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Porous molybdenum carbide nano-octahedrons synthesized via confined carburization in metal-organic frameworks for efficient hydrogen production.

Wu HB, Xia BY, Yu L, Yu XY, Lou XW - Nat Commun (2015)

Bottom Line: Here we demonstrate a metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbides based on the confined carburization in metal-organic frameworks matrix.Starting from a compound consisting of copper-based metal-organic frameworks host and molybdenum-based polyoxometalates guest, mesoporous molybdenum carbide nano-octahedrons composed of ultrafine nanocrystallites are successfully prepared as a proof of concept, which exhibit remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions.The present study provides some guidelines for the design and synthesis of nanostructured electrocatalysts.

View Article: PubMed Central - PubMed

Affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.

ABSTRACT
Electrochemical water splitting has been considered as a promising approach to produce clean and sustainable hydrogen fuel. However, the lack of high-performance and low-cost electrocatalysts for hydrogen evolution reaction hinders the large-scale application. As a new class of porous materials with tunable structure and composition, metal-organic frameworks have been considered as promising candidates to synthesize various functional materials. Here we demonstrate a metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbides based on the confined carburization in metal-organic frameworks matrix. Starting from a compound consisting of copper-based metal-organic frameworks host and molybdenum-based polyoxometalates guest, mesoporous molybdenum carbide nano-octahedrons composed of ultrafine nanocrystallites are successfully prepared as a proof of concept, which exhibit remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions. The present study provides some guidelines for the design and synthesis of nanostructured electrocatalysts.

No MeSH data available.


Characterizations of MoCx nano-octahedrons.(a–c) TEM images (scale bar, 200 nm; inset of c: SAED pattern), (d) magnified TEM image (scale bar, 5 nm), (e) HRTEM image (scale bar, 2 nm) and (f) elemental mapping (red: carbon; blue: molybdenum; scale bar, 50 nm) of porous MoCx nano-octahedrons.
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f3: Characterizations of MoCx nano-octahedrons.(a–c) TEM images (scale bar, 200 nm; inset of c: SAED pattern), (d) magnified TEM image (scale bar, 5 nm), (e) HRTEM image (scale bar, 2 nm) and (f) elemental mapping (red: carbon; blue: molybdenum; scale bar, 50 nm) of porous MoCx nano-octahedrons.

Mentions: The structure of the as-prepared MoCx nano-octahedrons is further examined by transmission electron microscopy (TEM) as depicted in Fig. 3. The sample appears as rhombic or cubic particles under TEM observation as the projections of octahedral particles from different directions (Fig. 3a–c). A closer examination on the MoCx nano-octahedrons reveals the highly porous texture throughout the whole particle. Each MoCx nano-octahedron is composed of numerous small nanocrystallites, and the polycrystalline nature is confirmed by selected-area electron diffraction (SAED) pattern as shown in the inset of Fig. 3c. An interesting observation is that some large particles appear at the corners of the octahedral particles. This is probably due to the higher surface activity and stress in these regions that cause easy collapse of the MOFs matrix and subsequent growth of MoCx nanocrystallites during the high-temperature reaction. Indeed, our initial attempt to prepare MoCx using much smaller NENU-5 nanoparticles (shown in Supplementary Fig. 1a) with high surface activity results in strongly aggregated particles with a poorly crystallized β-Mo2C phase that cannot be well dispersed into suspension for subsequent electrochemical measurements (Supplementary Fig. 4). Therefore, a robust secondary structure with a moderate size (for example, sub-micrometre-sized NENU-5 particles) is essential to successfully carry out the confined carburization reaction while providing large exposed surface for catalytic purpose.


Porous molybdenum carbide nano-octahedrons synthesized via confined carburization in metal-organic frameworks for efficient hydrogen production.

Wu HB, Xia BY, Yu L, Yu XY, Lou XW - Nat Commun (2015)

Characterizations of MoCx nano-octahedrons.(a–c) TEM images (scale bar, 200 nm; inset of c: SAED pattern), (d) magnified TEM image (scale bar, 5 nm), (e) HRTEM image (scale bar, 2 nm) and (f) elemental mapping (red: carbon; blue: molybdenum; scale bar, 50 nm) of porous MoCx nano-octahedrons.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4382699&req=5

f3: Characterizations of MoCx nano-octahedrons.(a–c) TEM images (scale bar, 200 nm; inset of c: SAED pattern), (d) magnified TEM image (scale bar, 5 nm), (e) HRTEM image (scale bar, 2 nm) and (f) elemental mapping (red: carbon; blue: molybdenum; scale bar, 50 nm) of porous MoCx nano-octahedrons.
Mentions: The structure of the as-prepared MoCx nano-octahedrons is further examined by transmission electron microscopy (TEM) as depicted in Fig. 3. The sample appears as rhombic or cubic particles under TEM observation as the projections of octahedral particles from different directions (Fig. 3a–c). A closer examination on the MoCx nano-octahedrons reveals the highly porous texture throughout the whole particle. Each MoCx nano-octahedron is composed of numerous small nanocrystallites, and the polycrystalline nature is confirmed by selected-area electron diffraction (SAED) pattern as shown in the inset of Fig. 3c. An interesting observation is that some large particles appear at the corners of the octahedral particles. This is probably due to the higher surface activity and stress in these regions that cause easy collapse of the MOFs matrix and subsequent growth of MoCx nanocrystallites during the high-temperature reaction. Indeed, our initial attempt to prepare MoCx using much smaller NENU-5 nanoparticles (shown in Supplementary Fig. 1a) with high surface activity results in strongly aggregated particles with a poorly crystallized β-Mo2C phase that cannot be well dispersed into suspension for subsequent electrochemical measurements (Supplementary Fig. 4). Therefore, a robust secondary structure with a moderate size (for example, sub-micrometre-sized NENU-5 particles) is essential to successfully carry out the confined carburization reaction while providing large exposed surface for catalytic purpose.

Bottom Line: Here we demonstrate a metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbides based on the confined carburization in metal-organic frameworks matrix.Starting from a compound consisting of copper-based metal-organic frameworks host and molybdenum-based polyoxometalates guest, mesoporous molybdenum carbide nano-octahedrons composed of ultrafine nanocrystallites are successfully prepared as a proof of concept, which exhibit remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions.The present study provides some guidelines for the design and synthesis of nanostructured electrocatalysts.

View Article: PubMed Central - PubMed

Affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.

ABSTRACT
Electrochemical water splitting has been considered as a promising approach to produce clean and sustainable hydrogen fuel. However, the lack of high-performance and low-cost electrocatalysts for hydrogen evolution reaction hinders the large-scale application. As a new class of porous materials with tunable structure and composition, metal-organic frameworks have been considered as promising candidates to synthesize various functional materials. Here we demonstrate a metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbides based on the confined carburization in metal-organic frameworks matrix. Starting from a compound consisting of copper-based metal-organic frameworks host and molybdenum-based polyoxometalates guest, mesoporous molybdenum carbide nano-octahedrons composed of ultrafine nanocrystallites are successfully prepared as a proof of concept, which exhibit remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions. The present study provides some guidelines for the design and synthesis of nanostructured electrocatalysts.

No MeSH data available.