Browsing by Subject "Water splitting"

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Open Access
Atomic layer deposition of NiOOH/Ni(OH) 2 on PIM-1-based N-Doped carbon nanofibers for electrochemical water splitting in alkaline medium
(Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Patil, Bhushan; Satılmış, Bekir; Khalily, Mohammad Aref; Uyar, Tamer
Portable and flexible energy devices demand lightweight and highly efficient catalytic materials for use in energy devices. An efficient water splitting electrocatalyst is considered an ideal future energy source. Well‐aligned high‐surface‐area electrospun polymers of intrinsic microporosity (PIM‐1)‐based nitrogen‐doped carbon nanofibers were prepared as a free‐standing flexible electrode. A non‐noble‐metal catalyst NiOOH/Ni(OH)2 was precisely deposited over flexible free‐standing carbon nanofibers by using atomic layer deposition (ALD). The morphology, high surface area, nitrogen doping, and Ni states synergistically showed a low onset potential (ηHER=−40 and ηOER=290 mV vs. reversible hydrogen electrode), small overpotential at η10 [oxygen evolution reaction (OER)=390.5 mV and hydrogen evolution reaction (HER)=−147 mV], excellent kinetics (Tafel slopes for OER=50 mV dec−1 and HER=41 mV dec−1), and high stability (>16 h) towards water splitting in an alkaline medium (0.1 m KOH). The performance was comparable with that of state‐of‐the‐art noble‐metal catalysts (e.g., Ir/C, Ru/C for OER, and Pt/C for HER). Post‐catalytic characterization with X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy further proved the durability of the electrode. This study provides insight into the design of 1D‐aligned N‐doped PIM‐1 electrospun carbon nanofibers as a flexible and free‐standing NiOOH/Ni(OH)2 decorated electrode as a highly stable nanocatalyst for water splitting in an alkaline medium.
Open Access
Covalent organic framework constructed by clicking azido porphyrin with perpropargyloxy-cucurbit[6]uril for electrocatalytic hydrogen generation from water splitting
(American Chemical Society, 2021-04-26) Khaligh, Aisan; Sheidaei, Yasaman; Tuncel, Dönüş
In the present study, we describe the synthesis and characterization of a new covalent organic framework (COF-TPP-CB[6]) which was assembled together by clicking perpropargyloxy cucurbit[6]uril (CB[6]) to the azido-functionalized tetraphenylporphyrin (TPP-4N3) through a copper-catalyzed azide–alkyne cycloaddition reaction (CuAAC). Perpropargyloxy CB[6] was synthesized through the direct oxidation of CB[6] to afford perhydroxy CB[6] followed by subsequent O-propargylation using NaH. We also demonstrated that the resulting framework (COF-TPP-CB[6]) can be employed as an efficient and stable electrocatalyst for hydrogen evolution reaction (HER) in alkaline medium upon loading it with a nickel cocatalyst. The effect of TiO2 and different loadings of Ni on the HER performance of TPP-CB[6] was also studied. Herein, 12%Ni@TPP-CB[6] as the optimum catalyst showed an impressive H2 production rate of 18.7 mmol h–1 g–1 with a low onset potential of −250 mV.
Open Access
Cyanoiron polypyridyl sensitized photoanodes for water oxidation
(2020-01) Batool, Samar
Dye-sensitized photoelectrochemical cells (DSPECs), which convert solar energy to hydrogen fuel via water splitting process, has markedly excelled as a multidisciplinary ﬁeld in the recent years. In this context, transition metal complexes (TMCs) are employed as eﬃcient photosensitizers because of their unique photochemical and photophysical properties. Ruthenium complexes, have frequently been preferred as both photosensitizers and water oxidation catalysts in DSPECs. However, their toxicity and preciousness have been their main disadvantages. Much research has now devoted to search for highly desirable alternatives. Hexacoordinated Fe-complexes (Fe(II)L6), being earth abundant and chemically stable, have attracted many researchers in this respect. Unfortunately, metal-to-ligand charge transfer (3MLCT) states of Fe-complexes experience ultrafast deactivation process into metal centered (MC) states lying lower in energy with respect to MLCT states, becoming unfavorable for electron injection into TiO2. A fundamental approach is to destabilize these MC states by associating strong ﬁeld ligands with Fe-center. Given the strong sigma-donating ability of cyanide ligand, the sensitization performance of cyanoiron polypyridyl complexes has also been investigated in earlier studies revealing excited state lifetimes much lower than desired. Herein, my study aims to tackle this problem by assisting donor iron complex not only with electron-donating cyanide groups but also with cobalt ions that are coordinated to nitrogen atoms of cyanide ligands. For this purpose, a series of cyanoiron polypyridyl complexes with diﬀerent polypyridyl groups and diﬀerent number of cyanide groups were prepared. These complexes were characterized by multiple techniques including UV-Visible absorption spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and Energy dispersive X-ray analysis (EDX). The foundation of this thesis is mainly built on the development of dyesensitized water oxidation photoanodes. In this study, water oxidation catalytic cobalt sites were connected to iron chromophores through cyanide bridging group aﬀording Prussian blue layer. The eﬀect of cyanide ligands on the rate of charge transfer has also been investigated. Various material characterizations were done to inquire about the eﬀect of cyanide ligands and cobalt catalyst. Photoelectrochemical studies performed on four diﬀerent dye-sensitized photoanodes reveal that both the type of polypyridyl ligand and the number of cyanide groups play a critical role on the eﬃciency of the iron photosensitizer. The results of this study suggest that Prussian blue analogues incorporating cyanoiron polypyridyl complexes could be promising assemblies for building eﬃcient DSPECs.
Open Access
Design, synthesis and application of electrospun heterostructured nanofibers for electrocatalytic hydrogen evolution reactions from water splitting
(2021-11) Yılmaz, Elif Begüm
Environmental problems and climate changes have increased the importance of studies on the development of sustainable and clean energy methods that can be an alternative to energy production technologies using fossil fuels in recent years. Green hydrogen is environmentally friendly and a high-capacity energy carrier, as it does not cause any toxic by-products during its production. For this reason, attempts are being made to increase the efficiency of green hydrogen produced from water splitting. Development of the catalytic activities and stability of electrocatalysts has gained great importance in order to increase the performance of the hydrogen evolution reaction (HER). This study examines the effect of Ni/NiO-reduced graphene oxide catalysts fabricated in the form of heterostructured fibers by electrospinning on their intrinsic and extrinsic activities and their performance for HER. In order to examine the stability, activity and kinetics of the synthesized electrocatalyst, studies such as linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), were carried out and Tafel curves were interpreted. It has been observed that the optimal electrocatalyst exhibits outstanding electrocatalytic performance with an over potential of -212 mV at 10 mA cm-2, and a Tafel slope of 90.6 mV dec-1 in alkaline electrolyte. Morphological and structural characterizations of electrocatalysts were investigated using X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) methods.
Open Access
In situ-Electrochemically reduced graphene oxide integrated with cross-linked supramolecular polymeric network for electrocatalytic hydrogen evaluation reaction
(Elsevier, 2021-08-26) Aoudi, Bouthaina; Khaligh, Aisan; Sheidaei, Yasaman; Tuncel, Dönüş
Herein, we report the synthesis of a new supramolecular polymeric network (PCN) assembled through crosslinking of propyl bromide substituted tetraphenyl porphyrin with perhydroxy-cucurbit [8]uril and its use in the electrocatalytic hydrogen evaluation reaction after loading with nickel and integrating with in situ-electrochemically reduced graphene oxide (ERGO). Electrode was prepared by first coating graphene oxide on the FTO substrate followed by layering the nickel loaded PCN and finally by applying an appropriate voltage to reduce the graphene oxide in situ electrochemical reaction. The loading of nickel cocatalyst into PCN together with the integration of ERGO layer substantially improved its HER efficiency. Effect of various concentrations of Ni and GO on the HER activity of the developed electrocatalyst were investigated. Therein, ERGO1/Ni2@PCN catalyst containing 41% Ni and 50% GO (with respect to PCN) with only one layer of each component demonstrated excellent HER activity and stability with low onset and overpotentials of −20 mV, η@10 mA cm−2 of −360 mV, respectively, and remarkable hydrogen generation rate of 27.5 mmol h−1 g−1 in 1 M KOH. This noble-metal-free catalytic system is simple yet highly promising for the efficient hydrogen evolution reaction from water splitting.
Open Access
Large scale compatible fabrication of gold capped titanium dioxide nanoantennas using a shadowing effect for photoelectrochemical water splitting
(Elsevier, 2020) T. Gamze, Ulusoy-Ghobadi; Ghobadi, Amir; Karadaş, Ferdi; Özbay, Ekmel
In this paper, a visible light driven plasmonic based photoelectrochemical water splitting (PEC-WS) cell is designed with an elegant two-step fabrication route. First, titanium dioxide (TiO2) nanowires (NWs) were synthesized using the hydrothermal method. Then, angled deposition was used to selectively coat the tips of the NWs yielding Au-capped TiO2 NWs with multiple sizes and shapes. The provided randomness leads to a multi-resonant system where the superposition of these resonance modes leads to an overall broadband absorption. The excited localized surface resonance (LSPR) modes contribute to the performance enhancement of the cell via near field effects and a hot electron injection mechanism. Moreover, these nanotips can trigger the formation of Fabry-Pérot (FP) cavity modes. The combination of the above-mentioned mechanisms leads to a high performance visible light driven plasmonic cell. At an applied potential of 1.23 V vs RHE, a photocurrent value as high as 82 μA/cm2 is acquired for the plasmonic based photoanode. The proposed design strategy is a large scale compatible route with no material restriction. Therefore, vast variety of semiconductor-metal pairs can be fabricated to obtain highly efficient water splitting cell for hydrogen generation.
Open Access
Metal dicyanamides as efficient and robust water-oxidation catalysts
(Wiley Blackwell, 2017) Nune, S. V. K.; Basaran, A. T.; Ülker, E.; Mishra, R.; Karadas, F.
Non-oxide cobalt-based water-oxidation electrocatalysts have received attention recently for their relative ease of preparation, they are stable both in acidic and basic media, and they have higher turnover frequencies than cobalt oxides. Recent studies show that one of the main bottlenecks in the implementation of non-oxide systems to water splitting is the low number of active metal sites, which is in the order of nmol cm−2. Herein, a new series of non-oxide water-oxidation catalysts has been introduced to the field. Cobalt dicyanamides are observed to have around four times higher surface active sites and better catalytic performances than cyanide-based systems. Long-term catalytic studies (70 h) at an applied potential of 1.2 V and electrochemical studies performed in solutions in pH values of 3.0–12.0 indicate that the compounds are robust and retain their structures even under harsh conditions. Moreover, the addition of Ni impurities to cobalt dicyanamides is a feasible method to improve their catalytic activities.
Open Access
Morphology-tailored synthesis of tungsten trioxide (Hydrate) thin films and their photocatalytic properties
(ACS Publications, 2011-01-10) Jiao, Z. H.; Wang, J. M.; Ke, L.; Sun, X. W.; Demir, Hilmi Volkan
Tungsten trioxide hydrate (3WO(3)center dot H(2)O) films with different morphologies were directly grown on fluorine doped tin oxide (FTO) subsi:rate via a facile crystal-seed-assisted hydrothermal method. Scanning electron microscopy (SEM) analysis showed that 3WO(3)center dot H(2)O thin films composed of platelike, wedgelike, and sheetlike nanostructures could be selectively synthesized by adding Na(2)SO(4), (NH(4))(2)SO(4), and CH(3)COONH(4) as capping agents, respectively. X-ray diffraction (XRD) studies indicated that these films were of orthorhombic structure. The as-prepared thin films after dehydration showed obvious photcicatalytic activities. The best film grown using CH(3)COONH(4) as a capping agent generated anodic photocurrents of 1.16 mA/cm(2) fork oxidization of methanol and 0.5 mA/cm(2) for water splitting with the highest photoconversion efficiency of about 0.3% under simulated solar illumination.
Open Access
Nanoscience for sustainable energy production
(2011) Ataca, Can
Hydrogen economy towards the utilization of hydrogen as a clean and sustainable energy source has three ingredients. These are (i) hydrogen production; (ii) hydrogen storage; and (iii) fuel cells. Optimization of fuel cells for desired applications is a challenging engineering problem. The subject matter of my thesis is to develop nanostructures and to reveal physical and chemical mechanisms for the production of free hydrogen and its high capacity storage. The predictions of this study are obtained from rst-principles density functional theory and nite temperature molecular dynamics calculations, phonon calculations and transition state analyses. Recent studies have revealed that single layer transition metal oxides and dichalcogenides (MX2; M:Transition metal, X:Chalcogen atom) may o er properties, which can be superior to those of graphene. Synthesis of single layer free standing MoS2 and its nanoribbons, fabrication of transistor using this nanostructure, active edges of akes of MoS2 taking a part in hydrogen evolution reaction (HER) boost the interest in these materials. The electronic, magnetic, mechanical, elastic and vibrational properties of three-, two- and quasi one-dimensional MoS2 are investigated. Dimensionality e ects such as indirect to direct band gap transition, shift of phonon modes upon three- to two- dimensional transition, half metallic nanoribbons are revealed. Functionalization of single layer MoS2 and its nanoribbons are achieved by creating vacancy defects and adatom adsorption. Moreover, out of 88 di erent combinations of MX2 compounds (transition metal dichalcogenides) it is also predicted that more than 50 single layer, free standing MX2 can be stable in honeycomb like structures and o er novel physical and chemical properties relevant for hydrogen economy. It is predicted that H2O can be split spontaneously into its constituents O and H at speci c vacancy defects of single layer MoS2 honeycomb structure. Interacting with the photons of visible light, H atoms adsorbed to two folded S atoms surrounding the vacancy start to migrate and eventually form free H2 molecules, which in turn, are released from the surface. Not only taking a part in HER, but also it is shown that MoS2 as a catalyst can release H2 molecule from water. Also other possible candidates among the manifold of stable MX2 compounds, which are capable of presenting similar catalytic activities are deduced. In an e ort to obtain a high capacity hydrogen storage medium, the functionalization of graphene with adatoms is investigated. It is found that Li-graphene complex can serve as a high capacity hydrogen storage medium. A gravimetric storage capacity of 12.8 wt % is attained, whereby each Li atom donates the significant part of its charge to graphene and eventually attracts up to four H2 through a weak interaction. Similarly Ca adatoms can hold H2 molecule on graphene up to 8.4 wt % through an interesting mechanism involving charge exchange among Ca, graphene and H2.
Open Access
A Noble-Metal-Free Heterogeneous Photosensitizer-Relay Catalyst Triad That Catalyzes Water Oxidation under Visible Light
(Wiley-VCH Verlag, 2018) Ulusoy-Ghobadi, Türkan Gamze; Yıldız, E. A.; Büyüktemiz, M.; Akbari, S. Sadigh; Topkaya, D.; İşçi, Ü.; Dede, Y.; Yağlioğlu, H. G.; Karadaş, Ferdi
An entirely earth-abundant chromophore-relay water oxidation catalyst triad system, which is robust and efficient at neutral pH, is presented. The synthesis involves the coordination of a porphyrin derivative to a bridging Fe(CN)5 group, which is then reacted with Co ions to prepare a covalently linked chromophore-Prussian blue analogue assembly. Light-driven water oxidation studies in the presence of an electron scavenger indicate that the triad is active and it maintains a steady activity for at least three hours. Transient absorption experiments and computational studies reveal that the Fe(CN)5 group is more than a linker as it takes part in electron-transfer and co-operates with porphyrin in the charge separation process.
Open Access
Photocatalytic water oxidation with a CoFe prussian blue analogue–layered niobate hybrid material
(American Chemical Society, 2021-11-22) Sadigh Akbari, Sina; Ünal, U.; Karadaş, Ferdi
A semiconductor–catalyst hybrid assembly for photocatalytic water oxidation was obtained by preparing CoFe Prussian blue particles on Dion–Jacobson type niobate nanosheets, which produces a p–n junction, as evidenced by the Mott–Schottky plot. The hybrid material with a precious-metal-free cocatalyst exhibits an enhanced photocatalytic activity (89.5 μmol g–1 h–1) in the presence of S2O82– as the electron scavenger. XPS, infrared, XRD, TEM, and SEM studies performed on both pristine and postcatalytic samples indicate that the hybrid assembly exhibits a proper band energy alignment for the photocatalytic water oxidation process and it is stable throughout a 12 h photocatalytic study.
Open Access
Porous organic polymers for electrochemical and energy storage application
(2022-08) Yau, Arma Musa
The intrinsic porosity and tunable morphology of Porous Organic Polymers (POPs), materials made from organic building blocks joined by strong covalent bonds, have become appealing in the context of electrochemical applications. In the first section of this thesis, a low-cost thiophene derivative and melamine were assembled into nitrogen and sulfur-enriched microporous organic polymer (MOP) using a pyrolysis-free one-pot Schiff-base type polycondensation reaction. The synthesized polymer is characterized by FT-IR, SEM, TEM, BET, XRD, XPS, TGA and UV-VIS. With 195.731 m2 g–1 surface area and 0.047 cm3 g–1 pore volume, the as-synthesized MOP has a cotton-like morphology and a micropore-dominated pore size distribution. After encapsulating it with a nickel co-catalyst, we showed that the obtained framework (MOP) could be used as an efficient catalyst for hydrogen evolution reaction (HER) in an alkaline electrolyte with the optimum composite (Ni2@MOP) exhibiting a remarkable onset overpotential of -66 mV. Furthermore, the optimum electrocatalyst showed good stability, delivering 90.84% faradaic efficiency (FE) after a 3.5 h chronoamperometry experiment. In the second section, the synthesized porous organic polymer and CB[6]-porphyrin covalent organic framework were investigated for potential use as electrode materials for supercapacitors.
Open Access
Precious metal‐free photocatalytic water oxidation by a layered double hydroxide‐Prussian blue analogue hybrid assembly
(Wiley-VCH Verlag, 2020-11) Akbari, Sina Sadigh; Karadaş, Ferdi
The development of earth‐abundant photocatalytic assemblies has been one of the bottlenecks for the advancement of scalable water splitting cells. In this study, a ZnCr layered double hydroxide and a CoFe Prussian blue analogue are combined to afford an earth‐abundant photocatalytic assembly involving a visible light‐absorbing semiconductor (SC) and a water oxidation catalyst (WOC). Compared to bare ZnCr‐LDH, the SC‐WOC hybrid assembly exhibits a threefold enhancement in photocatalytic activity, which is maintained for 6 h under photocatalytic conditions at pH 7. The band energy diagram was extracted from optical and electrochemical studies to elucidate the origin of the enhanced photocatalytic performance. This study marks a straightforward pathway to develop low‐cost and precious metal‐free assemblies for visible light‐driven water oxidation.
Open Access
A robust, precious‐metal‐free dye‐sensitized photoanode for water oxidation: A nanosecond‐long excited‐state lifetime through a Prussian blue analogue
(Wiley-VCH Verlag, 2020-02) Ulusoy-Ghobadi, T. Gamze; Ghobadi, Amir; Büyüktemiz, M.; Akhüseyin Yıldız, E.; Yıldız, D. B.; Yağlıoğlu, H. G.; Dede, Y.; Özbay, Ekmel
Herein, we establish a simple synthetic strategy affording a heterogeneous, precious metal‐free, dye‐sensitized photoelectrode for water oxidation, which incorporates a Prussian blue (PB) structure for the sensitization of TiO2 and water oxidation catalysis. Our approach involves the use of a Fe(CN)5 bridging group not only as a cyanide precursor for the formation of a PB‐type structure but also as an electron shuttle between an organic chromophore and the catalytic center. The resulting hetero‐functional PB‐modified TiO2 electrode demonstrates a low‐cost and easy‐to‐construct photoanode, which exhibits favorable electron transfers with a remarkable excited state lifetime on the order of nanoseconds and an extended light absorption capacity of up to 500 nm. Our approach paves the way for a new family of precious metal‐free robust dye‐sensitized photoelectrodes for water oxidation, in which a variety of common organic chromophores can be employed in conjunction with CoFe PB structures.
Open Access
Semiconductor thin film based metasurfaces and metamaterials for photovoltaic and photoelectrochemical water splitting applications
(WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Ghobadi, Amir; Ghobadi, Türkan Gamze Ulusoy; Karadaş, Ferdi; Özbay, Ekmel
In both photovoltaic (PV) and photoelectrochemical water splitting (PEC‐WS) solar conversion devices, the ultimate aim is to design highly efficient, low cost, and large‐scale compatible cells. To achieve this goal, the main step is the efficient coupling of light into active layer. This can be obtained in bulky semiconductor‐based designs where the active layer thickness is larger than light penetration depth. However, most low‐bandgap semiconductors have a carrier diffusion length much smaller than the light penetration depth. Thus, photogenerated electron–hole pairs will recombine within the semiconductor bulk. Therefore, an efficient design should fully harvest light in dimensions in the order of the carriers' diffusion length to maximize their collection probability. For this aim, in recent years, many studies based on metasurfaces and metamaterials were conducted to obtain broadband and near‐unity light absorption in subwavelength ultrathin semiconductor thicknesses. This review summarizes these strategies in five main categories: light trapping based on i) strong interference in planar multilayer cavities, ii) metal nanounits, iii) dielectric units, iv) designed semiconductor units, and v) trapping scaffolds. The review highlights recent studies in which an ultrathin active layer has been coupled to the above‐mentioned trapping schemes to maximize the cell optical performance.
Open Access
Triazine/thiophene-based microporous organic polymer for electrocatalytic hydrogen evolution reaction
(John Wiley and Sons, Ltd, 2022-12-07) Yau, Arma Musa; Khaligh, Aisan; Tuncel, Dönüş
In this study, sulfur-enriched microporous organic polymer (MOP) was prepared using one-pot Shiff-base type polycondensation reaction of thiophendicarboxaldehyde with melamine. With 195.731 m2 g−1 surface area and 0.047 cm3 g−1 pore volume, the as-synthesized MOP has a cotton-like morphology and a micropore-dominated pore size distribution. After loading MOP with nickel as a co-catalyst, we demonstrated that the obtained framework could be used as an efficient and robust electrocatalyst for hydrogen evolution reaction (HER) in an alkaline medium with the optimum composite (Ni2@MOP) exhibiting a low onset potential of −66 mV. Furthermore, the optimum electrocatalyst showed good stability, delivering 91% faradaic efficiency (FE) after a 3.5 h chronoamperometry experiment.