Porous niobium oxide films prepared by anodization–annealing–anodization

Choi, Jinsub; Lim, Jae Hoon; Lee, Jae Kwang; Kim, Kyung Ja

doi:10.1088/0957-4484/18/5/055603

Cited by 47 publications

(30 citation statements)

References 23 publications

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“…The data in Figure 6 was calibrated to the O 1s peak of Nb 2 O 5 . 44 A linear background was removed from the data, which was then submitted to Gaussian fitting to minimize noise in the signal. Binding energy values are tabulated in Table 2 31,46 After irradiation (spectrum B), the 4f 7/2 peak shifted slightly to 61.9 eV and was significantly broadened with a small peak on the shoulder at approximately 61.1 eV.…”

Section: Resultsmentioning

confidence: 99%

A Building Block Approach to Photochemical Water-Splitting Catalysts Based on Layered Niobate Nanosheets

et al. 2008

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We present a modular approach to the synthesis of nanostructured catalysts for photochemical splitting of water into hydrogen and oxygen. The catalysts are built from exfoliated, semiconducting niobate nanosheets derived from the layered perovskite HCa 2 Nb 3 O 10 . The latter is a catalyst for photochemical evolution of hydrogen from water under UV irradiation. After chemical modification with 3-aminopropyltrimethoxysilane (APS), IrO 2 or Pt particles can be attached to the nanosheets to produce various two-component nanostructures that were fully characterized with transmission electron microscopy and ultraviolet and infrared spectroscopy. Cyclic voltammetry was used to determine the onset potentials for O 2 and H 2 evolution. At pH ) 14, the observed values are in the range +0.61 to +1.24 V (NHE, water oxidation) and -1.36 to -1.62 V (NHE, water reduction). Under UV irradiation, all catalysts evolve hydrogen from water without any sign of deactivation for 5 h. The highest quantum efficiency of 3.49% is observed for a structure with Pt directly grown onto the nanosheets. No O 2 is evolved, which we attribute to the adsorption of O 2 to the catalyst surface. For Pt-[HCa 2 Nb 3 O 10 ], this process starts to shut down H 2 evolution after 9 h of constant irradiation, but the activity can be restored to >60% by evacuating the catalyst dispersion and purging it with Ar. Catalysts assembled from preformed citrate-coated Pt nanoparticles are slightly less active for H 2 evolution and so are catalysts that use the linker aminoethyl-aminoundecanetrimethoxysilane (AEAUS) instead of APS. The activity of IrO 2 -APS-[Ca 2 Nb 3 O 10 ] is lowest among two component catalysts, near the activities of the pure or APSmodified nanosheets. On the basis of XPS data, IrO 2 in this catalyst undergoes photochemical reduction to Ir(0) upon UV irradiation.

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Section: Resultsmentioning

confidence: 99%

A Building Block Approach to Photochemical Water-Splitting Catalysts Based on Layered Niobate Nanosheets

et al. 2008

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“…Oxide production rate was calculated through Equation 2. The values are listed on Figure 1 illustrates the scheme of different regions present on the potential versus time transients during niobium anodizing.…”

Section: Methodsmentioning

confidence: 99%

“…The oxide with oxidation number 4 + acts as an excellent semiconductor. However, Nb 2 O 5 is the most stable compound and demonstrates good corrosion resistance in acid and basic environments, high refractive index and low absorption in UV-visible region [1,2].…”

Section: Obtaining Niobium Oxides In Acetic Acid With Addition Of Hfmentioning

confidence: 99%

Obtaining Niobium Oxides in Acetic Acid With Addition of Hf

Marcolin¹,

Longhi²,

Caio³

et al. 2018

Tecnologia Em Metalurgia Materiais E Mineração

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During anodizing, the chemical attack of hydrofluoric acid (HF) electrolytes on niobium can promote the formation of oxides with porous structures. However, this chemical attack can also cause an intense dissolution of the oxide during its formation. This effect can be minimized by varying the HF concentration of the anodizing electrolyte, thereby controlling the growth of the porous oxide. Studies have alternative electrolytes that do not use HF to obtain porous oxides. Thus, organic electrolytes, such as acetic acid, may be a viable alternative. In this context, the objective of this study is to obtain and evaluate the anodization of niobium in acetic acid at different current densities (10, 20 and 50 mA/cm 2 ) and to study the influence of the addition of HF to the electrolyte. The results showed that the anodized anodic in acetic acid, under conditions of 100 V and 10 mA/cm 2 , presented porous oxide with less defects. Therefore, this result indicates that it is possible to produce porous niobium oxides by anodizing in HF-free electrolyte. Keywords: Niobium; Anodizing; Acetic acid. OBTENÇÃO DE ÓXIDOS DE NIÓBIO EM ÁCIDO ACÉTICO COM ADIÇÃO DE HF ResumoDurante a anodização, o ataque químico de eletrólitos de ácido fluorídrico (HF) sobre o nióbio pode promover a formação de óxidos com estruturas porosas. Contudo, este ataque químico pode causar uma intensa dissolução do óxido durante sua formação. Esse efeito pode ser minimizado variando-se a concentração de HF do eletrólito de anodização, controlando assim o crescimento do óxido poroso. Estudos têm buscado por eletrólitos alternativos que não utilizam HF na obtenção de óxidos porosos. Logo, eletrólitos orgânicos, como o ácido acético, podem ser uma alternativa viável. Neste contexto, o objetivo deste estudo é obter e avaliar a anodização de nióbio em ácido acético em diferentes densidades de correntes (10, 20 e 50 mA/cm2 ) e estudar a influencia da adição de HF ao eletrólito. Os resultados mostraram que a amostra de nióbio anodizada em ácido acético, nas condições de 100 V e 10 mA/cm 2 , apresentou óxido proroso com menor quantidade de defeitos. Portanto, este resultado indica que é possível a formação de óxidos de nióbio porosos por anodização em eletrólito livre de HF. Palavras-chave: Nióbio; Anodização; Ácido acético.

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“…In addition, the current density in both cases undergoes a sudden drop and acquires a null value by the end of the anodization process. This behavior is characteristic of the formation of barrier films, in which the entire current is used for the formation of the film 7,18,22,23 . The analysis of the anodizing curves of the samples with niobium oxalate and oxalic acid with the addition of HF (Table 3) also depicts a similar behavior in both electrolytes in relation to the anodization rate.…”

Section: Anodization Transientsmentioning

confidence: 99%

A Model for the Formation of Niobium Structures by anodization

et al. 2017

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The fluoride use for anodizing electrolytes has been primarily responsible for the formation of nanoporous oxides at valve metals, except aluminum, since it causes a dissolution process. This study presents the formation of an oxide model according to the following anodizing parameters: 100 V, 12.73 mA/cm², room temperature and the niobium samples anodized in niobium oxalate and oxalic acid electrolytes without and with the addition of HF for 5, 30 and 60 min. The anodized samples were analyzed morphologically by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM) and the hydrophobicity of the samples was assessed by the sessile drop method. The presence of fluor in the niobium oxalate electrolyte formed oxides with lower a dissolution and a low hydrophobicity compared to the one formed in oxalic acid was attributed to the incorporation of niobium and oxalate ions. Thereby, the model proposed in this paper showed that during anodization the migration of the fluoride ion into the oxide occurs at high speed, which results in the formation of microcones, leading to the formation of discrete layers of porous oxide.

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Porous niobium oxide films prepared by anodization–annealing–anodization

Cited by 47 publications

References 23 publications

A Building Block Approach to Photochemical Water-Splitting Catalysts Based on Layered Niobate Nanosheets

A Building Block Approach to Photochemical Water-Splitting Catalysts Based on Layered Niobate Nanosheets

Obtaining Niobium Oxides in Acetic Acid With Addition of Hf

A Model for the Formation of Niobium Structures by anodization

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