A simple femtosecond laser alloying process is applied under two different process gases nitrogen and air to create novel molybdenum-nickel alloyed and surface enhanced catalysts. A three-day electrochemical test protocol is applied in an alkaline half-cell at 298 K and 353 K to examine the catalytic activity and initial degradation mechanisms in the hydrogen evolution reaction. It is found, that the surface enhancement and the stability of the electrode significantly depends on the process gas. Molybdenum is degraded at the beginning of the test protocol, but it is shown that higher concentrations are not necessarily required for an increase performance. The highest catalytic activity on an electrode alloyed with molybdenum under nitrogen emerges in a steady state operation at 353 K. An overpotential of 135 mV at-100 mA cm-2 is measured. (c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

An entirely femtosecond laser (fs-laser) based process for the production of stable, enlarged and alloyed nickel surfaces is presented. The process allows the use of metal foils and aqueous salt solutions as alloying element sources. We alloy iron from an aqueous element source as well as molybdenum and cobalt from commercially available foils on nickel mesh surfaces without further coating process. It is shown that the content of alloyed iron on the nickel mesh surface structured with the fs-laser depends on the concentration of the aqueous iron(II) sulfate solution used. The alloy content of cobalt and molybdenum is controlled by adjustable laser parameters. Cross-sections prepared by a focused ion beam and subsequent energy dispersive X-ray spectroscopy shows that molybdenum and nickel form alloyed nanoscale particles on the structured nickel surface. The combination of an aqueous iron(II) sulfate solution and a molybdenum metal foil leads to a ternary nickel-molybdenum-iron surface alloy. The presented fs-laser alloying process can be applied to further metal combinations and offers the potential to create new materials and properties.

A femtosecond laser process is presented increasing the surface area of copper electrocatalysts for an electrochemical CO2 reduction reaction (CO2RR). The laser treatment allows us to tune the surface morphology and the chemical composition of the copper electrocatalysts. This tunability is used to correlate the role of the surface area and catalyst dopants with the selectivity of the CO2RR. The liquid products of the CO2RR are monitored through ex situ nuclear magnetic resonance spectroscopy. The products' distribution shows that the electrode surface area plays a key role in the electrochemical conversion of CO2 into multicarbon liquid products. We show that sulfur dopants boost the production of formate. Remarkably, by co-doping sulfur and fluoride, we show that the chalcogenide dopant counteracts the known boosting effect of fluoride to convert CO2 into multicarbon products. Oxygen doping in the range of 2-19 atom % does not significantly affect the distribution of liquid products from CO2 electroreduction. In a broad perspective, this work highlights the potential of the femtosecond laser process to fine-tune surfaces to produce photo- and electrocatalyst materials.

Ionic liquids (ILs) form a multilayered structure at the solid/electrolyte interface, and the addition of solutes can alter it. For this purpose, we have investigated the influence of the silver bis(trifluoromethylsulfonyl)amide (AgTFSA) concentration in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSA) on the layering using in situ atomic force microscopy. AFM investigations revealed that the Au(111)/electrolyte interface indeed depends on the concentration of the salt where a typical " IL" multilayered structure is retained only at quite low concentrations of the silver salt (e.g. ≤200 μM). However, at 200 μM AgTFSA/[Py1,4]TFSA and above this "IL" multilayered structure is disturbed/varied. A simple double layer structure was observed at 500 μM AgTFSA in [Py1,4]TFSA. Furthermore, the widths of the innermost layers have been found to be dependent on the concentration and on the applied electrode potentials. Our AFM results show that the concentration of solutes strongly influences the structure of the electrode/electrolyte interface and can provide new insights into the electrical double layer structure of the electrode/ionic liquid interface. We also introduce a semi-continuum theory to discuss the double layer structure.

Ionic liquids are potential electrolytes for safe lithium-ion batteries (LIB). Recent research has probed the use of silicon as an anode material for LIB with various electrolytes. However, the nanostructure of the ionic liquid/Si interface is unknown. The present communication probes the hydrogen terminated p-Si(111) interface using atomic force microscopy (AFM) in 1-ethyl-3-methylimidazolium bis(trifluoromethlysulfonyl)amide ([EMIm]TFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethlysulfonyl)amide ([Py1,4]TFSA). AFM measurements reveal that the imidazolium cation adsorbs at the H-Si(111)/[EMIm]TFSA interface leading to an ordered clustered facet structure of ∼3.8 nm in size. In comparison, the Si(111)/[Py1,4]TFSA interface appeared the same as the native surface in argon. For both pure ILs, repulsive forces were measured as the tip approached the surface. On addition of LiTFSA attractive forces were measured, revealing marked changes in the interfacial structure.