Perovskite‐Type Oxynitride Nanofibers Performing Photocatalytic Oxygen and Hydrogen Generation

Abstract

Ba5Nb4O15 nanofibers with tailored nanofiber diameters are prepared via electrospinning, and treated in ammonia gas to synthesize niobate oxynitride nanofibers. Most importantly, the nanofibers retain their fiber morphology during ammonolysis, and the nanofiber diameter of the converted fibers can be adjusted. Only a thorough characterization, including detailed Rietveld refinements, can reveal that the ammonolysis of Ba5Nb4O15 results not only in BaNbO2N, but also generates Ba2NbO3N as additional oxynitride phase. Such BaNbO2N–Ba2NbO3N composite nanofibers with adjusted nanofiber diameters are applied in photocatalytic water oxidation and hydrogen generation. After decoration with CoNbO4 or Pt cocatalyst, the materials show a diameter‐dependent photocatalytic activity, respectively, with an optimum nanofiber diameter. The presented synthesis demonstrates a novel sol–gel‐derived possibility for nanostructuring of oxynitrides, which can pave the way for new synthesis strategies of nanostructured complex oxynitrides.

Theoretical Insights into the Structure, Stability, Electronic, and Photocatalytic Properties of BaNbO2N Low-Index Surfaces

“…48−50 The hydrophilicity/hydrophobicity of materials and the intermediates generated from water decomposition are highly related to the activity of photocatalytic reactions. 51,52 Therefore, we have explored water adsorption and its dissociation on the (100) and (001) surfaces of BaNbO 2 N. The adsorption energy (E ads ) of a water molecule on a surface is defined according to the following equation 11) where E total is the total energy of a water molecule supported on a surface, E surface is the energy of a relaxed clean surface, and E H 2 O is the energy of a water molecule in a supercell with the same size as the clean surface. According to the definition, a negative value of E ads means a thermodynamically favorable adsorption process.…”

“…The material could be applied in photocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by decorating with Pt or CoNbO 4 cocatalysts. 11 Kodera et al reported that the morphology of single-crystalline BaNbO 2 N particles can be tuned by the effect of different kinds of alkali halide flux treatments. 12 The experimental results by Seo BaNbO 2 N were highly dependent on the annealing temperature.…”

“…BaNbO 2 N has an optical band gap of 1.7–1.8 eV with the conduction band minimum (CBM) and the VBM straddling the hydrogen and oxygen evolution potentials, which can be used in photocatalytic overall water splitting in principle. , It has the potential for providing a solar-to-hydrogen (STH) energy conversion efficiency of more than 28% in conjunction with an incident photon-to-current efficiency (IPCE) of unity. − BaNbO 2 N exhibits the longest light absorption edge of 740 nm and can be activated for photocatalytic water oxidation and reduction in the presence of sacrificial reagents by loading cocatalysts and modifying precursors. , Hofmann et al found that the ammonolysis of Ba 5 Nb 4 O 15 resulted in the BaNbO 2 N-Ba 2 NbO 3 N composite nanofibers. The material could be applied in photocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by decorating with Pt or CoNbO 4 cocatalysts . Kodera et al reported that the morphology of single-crystalline BaNbO 2 N particles can be tuned by the effect of different kinds of alkali halide flux treatments .…”

Photocatalytic hydrogen generation and electron storage capability of mesoporous TiO2 aerogels with adjustable surface area

“…This also shows that a normalization to surface area is important for a correct interpretation of the photocatalytic activity of photocatalysts, which was already shown before. [29,[36][37][38] The TiO2 aerogels were all regained after the photocatalytic hydrogen experiments by washing and supercritical drying. XRD pattern after the photocatalytic hydrogen production experiments are shown in Figure S3.…”

Strain-Induced Photocatalytic H2 Production over BiVO4 in Pure Water without Any Cocatalyst

“…To date, a variety of semiconductor photocatalysts have been developed for achieving efficient O 2 evolution. 12,13 Among these photocatalysts, bismuth vanadate (BiVO 4 ) has attracted much attention because of its narrow band gap, good photostability, nontoxicity, and high oxygen evolution activity under visible light. 14−19 However, pure BiVO 4 is not suitable for hydrogen production since the conduction band position of BiVO 4 is very close to the reduction potential of H + /H 2 (0 V vs NHE at pH = 0).…”