The synthesis and properties of a series of new structure‐directing triblock copolymers with PEO‐PB‐PEO structure (PEO = poly(ethylene oxide) and PB = polybutadiene) and their application as superior ...pore‐templates for the preparation of mesoporous titania coatings are reported. Starting from either TiCl4 or from preformed TiO2 nanocrystalline building blocks, mesoporous crystalline titanium oxide films with a significant degree of mesoscopic ordered pores are derived, and the pore size can be controlled by the molecular mass of the template polymer. Moreover, the triblock copolymers form stable micelles already at very low concentration, i.e., prior to solvent evaporation during the evaporation‐induced self‐assembly process (EISA). Consequently, the thickness of pore walls can be controlled independently of pore size by changing the polymer‐to‐precursor ratio. Thus, unprecedented control of wall thickness in the structure of mesoporous oxide coatings is achieved. In addition, the micelle formation of the new template polymers is sufficiently distinct from that of typical commercial PPO‐PEO‐PPO polymers (Pluronics; PPO = poly(propylene oxide)), so that a combination of both polymers facilitates bimodal porosity via dual micelle templating.
The synthesis of a series of new triblock copolymer templates, PEO‐PB‐PEO, is reported along with their application for mesoporous oxide coatings. Micelles of the polymers template large mesopores in crystalline TiO2 films using either molecular (TiCl4) or nanocrystalline precursors (anatase nanoparticles). Pore size and thickness of pore walls can be controlled independently.
Synthesis of mesoporous iridium oxide films via soft templating and evaporation-induced self-assembly is demonstrated employing an amphiphilic triblock-copolymer PEO-PB-PEO. Films possess ...nanocrystalline walls and feature locally ordered pores of about 16 nm diameter. Analysis of the film properties by SEM, TEM, EDX, XPS, SAXS, XRD, and BET along the thermal treatment that succeeds dipcoating shows that the polymer template is removed by calcination between 200 and 300 °C, accompanied by uniaxial shrinkage of film and pore system perpendicular to the substrate. Treating the film in excess of 450 °C leads to further growth of crystallite size and loss of surface area progressing gradually with increasing calcination temperature. Templated IrO2 films conditioned at 450 °C show substantially reduced electrocatalytic overpotentials (efficiency increases) for the oxygen evolution reaction (OER) compared to those of untemplated coatings. Pore templating thus enables direct control over surface catalytic properties of iridium oxide.
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•Novel synthesis approach for PEO-PB-PEO templated mesoporous Ir/TiOx.•Characterization of structural and electrocatalytical properties.•Ir/TiOx films need minimum loading of 30 wt% ...Ir for sufficient conductivity.•Calcination at 400 °C leads to highest electrocatalytic activity.
The depletion of fossil resources coupled with an increasing demand in both sustainable and renewable energy sources further strengthen the development of highly efficient electrocatalytic water splitting catalysts. Iridium oxide is well known for its excellent activity and stability during acidic oxygen evolution reaction (OER). However, high prices and rare abundance demand the most efficient utilization.
We report a new synthesis approach for iridium/titanium-based mixed oxides with a tailored mesopore structure employing iridium acetate and titanium chloride as precursors. The new Ir/TiOx system outperforms OER catalysts based on other titanium precursors by a factor of up to two. The material is used as a model system to investigate the impact of synthesis and structural parameters on OER performance.
We find that calcination temperature and iridium content are the main synthesis parameters to achieve tailored structures and superior electrochemical activity. The highest surface area and OER-activity are attained for samples with a fully developed mesoporous network and small crystallite sizes obtained by a moderate calcination around 400 °C. A minimum content of iridium is required to achieve sufficient electrical conductivity, whereas at higher iridium content the OER performance scales approximately linearly.
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