Tungsten Carbide Nanoparticles as Efficient Cocatalysts for Photocatalytic Overall Water Splitting

Garcia‐Esparza, Angel T.; Cha, Dongkyu; Ou, Yiwei; Kubota, Jun; Domen, Kazunari; Takanabe, Kazuhiro

doi:10.1002/cssc.201200780

Cited by 197 publications

(177 citation statements)

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“…Indeed, contact between TiN nanoparticles and conductive substrates has been found to be very effective in ensuring high electrochemical performance. 21 On the other hand, the crystallite particle sizes were in good agreement with the sizes estimated from XRD (typically 5-10 nm). It can be observed that the synthesis under NH 3 flow decreased the amount of amorphous species seen in the TEM image of the sample (Figure 3).…”

supporting

confidence: 73%

Titanium Nitride Nanoparticle Electrocatalysts for Oxygen Reduction Reaction in Alkaline Solution

Ohnishi

Katayama

Cha

et al. 2013

J. Electrochem. Soc.

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KAUST RepositoryMonodispersed TiN nanoparticles with a narrow size distribution (7-23 nm) were synthesized using mesoporous graphitic (mpg)-C 3 N 4 templates with different pore sizes. The nano-materials were examined as electrocatalysts for oxygen reduction reaction (ORR) in alkaline media. The TiN nanoparticles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N 2 sorption, transmission electron microscopy (TEM), and C-H-N elemental analysis. The ORR current increased as the TiN particle size decreased, and hence the surface area of TiN nanoparticles reactive to ORR increased. Rotating ring disk electrode (RRDE) measurements revealed that the ORR on TiN surfaces proceeded mainly via a two-electron pathway, producing H 2 O 2 as the main product. The oxygen reduction reaction (ORR) is one of the important electrocatalytic reactions for energy conversion in both acidic and alkaline media. [1][2][3][4][5][6] In polymer electrolyte fuel cells (PEFCs), the performance of the cathode for ORR is still the primary limitation on overall PEFC efficiency. An improved understanding of ORR electrocatalysis has paved the way for the development of cathodes for metal-air batteries.1,2 In particular, the lithium-air battery, one of the most promising among high-power secondary batteries, is expected to be commercialized in next-generation devices.12 At the cathodes of the current standard configuration, ORR takes place in an alkaline environment. Thus, ORR experiments are worth examining in both acidic and alkaline media.We have demonstrated that oxynitrides of group IV and V transition metals, when synthesized at the nanometer scale, show high electrocatalytic performance for ORR and high stability in acidic media. [13][14][15][16][17] One of advantages of group IV and V transition metals is their abundance on the earth rather than platinum group metals. Among these catalysts, titanium nitride (TiN) nanoparticles prepared using mesoporous graphitic (mpg)-C 3 N 4 templates have been found to be active. [15][16][17] Our studies have led us to conclude that TiN surfaces are at least partially oxidized once they are exposed to air and that the active sites could be oxygen vacancies or defect sites, which presumably facilitate the adsorption of molecular oxygen. 17In this study, we prepared mono-dispersed TiN nanoparticles of varying size by utilizing the varied pore size of mpg-C 3 N 4 , which reflects the original colloidal silica particle size. The TiN nanoparticles were tested for ORR in an alkaline medium. It was found that TiN nanoparticles showed a relatively high performance for ORR but led to two-electron pathways, generating H 2 O 2 as the primary product, which behaves similarly to a carbon electrode. ExperimentalCatalyst synthesis.-TiN nanoparticles were prepared using mpg-C 3 N 4 templates, by a process described elsewhere.15-20 Nanoparticles of varying size were obtained through the use of mpg-C 3 N 4 with different pore sizes. Three kinds of aqueous silica solutions, viz. LU-DOX ...

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confidence: 73%

Titanium Nitride Nanoparticle Electrocatalysts for Oxygen Reduction Reaction in Alkaline Solution

Ohnishi

Katayama

Cha

et al. 2013

J. Electrochem. Soc.

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“…While it can be difficult to directly benchmark catalytic performance against literature reports, these overpotentials compare favorably with those of other tungsten-based HER electrocatalysts at similar mass loadings in acidic media. For example, current densities of À10 mA cm À2 have been produced by exfoliated WS 2 nanosheets, 14 WC nanoparticles, 20 and W 2 N nanorods 16 with overpotentials of approx. À220 mV, À125 mV, and À500 mV, respectively.…”

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confidence: 99%

Electrocatalytic hydrogen evolution using amorphous tungsten phosphide nanoparticles

et al. 2014

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Amorphous tungsten phosphide (WP), which has been synthesized as colloidal nanoparticles with an average diameter of 3 nm, has been identified as a new electrocatalyst for the hydrogen-evolution reaction (HER) in acidic aqueous solutions. WP/Ti electrodes produced current densities of À10 mA cm À2 and À20 mA cm À2 at overpotentials of only À120 mV and À140 mV, respectively, in 0.50 M H 2 SO 4 (aq).Despite its scarcity and high cost, platinum is one of the most widely used catalysts for chemical reactions that underpin many clean energy technologies, including fuel cells and solar fuel generators. 1,2 For example, water electrolysis relies on the hydrogen-evolution reaction (HER), which in acidic solutions involves the electrocatalytic reduction of protons to molecular hydrogen. 3 Pt is an exceptional HER electrocatalyst, producing large cathodic current densities at low overpotentials. 3,4 Recently, several new acid-stable HER electrocatalysts have been identified as less expensive and more Earth-abundant alternatives to Pt, including MoS 2 , 5,6 CoSe 2 , 7 Co 0.6 Mo 1.4 N 2 , 8 Ni 2 P, 9,10 CoP, 11,12 and MoP. 13 Each of these systems represents an important development in the search for non-noble-metal HER electrocatalysts, which is important for global scalability where cost and performance must both be considered. Each unique catalyst offers a distinct combination of structure, composition, and properties that collectively can provide useful insights for predicting new catalytic materials and for beginning to interrogate the mechanisms by which they function.We report herein the colloidal synthesis of uniform amorphous tungsten phosphide (WP) nanoparticles with average diameters of 3 nm that remain amorphous upon heating beyond 450 1C. The amorphous tungsten phosphide nanoparticles are also active and acid-stable HER electrocatalysts, representing a new addition to the growing library of nonnoble-metal materials that catalyze the HER. These WP nanoparticles add to an important family of known tungsten-based HER catalysts as well, including WS 2 , 14 WC, 15 and W 2 N. 16 Interestingly, WP is also a known hydrodesulfurization (HDS) catalyst. 17 HDS and HER are distinct catalytic processes, but the reversible binding and dissociation of H 2 represents a possible mechanistic commonality. 3,18,19 The discovery that WP catalyzes the HER further strengthens the hypothesis that known HDS catalysts offer viable targets for active HER catalysts.To synthesize the amorphous WP nanoparticles, W(CO) 6 and trioctylphosphine (TOP) were heated to 320 1C for 2 h in squalane. (See ESI † for complete experimental details. Caution: This reaction should be considered to be highly flammable and corrosive, as it has the potential to liberate phosphorus, which is highly pyrophoric. Therefore, it should only be carried out under rigorously air-free conditions by appropriately trained personnel.) Fig. 1a and Fig. S1 (ESI †) show a transmission-electron microscopy (TEM) image of the isolated product, which formed quasi-spherical parti...

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“…Several newer methods involve mixing a metal precursor with a carbon precursor and applying conventional and unconventional heating techniques. [11][12][13][14][15][16][17][18] Excess carbon is used to prevent sintering, but this excess carbon results in extensive surface carbon, making these materials not suitable for catalytic applications.…”

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confidence: 99%

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

Hunt

Román‐Leshkov

2015

JoVE

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A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 °C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 °C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 °C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder. Video LinkThe video component of this article can be found at

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Tungsten Carbide Nanoparticles as Efficient Cocatalysts for Photocatalytic Overall Water Splitting

Cited by 197 publications

References 58 publications

Titanium Nitride Nanoparticle Electrocatalysts for Oxygen Reduction Reaction in Alkaline Solution

Titanium Nitride Nanoparticle Electrocatalysts for Oxygen Reduction Reaction in Alkaline Solution

Electrocatalytic hydrogen evolution using amorphous tungsten phosphide nanoparticles

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

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