Browsing by Subject "Iron chromophore"

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Open Access
Corrigendum: Building an iron chromophore incorporating prussian blue analogue for photoelectrochemical water oxidation
(Wiley-VCH Verlag GmbH & Co. KGaA, 2021-09-20) Ghobadi, T. Gamze Ulusoy; Ghobadi, Amir; Demirtaş, Merve; Büyüktemiz, M.; Kübra N., Özvural; Yıldız, E. A.; Erdem, E.; Yağlıgül, H. G.; Durgun, Engin; Dede, Y.; Özbay, Ekmel; Karadaş, Ferdi
The replacement of traditional ruthenium-based photosensitizers with low-cost and abundant iron analogs is a key step for the advancement of scalable and sustainable dye-sensitized water splitting cells. In this proof-of-concept study, a pyridinium ligand coordinated pentacyanoferrate(II) chromophore is used to construct a cyanide-based CoFe extended bulk framework, in which the iron photosensitizer units are connected to cobalt water oxidation catalytic sites through cyanide linkers. The iron-sensitized photoanode exhibits exceptional stability for at least 5 h at pH 7 and features its photosensitizing ability with an incident photon-to-current conversion capacity up to 500 nm with nanosecond scale excited state lifetime. Ultrafast transient absorption and computational studies reveal that iron and cobalt sites mutually support each other for charge separation via short bridging cyanide groups and for injection to the semiconductor in our proof-of-concept photoelectrochemical device. The reorganization of the excited states due to the mixing of electronic states of metal-based orbitals subsequently tailor the electron transfer cascade during the photoelectrochemical process. This breakthrough in chromophore-catalyst assemblies will spark interest in dye-sensitization with robust bulk systems for photoconversion applications.
Open Access
Design of multifunctional prussian blue analogues for solar driven water oxidation
(2021-07) Ghobadi, Türkan Gamze Ulusoy
The development of earth-abundant, robust, and low-cost photoanodes for water oxidation is one of the most critical steps in ‘artificial leaf’. A promising approach in this field is to build dye-sensitized photoanodes by coupling a molecular photosensitizer (PS) with a water oxidation catalyst (WOC) on a proper semiconductor (SC) for efficient charge separation. All dye-sensitized photoanodes reported in the literature consist of either a ruthenium photosensitizer, a ruthenium water oxidation catalyst, or both. We aim to overcome this critical challenge by developing a new family of organic- or iron-based donor-acceptor chromophores incorporated in a Prussian blue (PB) structure, which are coated on proper semiconductors. Our studies within this context could be divided into three sections: (i) PB based photocatalytic water oxidation: In this work-package, an entirely precious metal-free chromophore-donor-water oxidation catalyst triad system is developed. The synthesis involves the coordination of a porphyrin derivative to a bridging Fe(CN)5 group, which is then reacted with cobalt ions to prepare a covalently linked chromophore-Prussian blue analogue (CoFe(CN)5–Ligand) assembly. Light-driven water oxidation studies in the presence of an electron scavenger indicate that the triad is active and maintains a steady activity for at least 3 hours. Transient absorption experiments and computational studies reveal that the Fe(CN)5 group is more than just a linker. It takes part in electron donation and co-operates with porphyrin in the charge separation process. (ii) PB based photoelectrochemical water oxidation: Here, we move one step forward and design a ruthenium-free water oxidation photoanode by the sensitization of titanium dioxide (TiO2) nanowires with a PB-organic chromophore structure. A phenazine-based organic group, Janus Green B (JG), is chosen as the chromophore since it has a broad absorption response in the visible and near-infrared ranges. The resulting multifunctional PB modified TiO2 electrode demonstrates a low-cost and easy-to-construct photoanode, which exhibits a remarkable excited-state lifetime in the order of nanoseconds and an extended light absorption capacity of up to 500 nm. Moreover, the photoanode retains its structural integrity and photoelectrochemical activity for at least 2 hours. Despite all the above-mentioned improvements, the performance of the cell, [CoFe–JG]/TiO2, is relatively poor due to improper band energy alignment between the chromophore and the semiconductor. In a follow-up study, we tune the chromophore and the semiconductor to achieve a proper band energy alignment, and thus, to improve the performance. Another phenazine-based molecule, Safranin O (SF), is utilized as the organic photosensitizer. Moreover, a visible-light absorbing semiconductor, WO3, is used to utilize the solar spectrum completely. [CoFe–SF]/WO3 exhibits a record photocurrent density of 1.3 mA/cm2 at 1.23 VRHE, demonstrating that proper modification of components in PB based dye-sensitized photoanodes could pave the way for the development of high-performance water splitting cells. (iii) Iron chromophore based photoelectrochemical water oxidation: In this section, the iron site that has been previously utilized as a relay is promoted to an iron chromophore. Five cyanide ligands are coordinated to the iron site to destabilize the metal-centered states. At the same time, an electron-deficient cationic pyridinium group occupies the remaining coordination sphere of the octahedral iron site to facilitate the metal-to-ligand charge transfer (MLCT) process. This iron complex is coated initially on TiO2 nanowires and then reacted with cobalt ions to produce a CoFe PB (CoFe(CN)5-L) layer on the electrode surface. In this photoanode, the excited-state lifetime of the iron chromophore exceeds 1 ns, which demonstrates the first example of an iron-sensitized water oxidation cell in the literature. Overall, this thesis presents an alternative perspective to realize high performance, low-cost, stable, and robust dye-sensitized water oxidation systems. The impact of the acquired knowledge in this thesis is also discussed to define the current status, challenges, and future of PB based water oxidation systems.