Cathodic electrodeposition of SnS thin films from aqueous solution

SnS thin films were prepared by cathodic electrodeposition on ITO/glass and Ti substrates from a solution containing SnCl₂ and thiosulphate ions. Cyclic voltammetry experiments were performed to elucidate the electrodic processes occurred when potentials were applied and to determine the optimum potential for electrodeposition. The photoactivity of the deposited films and their conduction types were evaluated using the photoelectrochemical technique. The bandgap energy and type of optical transitions were determined from optical absorbance data. Structural and compositional analysis were accomplished using X-ray diffractometry, electron dispersive analysis of X-ray, and X-ray photoelectron spectroscopy. The morphology of the films were examined using scanning electron microscopy.     

Cathodic electrodeposition of Cu2S thin film for solar energy conversion

Cathodic electrodeposition in the presence of EDTA in aqueous solution was used to prepare Cu₂S thin film deposited on Ti substrate. The effect of deposition potential, concentration and deposition time was studied to determine the optimum condition for electro-deposition process. Cyclic voltammetry was performed to elucidate the electrodic processes that occur while potentials for electrodeposition were applied to determine the optimum potential for electrodeposition. The thin films are characterised by X-ray diffractometry. The photoactivity of the deposited films and their conduction types were evaluated using photoelectrochemical technique. The band gap energy and type of optical transitions were determined from optical absorbance data.     

Cathodic deposition and characterization of tin oxide coatings on graphite for electrochemical supercapacitors

Amorphous tin oxide (SnO_x) was cathodically deposited onto graphite electrode in a bath containing 0.1 M stannous chloride (SnCl₂), 0.5 M sodium nitrate (NaNO₃), and 0.4 M nitric acid (HNO₃) in an aqueous solution of 50% (v/v) ethanol. The SnO_x coatings grown on graphite were characterized as typical capacitive behaviors by cyclic voltammetry (CV), chronopotentiometric (CP) in 0.5 M KCl. Specific capacitance (in milli-farad per square centimeter, C_a) changes linearly with the deposition charge up to 4.5 C cm⁻², and a maximum of as high as 355 mF cm⁻² was obtained with the SnO_x coating grown at around 5 C cm⁻². For the SnO_x coating deposited at 0.2 C cm⁻², a maximum specific capacitance (in farad per gram, C_m) of 298 and 125 F g⁻¹ was achieved from CVs at a scan rate of 10, and 200 mV s⁻¹, respectively. The value of C_m significantly gets lower from 265 to around 95 F g⁻¹ when the deposition charge increases from 0.2 to around 6.0 C cm⁻². The long cycle-life and stability of the SnO_x coatings on graphite via the presented cathodic deposition were also demonstrated.     

Calculation of band offsets at the CdS/SnS heterojunction

SnS is a promising material for heterojunction solar cells, but the energy band alignment is not known for SnS-based heterojunctions. In this study, the energy band offset at the CdS/SnS heterojunction is calculated using the first principle, density-functional, pseudopotential method. A procedure analogous to that used in the core-level photoemission spectroscopy is adopted to calculate the band offset. The 4d core-level difference between Cd and Sn was estimated from the energy calculation of a superstructure consisting of zincblende CdS and rock-salt or zincblende SnS. The calculated valence-band offset is 0.1 eV when the rock-salt SnS is assumed and 0.84 eV when the zincblende SnS is assumed.     

Effects of annealing on the properties of SnSe films

Tin selenide thin films were deposited potentiostatically from an unstirred aqueous solution containing Sn-EDTA and Na₂SeO₃ onto indium-doped tin oxide glass substrates. The difference in the structural and compositional properties of the film before and after heat treatment in a nitrogen atmosphere were studied. The as-grown and treated films were characterised using various techniques such as X-ray diffractometry, scanning electron microscopy and energy-dispersive X-ray analysis. Photoactivity of the samples was studied using linear sweep voltammetry. An annealing temperature of 150°C was found to be the optimum temperature.     

Effect of electrodeposition conditions on the electrochemical capacitive behavior of synthesized manganese oxide electrodes

Galvanostatic electrodeposition techniques were applied for the preparation of novel electroactive manganese oxide electrodes. The effects of supersaturation ratio on the morphology and crystal structure of electrodeposited manganese oxide were studied. Manganese oxide electrodes were synthesized by anodic deposition from acetate-containing aqueous solutions on Au coated Si substrates through the control of nucleation and growth processes. By changing deposition parameters, a series of nanocrystalline manganese oxide electrodes with various morphologies (continuous coatings, rod-like structures, aggregated rods and thin sheets) and an antifluorite-type crystal structure was obtained. Detailed chemical and microstructural characterization of as-deposited electrodes was conducted using SEM, TEM and AAS. Manganese oxide thin sheets show instantaneous nucleation and single crystalline growth, rods have a mix of instantaneous/progressive nucleation and polycrystalline growth and continuous coatings form by progressive nucleation and polycrystalline growth.In addition, the electrochemical behavior was investigated by cyclic voltammetry. The experimental results show that manganese oxide electrodes, with rod-like and thin sheet morphology, exhibited enhanced electrochemical performance. The highest specific capacitance (∼230 F g⁻¹) and capacitance retention rates (∼88%) were obtained for manganese oxide thin sheets after 250 cycles in 0.5 M Na₂SO₄ at 20 mV s⁻¹.     

Characterization of electrical properties and photosensitivity of SnS thin films prepared by the electrochemical deposition method

Using the electrochemical deposition (ECD) method, we prepared tin sulfide thin films, which are suitable for the absorption layer in solar cells because of its bandgap energy (1 eV). We first optimized pulse-form biasing for ECD by characterizing deposited samples with scanning electron microscope, Auger electron spectroscopy and X-ray diffraction measurements. Then, we investigated the electrical properties of deposited SnS thin films and the properties of contacts with several different metals. Furthermore, we observed the photoconductivity of the films by means of photoelectrochemical measurements. From these results, we confirmed that the SnS thin films show p-type conduction.     

Solar radiation-induced polymerization of methyl methacrylate in the presence of semiconductor-based photocatalyst

The photopolymerization of methyl methacrylate (MMA) was carried out using semiconductor (CdS) as a photocatalyst in the presence of solar radiation. The photopolymerization of MMA has been achieved (6–9% conversion) on exposure to solar radiation for a stipulated time period in the intensity range 450–800 W/m². A little higher conversion (11%) with higher molecular weight was achieved in the presence of CdS as a photocatalyst. In the presence of an electron donor like Et₃N along with the photocatalyst (CdS), the highest conversion of 26–45% with lower molecular weight was achieved. The polymers have been characterized by viscometry and gel permeation chromatography (GPC).     

Stability of the SnO2/MgO dye-sensitized photoelectrochemical solar cell

Dye-sensitized solar cells made of TiO₂ are extensively studied as a cheap alternative to conventional photovoltaic cells. The other familiar stable oxide material of similar band gap suitable for dye sensitization is SnO₂. Although cells based only of SnO₂ are prone to severe recombination losses, the cells made of SnO₂/MgO films where the SnO₂ crystallite is surface covered with an ultra-thin shell of MgO, deliver reasonably high efficiencies. It is found that SnO₂/MgO cells resist dye and electrolyte degradation better than TiO₂ cells. Furthermore, the ultra-thin barrier of MgO on SnO₂ remains intact during prolonged usage or storage of the cell.     

Pd electrodeposition on a novel substrate of reduced graphene oxide/ poly(melem-formaldehyde) nanocomposite as an active and stable catalyst for ethanol electrooxidation in alkaline media

Palladium nanoparticles (Pd NPs) were successfully electrodeposited on a reduced graphene oxide/poly(melem-formaldehyde) nanocomposite (rGO/PMF) NC as a catalyst for ethanol electrooxidation in alkaline media; melem was used as a nitrogen-rich source in the substrate structure for the first time. The specific surface area and average pore diameter of (rGO/PMF) NC were 481.61 m² gr^?1 and 10.23 nm, respectively. High nitrogen doping and structural defects improved the dispersion and anchoring of Pd NPs on (rGO/PMF) NC. The onset potential (E_onset) of Pd/(rGO/PMF) NC was shifted negatively to 110 mV, in comparison to Pd/rGO. Also, the current density and electrochemical active surface area (EASA) of Pd/(rGO/PMF) NC were enhanced to 44 mA cm^?2 and 67.58 m² gr^?1, respectively, as compared to Pd/rGO. Furthermore, the stability of Pd/(rGO/PMF)NC was indicated against ethanol oxidation intermediates during 7000 s. This work also produced a superior graphene-based material for direct ethanol fuel cell anode catalysts applications.     

Comparison of hydrothermal and electrodeposition methods for the synthesis of CoSe2/CeO2 nanocomposites as electrocatalysts toward oxygen evolution reaction

Promoting efficacious and low-cost catalysts for the oxygen evolution reaction (OER), as the sluggish half-reaction of the water splitting, is inevitable to make sustainable energy technologies more promising. In this work, we report a series of novel nanocomposites comprising CeO₂ nanorods decorated with CoSe₂ nanoparticles. The nanocomposites were prepared via a conventional hydrothermal synthesis or a rapid electrodeposition process, and their structure, morphology, and electrochemical performance toward OER in alkaline solution were compared. To tune the electrocatalytic activity, the mass ratio of CoSe₂ to CeO₂ was systematically varied. Compared with the hydrothermal synthesis, the much faster electrodeposition method yielded a nanocomposite with a similar or slightly better performance in OER. This nanocomposite exhibited an overpotential of 290 mV (at 10 mA cm^?2 current density), a Tafel slope of 53 mV dec^?1, and excellent electrochemical stability for 15 h. Overall, these findings demonstrate the great potential of CoSe₂/CeO₂ nanocomposites as effective OER electrocatalysts for future applications.     

EDTA impregnation assisted synthesis of nickel nanoparticles embedded in activated carbon and its application for dry reforming of methane

In this paper, the catalysts with nanoscale nickel particles embedded in activated carbon were synthesized by Ethylenediaminetetraacetic acid (EDTA) assisted impregnation method. The experimental results revealed that EDTA addition could promote Ni particle dispersion and decrease Ni particle size. Ni particle size was significantly decreased from 18.23 to 4.57 nm when Ni/EDTA ratio was increased from 1:0 to 1:3. Catalytic performance of Ni₁₅-AC-E₃ demonstrated that CH₄ and CO₂ conversion rate under 850 °C were 90.05% and 96.28%, which were decreased by 1.08% and 1.27% after 72 h dry reforming methane (DRM) reaction. Moreover, the characteristic of the used catalyst showed that Ni particle size was only increased from 4.57 to 5.94 nm after the stability test, and NiO was not appeared. Meanwhile, the deposited carbon in the used catalyst was 5.02%. The above results meant that the catalyst prepared by EDTA assisted impregnation method had the ability of suppressing carbon deposition, Ni particle sintering and oxidation during DRM reaction.     

Photoelectrochemical characterisation of indium nitride and tin nitride in aqueous solution

Indium nitride (InN) and tin nitride (SnN_x) films were produced with reactive d.c. magnetron sputtering technique. The thin film semiconductors were optically and photoelectrochemically characterised and the energetic positions of the two semiconductors’ band edges were determined with respect to the normal hydrogen electrode. The sputtered InN thin film showed an indirect bandgap of 1.4 eV and a direct bandgap of 1.8 eV. The optical spectra of SnN_x indicated a bandgap energy of approximately 1.4 eV. All nitride films showed n-type photoresponse in KI (aq) electrolyte at an irradiation intensity of 1000 W/m². The photoelectrochemical characterisation indicated that InN and SnN_x with a bias of about 400 mV or less can be used for photo-oxidation of water.     

Preparation of carbon nanotube and graphene doped polyphenylene sulfide flexible film electrodes and the electrodeposition of Cu2O nanocrystals for hydrogen-generation

Through annealing and electrochemical reduction methods, we successfully fabricates reduced graphene oxide layer (RGOL) modified carbon nanotube and reduced graphene oxide (CNT + RGO) doped polyphenylene sulfide (PPS) flexible thin film electrodes. These composite structure films can not only overcome the brittle nature of PPS, but also make good use of the thermal stability of PPS. Furthermore, carbon nanotube and reduced graphene oxide enhance the electrical conductivity of the composite films. Truncated octahedral and cuboctahedral Cu₂O nanocrystals are synthesized on RGOL modified CNT + RGO doped PPS (RGOL@PPS/CNT + RGO) composite film by a facile electrodeposition method without using any surfactants or external heating. RGOL on the PPS/CNT + RGO substrate facilitates the formation of Cu₂O morphology. The obtained Cu₂O composite film shows a superior ability for the hydrogen evolution reaction (HER) compared with other Cu₂O electrocatalysts. The Cu₂O with a smaller loading less than 0.04 mg cm^?2 on the composite film exhibits excellent HER activities with a low onset potential of 0.05 V and large current densities. The results of the HER performance indicates that the RGOL@PPS/CNT + RGO composite film has a potential application in flexible hydrogen-producing devices.     

Photo induced hydrogen evolution from water in the presence of EDTA and a supported catalyst

A flow reaction system was developed to study the steady state kinetics of hydrogen evolution in the presence of Ru(bipy)²⁺, MV⁺², EDTA and a heterogeneous supported catalyst. Under the conditions used, steady state rates similar to those previously reported with colloidal Pt particles were attained. Furthermore, over much of the range of concentrations used, the reaction was zero order and it did not exhibit an Arrhenius behavior. Examination of the various rate determining steps involved led us to conclude that surface processes such as the recombination and desorption of hydrogen from the Pt surface might be rate determining.     

Depth profile analysis of CuInSe2 (CIS) thin films grown by the electrodeposition technique

In this study, we report the results obtained from the auger electron spectroscopy (AES) depth profiling of CIS thin films grown by the electrodeposition technique. This result enables one to do a comparison between the bulk and superficial elemental compositions. The AES result is also compared with that obtained by the inductively coupled plasma (ICP) spectroscopy. These results support our proposition that the electrodeposited CIS film has a Cu-rich bulk region and an In rich surface, which leads to the formation of an n-layer (CuIn₂Se_3.5) on the top of the p-type CIS (CuInSe₂) phase     

Performance studies of solid oxide fuel cell cathodes in the presence of bare and cobalt coated E-brite alloy interconnects

The electrochemical performances of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) electrodes were studied by half-cell measurements in the absence of chromia-forming alloy, in the presence of bare and Co coated E-brite alloy interconnects, respectively. The surface and cross-section properties of the bare and Co coated E-brite alloys, and LSCF electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and electron probe microanalysis (EPMA). The results showed a rapid degradation in LSCF performance when the bare E-brite alloy was used as interconnect. The growth of chromia scale on the E-brite alloy and the increase of Cr content throughout the LSCF electrode were observed. The uniform and dense Co coating process was developed to coat the E-brite alloy by using both electroless and electrodeposition methods. It was demonstrated that the Co layer effectively mitigates the Cr migration, leading to improved electrochemical stability of LSCF electrodes.     

Electrochemical quartz crystal microbalance study of the electrodeposition of Co,Pt and Pt–Co alloy

The electrochemical deposition of Co, Pt and Pt–Co alloy are studied with the electrochemical quartz crystal microbalance (EQCM) on a gold substrate. Co is deposited from acidic sulphate bath containing boric acid. Different processes are identified in this bath. Electrodeposition of Co on Au substrate is observed at potentials above redox potential, underpotential deposition, most probably due to formation of a Co–Au alloy. At more cathodic potentials, below −0.5 V, metallic Co is formed. The film is completely dissolved at positive potentials during the anodic scan, probably mediated by Co(OH)₂. The electrodeposition of platinum from acidic PtCl₆²⁻ bath occurs below the thermodynamic potential (0.74 V) with almost 100% efficiency. At potentials negative from 0.0 V the efficiency decreases due to parallel water reduction. The codeposition of Co and Pt is also studied in acidic bath. Here, the decrease of pH due to water reduction on Pt deposits gives rise to precipitation of Co(OH)₂, together with the deposition of metallic Pt and Co. The films contain as major component the Pt₃Co alloy.     

Carbon-supported PdM (M = Au and Sn) nanocatalysts for the electrooxidation of ethanol in high pH media

Carbon-supported Pd₄Au- and Pd_2.5Sn-alloyed nanoparticles were prepared by a chemical reduction method, and characterized by a wide array of experimental techniques including mass spectrometry, transmission electron microscopy, and X-ray diffraction spectroscopy. Ethanol electrooxidation on the as-synthesized catalysts and commercial Pt/C was then investigated and compared in alkaline media by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy studies at room temperature. Voltammetric and chronoamperometric measurements showed higher current density and longer term stability in ethanol oxidation with the palladium alloy nanocatalysts than with the commercial one. Electrochemical impedance spectroscopy and Tafel plots were employed to examine the charge-transfer kinetics of ethanol electrooxidation. The results suggest that whereas the reaction kinetics might be somewhat more sluggish on the Pd-based alloy catalysts than on commercial Pt/C, the former appeared to have a higher tolerance to surface poisoning. Overall, the Pd-based alloy catalysts represent promising candidates for the electrocatalytic oxidation of ethanol, and Pd₄Au/C displays the best catalytic activity among the series for the ethanol oxidation in alkaline media.     

Test of conductor and semiconductor electrocatalysts in high voltage alkaline electrolyzer as production media for green hydrogen

Despite the restricted success of conductor and semiconductor electrodes in solving hydrogen production problems, they provide a promising alternative to expensive conventional electrodes in water electrolysis investigations. Titanium dioxide (TiO₂) and silver (Ag) are widely used as photocatalysts in water splitting systems for hydrogen generation. Though TiO₂ is an inactive chemical semiconductor with poor conductivity, it has not been entirely investigated as an electrocatalyst yet. Two criteria were used to achieve this target: supplying high voltage to overcome the TiO₂ large band gap and immersing it in an alkaline solution to activate its inert surface. For comparison study, Ag noble metal nanoparticles coating was employed as a competitive electrocatalyst. In this regard, the application of Ag and TiO₂ coated on Ti electrodes in a hydrogen production system operated under high voltage was reported. The nanoparticles were synthesized using cost-effective and simple methods based on UV-deposition for Ag nanoparticles and the chemical precipitation method for TiO₂ nanoparticles. Then the synthesized nanoparticles were deposited on the Ti electrodes by simple immersion. The synthesized nanoparticles and coated electrodes were tested by XRD, SEM, and EDS to study their morphology, structure, particle size, and surface composition. Based on these results, TiO₂ nano-powder and coated electrodes exhibited homogenous spheres with a mixture of rutile and anatase phases, the majority being the anatase phase. The Ag-coated Ti substrate possessed a smaller crystallite size compared to TiO₂ coated substrate. To evaluate the performance of Ag/Ti and TiO₂/Ti electrodes toward hydrogen production, H₂ flow rates were measured in a 3.6 M KOH electrolytic solution at 6 V. Hydrogen flow rates obtained for pure Ti, Ag, and TiO₂ electrodes at a steady state were 21, 35, and 37 SCCM (standard cm³/min), respectively. Also, it was found that energy consumption was reduced when the electrodes were coated with nanoparticles. Furthermore, the electrolyzer's performance was assessed by calculating the hydrogen production efficiency and the voltage efficiency. The results showed that using TiO₂ electrodes gave the best hydrogen production and voltage efficiencies of 27% and 23%, respectively. This study brings new insights about Ag and TiO₂ coated electrodes in alkaline water electrolysis at high voltage regarding nanoparticle performance, hydrogen production, system performance, and energy consumption. In addition, minimizing the fabrication and operation costs of hydrogen production is the major enabler for the broad commercialization of water electrolysis devices.