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Molecular Engineering for Electrochemical Power Sources

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Molecular Diversity".

Deadline for manuscript submissions: closed (10 October 2015) | Viewed by 60645

Special Issue Editor

Department of Mechanical Engineering, National University of Singapore, Singapore 117575, Singapore
Interests: electrochemical batteries: photoelectrochemical cells; computational spectroscopy; potential energy surfaces; machine learning; ab initio modeling; large scale density functional methods
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear colleagues,

Electrochemical energy conversion and storage technologies are deemed to play an increasingly prominent role in the use of electricity in the coming decades. They hold the promise of economic solar-to-electricity energy conversion, high-rate grid storage, and of enabling all-electric vehicles. These technologies include metal ion batteries, dye sensitized and organic solar cells, fuel cells and redox flow batteries. While their respective research fields have mostly been developing in parallel, these technologies have to address similar issues of molecular engineering, e.g., band gap engineering, redox level tuning, reorganization energy modulation; these concerns crop up in electrolyte design for Li or post-Li electrochemical batteries, organic electrode materials for emerging organic batteries, chromophore and redox shuttle molecules for dye-sensitized cells and redox flow batteries. This Special Issue aims to foster cross-fertilization of ideas in molecular engineering coming from these different fields. It welcomes original research papers and reviews dealing with experimental or computational design of molecules for use in electrochemical power sources as well as measurements and simulations of molecules at interfaces and in environments characteristic of electrochemical devices.

Dr. Sergei Manzhos
Guest Editor

Dr. Sergei Manzhos

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Keywords

  • electrochemical batteries
  • redox-flow batteries
  • dye-sensitized solar cells
  • organic solar cells
  • organic batteries
  • fuel cells
  • bandgap engineering
  • redox level tuning
  • electrolyte
  • chromophore

Published Papers (7 papers)

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Editorial

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140 KiB  
Editorial
Special Issue “Molecular Engineering for Electrochemical Power Sources”
by Sergei Manzhos
Molecules 2016, 21(11), 1524; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules21111524 - 12 Nov 2016
Viewed by 2992
Abstract
Electrochemical energy conversion and storage technologies are expected to play an increasingly prominent role in the production and consumption of electricity in the coming decades.[...] Full article
(This article belongs to the Special Issue Molecular Engineering for Electrochemical Power Sources)

Research

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2173 KiB  
Article
Characterizing the Solvated Structure of Photoexcited [Os(terpy)2]2+ with X-ray Transient Absorption Spectroscopy and DFT Calculations
by Xiaoyi Zhang, Mátyás Pápai, Klaus B. Møller, Jianxin Zhang and Sophie E. Canton
Molecules 2016, 21(2), 235; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules21020235 - 19 Feb 2016
Cited by 9 | Viewed by 6001
Abstract
Characterizing the geometric and electronic structures of individual photoexcited dye molecules in solution is an important step towards understanding the interfacial properties of photo-active electrodes. The broad family of “red sensitizers” based on osmium(II) polypyridyl compounds often undergoes small photo-induced structural changes which [...] Read more.
Characterizing the geometric and electronic structures of individual photoexcited dye molecules in solution is an important step towards understanding the interfacial properties of photo-active electrodes. The broad family of “red sensitizers” based on osmium(II) polypyridyl compounds often undergoes small photo-induced structural changes which are challenging to characterize. In this work, X-ray transient absorption spectroscopy with picosecond temporal resolution is employed to determine the geometric and electronic structures of the photoexcited triplet state of [Os(terpy)2]2+ (terpy: 2,2′:6′,2″-terpyridine) solvated in methanol. From the EXAFS analysis, the structural changes can be characterized by a slight overall expansion of the first coordination shell [OsN6]. DFT calculations supports the XTA results. They also provide additional information about the nature of the molecular orbitals that contribute to the optical spectrum (with TD-DFT) and the near-edge region of the X-ray spectra. Full article
(This article belongs to the Special Issue Molecular Engineering for Electrochemical Power Sources)
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2574 KiB  
Article
Significant Improvement of Optoelectronic and Photovoltaic Properties by Incorporating Thiophene in a Solution-Processable D–A–D Modular Chromophore
by Aaron M. Raynor, Akhil Gupta, Christopher M. Plummer, Sam L. Jackson, Ante Bilic, Hemlata Patil, Prashant Sonar and Sheshanath V. Bhosale
Molecules 2015, 20(12), 21787-21801; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules201219798 - 04 Dec 2015
Cited by 10 | Viewed by 6901
Abstract
Through the incorporation of a thiophene functionality, a novel solution-processable small organic chromophore was designed, synthesized and characterized for application in bulk-heterojunction solar cells. The new chromophore, (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)acrylonitrile) (coded as AS2), was based on a donor–acceptor–donor (D–A–D) module [...] Read more.
Through the incorporation of a thiophene functionality, a novel solution-processable small organic chromophore was designed, synthesized and characterized for application in bulk-heterojunction solar cells. The new chromophore, (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)acrylonitrile) (coded as AS2), was based on a donor–acceptor–donor (D–A–D) module where a simple triphenylamine unit served as an electron donor, 1,4-phenylenediacetonitrile as an electron acceptor, and a thiophene ring as the π-bridge embedded between the donor and acceptor functionalities. AS2 was isolated as brick-red, needle-shaped crystals, and was fully characterized by 1H- and 13C-NMR, IR, mass spectrometry and single crystal X-ray diffraction. The optoelectronic and photovoltaic properties of AS2 were compared with those of a structural analogue, (2Z,2′Z)-2,2′-(1,4-phenylene)bis(3-(4-(diphenylamino)phenyl)-acrylonitrile) (AS1). Benefiting from the covalent thiophene bridges, compared to AS1 thin solid film, the AS2 film showed: (1) an enhancement of light-harvesting ability by 20%; (2) an increase in wavelength of the longest wavelength absorption maximum (497 nm vs. 470 nm) and (3) a narrower optical band-gap (1.93 eV vs. 2.17 eV). Studies on the photovoltaic properties revealed that the best AS2-[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM)-based device showed an impressive enhanced power conversion efficiency of 4.10%, an approx. 3-fold increase with respect to the efficiency of the best AS1-based device (1.23%). These results clearly indicated that embodiment of thiophene functionality extended the molecular conjugation, thus enhancing the light-harvesting ability and short-circuit current density, while further improving the bulk-heterojunction device performance. To our knowledge, AS2 is the first example in the literature where a thiophene unit has been used in conjunction with a 1,4-phenylenediacetonitrile accepting functionality to extend the π-conjugation in a given D–A–D motif for bulk-heterojunction solar cell applications. Full article
(This article belongs to the Special Issue Molecular Engineering for Electrochemical Power Sources)
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1941 KiB  
Article
Hazardous Doping for Photo-Electrochemical Conversion: The Case of Nb-Doped Fe2O3 from First Principles
by Natav Yatom and Maytal Caspary Toroker
Molecules 2015, 20(11), 19900-19906; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules201119668 - 04 Nov 2015
Cited by 27 | Viewed by 6506
Abstract
The challenge of improving the efficiency of photo-electrochemical devices is often addressed through doping. However, this strategy could harm performance. Specifically, as demonstrated in a recent experiment, doping one of the most widely used materials for water splitting, iron (III) oxide (Fe2 [...] Read more.
The challenge of improving the efficiency of photo-electrochemical devices is often addressed through doping. However, this strategy could harm performance. Specifically, as demonstrated in a recent experiment, doping one of the most widely used materials for water splitting, iron (III) oxide (Fe2O3), with niobium (Nb) can still result in limited efficiency. In order to better understand the hazardous effect of doping, we use Density Functional Theory (DFT)+U for the case of Nb-doped Fe2O3. We find a direct correlation between the charge of the dopant, the charge on surface of the Fe2O3 material, and the overpotential required for water oxidation reaction. We believe that this work contributes to advancing our understanding of how to select effective dopants for materials. Full article
(This article belongs to the Special Issue Molecular Engineering for Electrochemical Power Sources)
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14232 KiB  
Article
Imaging the Ultrafast Photoelectron Transfer Process in Alizarin-TiO2
by Tatiana Gomez, Gunter Hermann, Ximena Zarate, Jhon Fredy Pérez-Torres and Jean Christophe Tremblay
Molecules 2015, 20(8), 13830-13853; https://doi.org/10.3390/molecules200813830 - 30 Jul 2015
Cited by 28 | Viewed by 6589 | Correction
Abstract
In this work, we adopt a quantum mechanical approach based on time-dependent density functional theory (TDDFT) to study the optical and electronic properties of alizarin supported on TiO2 nano-crystallites, as a prototypical dye-sensitized solar cell. To ensure proper alignment of the donor [...] Read more.
In this work, we adopt a quantum mechanical approach based on time-dependent density functional theory (TDDFT) to study the optical and electronic properties of alizarin supported on TiO2 nano-crystallites, as a prototypical dye-sensitized solar cell. To ensure proper alignment of the donor (alizarin) and acceptor (TiO2 nano-crystallite) levels, static optical excitation spectra are simulated using time-dependent density functional theory in response. The ultrafast photoelectron transfer from the dye to the cluster is simulated using an explicitly time-dependent, one-electron TDDFT ansatz. The model considers the δ-pulse excitation of a single active electron localized in the dye to the complete set of energetically accessible, delocalized molecular orbitals of the dye/nano-crystallite complex. A set of quantum mechanical tools derived from the transition electronic flux density is introduced to visualize and analyze the process in real time. The evolution of the created wave packet subject to absorbing boundary conditions at the borders of the cluster reveal that, while the electrons of the aromatic rings of alizarin are heavily involved in an ultrafast charge redistribution between the carbonyl groups of the dye molecule, they do not contribute positively to the electron injection and, overall, they delay the process. Full article
(This article belongs to the Special Issue Molecular Engineering for Electrochemical Power Sources)
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3775 KiB  
Article
A Density Functional Tight Binding Study of Acetic Acid Adsorption on Crystalline and Amorphous Surfaces of Titania
by Sergei Manzhos, Giacomo Giorgi and Koichi Yamashita
Molecules 2015, 20(2), 3371-3388; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules20023371 - 17 Feb 2015
Cited by 41 | Viewed by 9683
Abstract
We present a comparative density functional tight binding study of an organic molecule attachment to TiO2 via a carboxylic group, with the example of acetic acid. For the first time, binding to low-energy surfaces of crystalline anatase (101), rutile (110) and (B)-TiO [...] Read more.
We present a comparative density functional tight binding study of an organic molecule attachment to TiO2 via a carboxylic group, with the example of acetic acid. For the first time, binding to low-energy surfaces of crystalline anatase (101), rutile (110) and (B)-TiO2 (001), as well as to the surface of amorphous (a-) TiO2 is compared with the same computational setup. On all surfaces, bidentate configurations are identified as providing the strongest adsorption energy, Eads = −1.93, −2.49 and −1.09 eV for anatase, rutile and (B)-TiO2, respectively. For monodentate configurations, the strongest Eads = −1.06, −1.11 and −0.86 eV for anatase, rutile and (B)-TiO2, respectively. Multiple monodentate and bidentate configurations are identified on a-TiO2 with a distribution of adsorption energies and with the lowest energy configuration having stronger bonding than that of the crystalline counterparts, with Eads up to −4.92 eV for bidentate and −1.83 eV for monodentate adsorption. Amorphous TiO2 can therefore be used to achieve strong anchoring of organic molecules, such as dyes, that bind via a -COOH group. While the presence of the surface leads to a contraction of the band gap vs. the bulk, molecular adsorption caused no appreciable effect on the band structure around the gap in any of the systems. Full article
(This article belongs to the Special Issue Molecular Engineering for Electrochemical Power Sources)
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Review

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2048 KiB  
Review
Redox Species of Redox Flow Batteries: A Review
by Feng Pan and Qing Wang
Molecules 2015, 20(11), 20499-20517; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules201119711 - 18 Nov 2015
Cited by 169 | Viewed by 21208
Abstract
Due to the capricious nature of renewable energy resources, such as wind and solar, large-scale energy storage devices are increasingly required to make the best use of the renewable power. The redox flow battery is considered suitable for large-scale applications due to its [...] Read more.
Due to the capricious nature of renewable energy resources, such as wind and solar, large-scale energy storage devices are increasingly required to make the best use of the renewable power. The redox flow battery is considered suitable for large-scale applications due to its modular design, good scalability and flexible operation. The biggest challenge of the redox flow battery is the low energy density. The redox active species is the most important component in redox flow batteries, and the redox potential and solubility of redox species dictate the system energy density. This review is focused on the recent development of redox species. Different categories of redox species, including simple inorganic ions, metal complexes, metal-free organic compounds, polysulfide/sulfur and lithium storage active materials, are reviewed. The future development of redox species towards higher energy density is also suggested. Full article
(This article belongs to the Special Issue Molecular Engineering for Electrochemical Power Sources)
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