| 1. |
- Islam, Jamil, et al.
(författare)
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Graphene as thinnest coating on copper electrodes in microbial methanol fuel cells
- 2023
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 17:1, s. 137-145
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Tidskriftsartikel (refereegranskat)abstract
- Dehydrogenation of methanol (CH3OH) into direct current (DC) in fuel cells can be a potential energy conversion technology. However, their development is currently hampered by the high cost of electrocatalysts based on platinum and palladium, slow kinetics, the formation of carbon monoxide intermediates, and the requirement for high temperatures. Here, we report the use of graphene layers (GL) for generating DC electricity from microbially driven methanol dehydrogenation on underlying copper (Cu) surfaces. Genetically tractable Rhodobacter sphaeroides 2.4.1 (Rsp), a nonarchetypical methylotroph, was used for dehydrogenating methanol at the GL-Cu surfaces. We use electrochemical methods, microscopy, and spectroscopy methods to assess the effects of GL on methanol dehydrogenation by Rsp cells. The GL-Cu offers a 5-fold higher power density and 4-fold higher current density compared to bare Cu. The GL lowers charge transfer resistance to methanol dehydrogenation by 4 orders of magnitude by mitigating issues related to pitting corrosion of underlying Cu surfaces. The presented approach for catalyst-free methanol dehydrogenation on copper electrodes can improve the overall sustainability of fuel cell technologies.
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| 2. |
- Asres, Georgies Alene, et al.
(författare)
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High photoresponse of individual WS2 nanowire-nanoflake hybrid materials
- 2018
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 112:23
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Tidskriftsartikel (refereegranskat)abstract
- van der Waals solids have been recognized as highly photosensitive materials that compete conventional Si and compound semiconductor based devices. While 2-dimensional nanosheets of single and multiple layers and 1-dimensional nanowires of molybdenum and tungsten chalcogenides have been studied, their nanostructured derivatives with complex morphologies are not explored yet. Here, we report on the electrical and photosensitive properties of WS2 nanowire-nanoflake hybrid materials we developed lately. We probe individual hybrid nanostructured particles along the structure using focused ion beam deposited Pt contacts. Further, we use conductive atomic force microscopy to analyze electrical behavior across the nanostructure in the transverse direction. The electrical measurements are complemented by in situ laser beam illumination to explore the photoresponse of the nanohybrids in the visible optical spectrum. Photodetectors with responsivity up to similar to 0.4 AW(-1) are demonstrated outperforming graphene as well as most of the other transition metal dichalcogenide based devices. Published by AIP Publishing.
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| 3. |
- Kordas, Krisztian, et al.
(författare)
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On the Interaction of Metal Nanoparticles with Supports
- 2015
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Ingår i: Topics in catalysis. - : Springer Science+Business Media B.V.. - 1022-5528 .- 1572-9028. ; 58:14-17, s. 1127-1135
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Tidskriftsartikel (refereegranskat)abstract
- Metal nanoparticles supported on surfaces often undergo sintering even at moderate temperatures. The degree of sintering is typically influenced by the surface chemistry indicating that besides the commonly believed Ostwald ripening also other processes associated with metal surface diffusion are responsible for the nanoparticle size growth. In addition to the deterioration in metal dispersion, carbon supports can show chemical instability leading to their partial degradation in the proximity of the nanoparticles both in reducing and oxidizing environments at elevated temperatures. This work reports a study of Pd, Pt and Ni nanoparticles anchored on carbon (activated carbon, graphite and carbon nanotubes) as well as titania (nanoparticles and microparticles) surfaces frequently applied as catalyst materials in heterogeneous catalysis and photocatalysis, and evaluate the potential events causing metal sintering and degradation of the supports using transmission electron microscopy analysis.
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| 4. |
- Li, Daobin, et al.
(författare)
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Atomically dispersed platinum supported on curved carbon supports for efficient electrocatalytic hydrogen evolution
- 2019
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Ingår i: Nature Energy. - : Nature Publishing Group. - 2058-7546. ; 4:6, s. 512-518
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Tidskriftsartikel (refereegranskat)abstract
- Dispersing catalytically active metals as single atoms on supports represents the ultimate in metal utilization efficiency and is increasingly being used as a strategy to design hydrogen evolution reaction (HER) electrocatalysts. Although platinum (Pt) is highly active for HER, given its high cost it is desirable to find ways to improve performance further while minimizing the Pt loading. Here, we use onion-like nanospheres of carbon (OLC) to anchor stable atomically dispersed Pt to act as a catalyst (Pt-1/OLC) for the HER. In acidic media, the performance of the Pt-1/OLC catalyst (0.27 wt% Pt) in terms of a low overpotential (38 mV at 10 mA cm(-2)) and high turnover frequencies (40.78 H-2 s(-1) at 100 mV) is better than that of a graphene-supported single-atom catalyst with a similar Pt loading, and comparable to a commercial Pt/C catalyst with 20 wt% Pt. First-principle calculations suggest that a tip-enhanced local electric field at the Pt site on the curved support promotes the reaction kinetics for hydrogen evolution.
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| 5. |
- Liu, Yang, et al.
(författare)
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Atomic layered titanium sulfide quantum dots as electrocatalysts for enhanced hydrogen evolution reaction
- 2018
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Ingår i: Advanced Materials Interfaces. - : John Wiley & Sons. - 2196-7350. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- The overall electrocatalytic activity toward hydrogen evolution reaction for layered transition metal dichalcogenides is governed by their intrinsic activity, the corresponding density of active sites, and the electron transfer resistance. Here, nanoengineering strategies to scale down both the lateral size and thickness of layered 1T-TiS2 powder to quantum dots (QDs) by bath sonication and probing sonication incision are employed. Uniform lateral size of 3-6 nm in the resulting QDs enhances the density of edge sites while the atomic layer thickness (1-2 nm) facilitates the electron transfer from the substrate to the edge sites. The obtained TiS2 QDs exhibit superior hydrogen evolution reaction activity over TiS2 nanosheets and MoS2 QDs prepared by the same method. The turnover frequency of TiS2 QDs with a small loading of 0.7 ng cm(-2) in an optimal deposition on electrode reached approximate to 2.0 s(-1) at an overpotential of -0.2 V versus RHE, several orders of magnitude higher than TiS2 nanosheets (0.01 s(-1)) and MoS2 QDs (0.07 s(-1)).
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| 6. |
- Mohl, Melinda, et al.
(författare)
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Formation of CuPd and CuPt Bimetallic Nanotubes by Galvanic Replacement Reaction
- 2011
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:19, s. 9403-9409
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Tidskriftsartikel (refereegranskat)abstract
- A galvanic replacement reaction has been successfully applied to prepare CuPd and CuPt bimetallic nanotubes. The nanotubes were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. Ultralong, single crystalline copper nanowires (NWs) with a diameter of similar to 64 nm and a length of several micrometers were used as template material. By controlling the amount of noble metal salt added, nanotubes with different compositions were obtained. After the replacement of Cu with Pt, nanotubes composed of a PtCu alloy were formed. EDS analysis revealed that the Pt content increased until about 66%. No further increase in the molar ratio resulted in any additional Pt incorporation into the alloy. As for the replacement of Cu with Pd, the thickening of the nanotubes was observed indicating that nanotubes composed of Pd nanoparticles were formed. Bacicscattered electron imaging and SEM-EDS revealed CuPd nanotubes with approximately 2.3% Cu content. These remarks indicate different evolution mechanism for the nanotubes in the two systems.
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| 7. |
- Sharifi, Tiva, et al.
(författare)
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Graphene as an electrochemical transfer layer
- 2019
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 141, s. 266-273
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Tidskriftsartikel (refereegranskat)abstract
- The capability of graphene to adopt a property from an adjacent material is investigated by measuring the electrochemical performance of a monolayer graphene placed on top of thin cobalt oxide (Co3O4) nanosheets. In this assembly, monolayer graphene works as an interfacial layer which inhibits the direct contact of the actual electroactive material and electrolyte during electrochemical reaction. The results show that while graphene is electrochemically inert, it behaves as an active material to catalyze oxygen evolution reaction (OER) once placed on top of Co3O4 nanosheets. The graphene-covered Co3O4 model system shows electrochemical performance similar to Co3O4 indicating complete transference of the electrochemical property of the metal oxide to the graphene. Based on density functional theory (DFT) calculations, charge transfer from graphene to Co3O4 is the key factor for turning the electrochemically inactive graphene to an apparent active material.
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| 8. |
- Sharifi, Tiva, et al.
(författare)
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Impurity-Controlled Crystal Growth in Low-Dimensional Bismuth Telluride
- 2018
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 30:17, s. 6108-6115
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Tidskriftsartikel (refereegranskat)abstract
- Topological insulators, such as layered Bi2Te3, exhibit extraordinary properties, manifesting profoundly only at nanoscale thicknesses. However, it has been challenging to synthesize these structures with controlled thicknesses. Here, control over the thickness of solvothermally grown Bi2Te3 nanosheets is demonstrated by manipulating the crystal growth through select and controlled impurity atom addition. By a comprehensive analysis of the growth mechanism and intentional addition of Fe impurity, we demonstrate that the nucleation and growth of few-layer nanosheets of Bi2Te3 can be stabilized in solution. Via optimization of the Fe concentration, nanosheets thinner than 6 nm, and as thin as 2 nm, can be synthesized. Such thicknesses are smaller than the anticipated critical thickness for the transition of topological insulators to the quantum spin Hall regime.
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| 9. |
- Swaminathan, Jayashree, et al.
(författare)
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Tuning the Electrocatalytic Activity of Co3O4 through Discrete Elemental Doping
- 2019
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 11:43, s. 39706-39714
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Tidskriftsartikel (refereegranskat)abstract
- To gain constructive insight into the possible effect of doping on the electrocatalytic activity of materials, a catalytic framework with a discrete distribution of dopants is an appropriate model system. Such a system assures well-defined active centers, maximum atom utilization efficiency, and hence enhanced selectivity, catalytic activity, and stability. Herein, a comprehensive investigation of the electrocatalytic activity of iron-doped cobalt oxide (Fe-Co3O4) nanosheets is presented. In order to understand the contribution of dopants, a series of materials with controlled doping levels are investigated. By controlled iron inclusion into the structure of Co3O4, an apparent improvement in the oxygen evolution reaction activity which is reflected in the decrease of 160 mV in the overpotential to reach the current density of 10 mA/cm(2) is manifested. Additionally, it is shown that there exists an optimum doping content above which the catalytic activity fades. Further investigation of the system with density functional calculations reveals that, along with the optimization of adsorption energy toward the reaction intermediates, substantial downshift of the Fermi level and delocalization of electron density occurs on introducing iron ions into the structure.
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| 10. |
- Wu, Jingjie, et al.
(författare)
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Emerging Carbon-Based Heterogeneous Catalysts for Electrochemical Reduction of Carbon Dioxide into Value-Added Chemicals
- 2019
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 31:13
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Forskningsöversikt (refereegranskat)abstract
- The electrocatalytic reduction of CO2 provides a sustainable way to mitigate CO2 emissions, as well as store intermittent electrical energy into chemicals. However, its slow kinetics and the lack of ability to control the products of the reaction inhibit its industrial applications. In addition, the immature mechanistic understanding of the reduction process makes it difficult to develop a selective, scalable, and stable electrocatalyst. Carbon-based materials are widely considered as a stable and abundant alternative to metals for catalyzing some of the key electrochemical reactions, including the CO2 reduction reaction. In this context, recent research advances in the development of heterogeneous nanostructured carbon-based catalysts for electrochemical reduction of CO2 are summarized. The leading factors for consideration in carbon-based catalyst research are discussed by analyzing the main challenges faced by electrochemical reduction of CO2. Then the emerging metal-free doped carbon and aromatic N-heterocycle catalysts for electrochemical reduction of CO2 with an emphasis on the formation of multicarbon hydrocarbons and oxygenates are discussed. Following that, the recent progress in metal-nitrogen-carbon structures as an extension of carbon-based catalysts is scrutinized. Finally, an outlook for the future development of catalysts as well as the whole electrochemical system for CO2 reduction is provided.
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