| 1. |
- Brülls, Steffen, 1991, et al.
(author)
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Bonding between π-Conjugated Polycations and Monolayer Graphene: Decisive Role of Anions
- 2023
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:4, s. 1917-28
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Journal article (peer-reviewed)abstract
- Functionalization and precise modulation of the electronic properties of graphene are key processes in the development of new applications of this promising material. This study examines the potential of using organic polycations as p-dopants and/or anchoring motifs for non-covalent functionalization. A library of hybrid materials was prepared through wet-chemical non-covalent functionalization. Both chemical vapor deposition graphene and reduced graphene oxide were functionalized with a series of neutral and polycationic benzimidazole-based systems. We report on how both the number of anions and the size, shape, and magnitude of the positive charge of the benzimidazole-based systems cooperatively affect the redox properties as well as the affinity for and the nature of bonding to graphene. The redox properties of the benzimidazole-based systems were studied by cyclic voltammetry. The functionalized graphene materials were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry. Density functional theory calculations were performed to make contact between the experimental results obtained for molecular samples and hybrid materials. No universal dependence of the binding affinity on a single parameter, such as the amount of positive charge or the size of the system, was found. Instead, the cooperative effect of the three-dimensional structure of the benzimidazole-based systems and the number of anions was found to play a pivotal role. Together, these parameters determine the degree of partial electron sharing and magnitude of dispersion forces involved in the binding of members of this family of benzimidazole-based systems to graphene.
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| 2. |
- Busch, Michael, 1983, et al.
(author)
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Water Oxidation on MnOx and IrOx: Why Similar Performance?
- 2013
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:1, s. 288-292
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Journal article (peer-reviewed)abstract
- The critical steps in water oxidation at a binuclear Mn(II–IV) oxide site are revisited. Ideal stabilities of intermediates are confirmed by comparing to results for a binuclear Ir(III–V) system. The latter in turn is known to be an excellent water oxidation catalyst. The inefficiency of the binuclear Mn(II–IV) site is owing to the high activation energy for the chemical step whereby MnIV═O double bonds on adjacent sites are broken prior to forming the MnIII—O—O—MnIII peroxy moiety. A rationale for Mn(II–IV)—Mn(III–V) mixed oxidation state for water oxidation catalysis, analogous to mixed transition metal oxide systems, is offered. Possible virtues of the kinetic stability of the binuclear MnIV═O moiety are discussed, utilizing its oxidizing power by sidestepping oxygen evolution.
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| 3. |
- Steegstra, Patrick, 1978, et al.
(author)
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Revisiting the Redox Properties of Hydrous Iridium Oxide Films in the Context of Oxygen Evolution
- 2013
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In: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:40, s. 20975-20981
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Journal article (peer-reviewed)abstract
- The electrochemistry of hydrous iridium oxide films (HIROF) is revisited. Cyclic voltammograms of HIROFs display two reversible redox couples commonly assigned to the Ir(III)/Ir(IV) and Ir(IV)/Ir(V) transitions, respectively. However, compared to the first, the second redox couple has significantly less charge associated to it. This effect is interpreted as partial oxidation of Ir(IV) as limited by nearest neighbor repulsion of resulting Ir(V) sites. Thus, the redox process is divided into two steps: one preceding and one overlapping the oxygen evolution reaction (OER). Here, the ``super-nernstian'' pH dependence of the redox processes in the HIROF is used to expose how pH controls the overpotential for oxygen evolution, as evidenced by the complementary increased formation of Ir(V) oxide. A recently formulated binuclear mechanism for the OER is employed to illustrate how hydrogen bonding may suppress the OER, thus implicitly favoring Ir(V) oxide formation above the thermodynamic onset potential for the OER at low pH.
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| 4. |
- Bauschlicher, C.W., et al.
(author)
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A further study of the products of scandium and dioxygen reactions
- 1999
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In: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 103:28, s. 5463-5467
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Journal article (peer-reviewed)abstract
- The products of the reaction of Sc and dioxygen have been reinvestigated. By adding the electron-trapping molecule CCl4 additional information about the IR spectra has been obtained, as well as the observation of new bands. New ab initio calculations are also performed on possible products of the Sc plus O-2 reaction. The previously observed band at 722.5 cm(-1) is assigned as the b(2) mode of ScO2-. Bands arising from ScO+, Sc(O-2)(+), and(O-2)ScO are also assigned. We are still unable to assign any bands to OScO. The problems associated with the computational study of ScO2 are discussed.
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| 5. |
- Björnström, Joakim, 1976, et al.
(author)
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Antagonistic effect of superplasticizer and colloidal nano-silica in the hydration of Alite and Belite pastes
- 2007
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In: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 42:11, s. 3901-3907
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Journal article (peer-reviewed)abstract
- The dependence on the hydration rate for Alite and Belite clinker phases in the presence of a polycarboxylate superplasticizer PC SP upon addition of colloidal nano-silica CNS were monitored by means of Diffuse Reflectance Infrared spectroscopy DR-FTIR. Spectral signatures of clinker dissolution and product formation were acquired for both materials. The rates for the build-up of product vibrational band intensities were found to depend sensitively on addition of CNS. The hydration product was proposed to be calcium-silicate-hydrate C-S-H. Details in the spectral signatures were found to differ. Quantum chemical calculations were employed and found to be consistent with the interpretation that small clusters dominate the Alite C-S-H spectrum, whereas the Belite C-S-H spectrum results from extended polymers.
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| 6. |
- Jirkovský, Jakub S, 1980, et al.
(author)
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Single Atom Hot-Spots at Au-Pd Nanoalloys for Electrocatalytic H2O2 Production
- 2011
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 133:48, s. 19432-19441
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Journal article (peer-reviewed)abstract
- A novel strategy to direct the oxygen reduction reaction to preferentially produce H2O2 is formulated and evaluated. The approach combines the inertness of Au nano-particles towards oxidation, with the improved O2 sticking probability of isolated transition metal “guest” atoms embedded in the Au “host”. DFT modeling was employed to screen for the best alloy candidates. Modeling indicates that isolated alloying atoms of Pd, Pt or Rh placed within the Au surface should enhance the H2O2 production relative to pure Au. Consequently, Au1-xPdx nanoalloys with variable Pd content supported on Vulcan XC-72 were prepared to investigate the predicted selectivity towards H2O2 production for Au alloyed with Pd. It is demonstrated that increasing of Pd concentration to 8% leads to an increase of the electrocatalytic H2O2 production selectivity up to nearly 95%, when the nanoparticles are placed in an environment compatible with that of a proton exchange membrane. Further increase of Pd content leads to a drop of H2O2 selectivity, below 10% for x = 0.5. It is proposed that the enhancement in H2O2 selectivity is caused by the presence of individual surface Pd atoms surrounded by gold whereas surface ensembles of contiguous Pd atoms support H2O formation. The results are discussed in the context of exergonic electrocatalytic H2O2 synthesis in Polymer Electrolyte Fuel Cells for the simultaneous cogeneration of chemicals and electricity, the latter a credit to production costs.
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| 7. |
- Johnson, J.R.T, et al.
(author)
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Water adsorption and hydrolysis in the Si2O4, P2O5 and P4O10 systems - essential roles of the phosphate system in biosynthesis
- 2002
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In: Chemical Physics. - 0301-0104. ; 276:1, s. 45-68
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Journal article (peer-reviewed)abstract
- Successive water addition to the mononuclear species SiO2(g) and PO2(OH)(g), as well as the corresponding binuclear Si2O4(g) and P2O5(g) molecules, is studied by means of density functional theory. Hydrolysis of (HO)3SiOSi(OH)3(g) is found to be slightly endothermic, and only an asymmetric energy minimum is found for this silicic acid dimer. Four stable conformations are determined for the pyrophosphoric acid system (HO)2OPOPO(OH)2(g). Depending on the choice of reference structure and basis set, the hydrolysis energetics ranges from 14–26 kJ/mol exothermic to 3–7 kJ/mol endothermic. In general, the hydrolysis reaction is best described as a near zero-energy process. Significant differences in the water chemistry of the final monomeric products, Si(OH)4(g) and PO(OH)3(g), appear in the first solvation shell. Connecting the P–OH and P=O groups by water bridges results in a greater tendency for proton delocalization in PO(OH)3(g), than is observed when water is used to connect two Si–OH groups in Si(OH)4(g). Taking the properties of pyrophosphoric acid as model for the P–O–P bridge in adenosine triphosphate (ATP), the results of the present study support the notion that this molecule and its hydrolysis products provide a nano-scale buffer, which is essential for sustaining biosynthesis by controlling the proton and water activities.
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| 8. |
- Johnson, J.R.T, et al.
(author)
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Water adsorption and hydrolysis on molecular Al oxides and hydroxides - solvation versus cluster formation
- 2001
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In: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 3:24, s. 5482-5488
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Journal article (peer-reviewed)abstract
- Addition of water to the AlO(OH)(g) molecule and to the corresponding binuclear anhydride Al2O3(g) are studied by means of quantum chemistry. The AlO bond and the Al–O–Al bridge are found to be highly reactive towards water, and the final products are determined as Al(OH)3(g) and the dimer Al2(OH)6(g). The addition of further H2O molecules to Al(OH)3(g) was used to model micro-solvation. Two different types of cluster structures are found for Al(OH)3·nH2O. One type contains an Al(OH)4−/H3O+ ion-pair, for which the core anion displays a four-coordinated geometry on Al. The second type displays a six-coordinate Al, while tending to form a cationic core. Both structures require a Al(OH)3·6H2O(g) system as computational model to be observed. For neutral environments, polymerization of Al(OH)3 is preferred over the solvation of monomeric species. The results are understood to reflect the amphoteric dissolution chemistry of aluminium hydroxide under acidic or alkaline conditions.
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| 9. |
- Snis, Anders, et al.
(author)
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Characterizations of (NO)(3)- and N3O2- molecular anions
- 1999
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In: Chemical Physics Letters. - 0009-2614. ; 305:3-4, s. 285-292
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Journal article (peer-reviewed)abstract
- Isomers of (NO)3− are characterized by means of B3LYP density functional theory and the wavefunction-based CASPT2 method. Stabilities, vertical electron detachment energies (VDEs), vertical electron excitation energies (VEEs), and vibration frequencies are determined. Experimental isotope shifts in the IR spectrum of (NO)3− and theory were previously employed to determine the structure of an N–N–N connected anion. Further support for this assignment is obtained in the present study by comparing experimental and theoretical VDEs and VEEs. A parallel analysis of a w-shaped N3O2− molecular anion along the above lines is performed for reference, as a comprehensive understanding of the two systems is sought.
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| 10. |
- Snis, Anders, et al.
(author)
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N2O2, N2O2- and N2O22-: structures, energetics and N-N bonding
- 1997
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In: Chemical Physics. - 0301-0104. ; 221:1-2, s. 1-10
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Journal article (peer-reviewed)abstract
- The density functional theory and the ab initio quantum chemistry methods, Becke3LYP and CASPT2, have been employed to determine structures and energetics of neutral and anionic N2O2 species. When going from a neutral NO dimer to an anionic species the N---N bond lengths decrease drastically and the corresponding N---N frequencies increase. The relative stabilities of the different N2O2− isomers suggest an ONNO structure in a Trans configuration to be the most stable mono valent anion. The formation energies of 1.4–1.7 eV relative to the NO + NO− asymptote are in agreement with experiments. Excitation energies are determined and specific formation channels for three N2O2− isomers are discussed. The hyponitrite ion, N2O22−, is also studied. Its total energy is 2.7–2.8 eV above the total energy of two NO−. In order to connect to an experimental study of NO adsorption on MgO the ability of two NO molecules to form a complex with Mg and Mg+ is investigated.
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