Antireflective Coatings with Adjustable Refractive Index and Porosity Synthesized by Micelle-Templated Deposition of MgF₂ Sol Particles

Minimizing efficiency losses caused by unwanted light reflection at the interface between lenses, optical instruments and solar cells with the surrounding medium requires antireflective coatings with adequate refractive index and coating thickness. We describe a new type of antireflective coating material with easily and independently tailorable refractive index and coating thickness based on the deposition of colloidal MgF₂ nanoparticles. The material synthesis employs micelles of amphiphilic block copolymers as structure directing agent to introduce controlled mesoporosity into MgF₂ film. The coatings thickness can be easily adjusted by the applied coating conditions. The coatings refractive index is determined by the materials porosity, which is controlled by the amount of employed pore template. The refractive index can be precisely tuned between 1.23 and 1.11, i.e., in a range that is not accessible to nonporous inorganic materials. Hence, zero reflectance conditions can be established for a wide range of substrate materials

Highly Active Binder-Free Catalytic Coatings for Heterogeneous Catalysis and Electrocatalysis: Pd on Mesoporous Carbon and Its Application in Butadiene Hydrogenation and Hydrogen Evolution

Heterogeneous catalysis performed in wall-coated reactors and electrocatalysis require homogeneous catalytic coatings with high surface area and good accessibility of the active sites. Conventional coating methods necessitate the use of binder components that often block pores and active sites, which limits catalytic efficiency, and utilization of expensive active metals. We report an approach for the direct and binder-free synthesis of chemically, mechanically, and thermally stable catalytic coatings based on ordered mesoporous carbon films employed as catalyst support. The synthesis relies on the codeposition of a structure-directing agent and small clusters of polymeric carbon precursors along with ionic metal species on a substrate. A sequence of thermal treatments converts the polymer into partly graphitized carbon, decomposes the structure-directing agent, and converts the metal precursor into highly active nanoparticles. Syntheses and catalytic applications are exemplarily demonstrated for palladium on carbon, a system widely used in heterogeneous catalysis and electrocatalysis. The obtained catalysts provide significantly higher space–time yields in the selective gas-phase hydrogenation of butadiene than all reported Pd/C catalysts while at the same time retaining isothermal reactor conditions. Moreover, when they were tested in the electrocatalytic hydrogen evolution reaction (HER), the catalysts outperformed reported Pd/C catalysts by a factor of 3, which underlines the benefits of the developed binder-free catalyst system

Efficient Electrochemical Hydrogen Peroxide Production from Molecular Oxygen on Nitrogen-Doped Mesoporous Carbon Catalysts

Electrochemical hydrogen peroxide (H₂O₂) production by two-electron oxygen reduction is a promising alternative process to the established industrial anthraquinone process. Current challenges relate to finding cost-effective electrocatalysts with high electrocatalytic activity, stability, and product selectivity. Here, we explore the electrocatalytic activity and selectivity toward H₂O₂ production of a number of distinct nitrogen-doped mesoporous carbon catalysts and report a previously unachieved H₂O₂ selectivity of ∼95–98% in acidic solution. To explain our observations, we correlate their structural, compositional, and other physicochemical properties with their electrocatalytic performance and uncover a close correlation between the H₂O₂ product yield and the surface area and interfacial zeta potential. Nitrogen doping was found to sharply boost H₂O₂ activity and selectivity. Chronoamperometric H₂O₂ electrolysis confirms the exceptionally high H₂O₂ production rate and large H₂O₂ faradaic selectivity for the optimal nitrogen-doped CMK-3 sample in acidic, neutral, and alkaline solutions. In alkaline solution, the catalytic H₂O₂ yield increases further, where the production rate of the HO₂^– anion reaches a value as high as 561.7 mmol g_catalyst^–1 h^–1 with H₂O₂ faradaic selectivity above 70%. Our work provides a guide for the design, synthesis, and mechanistic investigation of advanced carbon-based electrocatalysts for H₂O₂ production