Jacek Ryl

Enhanced photoelectrochemical and photocatalytic performance of iodine-doped titania nanotube arrays

The paper discusses the synthesis and performance of iodine doped titania nanotube arrays exhibited under irradiation. The doping procedure was performed as an additional, electrochemical process carried out after formation of nanotube arrays via anodization of the Ti substrate. The optical and structural properties were characterized using Raman, UV-vis, photoluminescence and X-ray photoelectron spectroscopy. The surface morphology and cross-section studies performed by means of scanning electron microscopy show that the ordered tubular architecture is not influenced by the doping method. However, iodine doping causes a reduction of bandgap energy and photoluminescence intensity. The nanotubular TiO2 electrodes have been monitored by electrochemical (using cyclic voltammetry and electrochemical impedance spectroscopy) and in situ UV-vis spectroelectrochemical measurements in contact with an aqueous electrolyte. Collected results show significant differences in electrochemical activity between pure and doped titania exhibited as i.e. change of Mott–Schottky relation or shift in the onset potential when a decrease in reflectance is initiated. The photocurrent density reached 155.2 and 142.2 μA cm−2 for iodine doped materials when KI and HIO4 were used as iodine precursors whereas only 25.6 μA cm−2 was registered for pure titania nanotubes under UV-vis illumination. Moreover, doped samples are far more efficient for the photodegradation progress than undoped material leading to decomposition of over 70% of methylene blue used as a model organic pollutant. The reported studies demonstrate for the first time the detailed optical, electrochemical and photoelectrochemical studies of iodine doped nanotube arrays.

Highly stable organic–inorganic junction composed of hydrogenated titania nanotubes infiltrated by a conducting polymer

A poly(3,4-ethylenedioxythiophene) conducting polymer doped with poly(2-styrene sulfonate) (pEDOT:PSS) was efficiently electrodeposited on a layer composed of ordered titania nanotubes. TiO2 nanotubes were formed during an anodization process and, after calcinations, a layer was subjected to hydrogen plasma. Hydrogenation leads to Ti(III) formation, a decrease in resistance, and a huge increase of donor density when compared with pure titania. According to a detailed structure analysis, the coverage by the polymer matrix is uniform on the entire titania surface as well as along the tubes. The composite material exhibits highly enhanced anodic photocurrent (106 μA cm−2) when compared with hydrogenated titania H–TiO2 (54 μA cm−2) or pure polymer film (2 μA cm−2). Moreover, H–TiO2/pEDOT:PSS is characterized with high photostability displayed during prolonged illumination. The proposed hydrogenation approach could be regarded as a facile titania modification for further electrochemical modifications.

Impedance Monitoring of Carbon Steel Cavitation Erosion under the Influence of Corrosive Factors

The degradation of carbon mild steel under cavitation erosion-corrosion exposure was studied by means of a 20 kHz ultrasonic device with a piezoelectric inducer. Possibilities of estimation of material failure by current measurement techniques are presented and discussed. The effect of cavitation exposure of the mild steel has been investigated in situ with the dynamic electrochemical impedance spectroscopy technique. Estimation of the surface degradation rate is enabled by an adequate equivalent circuit selection. A dynamic impedance method was used to verify the impedance parameters online during the measurement. These measurements are assisted by estimation of the weight loss function commonly used for the evaluation of erosion-corrosion resistance of materials.

Local impedance imaging of boron-doped polycrystalline diamond thin films

Local impedance imaging (LII) was used to visualise surficial deviations of AC impedances in polycrystalline boron-doped diamond (BDD). The BDD thin film electrodes were deposited onto the highly doped silicon substrates via microwave plasma-enhanced CVD. The studied boron dopant concentrations, controlled by the [B]/[C] ratio in plasma, ranged from 1 × 1016 to 2 × 1021 atoms cm−3. The BDD films displayed microcrystalline structure, while the average size of crystallites decreased from 1 to 0.7 μm with increasing [B]/[C] ratios. The application of LII enabled a direct and high-resolution investigation of local distribution of impedance characteristics within the individual grains of BDD. Such an approach resulted in greater understanding of the microstructural control of properties at the grain level. We propose that the obtained surficial variation of impedance is correlated to the areas of high conductance which have been observed at the grain boundaries by using LII. We also postulate that the origin of high conductivity is due to either preferential boron accumulation, the presence of defects, or sp2 regions in the intragrain regions. The impedance modulus recorded by LII was in full agreement with the bulk impedance measurements. Both variables showed a decreasing trend with increasing [B]/[C] ratios, which is consistent with higher boron incorporation into BDD film.

Ellipsometric investigation of nitrogen doped diamond thin films grown in microwave CH4/H2/N2 plasma enhanced chemical vapor deposition

The influence of N2 concentration (1%–8%) in CH_4/H_2/N_2 plasma on structure and optical properties of nitrogen doped diamond (NDD) films was investigated. Thickness, roughness, and optical properties of the NDD films in the VIS–NIR range were investigated on the silicon substrates using spectroscopic ellipsometry. The samples exhibited relatively high refractive index (2.6 ± 0.25 at 550 nm) and extinction coefficient (0.05 ± 0.02 at 550 nm) with a transmittance of 60%. The optical investigation was supported by the molecular and atomic data delivered by Raman studies, bright field transmission electron microscopy imaging, and X-ray photoelectron spectroscopy diagnostics. Those results revealed that while the films grown in CH_4/H_2 plasma contained micron-sized diamond grains, the films grown using CH_4/H_2/(4%)N_2 plasma exhibited ultranano-sized diamond grains along with n-diamond and i-carbon clusters, which were surrounded by amorphous carbon grain boundaries.

Boron-Enhanced Growth of Micron-Scale Carbon-Based Nanowalls: A Route toward High Rates of Electrochemical Biosensing

In this study, we have demonstrated the fabrication of novel materials called boron-doped carbon nanowalls (B:CNWs), which are characterized by remarkable electrochemical properties such as high standard rate constant (k°), low peak-to-peak separation value (ΔE) for the oxidation and reduction processes of the [Fe(CN)6]3-/4- redox system, and low surface resistivity. The B:CNW samples were deposited by the microwave plasma-assisted chemical vapor deposition (CVD) using a gas mixture of H2/CH4/B2H6 and N2. Growth results in sharp-edged, flat, and long CNWs rich in sp2 as well as sp3 hybridized phases. The achieved high values of k° (1.1 × 10-2 cm s-1) and ΔE (85 mV) are much lower compared to those of the glassy carbon or undoped CNWs. The enhanced electrochemical performance of the B:CNW electrode facilitates the simultaneous detection of DNA purine bases: adenine and guanine. Both separated oxidation peaks for the independent determination of guanine and adenine were observed by means of cyclic voltammetry or differential pulse voltammetry. It is worth noting that the determined sensitivities and the current densities were about 1 order of magnitude higher than those registered by other electrodes.

Titania nanotubes infiltrated with the conducting polymer PEDOT modified by Prussian blue – a novel type of organic–inorganic heterojunction characterised with enhanced photoactivity

A highly ordered p–n heterojunction was formed based on titania nanotubes containing a conducting polymer with Prussian blue matrix. The study demonstrates, for the first time, cases when a composite based on titania array scaffolding and Prussian blue embedded in PEDOT exhibits reversible FeII/FeIII redox activity. Highly enhanced photoactivity and capacitance of the obtained material are depicted in comparison to pristine titania. To the best of our knowledge this is the first report showing a heterojunction with titania nanotubes containing redox active species that may take part in efficient photocurrent generation.

Instantaneous Impedance Monitoring of Aluminum Alloy 7075 Corrosion in Borate Buffer with Admixed Chloride Ions

This study presents research capabilities of dynamic electrochemical impedance spectroscopy (DEIS) as a tool used for instantaneous online monitoring of corrosion processes on the example of aluminum alloy 7075. A borate buffer with admixed chloride ions in a quantity ranging from 0.05 mM to 25 mM was used to represent different types of corrosion attack. The surfaces of sample specimens were evaluated before and after the tests by means of scanning electron microscopy. DEIS was assisted in-situ by cyclic polarization and acoustic emission facilitating detection of corrosion attack.

Aluminum Titania Nanoparticle Composites as Nonprecious Catalysts for Efficient Electrochemical Generation of H2

In this paper, we demonstrated, for the first time, aluminum titania nanoparticle (Al-TiO2 NP) composites with variable amounts of TiO2 NPs as nonprecious active catalysts for the electrochemical generation of H2. These materials were synthesized by mixing desired amounts of hydrogen titanate nanotubes (TNTs), fabricated here by a cost-effective approach at moderate hydrothermal conditions, with aluminum powder (purity 99.7%; size 35 μm). The mixture was compacted under an applied uniaxial stress of 300 MPa followed by sintering at 500 °C for 1 h. After sintering had been completed, all TNTs were found to convert to TiO2 NPs (average particle size 15 nm). Finally, Al-xTiO2 NP nanocomposites (x = 1, 3, 5, and 10) were obtained and characterized by scanning electron microscopy/energy-dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscopy. The hydrogen evolution reaction (HER) activity of these materials was studied in 0.5 M H2SO4 at 298 K using polarization and impedance measurements. The nanocomposite of chemical composition Al-5% TiO2 NPs showed the best catalytic performance for the HER, with an onset potential (EHER), a Tafel slope (βc), and an exchange current density (j0) of -100 mV (RHE), 59.8 mV decade(-1), and 0.14 mA cm(-2), respectively. This HER activity is not far from that of the commercial platinum/carbon catalyst (EHER = 0.0 mV, βc = 31 mV dec(-1), and j0 = 0.78 mA cm(-2)). The best catalyst also exhibited good stability after 10000 repetitive cycles with negligible loss in current.

Opto-Electrochemical Sensing Device Based on Long-Period Grating Coated with Boron-Doped Diamond Thin Film

The fabrication process of thin boron-doped nanocrystalline diamond (B-NCD) microelectrodes on fused silica single mode optical fiber cladding has been investigated. The B-NCD films were deposited on the fibers using Microwave Plasma Assisted Chemical Vapor Deposition (MW PA CVD) at glass substrate temperature of 475 ℃. We have obtained homogenous, continuous and polycrystalline surface morphology with high sp 3 content in B-NCD films and mean grain size in the range of 100-250 nm. The films deposited on the glass reference samples exhibit high refractive index (n=2.05 at λ=550 nm) and low extinction coefficient. Furthermore, cyclic voltammograms (CV) were recorded to determine the electrochemical window and reaction reversibility at the B-NCD fiber-based electrode. CV measurements in aqueous media consisting of 5 mM K 3 [Fe(CN) 6 ] in 0.5 M Na 2 SO 4 demonstrated a width of the electrochemical window up to 1.03 V and relatively fast kinetics expressed by a redox peak splitting below 500 mV. Moreover, thanks to high-n B-NCD overlay, the coated fibers can be also used for enhancing the sensitivity of long-period gratings (LPGs) induced in the fiber. The LPG is capable of measuring variations in refractive index of the surrounding liquid by tracing the shift in resonance appearing in the transmitted spectrum. Possible combined CV and LPG-based measurements are discussed in this work.