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1.
Mater Horiz ; 2024 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-38742402

RESUMO

The synthesis of phase-pure carbide nanomaterials is crucial for understanding their structure-performance relationships, and for advancing their application in catalysis. Molybdenum carbides, in particular, have garnered increasing interest due to their Pt-like surface electronic properties and high catalytic activity. Traditional methods for synthesizing molybdenum carbide are often lengthy and energy-intensive, leading to an uncontrolled phase, low purity, and excessive carbon coverage, which hinder their catalytic performance improvement. This work introduces a novel pulsed Joule heating (PJH) technique that overcomes these limitations, enabling the controlled synthesis of high-purity molybdenum carbides (ß-Mo2C, η-MoC1-x, and α-MoC1-x) within seconds by using MoOx/4-Cl-o-phenylenediamine as the hybrid precursor. The PJH method allows precise control over the diffusion of carbon species in the Mo-C system, resulting in a significantly improved phase purity of up to 96.89 wt%. Moreover, the electronic structure of platinum catalysts on molybdenum carbide was modulated through electron metal-support interaction (EMSI) between Pt and MoxC, and contributed to enhanced catalytic performance compared to carbon-supported Pt catalysts during the hydrogen evolution reaction. Overall, this work paves the way for efficient production of high-quality molybdenum carbide nanomaterials, and thus is expected to accelerate their industrial deployments in practical catalytic reactions.

2.
Natl Sci Rev ; 10(6): nwad081, 2023 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-37404853

RESUMO

Thermally activated ultrafast diffusion, collision and combination of metal atoms comprise the fundamental processes of synthesizing burgeoning subnanometer metal clusters for diverse applications. However, so far, no method has allowed the kinetically controllable synthesis of subnanometer metal clusters without compromising metal loading. Herein, we have developed, for the first time, a graphene-confined ultrafast radiant heating (GCURH) method for the synthesis of high-loading metal cluster catalysts in microseconds, where the impermeable and flexible graphene acts as a diffusion-constrained nanoreactor for high-temperature reactions. Originating from graphene-mediated ultrafast and efficient laser-to-thermal conversion, the GCURH method is capable of providing a record-high heating and cooling rate of ∼109°C/s and a peak temperature above 2000°C, and the diffusion of thermally activated atoms is spatially limited within the confinement of the graphene nanoreactor. As a result, due to the kinetics-dominant and diffusion-constrained condition provided by GCURH, subnanometer Co cluster catalysts with high metal loading up to 27.1 wt% have been synthesized by pyrolyzing a Co-based metal-organic framework (MOF) in microseconds, representing one of the highest size-loading combinations and the quickest rate for MOF pyrolysis in the reported literature. The obtained Co cluster catalyst not only exhibits an extraordinary activity similar to that of most modern multicomponent noble metal counterparts in the electrocatalytic oxygen evolution reaction, but is also highly convenient for catalyst recycling and refining due to its single metal component. Such a novel GCURH technique paves the way for the kinetically regulated, limited diffusion distance of thermally activated atoms, which in turn provides enormous opportunities for the development of sophisticated and environmentally sustainable metal cluster catalysts.

3.
Nat Commun ; 14(1): 2294, 2023 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-37085505

RESUMO

Carbon-supported nanoparticles are indispensable to enabling new energy technologies such as metal-air batteries and catalytic water splitting. However, achieving ultrasmall and high-density nanoparticles (optimal catalysts) faces fundamental challenges of their strong tendency toward coarsening and agglomeration. Herein, we report a general and efficient synthesis of high-density and ultrasmall nanoparticles uniformly dispersed on two-dimensional porous carbon. This is achieved through direct carbothermal shock pyrolysis of metal-ligand precursors in just ~100 ms, the fastest among reported syntheses. Our results show that the in situ metal-ligand coordination (e.g., N → Co2+) and local ordering during millisecond-scale pyrolysis play a crucial role in kinetically dominated fabrication and stabilization of high-density nanoparticles on two-dimensional porous carbon films. The as-obtained samples exhibit excellent activity and stability as bifunctional catalysts in oxygen redox reactions. Considering the huge flexibility in coordinated precursors design, diversified single and multielement nanoparticles (M = Fe, Co, Ni, Cu, Cr, Mn, Ag, etc) were generally fabricated, even in systems well beyond traditional crystalline coordination chemistry. Our method allows for the transient and general synthesis of well-dispersed nanoparticles with great simplicity and versatility for various application schemes.

4.
Proc Natl Acad Sci U S A ; 119(37): e2121848119, 2022 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-36067324

RESUMO

Refractory carbides are attractive candidates for support materials in heterogeneous catalysis because of their high thermal, chemical, and mechanical stability. However, the industrial applications of refractory carbides, especially silicon carbide (SiC), are greatly hampered by their low surface area and harsh synthetic conditions, typically have a very limited surface area (<200 m2 g-1), and are prepared in a high-temperature environment (>1,400 °C) that lasts for several or even tens of hours. Based on Le Chatelier's principle, we theoretically proposed and experimentally verified that a low-pressure carbothermal reduction (CR) strategy was capable of synthesizing high-surface area SiC (569.9 m2 g-1) at a lower temperature and a faster rate (∼1,300 °C, 50 Pa, 30 s). Such high-surface area SiC possesses excellent thermal stability and antioxidant capacity since it maintained stability under a water-saturated airflow at 650 °C for 100 h. Furthermore, we demonstrated the feasibility of our strategy for scale-up production of high-surface area SiC (460.6 m2 g-1), with a yield larger than 12 g in one experiment, by virtue of an industrial viable vacuum sintering furnace. Importantly, our strategy is  also applicable to the rapid synthesis of refractory metal carbides (NbC, Mo2C, TaC, WC) and even their emerging high-entropy carbides (VNbMoTaWC5, TiVNbTaWC5). Therefore, our low-pressure CR method provides an alternative strategy, not merely limited to temperature and time items, to regulate the synthesis and facilitate the upcoming industrial applications of carbide-based advanced functional materials.

5.
Sci Rep ; 8(1): 1359, 2018 01 22.
Artigo em Inglês | MEDLINE | ID: mdl-29358720

RESUMO

Agglomeration-triggered deactivation of supported platinum electrocatalysts markedly hinders their application in methanol oxidation reaction (MOR). In this study, graphene-supported nickel-iron layered double hydroxide (NiFe-LDH/rGO), in which Fe3+ was introduced to replace Ni2+ partially in the Ni(OH)2 lattice to provide stronger metal-support bonding sites, was utilized to immobilize Pt nanoparticles (NPs). Given the optimized metal-support interfacial contact (Fe3+-O(H)-Pt) between Pt NPs and NiFe-LDH/rGO nanosheets for Pt/NiFe-LDH/rGO electrocatalysts, the Pt/NiFe-LDH/rGO electrocatalysts displayed dramatically enhanced durability than that of Pt/Ni(OH)2/rGO counterpart as well as commercial Pt/C, and 86.5% of its initial catalytic activity can be maintained even after 1200 cycles of cyclic voltammetry (CV) tests during MOR. First-principle calculations toward the resultant M-O(H)-Pt (M = Fe3+, Ni2+) interfacial structure further corroborates that the NiFe-LDH nanosheets can provide stronger bonding sites (via the Fe3+-O(H)-Pt bonds) to immobilize Pt NPs than those of Ni(OH)2 nanosheets (via the Ni2+-O(H)-Pt bonds).

6.
Chemphyschem ; 18(9): 1133-1139, 2017 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-28097772

RESUMO

Laser melting in liquids (LML) is one of the most effective methods to prepare bimetallic alloys; however, despite being an ongoing focus of research, the process involved in the formation of such species remains ambiguous. In this paper, we prepared two types of Pt-based bimetallic alloys by LML, including Pt-Au alloys and Pt-iron group metal (iM=Fe/Co/Ni) alloys, and investigated the corresponding mechanisms of alloying process. Detailed component and structural characterizations indicate that laser irradiation induced a quite rapid formation process (not exceeding 10 s) of Pt-Au alloy nanospheres, and the crystalline structures of Pt-Au alloys is determined by the monometallic constituents with higher content. For Pt-iM alloys, we provide direct evidence to support the conclusion that FeOx /CoOx /NiOx colloids can be reduced to elementary Fe/Co/Ni particles by ethanol molecules during laser irradiation, which then react with Pt colloids to form Pt-iM sub-microspheres. These results demonstrate that LML provides an optional route to prepare Pt-based bimetallic alloy particles with tunable size, components, and crystalline phase, which should have promising applications in biological and catalysis studies.

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