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Potential-dependent CO2 reduction reactions (CO2RR) were carried out on technical Cu mesh supports that were stepwise modified by (i) electrodeposition of dendritic Cu catalysts under mass transfer control of Cu(II) ions followed by (ii) an extra 3 h thermal annealing at 300 °C in air. The initial electrodeposition of dendritic Cu activates the technical supports for highly efficient formate production at low overpotentials (FEFormate = 49.2% at −0.7 V vs RHE) and in particular for C–C coupling reactions at higher overpotentials (FEC2H4 = 34.3% at −1.1 V vs RHE). The subsequent thermal annealing treatment directs the CO2RR product selectivity toward multicarbon alcohol formation (ethanol/EtOH and n-propanol/n-PrOH) resulting into a total Faradaic yield of FEalcohol = 24.8% at −1.0 V vs RHE (FEEtOH = 13%). Moreover, the EtOH and n-PrOH production rate of 155.2 μMLelectrolyte–1 cmECSA–2 h–1 and 101.4 μMLelectrolyte–1 cmECSA–2 h–1 (normalized with respect to the electrolyte volume and the electrochemically a...

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 resid...