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Special Issue "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)

Special Issue Editor

Guest Editor
Dr. Sergei Manzhos

Assistant Professor, Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore, Block EA #07-08, 9 Engineering Drive 1, Singapore 117576
Website | E-Mail
Phone: +65 6516 4605
Fax: +65 6779 1459
Interests: photoelectrochemical solar cells, electrochemical, molecule-surface interaction, ab initio modeling, computational vibrational spectroscopy

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

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.


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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Open AccessEditorial Special Issue “Molecular Engineering for Electrochemical Power Sources”
Molecules 2016, 21(11), 1524; doi:10.3390/molecules21111524
Received: 9 November 2016 / Revised: 10 November 2016 / Accepted: 10 November 2016 / Published: 12 November 2016
PDF Full-text (140 KB) | HTML Full-text | XML Full-text
(This article belongs to the Special Issue Molecular Engineering for Electrochemical Power Sources)

Research

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Open AccessArticle Characterizing the Solvated Structure of Photoexcited [Os(terpy)2]2+ with X-ray Transient Absorption Spectroscopy and DFT Calculations
Molecules 2016, 21(2), 235; doi:10.3390/molecules21020235
Received: 17 January 2016 / Revised: 12 February 2016 / Accepted: 15 February 2016 / Published: 19 February 2016
Cited by 5 | PDF Full-text (2173 KB) | HTML Full-text | XML Full-text
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)
Open AccessArticle Significant Improvement of Optoelectronic and Photovoltaic Properties by Incorporating Thiophene in a Solution-Processable D–A–D Modular Chromophore
Molecules 2015, 20(12), 21787-21801; doi:10.3390/molecules201219798
Received: 6 October 2015 / Revised: 24 November 2015 / Accepted: 25 November 2015 / Published: 4 December 2015
Cited by 4 | PDF Full-text (2574 KB) | HTML Full-text | XML Full-text | Supplementary Files
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)
Open AccessArticle Hazardous Doping for Photo-Electrochemical Conversion: The Case of Nb-Doped Fe2O3 from First Principles
Molecules 2015, 20(11), 19900-19906; doi:10.3390/molecules201119668
Received: 2 October 2015 / Revised: 26 October 2015 / Accepted: 26 October 2015 / Published: 4 November 2015
Cited by 14 | PDF Full-text (1941 KB) | HTML Full-text | XML Full-text | Supplementary Files
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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Open AccessArticle Imaging the Ultrafast Photoelectron Transfer Process in Alizarin-TiO2
Molecules 2015, 20(8), 13830-13853; doi:10.3390/molecules200813830
Received: 15 May 2015 / Revised: 9 July 2015 / Accepted: 20 July 2015 / Published: 30 July 2015
Cited by 13 | PDF Full-text (14232 KB) | HTML Full-text | XML Full-text | 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)
Open AccessArticle A Density Functional Tight Binding Study of Acetic Acid Adsorption on Crystalline and Amorphous Surfaces of Titania
Molecules 2015, 20(2), 3371-3388; doi:10.3390/molecules20023371
Received: 4 January 2015 / Revised: 12 February 2015 / Accepted: 13 February 2015 / Published: 17 February 2015
Cited by 15 | PDF Full-text (3775 KB) | HTML Full-text | XML Full-text
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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Open AccessReview Redox Species of Redox Flow Batteries: A Review
Molecules 2015, 20(11), 20499-20517; doi:10.3390/molecules201119711
Received: 16 October 2015 / Revised: 9 November 2015 / Accepted: 9 November 2015 / Published: 18 November 2015
Cited by 18 | PDF Full-text (2048 KB) | HTML Full-text | XML Full-text
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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