Electrochemical CO2 Conversion Using Skeleton (Sponge) Type of Cu Catalysts

Highly porous 3D Cu skeletons (sponges) modified by electropolishing, thermal annealing, and foam electrodeposition have been studied as catalysts for the electrochemical conversion of CO2 with a particular emphasis on C2 products formation. These catalyst materials appear to be promising for future applications where gaseous CO2 reactants can be transported through the 3D catalyst thereby tuning the mean residence time of reaction intermediates inside the catalyst, which crucially influences the final product distribution. In particular, the annealed skeleton (300 °C, 12 h) and the one modified by Cu foam electrodeposition show profound activities toward C2 product formation (C2H4, C2H6) with faradaic efficiencies reaching FEC2 = 32.3% (annealed skeleton sample, −1.1 V vs RHE) and FEC2 = 29.1% (electrodeposited sample, −1.1 V vs RHE), whereas the electropolished Cu skeleton remains largely inactive for both the C1 and the C2 pathway of hydrocarbon formation. This effect is discussed on the basis of residual impurities that are left behind from the investment casting approach on which the fabrication of these Cu skeleton support materials is based. In addition, a higher FEC2H4 /FEC2H6 ratio is observed for the annealed Cu skeleton as compared to the electrodeposited Cu foam. Such a switching in the C2 product distribution (FEC2H4 /FEC2H6 ratio) is discussed on the basis of particular morphological effects (residence time of intermediates inside the catalyst) related to the three-dimensional nature of the used catalysts.