Nano-sized TiO 2 photocatalytic water-splitting technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy. Presently, the solar-to-hydrogen energy conversion efficiency is too low for the technology to be economically sound. The main barriers are the rapid recombination of photo-generated electron/hole pairs as well as backward reaction and the poor activation of TiO 2 by visible light. In response to these deficiencies, many investigators have been conducting research with an emphasis on effective remediation methods. Some investigators studied the effects of addition of sacrificial reagents and carbonate salts to prohibit rapid recombination of electron/hole pairs and backward reactions. Other research focused on the enhancement of photocatalysis by modification of TiO 2 by means of metal loading, metal ion doping, dye sensitization, composite semiconductor, anion doping and metal ion-implantation. This paper aims to review the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production. Based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range. Therefore, they play an important role in the development of efficient photocatalytic hydrogen production.

A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production

1. Setting the Scope of the Challenge 6474 1.1. The Need for Solar Energy Supply and Storage 6474 1.2. An Imperative for Discovery Research 6477 1.3. Scope of Review 6478 2. Large-Scale Centralized Energy Storage 6478 2.1. Pumped Hydroelectric Energy Storage (PHES) 6479 2.2. Compressed Air Energy Storage (CAES) 6480 3. Smaller Scale Grid and Distributed Energy Storage 6481 3.1. Flywheel Energy Storage (FES) 6481 3.2. Superconducting Magnetic Energy Storage 6482 4. Chemical Energy Storage: Electrochemical 6482 4.1. Batteries 6482 4.1.1. Lead-Acid Batteries 6483 4.1.2. Alkaline Batteries 6484 4.1.3. Lithium-Ion Batteries 6484 4.1.4. High-Temperature Sodium Batteries 6484 4.1.5. Liquid Flow Batteries 6485 4.1.6. Metal-Air Batteries 6485 4.2. Capacitors 6485 5. Chemical Energy Storage: Solar Fuels 6486 5.1. Solar Fuels in Nature 6486 5.2. Artificial Photosynthesis and General Considerations of Water Splitting 6486

Solar Energy Supply and Storage for the Legacy and Nonlegacy Worlds

ZnS nanostructures: From synthesis to applications

The remarkable achievement by Fujishima and Honda (1972) in the photo-electrochemical water splitting results in the extensive use of TiO 2 nanomaterials for environmental purification and energy storage/conversion applications. Though there are many advantages for the TiO 2 compared to other semiconductor photocatalysts, its band gap of 3.2 eV restrains application to the UV-region of the electromagnetic spectrum ( λ  ≤ 387.5 nm). As a result, development of visible-light active titanium dioxide is one of the key challenges in the field of semiconductor photocatalysis. In this review, advances in the strategies for the visible light activation, origin of visible-light activity, and electronic structure of various visible-light active TiO 2 photocatalysts are discussed in detail. It has also been shown that if appropriate models are used, the theoretical insights can successfully be employed to develop novel catalysts to enhance the photocatalytic performance in the visible region. Recent developments in theory and experiments in visible-light induced water splitting, degradation of environmental pollutants, water and air purification and antibacterial applications are also reviewed. Various strategies to identify appropriate dopants for improved visible-light absorption and electron–hole separation to enhance the photocatalytic activity are discussed in detail, and a number of recommendations are also presented.

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Visible-light activation of TiO2 photocatalysts: Advances in theory and experiments

Environmental problems associated with organic pollutants and toxic water pollutants provide the impetus for sustained fundamental and applied research in the area of environmental remediation. Semiconductor photocatalysis offers the potential for complete elimination of toxic chemicals through its efficiency and potentially broad applicability. [1] Various new compounds and materials for photocatalysis have been synthesized in the past few decades. A successful example is TiO2, a metal oxide often used as a catalyst in photochemistry, electrochemistry, environmental protection, and in the battery industry. [2] Recently, transition-metal sulfides, in particular ZnS and CdS, have been intensively studied because of their unique catalytic functions compared to those of TiO2. [2, 3] These studies have revealed that ZnS nanocrystals (NCs) are good photocatalysts as a result of the rapid generation of electron– hole pairs by photoexcitation and the highly negative reduction potentials of excited electrons. The photocatalytic properties occur not only in the photoreductive production of H2 from water and the photoreduction of CO2, [4] but also in the phototransformation of various organic substrates such as the oxidative formation of carbon–carbon bonds from organic electron donors, cis–trans photoisomerization of alkenes, and the photoreduction of aldehydes and their derivatives. [5] The notable finding in nonmetalized ZnS photocatalysis is an irreversible two-electron-transfer photoreduction of organic substrates. [6] A favorable shift of the optical response into the visible region occurs subsequent to the doping of transition metal or rare-earth metal ions, such as Ni 2+ and Cu 2+ ; therefore, ZnS NCs can also be used as effective catalysts for photocatalytic evolution of H2 and photoreduction of toxic ions under visible-light irradiation. [7] An important application of ZnS is as a photocatalyst in environmental protection through the removal of organic

Mass Production and High Photocatalytic Activity of ZnS Nanoporous Nanoparticles

http://jes.ecsdl.org/content/162/3/H170.full.pdf

Electropolymerization of Octakis Diethlyamino Substituted Metallophthalocyanines and Their Electrochromic Characterization

Peripherally and non-peripherally terminal alkynyl substituted manganese phthalocyanines (MnPc) were synthesized and characterized and then used as functional materials in modified electrodes. MnPcs were substituted with alkynyl groups, which are reactive moieties in click electrochemistry (CEC) reactions. Mn(iii) cations were incorporated into the cavity of the Pc ring in order to increase the redox activity of the complexes. Electrochemical characterizations of the complexes were determined by voltammetric and in situ spectroelectrochemical measurements in order to determine their possible technological applications. MnPc complexes illustrated five redox couples and these redox couples were assigned as [Cl-MnIIIPc2-]/[Cl-MnIIPc2-]1-, [Cl-MnIIPc2-]1-/[Cl-MnIPc2-]2-, [Cl-MnIPc2-]2-/[ Cl-MnIPc3-]3-, and [Cl-MnIIIPc2-]/[Cl-MnIIIPc1-]1+ redox processes. The position of the substituents affected the mechanism of the redox reactions and influenced the tendency to react with the molecular oxygen. Moreover, changing the position of the substituents slightly influenced the peak potentials and reversibility of the redox processes. For the applications, modified electrodes (ITO/PANI-N3-MnPc and GCE/PANI-N3-MnPc) were constructed with CEC reaction between azido functionalized polyaniline (PANI-N3) and terminally alkynyl substituted MnPcs and these electrodes. Voltammetric characterizations of the modified electrodes illustrated suitable redox activity and conductivity for the practical applications. Finally, the GCE/PANI-N3-MnPc electrode was tested as a potential electrocatalyst for water splitting reaction. Although the GCE/PANI-N3-MnPc electrode did not catalyze the hydrogen evolution reaction (HER), it significantly catalyzed the oxygen evolution reaction (OER) in aqueous solution.

Immobilization of alkynyl functionalized manganese phthalocyanine via click electrochemistry for electrocatalytic oxygen evolution reaction

Electrochemical and in situ spectroelectrochemical behaviors and electrocatalytic reduction of molecular oxygen with titanyl phthalocyanines (TiPc) bearing 3,4-(methylenedioxy)-phenoxy substituents were performed in aprotic solvents. Multi electrons and metal-based and ring-based redox processes of TiPcs indicate their possible electrocatalytic activity toward many target species. Different numbers and positions of the substituents of the complexes affect the peaks’ character and assignment of the processes. The presence of O2 in the electrolyte system influences the electrochemical and spectral responses of TiPcs. Electrochemical and in situ spectroelectrochemical analysis indicates interaction of molecular oxygen with TiPcs and these interaction mechanisms depend on both the substituent environments of the complexes and the electrolyte system. Langmuir–Blodgett films of the complexes also catalyze molecular oxygen in aqueous media, which is a desired property for their practical application.

Oxygen reduction reaction catalyzed with titanyl phthalocyanines in nonaqueous and aqueous media.

Novel peripheral tetra-substituted phthalocyanines containing methoxylated chalcone group: Synthesis, spectral, electrochemical and spectroelectrochemical properties

The Synthesis, Characterization, Electrochemical and Spectroelectrochemical Properties of Novel Unsymmetrical Phthalocyanines Containing Naphthoic Acid and Di-tert-butylphenoxy Groups

Atıf Koca

Papers

Electropolymerization of Octakis Diethlyamino Substituted Metallophthalocyanines and Their Electrochromic Characterization

Immobilization of alkynyl functionalized manganese phthalocyanine via click electrochemistry for electrocatalytic oxygen evolution reaction

Oxygen reduction reaction catalyzed with titanyl phthalocyanines in nonaqueous and aqueous media.

Novel peripheral tetra-substituted phthalocyanines containing methoxylated chalcone group: Synthesis, spectral, electrochemical and spectroelectrochemical properties

The Synthesis, Characterization, Electrochemical and Spectroelectrochemical Properties of Novel Unsymmetrical Phthalocyanines Containing Naphthoic Acid and Di-tert-butylphenoxy Groups