Calomel Electrode Research Articles

Pt Concave Nanocubes with High-Index Facets as Electrocatalysts for Glucose Oxidation

The modification of the surface atomic arrangements, especially the exposure of high-index facets, has been considered as a valid strategy to strengthen the catalytic performance of Pt-based nanocrystals. In this article, Pt concave nanocubes (Pt CNCs) with exposed high-index (510) facets are facilely synthesized through a hydrothermal method. Polyvinylpyrrolidone (PVP) and glycine are required for shape control. The mechanism of electrocatalytic oxidation toward glucose by Pt CNCs is fully discussed. The exposed high-index facets consist of abundant low-coordinated atoms (containing edges, steps, and kinks), can supply sufficient active sites for the adsorption of reactants and intermediate species, and thus enhance the catalytic activity in glucose oxidation. By using saturated calomel electrode as the reference electrode, a 1 cm2 platinum sheet as the counter electrode, and glassy carbon electrode (GCE) as the working electrode, the Pt CNC catalyst-decorated GCE exhibits higher peak current densities of 0.25, 0.15, and 0.56 mA cm–2 than those of the commercial Pt/C (10 wt. %)-modified GCE. The Pt CNC catalyst shows a rapid response toward the changes in glucose concentration. The electrocatalytic oxidation of glucose exhibits better performance in neutral and alkaline conditions than in an acidic electrolyte. Above all, the prepared Pt CNC catalysts with high-index (510) facets are expected for their wide use as abiotic catalysts in the electrocatalytic oxidation of glucose.

Moderately Oxidizing Thioxanthylium Organophotoredox Catalysts for Radical-Cation Diels-Alder Reactions.

Moderately oxidizing thioxanthylium photoredox catalysts that operate under irradiation with green light have been developed. These catalysts exhibit relatively moderate excited-state reduction potentials [E1/2(C*/C•-) = 1.75-1.94 V vs saturated calomel electrode (SCE)] and can efficiently promote radical-cation Diels-Alder reactions under irradiation with green light. Interestingly, β-halogenostyrenes (Ep/2 = 1.57-1.61 V vs SCE) are well tolerated, affording synthetically useful halocyclohexenes.

Novel electrochemical sensor modified with molecularly imprinted polymers for determination of enrofloxacin in marine environment.

Molecularly imprinted polymers were synthesized by gel-sol method with multi-walled carbon nanotubes as support and enrofloxacin as a template and further modified on the surface of glassy carbon electrode to construct a molecularly imprinted electrochemical sensor. The performance of the imprinted electrochemical sensor was thoroughly investigated by using cyclic voltammetry and differential pulse voltammetry. The influence of imprinted polymers amount, electrolyte pH, and incubation time on the sensor performance was investigated for the detection of enrofloxacin. Under the optimal experimental conditions in a three-electrode system with the modified electrode as the working electrode the differential pulse voltammetry response current of the sensor had a good linear relationship at 0.2V (vs. saturated calomel reference electrode) with the enrofloxacin concentration within 2.8pM-28μM and the limit of detection of the method was 0.9pM. The competitive interference experiment showed that theimprinted electrochemical sensor could selectively recognize enrofloxacin. The method was applied to analyze spiked natural seawater, fish, and shrimp samples. The recovery was 96.4%-102%, and RSD was less than 4.3% (n = 3), indicating that the proposed imprinted electrochemical sensor was suitable for the determination of trace enrofloxacin in marine environment samples.

Catalytic cleavage and functionalization of bulky and inert Csp3–Csp3 bonds via a relayed proton-coupled electron transfer strategy

Catalytic cleavage and functionalization of unstrained carbon–carbon bonds represent a formidable challenge for synthetic chemistry. Despite tremendous advances in transition-metal catalysis and photoredox radical chemistry, methods for the cleavage of sterically crowded inert C sp3 –C sp3 bonds remain underdeveloped. Here we describe the direct, photoredox cleavage of hindered C sp3 –C sp3 bonds of alcohols under neutral conditions. A relayed proton-coupled electron transfer (PCET) strategy is employed that overcame the previous requirement of a Brønsted base. Heavily branched alcohols with a high oxidation potential ( E ox½ > +2 V versus saturated calomel electrode) are cleaved and functionalized with remarkable efficiency and versatility. A simple, non-substituted phenyl group can promote a relayed PCET process to deliver primary, secondary, and tertiary alkyl radicals under neutral conditions. • Proton-coupled electron transfer • C–C cleavage of alcohols • Alkyl radicals • Various radicalophiles Liao et al. report a Fukuzumi acridinium salt as a catalyst for the C–C bond cleavage of linear primary, secondary, and tertiary carbinols under neutral conditions. The resulting transient alkyl radical species can be intercepted using various radicalophiles, including electron-deficient alkenes, an electrophilic SCF 3 reagent, and a range of heteroaryls.

Cyanide-free electrolyte for Au/Co-Au nano-multilayer electrodeposition utilising 5,5-dimethylhydantoin as a complexing agent.

A novel cyanide-free electrolyte was used in electrodepositing Au/Co–Au nano-multilayers. Firstly, an optimised electrolyte for Au–Co alloy electrodeposition was obtained from orthogonal experiments. The effect of current density and potential values on the deposited composition was investigated. Results showed that low current density and over-potential value promoted Au deposition. A large current density and high over-potential value resulted in high cobalt concentration. The co-deposition of gold and cobalt in this study system was canonical. When the electrode potential was positive (−0.6 V, −0.7 V vs. saturated calomel electrode (SCE)), only gold was deposited; when the potential was negative (−0.8 V vs. SCE), gold and cobalt were co-deposited. Using an optimised cyanide-free electrolyte produced Au/94.07 at% Co–Au multi-layers with a gold layer of approximately 20 nm and a 94.07 at% Co–Au alloy layer of approximately 90 nm in the 5,5-dimethylhydantoin-containing, cyanide-free system.

Graphite-Polyurethane Composite Electrode Modified with Molecularly Imprinted Polymer for Determination of Diclofenac

A molecularly imprinted polymer (MIP) was prepared using the anti-inflammatory diclofenac (DCF) as a template. A non-imprinted polymer (NIP) was also prepared as a control. These MIP and NIP were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET), revealing a higher porosity in the first. Then both were used in the modification of graphite-polyurethane composites electrodes (GPUE). Differential pulse anodic stripping voltammetry was used for DCF determination at GPUE-MIP-DCF containing 2.5% (m/m) of the modifier in perchloric acid, pH = 2.0, after previously optimized conditions such as 300 s of accumulation time, +0.2 V accumulation potential (vs. SCE (saturated calomel electrode)), 50 mV pulse amplitude and 10 mV s–1 scan rate. A linear dynamic range from 0.010 to 0.20 μmol L–1 and a limit of detection (LOD) of 0.99 nmol L–1 were found, using GPUE-2.5-MIP-DCF. DCF was determined in commercial pharmaceutical formulations and in synthetic urine samples, with recoveries between 101 and 102% (n = 3) and 101% (n = 3), respectively. The results agreed with the reference high-performance liquid chromatography (HPLC) within 95% confidence level, according to Student’s t-test. Interference from meclofenamic and mefenamic acids, which are structurally similar to DCF, was also evaluated. Interferences could not be totally avoided, but MIPs presented a considerable ability in discriminating the voltammetric response for DFC, despite the close structural similarity with the interferents.

Nucleation and growth mechanism of cuprous oxide electrodeposited on ITO substrate

The electrodeposition mechanisms of cuprous oxide (Cu2O) from copper nitrate solutions on indium tin oxide (ITO) were investigated using the cyclic voltammetry and the chronoamperometry methods. Then the kinetics parameters, nucleation and growth mechanism were explored. The CV measurement showed that the electrodeposition of Cu2O takes place by cathodic reduction at potential −0.5 V versus saturated calomel electrode (SCE). Furthermore, the voltammograms at different scan rates revealed that the electrodeposition reaction of Cu2O is a quasi-reversible reaction controlled by the diffusion of copper ions. Moreover, the deposition mechanism of Cu2O on the ITO substrate determined by the Astley approach and confirmed by the Scharifker-Hills models follows an instantaneous three-dimensional (3D) nucleation controlled by diffusion with an average diffusion coefficient D of 0.549 10-6 cm2 s−1. The X-ray diffraction pattern of Cu2O film was indexed to cubic crystal structure. The scanning electron microscopy analysis indicated that the average size of the cuprous oxide particles is about 1.408 µm. The optical energy band gap (Eg) was calculated by Tauc’s plot for Cu2O is 2.16 eV. The theoretical analyses reveal that Cu2O has an energy band gap of 2.25 eV, which corresponds to experimental results.

Modified and simplified photogalvanic cells: Solar energy harvesting using bromo cresol green dye with different electrodes and cell dimensions

Fig. i-V characteristics (‘i’ vs ‘V’ curve) of the cells (cell no. 4–6) based on the electrolyte filled in non-coated simple glass tube during illumination for (a) Pt-Combination electrode pair (cell no. 4), (b) Pt-Cylindrical graphite electrode pair (cell no.5), and (c) Pt-Rectangular graphite electrode pair (cell no. 6); Power at power point (current vs power curve) of the cells based on the electrolyte filled in non-coated simple glass tube during illumination for (a′) Pt-Combination electrode pair based cell no.4 (power 804 µW at 2000 µA & 402 mV), (b’) Pt-Cylindrical graphite electrode pair based cell no.5 (power 1170 µW at 6000 µA & 195 mV), and (c′) Pt- Rectangular graphite electrode pair based cell no.6 (power 1080 µW at 4000 µA & 270 mV). • Various alternative electrode couples like, Pt and Combination electrode, Pt and cylindrical graphite electrode, and Pt and rectangular graphite electrode couples placed in the modified cell vessels have been exploited in present work. • Authors have used cell design as the simple glass tube instead of the conventional and complex H-shaped glass tube for cell fabrication. • The study has been done for H-shaped glass tubes, simple glass boiling tube, and simple glass beakers. • Authors have observed encouraging electrical output (power 1170 µW, current 8000 µA, and efficiency 9.02%) by simply simplifying the fabrication of the PG cell based on rectangular graphite electrode placed in simple non-blackened glass boiling tube. Photogalvanic cells fabricated of H-shaped glass tube having Platinum (Pt) and saturated calomel electrodes dipped in the electrolyte solution (photosensitizer-reductant-surfactant-alkali) are widely reported. The modification of the electrodes, shapes, and sizes of cells has evaded the attention of researchers in the field for further improvement in the cell performances. Therefore, the present study on the use of various alternative electrodes (combination electrode, cylindrical graphite, rectangular graphite) and alternative cell vessels (H-shaped tube, simple glass tube) has been done with aim of further increasing the electrical output of the photogalvanic cells. Various alternative electrode couples like Pt and Combination electrode, Pt and cylindrical graphite electrode, and Pt and rectangular graphite electrode couples placed in the modified cell vessels have been exploited in present work. The Bromo cresol green dye sensitizer-formaldehyde reductant photogalvanic cells using modified electrode couples dipped in the different types of the glass tube vessels (i.e., blackened H-shaped glass tube, non-blackened simple glass boiling tube) have been studied at an artificial sunlight illumination. For photogalvanic cell fabricated of the rectangular graphite electrode (0.6 cm × 2.3 cm) placed in a simple non-blackened glass boiling tube; the optimum cell performance in terms of the maximum power, short-circuit current, open-circuit potential, efficiency, and storage capacity is of the order of 1170 µW, 8000 µA, 1130 mV, 9.02 %, and 70 min, respectively. It is concluded that the use of readily available cheap graphite and cheap boiling tubes provides an opportunity for simplified fabrication of the photogalvanic cells at reduced cost with the advantage of greatly enhanced electrical output for future studies.

Impact of thermal modification of carbon felt on the performance of oxygen reduction reaction and mineralisation of dye in on-line electro fenton system

ABSTRACT Carbon felt (CF) is frequently used as an electrode in various processes of oxygen reduction reactions (ORR) and water treatment. Therefore, it is critical to increasing the performance of this material in ORR. In this study, the effect of the thermal modification, which is a simple and low-cost process, was examined. For testing the hydrogen peroxide generation efficiencies and the mineralisation of Acid Orange 7 (AO7) dye, the modified CF electrodes (under 0–900°C and N2 atmosphere for 1 hour) were used as cathodes with Ti/RuO2-IrO2-TiO2 as anode and saturated calomel electrode (SCE) as a reference electrode. In addition, to find the optimum Electro-Fenton (EF) process parameters, the potential of the cathode (0.8–3.0 V), pH (3.0–9.0), Fe2+ concentration (0.2–1.0 mM) and electrolyte (sodium sulphate) concentration (10–500 mM) were investigated. The highest efficiencies in dye and TOC removal were achieved at 0.8 V, 50 mM of electrolyte concentration with 0.3 mM of Fe2+ by using CF modified at 900°C as 96.26% at 10 min and 91.83% at 120 min, respectively. Besides, the modification process was increased the electroactive surface area (41.70%) and crystallite size (22.69%) of the electrode. Thus, more effective treatment was achieved. Thanks to the modification, the electrical energy and electrochemical energy saving are approximately 23.87% and 70.22%, respectively. On the other hand, a kinetic study was conducted with a large number of data coming from the on-line analysis system, which is different from most systems in the literature. At the end of the kinetic study, it was revealed that EF systems could not be explained by a single kinetic equation. It was found that the EF system has two different rate equations (first order and pseudo first order) with high correlation coefficients (R2 = 0.9965 and 9920).

Highly Conductive and CO‐Resistant Cobalt‐Based Monolithic Electrodes for the Catalytic Oxidation of Methanol

AbstractTo develop active and stable electrocatalysts for the methanol oxidation reaction (MOR), many non‐noble metal‐based nanomaterials have been explored, which are physically loaded on conductive substrates to form electrodes. During a long‐term MOR under high current density, these electrodes usually lose activity due to the aggregation or falling off of active nanomaterials. To overcome these problems, we report a simple strategy to synthesize an active, stable, and carbon monoxide (CO)‐resistant monolithic electrode for the MOR: cobalt nanocrystal/nitrogen, oxygen‐doped carbon (Co@N,O−C, CP) monolith. CP monolith shows a high electrical conductivity (1.54×104 S/cm), which can be directly used as an electrode without any substrate. Co nanocrystals are dispersed uniformly in the N,O−C matrix as the active site for MOR, whereas the N,O−C matrix protects Co nanocrystals and also facilitates the mass and charge transfer between electrolyte and the electrode. The optimized CP−FT‐500 electrode presents a high MOR activity of 352 mA/cm2 at 0.6 V vs SCE (unsaturated calomel electrode) in alkaline electrolyte, which exceeds most previously reported Co‐based MOR catalysts. The optimal CP−FT‐500 catalyst also presents excellent durability and anti‐CO poisoning capability (93.3 % retention of activity), which exceeds that of Pt/C (67.5 % retention). Based on its excellent catalytic activity, stability, and high resistance to CO poisoning, CP−FT‐500 catalyst is a promising low‐cost catalyst for MOR.

Response of 2,4,6-trichlorophenol-reducing biocathode to burial depth in constructed wetland sediments

Biocathode systems could be used for in-situ bioremediation of chlorophenols (CPs) in constructed wetland (CW) sediments. However, little is known regarding whether or how cathode burial depths affect the dechlorination of CPs in sediments. Here, 2,4,6-trichlorophenol (2,4,6-TCP)-dechlorinating biocathode systems were constructed under a cathode potential of − 0.7 V (vs. a saturated calomel electrode, SCE) at three different cathode burial depths (5, 10, and 15 cm). The 2,4,6-TCP removal efficiency and average transformation rate with the biocathode increased by 21.46–36.86% and 14.63–34.88% compared to those in the non-electrode groups. Deeper cathode burial depths enhanced the 2,4,6-TCP dechlorination performance. Furthermore, the oxidation-reduction potential (ORP) of the sediment decreased with sediment depth and the applied potential created a more favorable redox environment for the enrichment of functional bacteria. Deeper cathode burial depths also promoted the selective enrichment of electro-active and dechlorinating bacteria (e.g., Bacillus and Dehalobacter, respectively). The biocathode thus served as the carrier, electron source, and regulator of functional bacteria to accelerate the transformation of 2,4,6-TCP (2,4,6-TCP → 2,4-dichlorophenol → 4-chlorophenol → phenol) in sediments. These results offer insights into the effects of cathode burial depth on 2,4,6-TCP dechlorination in sediments from a redox environment and microbial community structure standpoint.

Co3O4 quantum dots-polyoxometalate nanocomposites as visible light photoelectrocatalysts for selective oxidation of benzyl alcohol

Highly efficient visible-light photoelectrocatalysts were developed for mild oxidation of benzyl alcohol and its derivatives to related aldehydes with air as a safe and environmental friendly oxidant. The photoelectrocatalysts were designed by electrostatic association of the amino acids and [PMo12O40]3- for achieving (amino acid)3PMA followed by covalent attachment to Co3O4-QDs. The prepared Co/(ABA)3PMA and Co/(gly)3PMA nanocomposites were immobilized on charcoal using an alternate electrophoretic approach. Interestingly, the formation of nanocomposite structures remarkably enhanced the photo-generated charge separation and photoelectrocatalytic performance. Comparison of the results of photoelectrocatalytic oxidation of benzyl alcohol with that of photocatalytic and catalytic ones revealed that no reaction occurred during the catalytic tests, while the photocatalytic performance was positively affected by the utilization of a small bias (0.9 V vs. saturated calomel electrode). The Co3O4-QDs increases the visible light absorption and H3PMo12O40 with appropriate energy levels increases the charge mobility in nanocomposites structures. A plausible mechanism for the photoelectrocatalytic oxidation was suggested and illustrated using the results of scavenger tests and energy level determination.

Nucleation/Growth and Optical Proprieties of Co-doped ZnO Electrodeposited on ITO Substrate

A Co-doped ZnO layer was prepared by electrodeposition method on indium doped tin oxide (ITO) substrate using a cathodic reduction from nitrate medium with different doping percentages of cobalt. The bath temperature was controlled at 70 °C. The films were cathodically electrodeposited in a bath containing 5 mM Zn(NO3)2. 6H2O, while the source of Co is Co(NO3)2.6H2O where 0.1M KNO3 was used as supporting electrolyte. The nucleation and growth mechanism of Co-doped ZnO nuclei have been studied by cyclic voltammetry and chronoamperometry. The cyclic voltammetry shows that the electrodeposition of ZnO and Co-doped ZnO at a negative potential around -1.0 V versus saturated calomel electrode (SCE) is a quasi-reversible reaction controlled by the diffusion process. Comparing current transients curves obtained by the chronoamperometric method with the theoretical curves of current density j versus t ½ allows us to say that the nucleation is 3D instantaneous, as shown in SEM analysis. The presence of Co does not modify the nucleation and growth mechanism. The XRD patterns show that the substitution of zinc by cobalt does not change the würtzite crystal structure, but the crystallite size decreases with the cobalt percentage. The transmittance spectra indicate that the Co-doped ZnO films are transparent in the visible range. The optical gap increases with the doping percentage of cobalt.

Liquid metal enabled continuous flow reactor: A proof-of-concept

Liquid metal enabled continuous flow reactor: A proof-of-concept

Radical versus Nonradical States of Azobis(benzothiazole) as a Function of Ancillary Ligands on Selective Ruthenium Platforms.

The paper deals with the electronic impact of ancillary ligands on the varying redox features of azobis(benzothiazole) (abbt) in the newly introduced mononuclear ruthenium complexes [Ru(pap)2(abbt)]n (1n) and [Ru(bpy)2(abbt)]n (2n), where pap = 2-phenylazopyridine and bpy = 2,2'-bipyridine. In this regard, the complexes [RuII(pap)2(abbt•-)]ClO4 ([1]ClO4), [RuII(pap)2(abbt0)](ClO4)2 ([1](ClO4)2), [RuII(bpy)2(abbt0)](ClO4)2 ([2](ClO4)2), and [RuII(bpy)2(abbt•-)]ClO4 ([2]ClO4) were structurally and spectroscopically characterized. Unambiguous assignments of the aforestated radical and nonradical forms of abbt in 1+/2+ and 12+/22+, respectively, were made primarily based on their redox-sensitive azo (N═N) bond distances as well as by their characteristic electron paramagnetic resonance (EPR)/NMR signatures. Although the radical form of abbt•- was isolated as an exclusive product in the case of strongly π-acidic pap-derived 1+, the corresponding moderately π-acidic bpy ancillary ligand primarily delivered an oxidized form of abbt0 in 22+, along with the radical form in 2+ as a minor (<10%) component. The oxidized abbt0-derived [1](ClO4)2 was, however, obtained via the chemical oxidation of [1]ClO4. Both 1+ and 22+ displayed multiple closed by reversible redox processes (one oxidation O1 and four successive reductions R1-R4) within the potential window of ±2.0 V versus saturated calomel electrode. The involvement of metal-, ligand-, or metal/ligand-based frontier molecular orbitals along the redox chain was assigned based on the combined experimental (structure, EPR, and spectroelectrochemisry) and theoretical [density functional theory (DFT): molecular orbitals, Mulliken spin densities/time-dependent DFT] investigations. It revealed primarily ligand (abbt/pap or bpy)-based redox activities, keeping the metal ion as a simple spectator. Moreover, frontier molecular orbital analysis corroborated the initial isolation of the radical and nonradical species for the pap-derived 1+ and bpy-derived 22+ as well as facile reduction of pap and abbt in 1+ and 2+, respectively.

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

Fabrication of Cu(II) oxide-hydroxide nanostructures onto graphene paper by laser and thermal processes for sensitive nano-electrochemical sensing of glucose

Glucose electrochemical sensors based on nanostructures of CuO/Cu(OH)2 onto graphene paper were prepared by thermal (solid) and nanosecond pulsed laser (molten phase) dewetting of a CuO layer 6 nm thin deposited by sputtering. Dewetted systems, obtained without the use of any binder, act as array of nanoelectrodes. Solid state and molten phase dewetting produce nanostructures of copper oxide-hydroxide with different average size, shape and surface composition. Molten phase dewetting originates particles with size below 100 nm, while solid state dewetting produces particles with average size of about 200 nm. Moreover, molten phase dewetting produce drop-shaped nanostructures, conversely nanostructures derived from solid state dewetting are multifaceted. X-ray photoelectron spectroscopy (XPS) characterization revealed that the surface of nanostructures is formed by a copper(II) species CuO and Cu(OH)2. Shape of anodic branch of the cyclic voltammograms of glucose in alkali solution evidenced a convergent diffusion mechanism. Analytical performances in amperometric mode are as good as or better than other sensors based on copper oxide. Amperometric detection of glucose was done at potential as low as 0.4 V versus saturated calomel electrode by both types of electrodes. Linear range from 50 μM to 10 mM, sensitivity ranging from 7 to 43 μA cm−2 mM−1 and detection limit of 7 μM was obtained. Good analytical performances were obtained by laser dewetted electrodes with a low copper content up to 1.2 by atoms percentage of the surface. Analytical performance of the proposed electrodes is compliant for the determination of glucose both in blood serum, saliva or tear.

Highly Active and Efficient Hybrid Sacrificial Anodes Based on High P Pig Iron, Zn and Mg

The work discusses the development of novel hybrid sacrificial anodes based on high phosphorus pig iron (HPPI), Zn and Mg with stoichiometry xP-y(Mg0.25Zn0.75) (x = 1.5, 3.5, 8.0 wt% of phosphorus (P) in the pig iron and y = 10, 20, 30 wt%). Mg results in highly active corrosion potentials (∼−1.0 V with respect to saturated calomel electrode) of the high P content sintered 8.0P-y(Mg0.25Zn0.75) as compared to the low P content sintered (1.5 P and 3.5 P)-y(Mg0.25Zn0.75) in 3.5%NaCl solution and artificial seawater. The formation of active MgZn2 after sintering and preferential dissolution of Mg in the 8P-y(Mg0.25Zn0.75) attribute to greater active behavior. The anodes show high anode capacity (∼773 to 815 Ah Kg−1) and efficiency (∼80 to 85%).

Analysis of Decay of Photocatalytic Effect of Titanium Dioxide Electrode

Titanium Dioxide (TiO2) has been studied for its important photocatalytic semiconductor characteristics. Among many applicable areas of TiO2 photocatalysts, we have been studying to use as an anode electrode of the marine wet solar cells or marine microbial fuel cell. These studies include the analysis of TiO2 electrode prepared by the screen-printing method, and also the dye sensitizing effect on TiO2 electrode. In those studies, it was appeared that there is an open circuit potential that shifted to noble direction after TiO2 electrode was irradiated by the light source and measured its electrochemical properties. This phenomenon usually occurred after a few minutes the electrode showed its photocatalytic characteristics. It is unclear which caused the potential loss during the measurement. In this study, we have been trying to understand the mechanism affecting the potential degradation of the TiO2 electrode and the factors affecting that decay.The TiO2 electrodes were prepared by screen printing method. Type 329J4L stainless steel which exhibits duel phase properties was used as a base substrate for the electrode. Firstly, the surface of the substrate was polished and the substrate was cleaned with acetone using the ultrasonic cleaner for 10 minutes. Then, the substrate was passivated with 10% nitric acid (HNO3) solution at 60 ºC for 30 minutes. After that, the substrate was screen printed with TiO2 paste followed by heat treating for 60 minutes and the first layer of TiO2 was formed. For the second layer forming, the substrate was again screen printed with TiO2 paste and heat treated for 30 minutes. With these processes, double-layered heterojunction TiO2 electrode was prepared. The electrode was then coated with insulating epoxy resins and prepared ready for the electrochemical measurements and analysis.The electrochemical measurements of TiO2 electrodes were performed in an artificial seawater used as an electrolyte. The irradiation was carried out on the electrodes using a calibrated Xenon lamp with 150 W (wavelength ranging from 250 nm to 800 nm). The lamp was set to produce an output light intensity of 10.5 mW/cm2. The saturated calomel electrode (SCE) was used as the reference electrode. During the photopotential measurement, the potentials dropped to active direction as the electrodes were exposed to the light irradiation. But the potential values were ennobled rapidly after a few minutes the electrode was irradiated. Preliminary examinations showed that there is a relation between the rebounded potential values (open circuit potential loss) and the heat treatment temperatures of the electrodes. For example, the rebound rate of the electrode with second layer heat treatment temperature of 150 ºC was higher and longer compared to that of the electrode with 550 ºC one. Detailed mechanism was yet under investigation. Those investigation includes the photopotential measurement and the electrochemical impedance spectroscopy (EIS) analysis. The surfaces of the electrodes before and after the measurements of photopotential were compared and observed using the scanning electron microscope (SEM). The X-ray powder diffraction (XRD) analysis and differential thermal analysis (DTA) were also included for analysis of decay mechanism of photocatalytic on the TiO2 electrode. The results of those analyses and the mechanism affecting the open circuit potential decay in the TiO2 electrode will be presented to the upcoming ECS conference meeting.

Enhancement of Photocatalytic Effect By Hydroxyapatite Coating on Titanium Dioxide Electrode

Titanium dioxide (TiO₂) electrodes are used as anode electrodes in dye-sensitized solar cells, and when hydroxyapatite was coated on the TiO₂ layer to facilitate the dye-sensitizing such as ruthenium on TiO₂ electrodes, HAp itself was found to act as a photocatalyst to improve the electrode properties of TiO₂ electrodes. It was found that HAp itself acts as a photocatalyst to improve the electrode properties of TiO2 Therefore, before dye-sensitizing, the photocatalytic effect of HAp was tested to find the optimal coating method, and as a result, the electrode property of TiO₂ electrode was improved.Type 329J4L stainless steel was used as the base metal for the electrode; before coating the TiO₂ layer, the surface was cleaned and passivation treated with HNO3. The passivated substrate was coated with TiO₂ paste in two steps by screen printing method. The first layer was coated on the electrodes by screen printing method and heat treated at 150°C for 60 minutes. The second layer was coated by the screen-printing method like the first layer and then heat-treated at 550°C for 30 min. The HAP layer was coated in the same way. The HAp layer is prepared by processing the powdered HAp powder into a slurry, coating it on the TiO₂ layer by the screen-printing method, and then heat-treating it.The photopotential characteristics of the electrode are measured and compared with the electrochemical characteristics of the TiO₂ electrode coated with HAp. The photopotential was measured using a potentiostat. Artificial seawater was used as the electrolyte and a saturated calomel electrode (SCE) was used as the reference electrode. The light used in the experiment was a xenon lamp (150W, wavelength range 250~800nm), generating a light intensity of 10.5mW/cm². The potential was measured for 2 hours. The measurements were carried out in the dark for the first 3 minutes, followed by light illumination conditions.The photopotential of the TiO₂ electrode coated with HAp was more active than that of the TiO₂ electrode not coated with HAp. However, there is a problem that HAP is peeled off from the electrode surface during a photopotential measurement experiment using a xenon lamp and potentiometer for 2 hours. This issue was caused by the way the HAp paste was made. Initially, carboxymethyl cellulose (CMC) was used to make HAp paste due to its advantages of physical dispersibility and moderate viscosity. It was a good material that could take on viscosity and dispersibility, but it had durability problems. This was because CMC has a good affinity for water, so it contained the water in the electrolyte solution, causing the HAp layer to peel off from the TiO₂ layer. To make it clear this matter, we used nitric acid, acetylacetone, and Triton X-100, which are commonly used for making titanium dioxide slurries. Nitric acid and acetylacetone were used to improve the dispersibility of the HAP, while Triton X-100 was used as a surfactant.As a result, we could fabricate titanium dioxide and HAp layers as an electrode that were sufficient to withstand two hours of photopotential measurements.In the photopotential measurement, the prepared HAp-coated titanium dioxide electrode showed an apparent improvement in photopotential characteristics compared to the electrode with only titanium dioxide. In order to verify this effect, photopotential measurements were carried out on an electrode coated only with HAp. The relationship between the heat treatment temperature of HAp and the photocatalytic effect will be investigated in the later experiment.The current titanium dioxide electrodes do not adsorb dyes and can only utilize the photon energy of ultraviolet region. In the future, we aim to improve the electrode properties by adsorbing ruthenium dyes on the titanium dioxide and HAp layers to make the electrode capable of utilizing energy in the visible light region. In the meeting, it will be considered for use as an electrode in dye-sensitized solar cells.