Understanding fundamental processes in carbon materials with well-defined colloidal graphene quantum dots

Noffke, Benjamin W.; Liu, Yijun

doi:10.1016/j.cocis.2015.10.008

Cited by 22 publications

(7 citation statements)

References 70 publications

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“…In our calculations, we explicitly study well-defined N-doped colloidal graphene nanostructures − as a model system for mechanistic studies of graphitic carbon materials. As reported previously, the graphene nanostructures are made with stepwise solution chemistry, and consequently they not only have a uniform size but also contain nitrogen dopants with a uniform bonding configuration.…”

Section: Methods and Computational Detailsmentioning

confidence: 99%

A Model for the pH-Dependent Selectivity of the Oxygen Reduction Reaction Electrocatalyzed by N-Doped Graphitic Carbon

Noffke

Raghavachari

et al. 2016

J. Am. Chem. Soc.

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Nitrogen-doped graphitic carbon materials have been extensively studied as potential replacements for Pt-based electrocatalysts for the oxygen reduction reaction (ORR). However, little is known about the catalytic mechanisms, including the parameters that determine the selectivity of the reaction. By comparing theoretical calculations of the ORR selectivity at a well-defined graphene nanostructure with experimental results, we propose a model based on interfacial solvation to explain the observed preference for the four-electron pathway in alkaline electrolytes. The hydrophobic environment around the active sites, as in enzymatic catalysis, restricts the access of water and destabilizes small ionic species such as peroxide, the product of the two-electron pathway. This model, when applied to acidic electrolytes, shows the ORR preferring the two-electron pathway, consistent with the well-known pH-dependent ORR selectivity catalyzed by graphitic carbon materials. Because of the similarity between more complex N-doped graphitic carbon materials and our model system, we can extend this model to the former and rationalize nearly all of the previously reported experimental results on the selectivity of ORR catalyzed by these materials.

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Section: Methods and Computational Detailsmentioning

confidence: 99%

A Model for the pH-Dependent Selectivity of the Oxygen Reduction Reaction Electrocatalyzed by N-Doped Graphitic Carbon

Noffke

Raghavachari

et al. 2016

J. Am. Chem. Soc.

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“…Our previous studies have shown, as a result of quantum confinement in the two-dimensional semiconductor, nanographenes have size-dependent optical and redox properties . In particular, nanographene 2 containing a pyrazinyl moiety can undergo a proton-coupled two-electron reduction in alkaline aqueous electrolytes to electrocatalyze the oxygen reduction reaction, another kinetically sluggish multielectron reaction . We anticipate such a structure may serve as electron storage for multielectron CO 2 reductions as well, and thus we synthesized nanographene 1 similar in structure with a phenanthroline moiety to form complex 3 .…”

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confidence: 98%

Well-Defined Nanographene–Rhenium Complex as an Efficient Electrocatalyst and Photocatalyst for Selective CO₂ Reduction

Qiao

Schaugaard

et al. 2017

J. Am. Chem. Soc.

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Improving energy efficiency of electrocatalytic and photocatalytic CO conversion to useful chemicals poses a significant scientific challenge. We report on using a colloidal nanographene to form a molecular complex with a metal ion to tackle this challenge. In this work, a well-defined nanographene-Re complex was synthesized, in which electron delocalization over the nanographene and the metal ion significantly decreases the electrical potential needed to drive the chemical reduction. We show the complex can selectively electrocatalyze CO reduction to CO in tetrahydrofuran at -0.48 V vs NHE, the least negative potential reported for a molecular catalyst. In addition, the complex can absorb a significant spectrum of visible light to photocatalyze the chemical transformation without the need for a photosensitizer.

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“…At the core of the high complexity of GQD photoluminescence properties lies the nonuniformity of their structure that makes properties of every particle different. ,, By analogy with dye molecules and emission centers in dielectric nanoparticles, the variation of local chemical structure around emission centers at the edges of GQDs can lead to variation of their individual properties, such as spectral position of emission, excited state lifetime, or quantum yield. , As a result, ensemble measurements average out individual properties of single emission centers. Although enormous efforts have been focused on achieving better uniformity of GQDs, making them chemically identical would require control of their structure at the atomic level, which is challenging to achieve (see refs , , , and and citations therein). Alternatively, single-particle spectroscopy is capable of investigating the spectroscopic properties of GQDs on a single-particle level, thus generating full distributions of values for the various emission characteristics without ensemble averaging.…”

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confidence: 99%

Emission States Variation of Single Graphene Quantum Dots

Ghosh

Oleksiievets

Enderlein

et al. 2020

J. Phys. Chem. Lett.

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Graphene quantum dots (GQDs) are nanoparticles that consist of a nanometer-sized core of graphene with diverse chemical groups on its boundary. Due to their advantageous properties, they are considered to be a promising material for optoelectronics, bioimaging, or photovoltaics. Despite considerable efforts that have been focused on unraveling the mechanism of their photoluminescence, many fundamental details are still unclear. Here, we report on a single-particle multimodal study that provides new insight into the photoluminescence properties of emission centers of GQDs in various local chemical environments. In particular, we show that the properties that are associated with emission centers of GQDs are significantly more sensitive to the structure of the particle itself than to a nonuniform local chemical environment. A better understanding of the dependence of GQDs’ emission states on the complex local chemical environment is an important step toward finding new ways of controlling the optical properties of GQDs and of optimizing their use in various applications.

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Understanding fundamental processes in carbon materials with well-defined colloidal graphene quantum dots

Cited by 22 publications

References 70 publications

A Model for the pH-Dependent Selectivity of the Oxygen Reduction Reaction Electrocatalyzed by N-Doped Graphitic Carbon

A Model for the pH-Dependent Selectivity of the Oxygen Reduction Reaction Electrocatalyzed by N-Doped Graphitic Carbon

Well-Defined Nanographene–Rhenium Complex as an Efficient Electrocatalyst and Photocatalyst for Selective CO₂ Reduction

Emission States Variation of Single Graphene Quantum Dots

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Understanding fundamental processes in carbon materials with well-defined colloidal graphene quantum dots

Cited by 22 publications

References 70 publications

A Model for the pH-Dependent Selectivity of the Oxygen Reduction Reaction Electrocatalyzed by N-Doped Graphitic Carbon

A Model for the pH-Dependent Selectivity of the Oxygen Reduction Reaction Electrocatalyzed by N-Doped Graphitic Carbon

Well-Defined Nanographene–Rhenium Complex as an Efficient Electrocatalyst and Photocatalyst for Selective CO2 Reduction

Emission States Variation of Single Graphene Quantum Dots

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Well-Defined Nanographene–Rhenium Complex as an Efficient Electrocatalyst and Photocatalyst for Selective CO₂ Reduction