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The long-term operation of refractory-metal-based metamaterials is crucial for applications such as thermophotovoltaics. The metamaterials based on refractory metals like W, Mo, Ta, Nb, and Re fail primarily by oxidation. Here, the use of the noble metal Ir is proposed, which is stable to oxidation and has optical properties comparable to gold. The thermal endurance of Ir in a 3-layer-system, consisting of HfO 2 /Ir/HfO 2 , by performing annealing experiments up to 1240 °C in a pressure range from 2 × 10 -6  mbar to 1 bar, is demonstrated. The Ir layer shows no oxidation in a vacuum and inert gas atmosphere. At temperatures above 1100 °C, the Ir layer starts to agglomerate due to the degradation of the confining HfO 2 layers. An in situ X-ray diffraction experimental comparison between 1D multilayered Ir/HfO 2 and W/HfO 2 selective emitters annealed at 1000 °C, 2 × 10 -6  mbar, over 100 h, confirms oxidation stability of Ir while W multilayers gradually disappear. The results of this work show that W-based metamaterials are not long-term stable even at 1000 °C. However, the oxidation resistance of Ir can be leveraged for refractory plasmonic metamaterials, such as selective emitters in thermophotovoltaic systems with strong suppression of long wavelength radiation., (© 2023 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

Conductive metal oxides represent a new category of functional material with vital importance for many modern applications. The present work introduces a new conductive metal oxide V 13 O 16 , which is synthesized via a simplified photoelectrochemical procedure and decorated onto the semiconducting photocatalyst BiVO 4 in controlled mass percentages ranging from 25% to 37%. Owing to its excellent conductivity and good compatibility with oxide materials, the metallic V 13 O 16 -decorated BiVO 4 hybrid catalyst shows a high photocurrent density of 2.2 ± 0.2 mA cm -2 at 1.23 V versus reversible hydrogen electrode (RHE). Both experimental characterization and density functional theory calculations indicate that the superior photocurrent derives from enhanced charge separation and transfer, resulting from ohmic contact at the interface of mixed phases and superior electrical conductivity from V 13 O 16 . A Co-Pi coating on BiVO 4 -V 13 O 16 further increases the photocurrent to 5.0 ± 0.5 mA cm -2 at 1.23 V versus RHE, which is among the highest reported for BiVO 4 -based photoelectrodes. Surface photovoltage and transient photocurrent measurements suggest a charge-transfer model in which photocurrents are enhanced by improved surface passivation, although the barrier at the Co-Pi/electrolyte interface limits the charge transfer., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)