The optical band gap is a major selection criterion for an absorber in photocatalytic water splitting. Due to its ideal value hematite has been intensively investigated without reaching the expectation, yet. In this work, the Fermi level positions in hematite due to doping and contact formation are investigated. An upper boundary for the Fermi level position at 1.8 eV above the valence band maximum due to the formation of polarons is identified. This results in a different concept of the effective band gap for hematite which we believe is transferable to any material with competing polaron formation after optical excitation: the optical band gap of 2.2 eV deviates from an effective electronic band gap of 1.75 eV. The polaron state acts as a limit in (quasi-)Fermi level shift, restricting the potential of charge transfer reactions. Additionally, it has led to an incorrect determination of the band edge positions of hematite in electrochemical contacts.

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The tailored structure of a bifunctional, semi-homogeneous NiCo-nanotube catalyst system with embedded Pd nanoparticles, is synthesised by electroless plating.

Due to its simplicity, flexibility and conformity, electroless plating presents itself as an attractive route towards functional metal nanostructures. Despite the importance for creating multimetallic materials with enhanced properties, the complex interactions between the components in electroless plating baths make alloy formations a challenging objective. In this work, we outline an electroless plating strategy fabricating Pd−Pt alloy nanomaterials, which is based on arbitrarily miscible plating baths for the individual metals. To demonstrate the excellent nanoscale conformity and homogeneity of our plating system, we apply it to ion track‐etched polymer templates with large inner surfaces as ambitious substrates, resulting in the formation of 3D free‐standing PdxPt100‐x‐nanotube‐networks (NTNWs). Based on the electro‐oxidation of methanol as a model reaction, we utilize the compositional freedom provided by our syntheses for optimizing the catalytic performance of our metal NTNWs, which heavily depends on the Pd−Pt ratio. Within our system, the highest surface normalized activity was found for the Pd20Pt80 NTNW, reaching more than a two‐fold increase of the peak current density in comparison to pure Pt. Overall, our reaction system provides a versatile toolkit for fabricating intricate Pd−Pt nanostructures of arbitrary elemental composition, and constitutes a starting point for designing new electroless alloy plating baths.

Water photolysis is a key technology to convert solar energy into clean, sustainable fuel. Hematite Fe2O3 thin films are considered as a potential photoanode for this purpose. The performance of hematite‐based devices is limited by charge carrier transport and recombination, which are intimately linked to the electronic structure. Investigations of the electronic structure of hematite by photoemission exhibit pronounced differences in the reported spectra. A combination of structural and spectroscopic characterization methods is used to unravel the relation between the crystalline and the electronic structure of hematite thin films, which provides unique fingerprint spectra for different crystalline states. The combination with valence band DOS calculations from literature allows for an assignment of the contribution of iron and oxygen (hybrid‐) states to the valence band DOS.