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Öğe 3D TiO2 modified with reduced graphene embed into polyvinyl alcohol: photoanode electrode for oxygen evolution reaction(2023) Tezcan, Fatih; Demir, DidemThe photocatalytic hydrogen production from water splitting using solar energy is one of the promising trend research topics within the scope of green energy production. A photoelectrochemical set up consists of photoelectrode materials that directly uses photon energy convers water to hydrogen and oxygen. The photoelectrodes are photoanode and photocathode materials n-type and p-type semiconductor, respectively. In this study, the 3D TiO2 photoanode surface was modified by coating it with reduced graphene (rG) added polyvinyl alcohol (PVA) gel. PVA synthetic polymer with thermal stability, mechanical stability and low cost was preferred to provide distribution of rG material on 3D TiO2 active surfaces. In this context, different amounts of rG (2.5, 5, 10 and 20%, based on polymer weight) impregnated with PVA gel coated on the 3D TiO2 semiconductor surface were investigated. The solar light absorption behaviour and molecular interactions of the different amounts of rG in PVA on 3D TiO2 semiconductor were monitored by UV-vis and Raman spectrometer. A photocatalytic performance of photoelectrodes were conducted by Electrochemical Impedance spectroscopy (EIS), linear sweep voltammetry (LSV) and chronoamperometric measurement under 100 mW cm-2 solar light. Raman spectrum showed dispersion of RG in PVA. EIS measurement showed that the polarization resistance (Rp) increased in 3D TiO2 with only PVA coating, while the addition of rG to PVA caused a decrease in Rp at the semiconductor/electrolyte interface under sunlight. Furthermore, LSV and chronoamperometric measurement concluded that the increased amount of rG added to PVA increased the photoresponse of 3D TiO2 up to the limit rG value.Öğe A new synthesis route of Bi2S3 with solvothermal deposition in photoelectrochemical hydrogen production(Elsevier, 2024) Tezcan, FatihBi2S3 semiconductor is widely preferred in photocatalytic applications due to its absorption in the visible region and near-infrared regions. In this paper, Bi2S3 is synthesized with a novel S2- source including thiosalicylic acid and 2-thiouracil compounds containing by only a one-step solvothermal method at different pHs (1, 2 and 3 called S_pH1, S_pH2 and S_pH3), apply KCl agent to enhanced surface homogeneity to the most catalytic deposition bath (S_K_pH1) and examine surface morphology, crystal structure, solar light absorption and photoelectrochemical hydrogen production performance. FESEM images show that Bi2S3 nanosphere structures are formed and that changing the pH of the deposition bath and the addition of a KCl surface agent changed the homogeneity of the size of the nanosphere structures. The photoelectrochemical performance test indicates that S_K_pH1 photoanode performs the highest catalytic photocurrent density of 2.28 mA cm-2 (vs. 1.23 V RHE) followed by S_pH1 (1.86 mA cm-2), S_pH2 (1.74 mA cm-2) and S_pH3 (1.40 mA cm-2) in LSV measurement. Mott-Schottky results show Bi2S3 electrodes as a n-type semiconductor and Vfb of S_K_pH1 is the most negative, enabling improved photocatalytic performance. EIS measurement shows that decreasing pH of the deposition bath and KCl addition provide reducing Rct (faradaic process) and Rp with applied 1.23 V (vs. NHE) under 100 mW cm- 2.Öğe Architecture design of TiO2 with Co-doped CdS quantum dots photoelectrode for water splitting(Tubitak Scientific & Technological Research Council Turkey, 2023) Tezcan, Fatih; Ahmad, Abrar; Kardas, GulfezaPhotoelectrochemical hydrogen production is a critical key to solving the carbon-zero goal of countries due to renewable sources of solar light and combustion products of hydrogen-only water. Here, an architecture design for an n-type nano rosettes-rod TiO2 (RT) surface using CdS and Co-doped CdS quantum dots (QDs) is carried out utilizing the SILAR (simple ionic layer adsorption and reaction) method. Furthermore, the photocatalytic behaviour of Co-doped CdS QDs SILAR cycles deposition is investigated in various cycles, including 5, 8, 10, and 12. The FESEM, Raman XRD, Uv-Vis spectrometer, and vibration modes are used to evaluate the photoelectrode surface structure, crystal structure, and solar light absorption, respectively. FESEM images and XRD pattern revealed successive CdS QDS and Co-doped CdS QDs deposition on the RT boundary and rising SILAR cycles of Co-doped CdS QDs lead to further coverage of RT surface. UV-vis spectrometer indicated shifting solar light absorption to the visible region by applying more SILAR cycles of Co-doped CdS QDs deposition. The electrochemical parameters obtained from EIS showed total polarization resistance (Rp) of the RT electrode dramatically decreased with 10 SILAR cycle Co-doped CdS QDs deposition (5093 1 cm2 and 617 1 cm2). Linear sweep voltammetry (LSV) and chronoamperometric photocatalytic performance measurements indicated Co-doped CdS QDs on RT extremely enhanced photoresponse under solar irradiation and 10 SILAR cycle Co-doped CdS QDs improved photocurrent density about fourfold according to blank RT electrode.Öğe Criss-crossed a-Fe2O3 nanorods/Bi2S3 heterojunction for enhanced photoelectrochemical water splitting(Elsevier Sci Ltd, 2022) Tezcan, Fatih; Ahmad, Abrar; Yerlikaya, Gurbet; Zia-ur-Rehman, Guelfeza; Paksoy, Halime; Kardas, GulfezaIn this research work, alpha-Fe2O3/Bi2S3 heterojunction photoelectrodes for improved photoelectrochemical water splitting have been successfully fabricated on FTO substrate by applying hydrothermal and solvothermal approaches. A seed layer approach is also applied before the solvothermal step for the homogeneous distribution of Bi2S3 over alpha-Fe2O3 nanorods to obtain a uniform heterojunction. The physicochemical and optical techniques results of alpha-Fe2O3/Bi2S3 indicate high crystallinity, presence of two distant phases with different bandgap positions. Linear sweep voltammetry (LSV) results indicate that the optimized alpha-Fe2O3/Bi2S3 photoanode performs a maximum photocurrent density of 2.550 mA cm(-2) at 1.23 V-RHE which is almost 20 times higher than pristine alpha-Fe2O3 (0.123 mA cm(-2) at 1.23 V (RHE)). Electrochemical Impedance Spectroscopy (EIS) entirely shows alpha-Fe2O3/ Bi2S3.6 h is the lowest R-p (180.9 omega cm(2)) compare to pristine Fe2O3 (5810 omega cm(2)), indicating enhanced photo catalytic performance on OER and S2-/S-2(2-) cycle followed under 100 mW cm(-2) solar irradiation. This significant upsurge in the photocurrent density and applied biased photon-to-current conversion efficiency shown by the heterojunction is attributed to the improved light-harvesting efficiency, enhanced conductivity, and effective charge separation at the alpha-Fe2O3/Bi2S3 interface.Öğe Fotoelektrokimyasal Yolla Hidrojen Gazı Üretiminde Kullanılan BiVO4/Cr2O3 Fotoelektrodunun RuO2 İle Katalitik Etkinliğinin Artırılması(2023) Tezcan, Fatih; Düdükcü, Meltem KahyaBu çalışmada, suyun ayrıştırılmasında fotokatalitik özelliğe sahip BiVO4/Cr2O3 n-p ikili fotoelektrodun üzerine oksijen oluşum reaksiyonunda (OER) katalitik özellik gösteren RuO2, dönüşümlü voltametri (DV) tekniği kullanılarak farklı döngülerde (2, 5, 7 ve 10) katkılanmıştır. Farklı döngülerde sentezlenen BiVO4/Cr2O3/RuO2 elektrotlarının karakterizasyonu taramalı elektron mikroskobu (SEM), X-ışını kırınımı (XRD) ve UV-vis spektrometresiyle gerçekleştirilmiştir. Suyun fotoelektrokimyasal ayrıştırılmasıyla hidrojen gazı üretiminde fotokatalitik performanslar doğrusal tarama voltametrisi (LSV), elektrokimyasal impedans spektroskopisi (EIS) ve kronoamperometrik ölçümlerle gerçekleştirilmiştir. EIS ölçümü, BiVO4/Cr2O3 (413,1 cm2) üzerine katkılanan RuO2 ile polarizasyon direncinin azaldığını ve BiVO4/Cr2O3/RuO2 elektrotları arasında en düşük polarizasyon direncinin 7 döngü sonunda elde edilen elektrotta ait olduğunu Rp (102,8 ohm cm2) göstermektedir. LSV ve kronoamperometrik ölçümleri, RuO2 sentezindeki DV döngüsünün artmasıyla fotoelektrodun OER katalitik aktivitesinin artığını ancak 10 döngüde BiVO4/Cr2O3 n-p ikili elektrodun katalitik performansın azaldığını göstermektedir.Öğe Hidrojen oluşum reaksiyonu için p-tipi Cr2O3 fotokatodun fotokatalitik performansının incelenmesi(2024) Fakı, Ender; Tezcan, Fatih; Kardaş, GülfezaAtmosfere salınan sera gazları, küresel çapta iklim değişikliğine neden olmaktadır bu nedenle ivedilikle yenilenebilir enerji kaynaklarının kullanıldığı enerji üretim sistemlerine geçilmesi gerekmektedir. Yenilenebilir enerji kaynaklarından bir tanesi olan güneş enerjisi ile hidrojen gazı üretimi, sürdürülebilir ve çevre dostu olması nedeniyle umut vericidir. Foto-elektrokimyasal hidrojen üretimi için n-tipi/p-tipi yarı iletkenleri kullanılmaktadır. Kullanılan bu yarı iletkenlerin daha verimli hale getirebilmek için fotokatalitik ve foto-dayanıklılık özelliklerinin geliştirilmesi gerekmektedir. Bir p-tipi yarı iletken olan Cr2O3, foto-dayanıklı ve görünür bölgede absorpsiyon gösterme gibi avantajlara sahiptir. Gerçekleştirdiğimiz bu çalışmada, p-tipi Cr2O3 yarı iletkeni, glikoz (G) ile KCl içeren ve içermeyen hidrotermal yöntemlerle flor katkılı kalay oksit (FTO) üzerine çöktürülmüştür. Fotoelektrokimyasal suyun ayrıştırılmasında fotokatot olarak hidrojen oluşum reaksiyonunda (HER) elektrotların fotokatalitik performansı incelenmiştir. Fotoelektrotların kristal yapısının karakterizasyonu X-ışını kırınımı (XRD), yüzey topografisi emisyon taramalı elektron mikroskobu (SEM) ile, güneş ışığı absorpsiyonu da Uv-vis spektrometresi ile gerçekleştirilmiştir. HER sürecindeki fotokatalitik performans doğrusal tarama voltametrisi (LSV) ile gerçekleştirilmiştir. Elektriksel çift tabakanın direnç ve kapasitans değerleri elektrokimyasal empedans spektroskopisi (EIS) ve foto-stabilite testleri kronoamperometrik ölçüm ile gerçekleştirilmiştir. FESEM görüntüleri, hidrotermal yöntemle G/KCl içeren çöktürme banyosunun glikoz içermeyenlere kıyasla yüzey homojenliğini geliştirdiğini ve daha küçük nano boyutlarda Cr2O3 sentezlendiğini göstermiştir. XRD deseni ölçümü tüm ortam ve koşullarda Cr2O3 elektrotlarının hekzagonal yapıda sentezlendiğini göstermiştir. LSV ölçümü, G/KCl elektrodunun p-tipi yarı iletken olarak daha yüksek fotokatalitik performans sergilediğini göstermektedir.Öğe Photocorrosion protection of BiVO4 electrode by α-Cr2O3 core-shell for photoelectrochemical hydrogen production(Elsevier Science Sa, 2022) Tezcan, Fatih; Dudukcu, Meltem Kahya; Kardas, GulfezaThe development of high-performance and robust photoelectrode with architecture design is a popular research area. In this study, BiVO4 photo corrosion protection carries out with alpha-Cr2O3 core-shell under solar light irradiation for photoelectrochemical hydrogen production. BiVO4 nanoparticles are coated with alpha-Cr2O3 core-shell by various hydrothermal deposition solutions at various pH values (4.0, 4.5, 5.0 and 5.5), indicating coverage processes of alpha-Cr2O3 on BiVO4 depend on the pH of deposition bath. A p-type alpha-Cr2O3 core-shell layer leads to the Vfb value of n-type BiVO4 shifting to a positive energy level, suggesting reducing BiVO4 ano-dic photocorrosion under solar light. BiVO4/Cr2O3 photo corrosion efficiency is investigated by Electrochemical Impedance Spectroscopy, Cr2O3 core-shell layer photocorrosion protection efficiency (cef %) of BiVO4/Cr2O3 pH 4.0, BiVO4/Cr2O3 pH 4.5 and BiVO4/Cr2O3 pH 5.0 electrodes are calculated as 34.7 %, 54.3 % and 49.2 %, respectively. The photoelectrochemical hydrogen production performance demonstrates that BiVO4 photo response enhanced in terms of surface passivation layers cause to improve the charge-separation and excited electron pathway semiconductor-electrolyte boundary.Öğe Solar light driven photoelectrochemical water splitting using Mn-doped CdS quantum dots sensitized hierarchical rosette-rod TiO2 photoanodes(Elsevier Science Sa, 2022) Ahmad, Abrar; Tezcan, Fatih; Yerlikaya, Gurbet; Zia-ur-Rehman; Paksoy, Halime; Kardas, GulfezaHerein we investigated the photoelectrochemical performance of manganese (Mn) doped cadmium sulfide (CdS) quantum dots (QDs) decorated onto the surface of hierarchical double-layered rosette-rod titanium dioxide (TiO2) photoanode. The rosette-rod TiO2 architectures are synthesized by two steps hydrothermal process while Mn-doped CdS QDs deposition is taken out by successive ionic layer adsorption and reaction (SILAR) approach. Two different kinds of structures exist simultaneously in rosette-rod TiO2, one-dimensional TiO2 nanorod arrays present at the bottom, while the upper three-dimensional nano rosette consists of small TiO2 nanorods as building units. Photoelectrochemical performance of the as-prepared photoanodes are explored in terms of photocurrent density and applied biased to photon conversion efficiency by varying Mn concentration and the number of SILAR cycles to find the best performing photoanodes. Linear sweep voltammetry results show that 35 mM shows the maximum photo-current density of 2.12 mA cm(-2) at 1.23 VRHE with a maximum photoconversion efficiency of similar to 1.61% at 0.4 VRHE, while 8 numbers of SILAR cycles shows the highest photo current-density of 2.73 mA cm(-2) at 1.23 VRHE and maximum photoconversion efficiency of 2.19% at 0.2 V-RHE.Öğe The investigation of CdS-quantum-dot-sensitized Ag-deposited TiO2 NRAs in photoelectrochemical hydrogen production(Royal Soc Chemistry, 2022) Tezcan, Fatih; Ahmad, Abrar; Yerlikaya, Gurbet; Zia-ur-Rehman; Paksoy, Halime; Kardas, GulfezaPhotoelectrochemical hydrogen production using photoelectrodes with sophisticated hierarchical architecture designs combined with effective photoactive materials, has been found to be an impressive route for achieving high photoelectrocatalytic efficiency. Here, we investigated the photoelectrocatalytic hydrogen production of CdS quantum dot (QD)-sensitized TiO2 nanorod arrays (NRAs) decorated with Ag nanoparticles synthesized using simple and cost-effective routes. TiO2 NRAs were grown on a fluorine-doped tin oxide (FTO) substrate via a hydrothermal method, followed by loading with Ag nanoparticles and deposition of CdS QDs using electrochemical and successive ionic layer adsorption and reaction (SILAR) approaches. In this arrangement, the Ag nanoparticles were found to be sandwiched between the photo-electron collector TiO2 and the photosensitizer CdS QDs that act as an electron relay, thus speeding the electron transport and improving photogenerated charge separation. CdS QDs significantly enhance the solar light absorption capability of the photoelectrode from the ultraviolet to the visible portion of the solar spectrum, improving the photoconversion efficiency. The surface morphology and optical properties of the as-prepared photoanodes were investigated using scanning electron microscopy and a UV-vis spectrometer. Scanning electron microscopy (SEM) images confirm that increasing the number of SILAR cycles caused agglomeration of the CdS QDs on the TiO2 NRAs surface. Photoelectrochemical hydrogen production performance was investigated with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) under simulated solar light of 100 mW cm(-2). The LSV results confirm that the bare TiO2 NRAs exhibit a maximum photocurrent density of 0.17 mA cm(-2) at 1.23 V-RHE. However, upon the deposition of CdS QDs, an optimum photocurrent density of 0.623 mA cm(-2) at 1.23 V-RHE was observed for the 10 SILAR cycle samples, which was further improved to 0.931 mA cm(-2) at 1.23 V-RHE upon the introduction of Ag nanoparticles.
