Electrochemical CO 2 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 CO 2 with a particular emphasis on C 2 products formation. These catalyst materials appear to be promising for future applications where gaseous CO 2 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 C 2 product formation (C 2 H 4, C 2 H 6 ) with faradaic efficiencies reaching FE C 2 = 32.3% (annealed skeleton sample, −1.1 V vs RHE) and FE C 2 = 29.1% (electrodeposited sample, −1.1 V vs RHE), whereas the electropolished Cu skeleton remains largely inactive for both the C 1 and the C 2 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 FE C 2 H 4 /FE C 2 H 6 ratio is observed for the annealed Cu skeleton as compared to the electrodeposited Cu foam. Such a switching in the C 2 product distribution (FE C 2 H 4 /FE C 2 H 6 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.