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.

Graphite represents a promising material for solid lubrication of highly loaded tribological contacts under extreme environmental conditions. At low loads, graphite’s lubricity depends on humidity. The adsorption model explains this by molecular water films on graphite leading to defect passivation and easy sliding of counter bodies. To explore the humidity dependence and validate the adsorption model for high loads, a commercial graphite solid lubricant is studied using microtribometry. Even at 1 GPa contact pressure, a high and low friction regime is observed - depending on humidity. Transmission electron microscopy reveals transformation of the polycrystalline graphite lubricant into turbostratic carbon after high and even after low load (50 MPa) sliding. Quantum molecular dynamics simulations relate high friction and wear to cold welding and shear-induced formation of turbostratic carbon, while low friction originates in molecular water films on surfaces. In this work, a generalized adsorption model including turbostratic carbon formation is suggested.

We report on the development and validation of a compact laser instrument using mid-IR direct absorption spectroscopy (DAS) for high-precision measurements of ethanol in breath-like air mixtures. Leveraging the intermittent continuous wave (iCW) driving for conventional narrow-band distributed feedback (DFB) quantum cascade laser (QCL) emitting around 9.3 µm and using a 25 m path length multiple-pass absorption cell at reduced pressure, a precision of 9 ppb (amount fraction, nmol mol −1) at 60 s integration time is achieved even in the presence of 5% of H 2 O and CO 2. Thus, the instrument is well suitable for metrological studies to investigate observed, but yet unquantified, discrepancies between different breath alcohol reference-generation methods. The approach can be generalized and applied for other organic molecules in a wide range of applications.