• Journal of Electrochemical Science and Technology
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• v.13 no.3
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• pp.377-389
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• 2022

The current global energy supply depends heavily on fossil fuels. This makes technology such as direct water splitting from harvesting solar energy in photoelectrochemical (PEC) systems potentially attractive due to its a promising route for environmentally benign hydrogen production. In this study, undoped and nickel-doped molybdenum oxide photoanodes (called photoanodes S₁ and S₂ respectively) were synthesized through electrodeposition by applying -1.377 V vs Ag/AgCl (3 M KCl) for 3 hours on an FTO-coated glass substrate immersed in molibdatecitrate aqueous solutions at pH 9. Scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were used for microstructural and compositional characterizations of the photoanodes. In addition, the optical and photoelectrochemical characterizations of these photoanodes were performed by UV-Visible spectroscopy, and linear scanning voltammetry (LSV) respectively. The results showed that all the photoanodes produced exhibit conductivity and catalytic properties that make them attractive for water splitting application in a photoelectrochemical cell. In this context, the photoanode S₂ exhibited better photocatalytic activity than the photoanode S₁. In addition, photoanode S₂ had the lowest optical band-gap energy value (2.58 eV), which would allow better utilization of the solar spectrum.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.71-71
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• 2011

Dye-sensitized solar cells (DSCs) have drawn great academic attention due to their potential as low-cost renewable energy sources. DSCs contain a nanostructured TiO2 photoanode, which is a key-component for high conversion efficiency. Particularly, one-dimensional (1-D) nanostructured photoanodes can enhance the electron transport for the efficient collection to the conducting substrate in competition with the recombination processes. This is because photoelectron colletion is determined by trapping/detrapping events along the site of the electron traps (defects, surface states, grain boundaries, and self-trapping). Therefore, 1-D nanostructured photoanodes are advantageous for the fast electron transport due to their desirable features of greatly reduced intercrystalline contacts with specified directionality. In particular, anodic TiO2 nanotube (NT) electrodes recently have been intensively explored owing to their ideal structure for application in DSCs. Besides the enhanced electron transport properties resulted from the 1-D structure, highly ordered and vertically oriented nanostructure of anodic TiO2 NT can contribute additional merits, such as enhanced electrolyte diffusion, better interfacial contact with viscous electrolytes. First, to confirm the advantages of 1-D nanostructured material for the photoelectron collection, we compared the electron transport and charge recombination characteristics between nanoparticle (NP)- and nanorod (NR)-based photoanodes in DSCs by the stepped light-induced transient measurements of photocurrent and voltage (SLIM-PCV). We confirmed that the electron lifetime of the NR-based photoanode was much longer than that of the NP-based photoanode. In addition, highly ordered and vertically oriented TiO2 NT photoanodes were prepared by electrochemical anodization method. We compared the photovoltaic properties of DSCs utilizing TiO2 NT photoanodes prepared by one-step anodization and two-step anodization. And, to reduce the charge recombination rate, energy barrier layer (ZnO, Al2O3)-coated TiO2 NTs also applied in DSC. Furthermore, we applied the TiO2 NT photoanode in DSCs using a viscous electrolyte, i.e., cobalt bipyridyl redox electrolyte, and confirmed that the pore structure of NT array can enhance the performances of this viscous electrolyte.

• Rapid Communication in Photoscience
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• v.3 no.1
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• pp.20-24
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• 2014

N-doped anatase $TiO_2$ nanoparticles were prepared by the sol-gel process followed by a hydrothermal treatment and successfully used as the photoanodes in organic dye-sensitized solar cells (DSSCs). As expected, the power conversion efficiency (PCE) of 8.44% was obtained for the NKX2677/HC-A-sensitized DSSC based on the 30 mol% N-doped $TiO_2$ photoanode, which was an improvement of 23% relative to that of the DSSC based on the NKX2677/DCA.

• Journal of Electrochemical Science and Technology
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• v.13 no.4
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• pp.504-504
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• 2022

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.1
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• pp.113-120
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• 2022

Quantum dots (QDs) are attractive photosensitizer candidates for application not only in solar cells but also in solar hydrogen generation. For the prepartion of highly efficient QD-sensitized photoelectrodes, it is important to reduce electron recombination at the photoanode/electrolyte interface. Here, we study on the coating condition of ZnS passivation layers on the photoanodes in QD-sensitized solar cells (QDSCs). The ZnS passivation layers are coated by successive ionic layer adsorption and reaction method, and as the cation precursor, zinc acetate and zinc nitrate are empolyed. Due to the higher pH of cation precursor solution, the ZnS loading is improved when the zinc acetate is used, compared to the zinc nitrate. This improved loading of ZnS leads to the reduced electron recombination at the surface of photoanodes and the enhaced conversion efficiency of QDSCs from 6.07% to 7.45%.

• Journal of the Korean Ceramic Society
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• v.55 no.3
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• pp.244-260
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• 2018

Issues in the electrical characterization of semiconducting photoanodes in a photoelectrochemical (PEC) cell, such as the cell geometry dependence, scan rate dependence in DC measurements, and the frequency dependence in AC measurements, are addressed, using the example of a $TiO_2$ photoanode. Contrary to conventional constant phase element (CPE) modeling, the capacitive behavior associated with Mott-Schottky (MS) response was successfully modeled by a Havriliak-Negami (HN) capacitance function-which allowed the determination of frequency-independent Schottky capacitance parameters to be explained by a trapping mechanism. Additional polarization can be successfully described by the parallel connection of a Bisquert transmission line (TL) model for the diffusion-recombination process in the nanostructured $TiO_2$ electrode. Instead of shunt CPEs generally employed for the non-ideal TL feature, TL models with ideal shunt capacitors can describe the experimental data in the presence of an infinite-length Warburg element as internal interfacial impedance - a characteristic suggested to be a generic feature of many electrochemical cells. Fully parametrized impedance spectra finally allow in-depth physicochemical interpretations.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.100-100
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• 2011

Nanomaterial architecture with highly ordered, vertically oriented $TiO_2$ nanotube arrays shows a good promise for diverse technological applications. As inspired from the literature reports that Nickel modification can improve the photocatalytic activity of $TiO_2$, it was planned to coat Ni into the $TiO_2$ matrix. In this study, first $TiO_2$ nanotubes(TiNTs) were prepared by anodization (60V,3min) in HF-free aqueous electrolyte on ultrasonically cleaned polished titanium sheet substrates ($1{\times}7cm^2$). The typical thickness of the sintered TiNT ($500^{\circ}C$for10min) was ~1 micronas confirmed from the FESEM study. In the next part, as-anodized and sintered TiNT/Ti photoanodes were used to coat Ni by AC electrodeposition from aqueous 0.1M nickel sulphate solution. During AC electrodeposition, conditions such as 1V DC offset voltage, 9V amplitude (peak-to-peak) and 750 Hz frequency were fixed constant and the deposition time was varied as 0.5 min, 1 min, 2 min and 10 min. The photoelectrochemical performance of pristine and Ni modified TiNT/Ti photoanodes was measured in 1N NaOH electrolyte under 1 SUN illumination in the potential range of -1V and 1.2V versus Ag/AgCl reference electrode. The photocurrent performance of TiNT/Ti photoanode decreased upon Ni modification and the results were confirmed after repeated experiments. This suggests us that Ni modification inhibits the photoelectrochemical performance of $TiO_2$ nanotubes.

• Solar Energy
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• v.11 no.2
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• pp.70-76
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• 1991

Electrochemical reaction utilizing the semiconducting photoanodes can be applied to the photoelectrolysis of water to produce hydrogen. In this preliminary experiment, $TiO_2$ photoanodes were prepared by sintering anatase-$TiO_2$ powder at $1,250^{\circ}C$ and thermal oxidizing titanium plate at $850^{\circ}C$ in air and oxygen, respectively. Their surface structures were observed by XRD and optical microscope. I-E characteristics of thermally oxidized $TiO_2$ photoanode were also investigated under illuminated and dark conditions using 1 N and 0.1 N NaOH electrolyte solutions.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.75.2-75.2
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• 2013

Atomic layer deposition (ALD), utilizing self-limiting surface reactions, could offer promising perspectives for future efficient energy conversion devices. The capabilities of ALD for surface/interface modification and construction of novel architectures with sub-nanometer precision and exceptional conformality over high aspect ratio make it more valuable than any other deposition methods in nanoscale science and technology. In the context, a variety of researches on fabrication of active materials for energy conversion applications by ALD are emerging. Among those materials, one-dimensional nanotubular titanium dioxide, providing not only high specific surface area but also efficient carrier transport pathway, is a class of the most intensively explored materials for energy conversion systems, such as photovoltaic cells and photo/electrochemical devices. The monodisperse, stoichiometric, anatase, TiO2 nanotubes with smooth surface morphology and controlled wall thickness were fabricated via low-temperature template-directed ALD followed by subsequent annealing. The ALD-grown, anatase, TiO2 nanotubes in alumina template show unusual crystal growth behavior which allows to form remarkably large grains along axial direction over certain wall thickness. We also fabricated dye-sensitized solar cells (DSCs) introducing our anatase TiO2 nanotubes as photoanodes, and studied the effect of blocking layer, TiO2 thin films formed by ALD, on overall device efficiency. The photon convertsion efficiency ~7% were measured for our TiO2 nanotubebased DSCs with blocking layers, which is ~1% higher than ones without blocking layer. We also performed open circuit voltage decay measurement to estimate recombination rate in our cells, which is 3 times longer than conventional nanoparticulate photoanodes. The high efficiency of our ALD-grown, anatase, TiO2 nanotube-based DSCs may be attributed to both enhanced charge transport property of our TiO2 nanotubes photoanode and the suppression of recombination at the interface between transparent conducting electrode and iodine electrolytes by blocking layer.

• Journal of Electrochemical Science and Technology
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• v.13 no.4
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• pp.453-461
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• 2022

A chemically sintered and binder-free paste of TiO₂ nanoparticles (NPs) was prepared using a binary-liquid mixture of 1-octanol and CCl₄. The 1:1 (v/v) complex of CCl₄ and 1-octanol easily interacted chemically with the TiO₂ NPs and induced the formation of a highly viscous paste. The as-prepared binary-liquid paste (P_BL)-based TiO₂ film exhibited the complete removal of the binary-liquid and residuals with the subsequent low-temperature sintering (~150℃) and UV-O₃ treatment. This facilitated the fabrication of TiO₂ photoanodes for flexible dye-sensitized solar cells (f-DSSCs). For comparison purposes, pure 1-octanol-based TiO₂ paste (P_O) with moderate viscosity was prepared. The P_BL-based TiO₂ film exhibited strong adhesion and high mechanical stability with the conducting oxide coated glass and plastic substrates compared to the P_O-based film. The corresponding low-temperature sintered P_BL-based f-DSSC showed a power conversion efficiency (PCE) of 3.5%, while it was 2.0% for P_O-based f-DSSC. The P_BL-based low- and high-temperature (500℃) sintered glass-based rigid DSSCs exhibited the PCE of 6.0 and 6.3%, respectively, while this value was 7.1% for a 500℃ sintered rigid DSSC based on a commercial (or conventional) paste.