Tantalum Oxynitride for a Novel Cathode of PEFC

Ishihara, Akimitsu; Lee, Kunchan; Doi, Shotaro; Mitsushima, Shigenori; Kamiya, Noriho; Hara, Michikazu; Domen, Kazunari; Fukuda, K.; Ota, Ken Ichiro

doi:10.1149/1.1865612

Cited by 156 publications

(130 citation statements)

References 13 publications

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“…To compare against other Ta-based catalysts, our ORR mass activity is higher than TaO 0.92 N 1.05 (0.029 A g cat −1 at 0.3 V vs. RHE, tested under O 2 -saturated H 2 SO 4 0.1 mol L −1 ). 22 Even without a carbon support, our Ti-Ta-ON catalyst has a higher mass activity of 0.11 A g cat −1 (from Figure 6b), which is still an order of magnitude higher than the literature value. Additionally, our Ti-Ta-ON catalyst was also synthesized using a more benign, ammonia-free synthesis route.…”

Section: Resultsmentioning

confidence: 58%

Influence of Aliovalent Substitutions on Oxygen Reduction on Tantalum Oxynitrides

Pasqualeti

Padgett

Kuo

et al. 2017

J. Electrochem. Soc.

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The development of active and stable oxygen reduction reaction (ORR) electrocatalysts using low-cost, abundant elements is of critical importance to the widespread adoption of proton-exchanged membrane fuel cells (PEMFCs). Tantalum-containing compounds, such as tantalum oxynitrides, can catalyze ORR in acid, with the degree of oxidation proposed to play a central role in controlling the ORR activity. Herein, we report the incorporation of aliovalent ions in tantalum oxynitrides (Ta-ON) and their effect on the ORR activity in acid. We synthesize Ta-ON by utilizing urea as the nitrogen source and use aliovalent (Ti 4+ ) and isovalent (Nb 5+ ) substitutions to evaluate the influence of the aliovalent substitution on the ORR activity. We found that an aliovalent Ti 4+ substitution increases the ORR activity by 3x, which we attribute to improved electrical conductivity and increased ORR active sites. In comparison, isovalent Nb 5+ substitution or carbon inclusion as oxycarbonitride did not positively affect the ORR activity. Our finding points to the important role of defects and conductivity in the Ta Active, acid-stable, and cost-effective cathodes for the oxygen reduction reaction (ORR) play an enabling role in the commercialization of proton-exchanged membrane fuel cells (PEMFCs). Platinum nanoparticles supported on high surface-area carbon supports (Pt/C) are currently the most active ORR electrocatalyst; 1 however, there are concerns with the scalability and stability 2 of Pt. 3,4 To identify alternatives, many groups have examined non-Pt ORR electrocatalysts made of inorganic, organic, and hybrid organic-inorganic materials. Examples include Fe-N-C, 5 and polyaniline (PANI)-Fe/Co-C, 6,7 some of which have ORR kinetics almost already comparable to Pt/C. 8,9 However, these electrocatalysts are not yet stable under longterm operations.3 While many efforts have been made to improve the stability 10 and identify the active sites, 11 long-term stability of these carbon-based electrocatalysts remains a challenge.Valve metal compounds such as tantalum-based compounds are among a few classes of non-precious-metal materials that are stable in acid.12 Their exceptional stability has spurred investigations of how they can be used as electrocatalysts. Examples include tantalum oxynitride (TaON) and tantalum nitride (Ta 3 N 5 ), which have also been investigated for solar-driven water splitting. [13][14][15][16] However, most valvemetal oxides are not active toward the ORR. As a result, significant efforts have been devoted to activating these materials for the ORR. Ota et al. have shown that controlling the degree of oxidation can improve the ORR in tantalum oxynitrides.17,18 By surveying TaC x N y , 17Ta-CNO 17,19 and TaO x N y /Ti, 20 they have proposed that an ideal interaction between the oxygen molecule and the surface tantalum must be optimized via this degree of oxidation to improve the ORR activity. 21The same group has also demonstrated correlations between the ORR and oxygen vacancies, which they proposed as the ...

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Section: Resultsmentioning

confidence: 58%

Influence of Aliovalent Substitutions on Oxygen Reduction on Tantalum Oxynitrides

Pasqualeti

Padgett

Kuo

et al. 2017

J. Electrochem. Soc.

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“…Based on the high stability of Group 4 and 5 metal oxide-based compounds in acidic media, low cost, [5,6] and lower solubility in acid solution compared to platinum-based catalysts, these compounds have piqued our interest as they are expected to be stable even under the conditions encountered at the PEFC cathode. Recently, we successfully synthesized oxide-based nanoparticles using oxy-metal phthalocyanines (MeOPc; Me = Ta, Zr, and Ti) as the starting material and multi-walled carbon nanotubes (MWCNTs) as the support as well as the electro-conductive material [7,8].…”

Section: Introductionmentioning

confidence: 99%

Titanium-Niobium Oxides as Non-Noble Metal Cathodes for Polymer Electrolyte Fuel Cells

et al. 2015

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Abstract:In order to develop noble-metal-and carbon-free cathodes, titanium-niobium oxides were prepared as active materials for oxide-based cathodes and the factors affecting the oxygen reduction reaction (ORR) activity were evaluated. The high concentration sol-gel method was employed to prepare the precursor. Heat treatment in Ar containing 4% H2 at 700-900 °C was effective for conferring ORR activity to the oxide. Notably, the onset potential for the ORR of the catalyst prepared at 700 °C was approximately 1.0 V vs. RHE, resulting in high quality active sites for the ORR. X-ray (diffraction and photoelectron spectroscopic) analyses and ionization potential measurements suggested that localized electronic energy levels were produced via heat treatment under reductive atmosphere. Adsorption of oxygen molecules on the oxide may be governed by the localized electronic energy levels produced by the valence changes induced by substitutional metal ions and/or oxygen vacancies. OPEN ACCESSCatalysts 2015, 5 1290

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“…Various approaches have been taken to overcome these problems, with a particular focus on searching for suitable non-platinum elements, including oxides [6][7][8][9], carbides [10], nitrides, silicides, metal complexes [11,12], and other compounds [13][14][15]. Recently, some interesting studies were reported on the development of Pt-free oxide cathodes, such as Ta-O-N, Ta-C-N-O, and Nb-C-N-O [16][17][18][19][20][21]. In previous investigations [8,9], we reported the ORR activity of dip-coated IrO 2 /Ti catalyst electrodes.…”

Section: Introductionmentioning

confidence: 99%

Oxygen reduction characteristics of several valve metal oxide electrodes in HClO4 solution

Takasu

Suzuki

Yang

et al. 2010

Electrochimica Acta

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In the search for active cathode catalysts for polymer electrolyte fuel cells (PEFCs) using inexpensive materials, several valve metal oxide electrodes, TiO x , ZrO x , TaO x , with corresponding binary oxide electrodes were selected for the evaluation of catalytic activity for oxygen reduction reaction (ORR) by means of cyclic voltammetry in 0.1 M HClO 4 at 60°C. These oxide electrodes were prepared mainly by the dip-coating method on a titanium plate substrate at a temperature between 400°C and 500°C and were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). Among the oxide-coated electrodes investigated, Ti 0.7 Zr 0.3 O x /Ti provided the highest ORR specific activity, with an onset potential, E ORR , of 0.86 V vs. RHE during the cathodic potential sweep.Fine TaO x particles prepared as an extension of the dip-coating method, showed very high catalytic activity determined by means of hydrodynamic voltammetry in 0.1 M HClO 4 at 30°C with an E ORR of 0.90 V vs. RHE.２

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Tantalum Oxynitride for a Novel Cathode of PEFC

Cited by 156 publications

References 13 publications

Influence of Aliovalent Substitutions on Oxygen Reduction on Tantalum Oxynitrides

Influence of Aliovalent Substitutions on Oxygen Reduction on Tantalum Oxynitrides

Titanium-Niobium Oxides as Non-Noble Metal Cathodes for Polymer Electrolyte Fuel Cells

Oxygen reduction characteristics of several valve metal oxide electrodes in HClO4 solution

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