Ag-foam catalysts have been developed for the electrochemical CO2 reduction reaction (ec-CO2RR) based on a concerted additive- and template-assisted metal-deposition process. In aqueous media (CO2-saturated 0.5 M KHCO3 electrolyte), these Ag foams show high activity and selectivity toward CO production at low and moderate over-potentials. Faradaic efficiencies for CO (FECO) never fell below 90% within an extremely broad potential window of ∼900 mV, starting at −0.3 V and reaching up to −1.2 V versus a reversible hydrogen electrode (RHE). An increased adsorption energy of CO on the Ag foam is discussed as the origin of the efficient suppression of the competing hydrogen-evolution reaction (HER) in this potential range. At potentials of <−1.1 V versus RHE, the FEH2 values significantly increase at the expense of FECO. Superimposed on this anti-correlated change in the CO and H2 efficiencies is the rise in the CH4 efficiency to the maximum of FECH4 = 51% at −1.5 V versus RHE. As a minor byproduct, even C–C-coupled ethylene could be detected reaching a maximum Faradaic efficiency of FEC2H4 = 8.6% at −1.5 V versus RHE. Extended ec-CO2RR reveals the extremely high long-term stability of the Ag foam catalysts, with CO efficiencies never falling below 90% for more than 70 h of electrolysis at −0.8 V versus RHE (potential regime of predominant CO production). However, a more-rapid degradation is observed for extended ec-CO2RR at −1.5 V versus RHE (potential regime of predominant CH4 production), in which the FECH4 values drop to 32% within 5 h of electrolysis. The degradation behavior of the Ag-foam catalyst is correlated to time-resolved identical-location scanning electron microscopy investigations that show severe morphological changes, particularly at higher applied over-potentials (current densities) at −1.5 V versus RHE. This study reports on the first ec-CO2RR catalyst beyond copper that demonstrates a remarkably high selectivity toward hydrocarbon formation, reaching a maximum of ∼60% at −1.5 V versus RHE. The experimental observations presented herein strongly suggest that this newly designed Ag-foam catalyst shares, in part, mechanistic features with common Cu catalysts in terms of ec-CO2RR product selectivity and catalyst degradation behavior.

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The recognition of biosignatures on planetary bodies requires the analysis of the putative microfossil with a set of complementary analytical techniques. This includes localized elemental and isotopic analysis of both, the putative microfossil and its surrounding host matrix. If the analysis can be performed with spatial resolution at the micrometer level and ppm detection sensitivities, valuable information on the (bio)chemical and physical processes that influenced the sample material can be gained. Our miniaturized laser ablation ionization mass spectrometry (LIMS)-time-of-flight mass spectrometer instrument is a valid candidate for performing the required chemical analysis in situ. However, up until now it was limited by the spatial accuracy of the sampling. In this contribution, we introduce a newly developed microscope system with micrometer accuracy for Ultra High Vacuum application, which allows a significant increase in the measurement capabilities of our miniature LIMS system. The new enhancement allows identification and efficient and accurate sampling of features of micrometer-sized fossils in a host matrix. The performance of our system is demonstrated by the identification and chemical analysis of signatures of micrometer-sized fossil structures in the 1.9 billion-year-old Gunflint chert.

In this work, we aim to develop a Zn-based metal foam catalyst with very large specific area suitable for efficient CO production. Its manufacture is based on the dynamic hydrogen bubble template method that consists of the superposition of metal deposition and hydrogen evolution at the solid-liquid interface. We employed Cu ions in the Zn-rich electroplating bath as foaming agent. The concentration of Cu as foaming agent was systematically studied and an optimized ZnCu foam alloy was developed, which, to the best of our knowledge, is the most selective Zn-based CO electrocatalyst toward CO in aqueous bicarbonate solution (FE = 90% at -0.95 V vs reversible hydrogen electrode). This high efficiency is ascribed to the combination of high density of low-coordinated active sites and preferential Zn(101) over Zn(002) texturing. X-ray photoelectron spectroscopy investigations demonstrate that the actual catalyst material is shaped upon reduction of an oxide/hydroxide-terminating surface under CO electrolysis conditions. Moreover, intentional stressing by oxidation at room conditions proved to be beneficial for further activation of the catalyst. Identical location scanning electron microscopy imaging before and after CO electrolysis and long-term electrolysis experiments also showed that the developed ZnCu foam catalyst is both structurally and chemically stable at reductive conditions.

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