (CO2RR) presents a unique opportunity to convert carbon dioxide (CO2) to value-added products while simultaneously storing renewable energy in the form of chemical energy. However, particle applications of this technology are limited due to the poor efficiency and product selectivity of the existing catalyst. In this study, we demonstrate a facile method for the heat-induced transformation of copper nanowires into CuOx/Cu nanotubes with defect-enriched surfaces. During this transformation, the outward migration of copper results in the formation of tubular structures encased within nanosized oxide grains. Notably, the hydrogen faradaic efficiency (FE) decreases with extended heat treatment, while carbon monoxide (CO) FE increases. As compared to Cu NWs, Cu NTs exhibit lower selectivity towards H2 and single-carbon (C1) products and favor the formation of multi-carbon (C2+) products. Consequently, a 2-fold increase in the single pass CO2 conversion (SPCC) and C2+ half-cell energy efficiency (EEhalf cell) was noted after heat treatment. The Cu NT-4 variant, synthesized under optimized conditions, exhibits the highest FE of 72.1 % for C2+ products at an operating current density (ID) of 500 mA cm-2.

Highly dispersed Cu-Cu2O-CeOx interfaces on reduced graphene oxide for CO2 electroreduction to C2+ products

The Cu0-Cu+ interfaces play a key role in the electrochemical CO2 reduction reaction (CO2RR) to produce multi-carbon products (C2+), however, it is difficult for Cu+ to exist stably under reducing conditions. Herein, we construct highly dispersed and stable Cu-Cu2O-CeOx interface on reduced graphene oxide (rGO) for CO2 electroreduction to C2+ products. During the synthesis process, utilizing strong electrostatic interactions, the complex ions of Cu2+ and Ce3+ are uniformly adsorbed on the surface of graphene oxide. Then, under the solvothermal reaction of ethylene glycol and thiourea, the two metal complex ions are converted into highly dispersed and ultrafine Cu2S-CeOx nanocomposites on rGO. Interestingly, CeOx and thiourea synergistically regulate the generation of only Cu+. Under the CO2RR process, the reconstruction of Cu2S promotes the formation of Cu0 and Cu2O species. CeOx stabilizes partial Cu+ species and promotes the formation of Cu-Cu2O-CeOx composite interface. With the help of synergistic effect of Cu0, Cu+ and CeOx, the optimized reaction interface achieves the Faradaic efficiency (FE) of 74.5 % for C2+ products with the current density of 230 mA cm-2 at -0.9 V versus the reversible hydrogen electrode. In situ attenuate total reflectance-infrared absorption spectroscopy (ATR-IRAS) spectra show that the composite interfaces promote the adsorption and activation of H2O and CO2, improve the surface coverage of CO intermediates (*CO), and thus accelerate the CC coupling process.