Special Issue "Photochemical Water Splitting"

A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Organometallic Chemistry".

Deadline for manuscript submissions: closed (31 January 2017)

Special Issue Editor

Guest Editor
Prof. Dr. Matthias Bauer

Department Chemie, Fakultät für Naturwissenschaften, Universität Paderborn, Warburgerstrasse 100, 33098 Paderborn, Germany
Website | E-Mail
Interests: transition metal complexes for sustainable chemistry; water splitting; iron chemistry; photochemistry; X-ray absorption spectroscopy; X-ray emission spectroscopy; time-resolved spectroscopy

Special Issue Information

Dear Colleagues,

With the increasing awareness of the upcoming ebbing of fossil fuels, the search for alternate energy and chemical resources has sped up tremendously. Photochemical water splitting, using the unlimited availability of sunlight, is used to generate hydrogen and oxygen from the Earth-abundant resource of water. Both small molecules are in high demand and useful chemical feedstocks, and ideally can be used in “green” applications like fuel cells. The ways to split water photocatalytically are manifold: Using purely light by combination of a photosensitizer with a catalyst, with the help of electricity, using the reduction and oxidation reaction independently with electron donors or acceptors, homogeneously or heterogeneously, or in artificial leaves. Transition metals play a crucial role in these processes, be it as a photoactive or catalytic compound.

This Special Issue focuses on the most recent advances in photochemical water splitting research with transition metal complexes as the key reagents. It includes investigations on photocatalytic activity of such complexes, their working principles, either as catalyst or photoactive compounds, as well as their spectroscopic and theoretical characterization. The aim of this Special Issue is to bring chemists and physicists together and to share important contributions to the field in an openly accessible journal. This is still a task of high impact, since, despite the tremendous advances that have been achieved in the field, the breakthrough to a real alternative to fossil fuels is still lacking.

Prof. Dr. Matthias Bauer
Guest Editor

Manuscript Submission Information

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Keywords

  • Photocatalytic water splitting
  • Transition metal complexes
  • Photosensitizers
  • Catalysts
  • Photochemistry and photophysics
  • Theory
  • Spectroscopy

Published Papers (7 papers)

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Research

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Open AccessArticle Chemical Tuning and Absorption Properties of Iridium Photosensitizers for Photocatalytic Applications
Inorganics 2017, 5(2), 23; doi:10.3390/inorganics5020023
Received: 28 February 2017 / Revised: 7 April 2017 / Accepted: 8 April 2017 / Published: 12 April 2017
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Abstract
Cyclometalated Ir(III) complexes are of particular interest due to the wide tunability of their electronic structure via variation of their ligands. Here, a series of heteroleptic Ir-based photosensitizers with the general formula [Ir(C^N)2(N^N)]+ has been studied theoretically by means of an optimally-tuned long-range
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Cyclometalated Ir(III) complexes are of particular interest due to the wide tunability of their electronic structure via variation of their ligands. Here, a series of heteroleptic Ir-based photosensitizers with the general formula [Ir(C^N)2(N^N)]+ has been studied theoretically by means of an optimally-tuned long-range separated density functional. Focusing on the steady-state absorption spectra, correlations between the chemical modification of both ligand types with the natures of the relevant dark and bright electronic states are revealed. Understanding such correlations builds up a basis for the rational design of efficient photocatalytic systems. Full article
(This article belongs to the Special Issue Photochemical Water Splitting)
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Open AccessArticle Photophysics of BODIPY Dyes as Readily-Designable Photosensitisers in Light-Driven Proton Reduction
Inorganics 2017, 5(2), 21; doi:10.3390/inorganics5020021
Received: 27 February 2017 / Revised: 28 March 2017 / Accepted: 29 March 2017 / Published: 5 April 2017
Cited by 2 | PDF Full-text (2420 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A series of boron dipyrromethene (BODIPY) dyes was tested as photosensitisers for light-driven hydrogen evolution in combination with the complex [Pd(PPh3)Cl2]2 as a source for catalytically-active Pd nanoparticles and triethylamine as a sacrificial electron donor. In line with
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A series of boron dipyrromethene (BODIPY) dyes was tested as photosensitisers for light-driven hydrogen evolution in combination with the complex [Pd(PPh3)Cl2]2 as a source for catalytically-active Pd nanoparticles and triethylamine as a sacrificial electron donor. In line with earlier reports, halogenated dyes showed significantly higher hydrogen production activity. All BODIPYs were fully characterised using stationary absorption and emission spectroscopy. Time-resolved spectroscopic investigations on meso-mesityl substituted compounds revealed that reduction of the photo-excited BODIPY by the sacrificial agent occurs from an excited singlet state, while, in halogenated species, long-lived triplet states are present, determining electron transfer processes from the sacrificial agent. Quantum chemical calculations performed at the time-dependent density functional level of theory indicate that the differences in the photocatalytic performance of the present series of dyes can be correlated to the varying efficiency of intersystem crossing in non-halogenated and halogenated species and not to alterations in the energy levels introduced upon substitution. Full article
(This article belongs to the Special Issue Photochemical Water Splitting)
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Review

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Open AccessReview Metal–Organic Frameworks and Their Derivatives for Photocatalytic Water Splitting
Inorganics 2017, 5(3), 40; doi:10.3390/inorganics5030040
Received: 19 April 2017 / Revised: 19 June 2017 / Accepted: 24 June 2017 / Published: 28 June 2017
Cited by 1 | PDF Full-text (4494 KB) | HTML Full-text | XML Full-text
Abstract
Amongst many strategies for renewable energy conversion, light-driven water splitting to produce clean H2 represents a promising approach and has attracted increasing attention in recent years. Owing to the multi-electron/multi-proton transfer nature of water splitting, low-cost and competent catalysts are needed. Along
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Amongst many strategies for renewable energy conversion, light-driven water splitting to produce clean H2 represents a promising approach and has attracted increasing attention in recent years. Owing to the multi-electron/multi-proton transfer nature of water splitting, low-cost and competent catalysts are needed. Along the rapid development of metal–organic frameworks (MOFs) during the last two decades or so, MOFs have been recognized as an interesting group of catalysts or catalyst supports for photocatalytic water splitting. The modular synthesis, intrinsically high surface area, tunable porosity, and diverse metal nodes and organic struts of MOFs render them excellent catalyst candidates for photocatalytic water splitting. To date, the application of MOFs and their derivatives as photocatalysts for water splitting has become a burgeoning field. Herein, we showcase several representative MOF-based photocatalytic systems for both H2 and O2 evolution reactions (HER, OER). The design principle of each catalytic system is specifically discussed. The current challenges and opportunities of utilizing MOFs for photocatalytic water splitting are discussed in the end. Full article
(This article belongs to the Special Issue Photochemical Water Splitting)
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Open AccessReview First-Principles View on Photoelectrochemistry: Water-Splitting as Case Study
Inorganics 2017, 5(2), 37; doi:10.3390/inorganics5020037
Received: 30 March 2017 / Revised: 19 May 2017 / Accepted: 24 May 2017 / Published: 1 June 2017
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Abstract
Photoelectrochemistry is truly an interdisciplinary field; a natural nexus between chemistry and physics. In short, photoelectrochemistry can be divided into three sub-processes, namely (i) the creation of electron-hole pairs by light absorption; (ii) separation/transport on the charge carriers and finally (iii) the water
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Photoelectrochemistry is truly an interdisciplinary field; a natural nexus between chemistry and physics. In short, photoelectrochemistry can be divided into three sub-processes, namely (i) the creation of electron-hole pairs by light absorption; (ii) separation/transport on the charge carriers and finally (iii) the water splitting reaction. The challenge is to understand all three processes on a microscopic scale and, perhaps even more importantly, how to combine the processes in an optimal way. This review will highlight some first-principles insights to the above sub-processes, in~particular as they occur using metal oxides. Based on these insights, challenges and future directions of first-principles methods in the field of photoelectrochemistry will be discussed. Full article
(This article belongs to the Special Issue Photochemical Water Splitting)
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Open AccessReview Product Selectivity in Homogeneous Artificial Photosynthesis Using [(bpy)Rh(Cp*)X]n+-Based Catalysts
Inorganics 2017, 5(2), 35; doi:10.3390/inorganics5020035
Received: 2 March 2017 / Revised: 15 May 2017 / Accepted: 19 May 2017 / Published: 25 May 2017
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Abstract
Due to the limited amount of fossil energy carriers, the storage of solar energy in chemical bonds using artificial photosynthesis has been under intensive investigation within the last decades. As the understanding of the underlying working principle of these complex systems continuously grows,
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Due to the limited amount of fossil energy carriers, the storage of solar energy in chemical bonds using artificial photosynthesis has been under intensive investigation within the last decades. As the understanding of the underlying working principle of these complex systems continuously grows, more focus will be placed on a catalyst design for highly selective product formation. Recent reports have shown that multifunctional photocatalysts can operate with high chemoselectivity, forming different catalysis products under appropriate reaction conditions. Within this context [(bpy)Rh(Cp*)X]n+-based catalysts are highly relevant examples for a detailed understanding of product selectivity in artificial photosynthesis since the identification of a number of possible reaction intermediates has already been achieved. Full article
(This article belongs to the Special Issue Photochemical Water Splitting)
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Open AccessReview Dye-Sensitized Photocatalytic Water Splitting and Sacrificial Hydrogen Generation: Current Status and Future Prospects
Inorganics 2017, 5(2), 34; doi:10.3390/inorganics5020034
Received: 16 March 2017 / Revised: 27 April 2017 / Accepted: 6 May 2017 / Published: 18 May 2017
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Abstract
Today, global warming and green energy are important topics of discussion for every intellectual gathering all over the world. The only sustainable solution to these problems is the use of solar energy and storing it as hydrogen fuel. Photocatalytic and photo-electrochemical water splitting
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Today, global warming and green energy are important topics of discussion for every intellectual gathering all over the world. The only sustainable solution to these problems is the use of solar energy and storing it as hydrogen fuel. Photocatalytic and photo-electrochemical water splitting and sacrificial hydrogen generation show a promise for future energy generation from renewable water and sunlight. This article mainly reviews the current research progress on photocatalytic and photo-electrochemical systems focusing on dye-sensitized overall water splitting and sacrificial hydrogen generation. An overview of significant parameters including dyes, sacrificial agents, modified photocatalysts and co-catalysts are provided. Also, the significance of statistical analysis as an effective tool for a systematic investigation of the effects of different factors and their interactions are explained. Finally, different photocatalytic reactor configurations that are currently in use for water splitting application in laboratory and large scale are discussed. Full article
(This article belongs to the Special Issue Photochemical Water Splitting)
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Open AccessReview Light to Hydrogen: Photocatalytic Hydrogen Generation from Water with Molecularly-Defined Iron Complexes
Inorganics 2017, 5(1), 14; doi:10.3390/inorganics5010014
Received: 27 January 2017 / Revised: 27 February 2017 / Accepted: 27 February 2017 / Published: 9 March 2017
Cited by 3 | PDF Full-text (3195 KB) | HTML Full-text | XML Full-text
Abstract
Photocatalytic hydrogen generation is considered to be attractive due to its combination of solar energy conversion and storage. Currently-used systems are either based on homogeneous or on heterogeneous materials, which possess a light harvesting and a catalytic subunit. The subject of this review
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Photocatalytic hydrogen generation is considered to be attractive due to its combination of solar energy conversion and storage. Currently-used systems are either based on homogeneous or on heterogeneous materials, which possess a light harvesting and a catalytic subunit. The subject of this review is a brief summary of homogeneous proton reduction systems using sacrificial agents with special emphasis on non-noble metal systems applying convenient iron(0) sources. Iridium photosensitizers, which were proven to have high quantum yields of up to 48% (415 nm), have been employed, as well as copper photosensitizers. In both cases, the addition or presence of a phosphine led to the transformation of the iron precursor with subsequently increased activities. Reaction pathways were investigated by photoluminescence, electron paramagnetic resonance (EPR), Raman, FTIR and mass spectroscopy, as well as time-dependent DFT-calculations. In the future, this knowledge will set the basis to design photo(electro)chemical devices with tailored electron transfer cascades and without the need for sacrificial agents. Full article
(This article belongs to the Special Issue Photochemical Water Splitting)
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