Mesoporous Cu foams formed by a template-assisted electrodeposition process have been identified as CO2 electrocatalysts that are highly selective toward C2 product formation (C2H4 and C2H6) with C2 efficiencies (FEC2) reaching 55%. The partial current of C2 product formation was found to be higher than that of the (parasitic) hydrogen evolution reaction (HER) at any potential studied (−0.4 to −1.0 vs the reversible hydrogen electrode). Moreover, formate production could largely be suppressed at any applied potential down to efficiencies (FEformate) of ≤6%. A key point of the Cu foam catalyst activation is the in operando reduction of a Cu2O phase, thereby creating a large abundance of surface sites active for C–C coupling. The cuprous oxide phase has been formed after the Cu electrodeposition step by exposing the large-surface area catalyst to air at room temperature. The superior selectivity of the Cu foam catalyst studied herein originates from a combination of two effects, the availability of specific surface sites for C–C coupling [dominant (100) surface texture] and the temporal trapping of gaseous intermediates (in particular CO and C2H4) inside the mesoporous catalyst material during CO2 electrolysis. A systematic CO2 electrolysis study reveals a strong dependence of the C2 efficiencies on the particular surface pore size of the mesoporous Cu catalysts with a maximal FEC2 between 50 and 100 μm pore diameters.

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.

Femtosecond laser ablation/ionization mass spectrometry (LIMS) has been applied to probe the spatial element composition of three ternary Cu-Sn-Pb model bronze alloys (lead bronzes: CuSn10Pb10, CuSn7Pb15, and CuSn5Pb20), which were recently identified as high-performance cathode materials in the context of electro-organic synthesis (dehalogenation, deoxygenation) of pharmaceutically relevant building blocks. The quantitative and spatially resolved element analysis of such cathode materials will help in understanding the observed profound differences in their electrochemical reactivity and stability. For that purpose, we developed a measurement procedure using the LIMS technique which allows analyzing the element composition of these ternary alloys in all three spatial dimensions. Their chemical composition was determined spotwise, by ablating material from various surface locations on a 4 × 4 raster array (50 μm pitch distance, ablation crater diameter of ∼20 μm). The element analyses show significant chemical inhomogeneities in all three ternary bronze alloys with profound local deviations from their nominal bulk compositions and indicate further differences in the nature and origin of these compositional inhomogeneities. In addition, the element analyses showed specific compositional correlations among the major elements (Cu, Sn, and Pb) in these alloys. On selected sample positions minor (Ni, Zn, Ag, and Sb) and trace elements (C, P, Fe, and As) were quantified. These results are in agreement with inductively coupled plasma collision/reaction interface mass spectrometry (ICP-CRI-MS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) reference measurements, thus proving the LIMS depth profiling technique as a powerful alternative methodology to conventional quantification techniques with the advantage, however, of a highly localized measurement capability.

Abstract. Insulated atomic force microscopy probes carrying gold conductive tips were fabricated and employed as bifunctional force and current sensors in electrolyte solutions under electrochemical potential control. The application of the probes for current-sensing imaging, force and current-distance spectroscopy as well as scanning electrochemical microscopy experiments was demonstrated.