Lars Fast

In the search for alternative and renewable energies that will finally allow abandoning the use of fossil fuels once and for all, hydrogen energy is among the most promising solutions able to fuel any kind of device independent of its size. The energy cycle of hydrogen needs a large infrastructure of highly efficient catalysts used in both electrolysers, which produce hydrogen gas, as well as fuel cells, where the energy stored in the hydrogen bond is converted into electrical current. The conversion of hydrogen works most effectively in acidic media, where the most effective and chemically stable material is platinum. The low abundancy and associated high cost of Pt make it impossible to provide a large-scale infrastructure using the commercial Pt/C catalyst. Alternatives must be found to substantially reduce the amount of Pt used as catalyst material without compromising its sustainability. A facile electrodeposition process from aqueous media allows the one-step synthesis of a Ni-Mo-Pt alloy for use in both hydrogen evolution reaction (HER) and energy conversion systems such as fuel cells. In a previous study, mesoporous Ni-Pt films were synthesised by electrodeposition and thoroughly characterised towards HER, finding that the reaction in 0.5 M H₂SO₄ was efficient, stable and reproducible. However, some leaching of Ni into the sulfuric acid was observed under open circuit conditions [1,2]. In this study, molybdenum is introduced into the previously investigated Ni-Pt alloy to increase the stability of the material in acidic media. With respect to the electrolyte used for the synthesis of the Ni-Pt alloy, all bath components were kept the same except for the addition of sodium molybdate and citric acid. The latter complexes Mo(VI), thus enabling its co-deposition. Due to a pH-dependent complexation of Mo(VI) by citric acid, the composition of the Ni-Mo-Pt alloy is strongly pH-dependent and can further be fine-tuned to the needs of the specific application by changing the electrodeposition parameters. The Mo contents obtained reach from 10 at% up to 50 at%. Alloys with the highest Mo content, however, trigger phase separation. Using potentiostatic electrodeposition, continuous thin films of Ni-Mo-Pt are obtained on a Cu-coated Si substrate. However, the growth of globular particles is favoured on a hydrophobic substrate, such as a carbon-based gas diffusion layer (GDL) typically found in a fuel cell set-up. Further, using pulse electrodeposition, nanoparticles with a mean diameter down to 10 nm are successfully obtained. For HER in 0.5 M H₂SO₄, Ni rich alloys with low Pt contents (between 1 at% and 5 at%) are investigated, while alloys with higher Pt contents can provide sufficient electrochemical stability for oxygen reduction reaction (ORR) in a proton exchange membrane (PEM) fuel cell. The stability of alloys with varying composition is determined by incubation in 0.5 M H₂SO₄. Cyclic voltammetry curves in the same media are performed on Ni-Mo-Pt nanoparticles in order to activate the surface and remove any contaminants as a preparation for tests in a PEM fuel cell, and to determine their electrochemically active surface area (ECSA). The electrochemical experiments are supplemented with microstructural analysis by SEM and XRD. Acknowledgement: This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 764977. Additional support from the Generalitat de Catalunya (2017-SGR-292) and the Spanish Government (MAT2017-86357-C3-1-R and associated FEDER) is also acknowledged. References: [1] K. Eiler, S. Suriñach, J. Sort, E. Pellicer, Appl. Catal. B, 2020, 265, 118597 [2] K. Eiler, J. Fornell, C. Navarro-Senent, E. Pellicer, J. Sort, Nanoscale, 2020, 12, 7749

Nb-Ge-C nanocomposite thin films were deposited by dc magnetron sputtering using three elemental targets. The films consist of substoichiometric NbCx in a nanometer-thick matrix of amorphous C and Ge. Films with no Ge contain grains that are elongated in the growth direction with a (111) preferred crystallographic orientation. With the addition of ∼12 at. % Ge, the grains are more equiaxed and exhibit a more random orientation. At even higher Ge contents, the structure also becomes denser. The porous structure of the low Ge content films result in O uptake from the ambient. With higher C content in the films both the amount of amorphous C and C/Nb-ratio increases. The contact resistance was measured by four-point technique as a function of contact force between 0 and 10 N. The lowest contact resistance (1.7 mΩ) is obtained at 10 N. The resistivity varies between 470 and 1700 μΩ·cm depending on porosity and O content.

Textile fibers and yarns of high conductivity, and their integration into wearable textiles for different electronic applications, have become an important research field for many research groups throughout the world. We have produced novel electrically conductive textile yarns by vapor‐phase polymerization (VPP) of a conjugated polymer, poly(3,4‐ethylenedioxythiophene) (PEDOT), on the surface of commercially available textile yarns (viscose). In this article, we have presented a novel setup for electrical resistance measurements, which can be used not only for fibrous structures but also for woven structures of specific dimensions. We have reported a two‐point resistance‐measuring method using an already manufactured setup and also a comparison with the conventionally used method (so‐called crocodile clip method). We found that the electrical properties of PEDOT‐coated viscose fibers strongly depend on the concentration of oxidant (FeCl₃) and the doping (oxidation) process of PEDOT. To evaluate the results, we used mass specific resistance values of PEDOT‐coated viscose yarns instead of normal surface resistance values. The voltage–current (V–I) characteristics support the ohmic behavior of coated fibers to some extent. Monitoring of the charging effect of the flow of current through conductive fibers for prolonged periods of time showed that conductivity remains constant. The change in electrical resistance values with increase in the length of coated fibers was also reported. The resistance‐measuring setup employed could also be used for continuous measurement of resistance in the production of conductive fibers, as well as for four‐point resistance measurement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

This paper is a brief review of our recent work and a follow up study on nanocomposite coatings comprising nanocrystalline TiC embedded in an amorphous SiC matrix (nc-TiC/a-SiC) with and without Ag additions applied as electrical contacts. These coating materials are deposited at very high deposition rates (>10 μm/h), to meet industrial demands of high productivity. Here we consider Ti-Si-C-Ag nanocomposite coatings with Ag content in the range of 0-22 at.% deposited in a pilot-plant or an industrial deposition system by dc magnetron sputtering from compound targets onto Si(100) and SiO 2 (100) substrates. The microstructure, electrical, and mechanical properties of the coatings were studied with transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, electrical contact resistance, resistivity, and nanoindentation measurements. Varying the deposition parameters bias and pressure within ranges typical of coating processing had no effect on the structure. A variation was, however, observed for the contact resistance, that was determined to be in the range 400-900 mΩ at a contact force between 1.9-2.65 N. The coatings with highest Ag content had the lowest contact resistance.