Browsing by Subject "Prussian Blue"
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Item Open Access CoFe prussian blue coordination compounds incorporating metallopolymers: Investigation of electrocatalytic water oxidation activities(Bilkent University, 2016-02) Demirkıran, MerveHydrogen economy, which depends on water and sunlight as energy source, needs to be implemented as an alternative to carbon based economy. For the development of a technology that incorporates hydrogen energy to our daily lives, it is required to split the water with the help of an efficient water oxidation catalyst. CoFe Prussian Blue analogues have recently been investigated as heterogeneous water oxidation catalysts. Even though they exhibit they exhibit high electrocatalytic activity in addition to superior stability in both acidic and neutral media low current densities were obtained with CoFe PB modified FTO electrodes due to their low surface coverage. This challenge could be overcome by developing novel synthetic methods that will enforce the formation of amorphous CoFe Prussian Blue analogues. Herein this thesis, pentacyanoferrate based metallopolymers were used as precursors to prepare amorphous Co-Fe analogues. The project focuses on the improving surface concentration by using Poly 4-vinyl pyridine (P4VP) not only as a capping ligand connected to pentacyanoferrate complexes but also as a surfactant to prevent the formation of long-range ordering between Co-Fe networks. Surface concentration was improved approximately seven fold, which resulted in an increase in the catalytic activity. A current density of 1 mA.cm-2 was obtained only at η = 510 mV while the same current density could be obtained only at higher overpotentials (>600 mV) with the previously studied Prussian Blue analogues. The stability of CoFe-PVP coated FTO electrodes were investigated before and after the electrocatalytic process using Infrared, XPS, and EDX studies. The results of this study indicate that the rich and diverse chemistry of pentacyanoferrates make them potential candidates for application in heterogeneous water oxidation catalysis.Item Open Access Inorganic / polymeric assemblies as catalysts for water splitting(Bilkent University, 2018-09) Kap, ZeynepSplitting water with sunlight is an attractive and promising research topic over the last two decades since it produces a non-carbon-based resource, hydrogen, which is a suitable energy carrier due to its high energy output and for being environmentally friendly. A great deal of research in this eld has been centered on the development of e cient water oxidation and reduction catalysts. The rst part of the thesis focuses on a novel photosensitizer-water oxidation catalyst (PS-WOC) dyad. A Ru metal coordinated pyridine-based ligand and a cobalt-iron pentacyanoferrate have been used as the photosensitizer and water oxidation catalyst, respectively. In this assembly, poly(4-vinylpyridine) serves as the bridging group between two units mainly to enhance the performance and stability of the system compared to its analogous intermolecular system. A 5-fold improvement on the catalytic activity has been achieved with a turnover frequency (TOF) of 5:6 10-4 s-1 under 1 hour light illumination and a turnover number (TON) of 11 in a 6-hour catalytic study. Evolved oxygen was quanti ed with gas chromatography. Structural characterization was carried out by Fourier Transform Infrared Spectroscopy (FTIR), Ultraviolet-Visible Spectroscopy (UV-Vis), X-Ray Photoelectron Spectroscopy (XPS), X-Ray Powder Di raction (XRD), Scanning Electron Microscopy (SEM), and Energy-dispersive X-Ray Spectroscopy (EDX) techniques. Comparative XPS and FTIR studies were performed on pristine and post-catalytic samples to con rm the stability of the dyad. In the second part of the study, a facile synthetic pathway using poly(4- vinylpyridine) as a polypyridyl platform has been reported for the formation of a cobalt-based metallopolymer. Electrochemical studies indicate that the metallopolymer acts as an e cient H2 evolution catalyst similar to cobalt-polypyridyl complexes. Furthermore, metallopolymer can be transformed to cobalt particles when a cathodic potential is applied in the presence of an acid. It has been found that these cobalt particles also serve as e cient hydrogen evolution catalysts. Approximately 80 µmoles of H2 gas can be collected during 2 h of electrolysis at -1.5 V (vs. Fc+/0) in the presence of 60 mM of acetic acid. A comprehensive study of the electrochemical and electrocatalytic behavior of cobalt-poly(4-vinylpyridine) was discussed in detail.Item Open Access Investigation of electrocatalytic performance of prussian blue analogues for water splitting(Bilkent University, 2017-09) Alsaç, Elif PınarResearch on H2 production has recently been directed to the development of cost-efficient and robust heterogeneous catalysts for splitting of water. While several Prussian blue analogues (PBAs) have been investigated as water oxidation catalysts, the field lacks a comprehensive study that focuses on the design of the ideal PBA for efficient water oxidation. Herein this thesis, a series of PBAs with different cyanide precursors were investigated to study the effect of hexacyanometal group to their electrocatalytic catalytic water oxidation activities. Cyclic voltammetry, chronoamperometry, and chronopotentiometry measurements reveal the close relation between the electron density of electroactive cobalt sites and electrocatalytic activity, which is also confirmed by Infrared and XPS studies. pH dependent cyclic voltammetry studies were also performed to gain insight about the catalytic mechanism and electronic structure of cyanide-based systems, to identify possible intermediates, and assign the rate-determining step of the process. In addition, a N-donor ligand, 1-heptyl 4-(4 pyridyl) pyridinium bromide, was used to prepare a new pentacyanoferrate complex. This complex was used to make a new series of PB analogues to investigate the effect of the change in the morphology to electrocatalytic water oxidation performance. Synthesis, characterization, and electrochemical experiments were performed to investigate electrocatalytic properties of PB analogues. With this synthesis route, the electroactive cobalt sites are increased approximately two-fold. It is observed that amorphous nature has positive impact on the catalytic activity when compared to cobalt hexacyanoferrates. A current density of 1 mA.cm-2 was achieved at an overpotential of 421 mV, which is much lower than those obtained with metal hexacyanometalates. Given the promising catalytic activities of several cobalt-based systems and the robustness of Prussian blue analogues in harsh catalytic processes including water oxidation, a Co-Co Prussian blue analogue was investigated as a Hydrogen evolution catalyst for the first time. Co-Co Prussian Blue modified FTO electrode demonstrated a significant Hydrogen evolution activity with an onset overpotential of 257 mV, a Tafel slope of 80.2 mV.dec-1, and a turnover frequency of 0.090 s-1 at an overpotential of 250 mV. Comparative XPS, Infrared, and XRD studies performed on pristine and post-catalytic electrodes confirm the stability of the catalyst.Item Open Access Tuning the electronic properties of prussian blue analogues for efficient water oxidation electrocatalysis: experimental and computational studies(Wiley-VCH Verlag, 2018) Alsaç, Elif Pınar; Ülker, E.; Nune, Satya Vijaya Kumar; Dede, Y.; Karadaş, FerdiAlthough several Prussian Blue analogues (PBAs) have been investigated as water oxidation catalysts, the field lacks a comprehensive study that focuses on the design of the ideal PBA for this purpose. Here, members of a series of PBAs with different cyanide precursors have been investigated to study the effect of hexacyanometal groups on their electrocatalytic water oxidation activities. Cyclic voltammetric, chronoamperometric, and chronopotentiometric measurements have revealed a close relationship between the electron density of electroactive cobalt sites and electrocatalytic activity, which has also been confirmed by infrared and XPS studies. Furthermore, pH-dependent cyclic voltammetry and computational studies have been performed to gain insight into the catalytic mechanism and electronic structure of cyanide-based systems to identify possible intermediates and to assign the rate-determining step of the target process.