Sharif Digital Repository

In this study, the performance of a Photovoltaic Thermal-Organic Rankine Cycle (PVT-ORC) system combined with a Proton Exchange Membrane Electrolysis Cell (PEMEC) is investigated. A combined numerical/theoretical model of the system is developed and used to evaluate the effect of various system design parameters. In addition, the effects of using water, ethylene glycol, and a mixture of water and ethylene glycol (50/50) as the working fluid of the PVT system and R134a, R410a, and R407c as the working fluid of the ORC cycle on the performance of the PVT-ORC-PEMEC system are studied. Based on the results, R134a and water demonstrated the best performance as the working fluid of the ORC and PVT... 

Modification of orthopedic implant surfaces through advanced nanoscale coating methods has made a major breakthrough in maximizing implantation success. Adjustable drug release and biocompatibility are among the most momentous features since they can significantly prevent the implantation failure. In this study, the potential of silk fibroin (SF) nanofibers fabricated via electrospinning, along with titanium oxide nanotube arrays (TNTs) formed through anodization, were exploited to produce a cyto-biocompatible, well-controlled drug delivery system. Highly-ordered TNTs were formed in an organic electrolyte solution within 2 h at the voltage of 60 V under temperature controlling (16 °C).... 

The mechanism of gold nanowire (AuNW) and nanotube (AuNT) electrodeposition in a cyanide-free solution is investigated for the first time based on the analytical model of Szabo et al. (A. Szabo et al., J. Electroanal. Chem. 217 (1987) 417) for recessed cylindrical ultramicroelectrode (UME). Track-etched Polycarbonate Template (PCT) is served as cylindrical UME ensemble/arrays. Firstly, Au is nucleated through a charge transfer step and when the Nernst thickness exceeds the pore length, the radial diffusion is established around pore mouths. By overlapping of these domains, the planar diffusion toward the whole PCT surface is obtained. An analytic expression for global diffusion coefficient... 

Nanostructured molybdenum oxide having a particle size in the range of 30-80 nm was prepared by potentiodynamic electrodeposition method, and the effects of H2SO4 concentration on its capacitive behavior were studied by cyclic voltammetry, galvanostatic discharge, and electrochemical impedance spectroscopy. Poor to fair capacitive behaviors were witnessed depending on the electrolyte concentration and conditions of charge/discharge. Increasing acid concentration to 0.02 M had favorable effect, while beyond that, the effect was detrimental. Capacitance around 600 F g-1 was recorded in the potential range of 0 to -0.55 V vs. Ag/AgCl  

The mean spherical approximation (MSA) has been applied to accurately correlate the activity coefficients of individual ions in aqueòus solutions of single 1:1 electrolytes. In order to account for changes in the hydration of the ions, the size parameters of the ions are considered to be composition dependent. The values of the size parameters show that the hydration of the ions decreases as the electrolyte concentration increases. Results obtained from the full MSA and from a simplified version of MSA (SMSA), were compared. The use of the simplified version had a small effect on the final results and dramatically reduced the computation of the effort  

Solar energy exists extensively in all parts of the world. However the intermittency of solar energy presents critical challenges to PV system. The intermittency can be covered by storing solar energy in chemical bonds such as hydrogen. This process can be performed by photovoltaic powered electrolysis of water. The energy transfer efficiency between PV and electrolyzer is subject to the distance between maximum power points (MPP) of PV module and operating points. The operating points can be adjusted by optimizing the design parameters of the electrolyzer but the maximum power points are function of PV module characteristics, solar radiation and ambient temperature. Therefore the weather... 

The catalyst layers are the most important part of the polymer electrolyte membrane (PEM) fuel cells, and the cell performance is highly related to its structure. The gas diffusion layers (GDLs) are also the essential components of the PEM fuel cell since the reactants should pass through these layers. Model prediction shows that electrical current in catalyst layer is non-uniform, influenced by the channel-land geometry. In addition, the compression effect of GDLs and water generation due to the electrochemical reaction may cause non-uniformity in porosity and, therefore, increases the non-uniformity in reactant concentration in GDL/catalyst layer interface. Simulation results suggest that... 

Using multi-walled carbon nanotubes (MWCNTs), the present study focuses on their electrochemical hydrogen storage capacities. The results showed that the hydrogen desorption process is composed of two steps with voltages around -0.75 and -0.15 V. Hydrogen adsorption at -0.15 V took place at temperatures above 30 °C, and the amount of energy required for adsorbing hydrogen was 1.68 eV. The hydrogen storage capacity increased with increasing electrolyte temperature from 30 to 60 °C in both steps. The hydrogen storage capacity of the MWCNTs treated at different atmospheres showed that the decrease in the graphitization of MWCNTs led to the increase in hydrogen adsorption. The results also... 

The distribution of water fluxes is strongly influenced by the properties of the media adjacent to the cathode catalyst layer (CCL), viz. polymer electrolyte membrane (PEM) and gas diffusion media (GDM). We propose a model that is applied under varying humidification of the cathode feed gas, with water removal in liquid and vapor form. The model warrants the definition of a critical current density up to which water removal out of the CCL could proceed completely via vapor diffusion to the cathode side. Above the critical current density, excessive water generation leads to the build-up of an excess liquid pressure in the CCL, which drives hydraulic fluxes to PEM and GDM sides. Experimental... 

In this research, the effect of applied voltage and electrolyte concentration on structure, chemical composition, optical properties, and especially photo-catalytic activity of the TiO2 layers containing micro/nano-sized pores are discussed. TiO2 layers were synthesized by micro arc oxidation (MAO) process using different electrolyte concentrations and applied voltages. Surface structure of the layers was studied by scanning electron microscope (SEM); furthermore, energy dispersive spectrophotometry (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques were employed to determine phase structure and chemical composition of the layers. Photo-activity of the... 

Models play an important role in fuel cell design and development. One of the critical problems to overcome in the proton exchange membrane (PEM) fuel cells is the water management. In this work a steady state, two-dimensional, isothermal model in a single PEM fuel cell using individual computational fluid dynamics code was presented. Special attention was devoted to the water transport through the membrane which is assumed to be combined effect of diffusion, electro-osmotic drag and convection. The effect of current density variation distribution on the water content (λ) in membrane/electrode assembly (MEA) was determined. In this work the membrane heat conductivity is considered as a... 

The most applications of gold nanoparticles are in the photo-electronical accessories and bio-chemical sensors. Chloride solution with cysteine additive was used as electrolyte in gold nanoparticles electrodeposition. The nucleation and growing mechanism were studied by electrochemical techniques such as cyclic voltammetry and chronoamperometry, in order to obtain a suitable nano structure. The deposition mechanism was determined as instantaneous nucleation and the dimension of particles was controlled in nanometric particle size range. Atomic Force Microscope was used to evaluate the effect of cysteine on the morphology and topography of gold nanoparticles. Finally the catalytic property of... 

The Cu-0.5Co/WC nano-composite coating was synthesized on CP-copper substrate using Direct Current (DC) electrodeposition method. In this work, it was tried to increase the hardness of surface without considerable degradation of copper's particular physical properties such as electrical conductivity. The effect of current density on microstructural homogeneity, hardness, fracture toughness, and electrochemical behavior of coating was investigated. The copper plates with the purity of 99.99% were used as electrodes. The electrolyte consists of tungsten carbide particles (30 g/l), copper sulfate (200 g/l), sulfuric acid (50 g/l), cobalt sulfate (50 g/l), and Sodium Dodecyl Sulfate (SDS) (0.3... 

In copper electrorefining process, some additives are added to the electrolyte to improve the morphology of cathode deposits as well as the quality of products. In the present investigation, the effects of thiourea, glue and chloride ions (as additives) on the passivation of industrial copper anodes under high current densities have been reported. Experiments were conducted at 65 °C; using a synthetic electrolyte containing 40 g/l Cu2+ and 160 g/l H2SO4. Results obtained from chronopotentiometry experiments showed that increasing the concentration of chloride ion leads to increase in passivation time. The results also indicated that from a certain level on, namely 2 ppm, the increase in... 

The power-to-liquid concept is a promising strategy to convert the power plants' flue gas to value-added liquid fuels using renewable energy. This technology could potentially reduce global greenhouse gases emissions and mitigate the environmental problems associated with the fossil fuels industry. In this regard, the main objective of the present study is to propose a novel power-to-liquid plant for the synthesis of formic acid and ammonia from power plants' flue gas, emphasizing the role of electrochemical technologies and renewable energy. The system's basis is developed by the integration of CO2 electroreduction cell, alkaline water electrolysis cell, and photovoltaic panel technologies.... 

In this work, attempt is made to development of active non-precious metal catalysts (NPMCs) for the oxygen reduction reaction in polymer electrolyte fuel cells (PEFCs) based on the heat treatment of poly-aniline/transition metal/carbon precursors. All the materials have been characterized by X-ray diffraction (XRD) small and wide angle, N2 adsorption-desorption isotherms, high-resolution transmission electron microscopy (TEM), Scanning electron microscope (SEM) and X-ray photo-electron spectroscopy (XPS). Moreover for electrochemical evaluation of samples, Rotating Disk electrode (RDE) technique and Fuel Cell test were employed. The results showed that onset potential for the optimized... 

In this study, biocompatible ceramic layers containing TiO2 and hydroxyapatite (HA) nanoparticles (TiO2/HA) were deposited on pure commercial titanium (Grade 2) by using plasma electrolytic oxidation and AC power supply. The coating process was carried out in five different solutions for various times at a current density of 500 mA cm−2. To achieve the optimum conditions for thickness and microstructure, the coating process was conducted in solutions with a 3 g L−1 concentration of HA nanoparticles. FESEM, XRD, and FTIR results showed that HA nanoparticles were successfully incorporated into the pores of the layer. Furthermore, the corrosion behavior of the coating layers in the simulated... 

In this study, electrochromic properties of cuprous oxide nanoparticles, self-accumulated on the surface of a sol-gel silica thin film, have been investigated by using UV-visible spectrophotometry in a lithium-based electrolyte cell. The cuprous oxide nanoparticles showed a reversible electrochromic process with a thin film transmission reduction of about 50% in a narrow wavelength range of 400-500 nm, as compared to the bleached state of the film. Using optical transmission measurement, we have found that the band gap energy of the films reduced from 2.7 eV for Cu2O to 1.3 eV for CuO by increasing the annealing temperature from 220 to 300 °C in an N2 environment for 1 h. Study of the band... 

Here, a solvothermal method for synthesis of porous Ni–Co binary oxide (NiCo2O4) nanorods followed by thermal decomposition is described. The prepared nanorods were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer Emmett Teller (BET) methods. These porous NiCo2O4 nanostructures were promising candidates in the development of high capacity supercapacitors and having excellent cycling performance due to high specific surface area. In addition, the influence of annealing rate on the structure and electrochemical behavior of the synthesized nanorods was investigated. The results showed that the annealing rate had a direct effect on the crystalline... 

Ag@Pt nanoparticles synthesized with different Ag/Pt mass ratios utilizing ultrasonic treatment method. These materials were supported on Vulcan XC-72 and utilized as cathode in a proton exchange membrane fuel cell (PEMFC). The morphology of this material characterized through the x-ray diffraction (XRD), induced coupled plasma atomic emission spectroscopy (ICP-OES) as well as; high resolution transmission electron microscopy (HRTEM) techniques. To begin with, it was proven that, the prepared Ag@Pt/C catalyst possessed a core–shell nanostructure. The electrochemical properties of this material investigated through the Cyclic Voltammetry (CV), linear sweep voltammetry (LSV) and...