Logo: to the web site of Uppsala University

Using seawater can reduce the dependence on freshwater resources to generate hydrogen by electrocatalytic water splitting. However, the stability and activity of hydrogen evolution reaction (HER) electrocatalysts are highly influenced by the pH of seawater. In this regard, the development of the practical application of HER depends on the creation of highly active non-noble metal electrocatalysts. Here, we propose a technique to optimize the electrocatalytic activity and stability of MoO3 by utilizing titanium felt as the substrate. We show an HER overpotential as low as 83 mV at -10 mA cm-2 in neutral pH conditions. The present results show that electrocatalysts based on earth-abundant metals can perform well in saltwater HER, especially at a near-neutral pH (pH similar to 7). In a neutral saltwater electrolyte (0.55 M PBS + 0.5 M NaCl), this electrocatalyst showed stable performance for 250 h at a constant current density of -100 mA cm-2, indicating its promising application in seawater-based hydrogen generation. Compared with noble metals, this electrocatalyst provides a cost-effective option for economic seawater hydrogen generation, promoting the potential of seawater electrolysis.

Nanofibers and nanorods of NiCo- and NiCoFe- oxides and phosphides were synthesized by hydrothermal methods, followed by phosphidation to yield (Ni,Co)P, (Ni,Co)2P, and FeP. The materials were evaluated as electrocatalysts for the oxygen evolution reaction (OER) in water splitting in the presence of a magnetic field in two electrolytes: 1 M KOH and 1 M phosphate buffer saline (PBS) solution. A standard electrochemical cell was equipped with disk magnets directed perpendicular to the electric field. The magnetic field affected the catalyst interface and increased the reaction rate. The best catalyst was found to be NiCoP, and the overpotential (at 10 mA/cm2) was reduced from 330 to 260 mV when a magnetic field of 100 mT was applied and further to 170 mV when a magnetic field of 200 mT was applied. NiCoP has the highest proportion of magnetic domains aligned due to having the highest saturation magnetization (Ms), remanence magnetization (Mr), and the lowest coercivity (Hc). The mixed transition metal phosphide catalysts were found to partly transform into (Ni,Co)3(PO4)2 during electrocatalysis; however, they still responded to a change in the magnetic field. The results show that a weak magnetic field can improve the performance of electrocatalysts based on certain transition metals in a neutral pH electrolyte mimicking seawater.

Photochromic coatings are attractive materials for achieving dynamic transmittance control in glazing. However, state-of-the-art photochromic materials are either not durable enough (the case of organic photochromic dyes), or not easily manufactured onto large glass panes (the case of silver halides). The requirements of durability and large area fabrication have hitherto hindered the application of photochromism in smart glazing. Thus, the importance of rare-earth oxyhydrides, which have emerged during the last decade as an inorganic (and hence, in principle, durable) photochromic family of materials that can be prepared onto large area glass panes by magnetron sputtering. In this work, we will discuss in detail the photochromic effect in oxyhydrides, how to prepare and optimize photochromic coatings with excellent switching kinetics, as well as answer other frequently asked questions when it comes to the applications of rare earth oxyhydrides in glazing.

Gadolinium oxyhydride GdHO is a photochromic material that darkens under illumination and bleaches back by thermal relaxation. As an inorganic photochromic material that can be easily deposited by magnetron sputtering, GdHO has very interesting potential applications as a functional material, specially for smart glazing applications. However, the underlying reasons behind the photochromic mechanism - which can be instrumental for the correct optimisation of GdHO for different applications - are not completely understood. In this paper, we rely on the well-established magnetic properties of Gd3+ to shed light on this matter. GdHO thin films present paramagnetic behaviour similar to other Gd3+ compounds such as Gd2O3. Illumination of the films result in a reversible increase of the Curie-Weiss temperature pointing to Ruderman-Kittel-Kasuya-Yosida RKKY interactions, which is consistent with the resistivity decrease observed in the photodarkened films.

Vanadium oxide thin films were prepared using reactive magnetron sputtering method, varying the deposition pressures from 4 to 10 mTorr while maintaining the other sputtering parameters constant. Our investigations revealed sensitive dependence of deposition pressure, chemical states of the V and O atoms, crystal phases, and thermochromic (TC) optical modulation. Specifically, the film deposited at 8 mTorr displayed distinct TC characteristics with a prevalent monoclinic m-VO₂ phase according to X-ray diffraction (XRD), supported by X-ray photoelectron spectroscopy (XPS). Optical transmittance modulation and electrical property measurements revealed a metal–insulator transition (MIT), confirming the intimate connection between TC characteristics and presence of the m-VO₂ phase. Films deposited at pressures lower or higher than 8 mTorr exhibited typical semiconductor behavior without TC characteristics, further supported by in situ XRD, where (110) plane shifted to lower angle upon heating above τ_C. Chemical state analysis by XPS revealed a clear correlation between V−O peaks and the presence of a VO₂ phase, with the film deposited at 8 mTorr displaying relatively large peak fitted area indicative of the VO₂ phase. These findings highlight the critical and sensitive dependence of the deposition conditions in tailoring the properties of vanadium oxide thin films and provide valuable insights for potential applications in chromogenic films.

Chromogenic materials can have many technological uses, including their uses in ophthalmic lenses, rear-view mirrors in cars, displays, etc. However, in the context of energy applications—the topic of this book—the implementation of chromogenic devices in smart (dynamic) windows stands out.

Jupyter Notebooks allow the presentation of programming code, text, figures and other multimedia content in an interactive way which, in principle, makes them an ideal tool for education. Not surprisingly, the number of publications dealing with Jupyter Notebooks in teaching have increased rapidly during recent years. Inspired by the Open Software philosophy, most of these notebooks are intended as open educational resources. However, few of these notebooks take into consideration basic teaching and learning principles, a problem that potentially results in poorly designed content and/or little reuse. This talk is a wake-up call on the need for implementing well-established educational principles into Jupyter Notebooks for creating content of superior educational value. We will address this subject putting a special emphasis on the development of Jupyter notebooks in an inquiry-based learning (IBL) context. In the talk, we will address the different steps of creating an IBL activity using Jupyter: (i) formulating the initial question, (ii) the resources for solving this question (the Jupyter notebook itself), (iii) guidance of the students through the notebook and (iv) assessment.

Vanadium dioxide (VO2) is a thermochromic (TC) material, exhibits a reversible transmittance change in the near-infrared (NIR) region upon heating above a critical temperature tic, due to an insulator-to-metal phase transition. Numerous studies on the V-O system can be found in the literature, including the synthesis of VO2 films. The phase diagram of the V-O system involves complicated suboxide phases that prevent pure VO2 for-mation and obscures quantitative analysis. Here, VO2 thin films were systematically prepared with various ox-ygen flow ratios (r) using reactive magnetron sputtering. Thin films prepared with r = 4.1% show dominant VO2 phase and the highest TC performance. The r -range producing dominant VO2 phase is found to be narrow: 3.7% < r<4.2%. At lower and higher r, TC characteristics are shown to be accompanied, as expected, by electrical conductivity changes, but also by microstructure transformations. The latter producing textured films that gradually develop upon cycling around tic. In particular, a change of texture, yielding oriented VO2 crystallites, is observed by in-situ XRD around tic. Our results shed light on the VO2 formation and associated structural, chemical and electrical properties under various oxidizing conditions during magnetron sputtering, which calls for careful preparation and strategies to stabilize the VO2 phase.

Most transparent conducting materials are based on Sn:In2O3 (ITO). When applied onto flexible substrates, ITO can be prepared in an oxide-metal-oxide (OMO) configuration, typically ITO/Ag/ITO, where the ductility of the embedded metal layer is intended to reduce the mechanical brittleness and improve the electrical conductivity of the OMO multilayer. Hitherto, the lower limit of the thickness of the Ag layer has been limited by the percolation threshold, which limits the Ag layer to be thicker than similar to 10 nm to avoid agglomeration and to ensure conductivity and structural stability. Metal layers of thicknesses below 10 nm are, however, desirable for obtaining OMO coatings with better optical properties. It is known that agglomeration of the metal layer can, to some extent, be suppressed when substituting Ag by an Ag-Pd-Cu (APC) alloy. APC-based OMO films exhibit excellent optical and electrical properties, but still continuous APC films well below 10 nm thickness cannot be achieved. In this work we demonstrate that controlled oxidation of APC results in smooth, ultrathin APC:O continuous coatings (of thickness similar to 5 nm) on ITO-coated PET substrates. Moderate oxidation yields superficial PdOx formation, which suppresses Ag agglomeration, while still maintaining excellent conductivity. On the other hand, extensive oxidation of APC leads to extensive Pd oxide nucleation deteriorating the conductivity of the film. The ITO/APC:O/ITO films exhibit low resistivity, attributed to a high Hall mobility associated with suppressed agglomeration, good stability in high humidity/temperature environments, superior transmittance in the visible and infrared region, and excellent mechanical bending properties, thus providing new opportunities for fabricating superior transparent conducting coatings on polymer substrates.

The ability to control electronic states by utilizing quantum confinement of one of the material components in heterojunctions is a promising approach to perform energy-level matching. In this work, we report the possibility to achieve optimum energy alignment in heterojunctions made from size-controlled quantum dots (Q-dots) of ZnO in combination with three copper oxides: Cu₂O, Cu₄O₃, and CuO. Quantum confinement effects on the ZnO nanoparticles in the diameter range 2.6–7.4 nm showed that the direct optical band gap decreased from 3.99 to 3.41 eV, with a dominating shift occurring in the conduction band (CB) edge, and thus the possibility to obtain close to 0.6 eV CB edge shift by controlling the size of ZnO. The effect was utilized to align the electronic bands in the ZnO Q-dot/copper oxide heterojunctions to allow for charge transfer between the materials and to test the ability to improve the photocatalytic performance for the system, evaluated by the transformation of a dye molecule in water. The catalyst materials were investigated by X-ray diffraction, scanning electron microscopy, ultraviolet–visible (UV–vis), photoluminescence, and Raman spectroscopy. The most promising material combination was found to be the Cu₂O copper oxide in combination with an energy aligned ZnO Q-dot system with approximately 7 nm diameter, showing strong synergy effects in good agreement with the energy-level analysis, outperforming the added effect of its individual components, ZnO-Q-dots and Cu₂O, by about 140%. The results show that utilization of a heterojunction with controllable energy alignment can provide a drastically improved photocatalytic performance. Apart from increased photocatalytic activity, specific surface states of ZnO are quenched when the heterojunction is created. It is anticipated that the same approach can be utilized in several material combinations with the added benefit of a system with controllable overpotential and thus added specificity for the targeted reduction reaction.