Decrease In Capacitance Research Articles

Preparation of NiO nanoflakes under different calcination temperatures and their supercapacitive and optical properties

The NiO nanocrystals were successfully prepared by calcinating Ni(OH)2 precursor synthesized via a facile ion diffusion controlled by ion exchange membrane without adding any solvent or template. X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) isotherm, X-ray photoelectron spectroscopy (XPS) and Ultraviolet–visible (UV–vis) analysis were used to investigate the crystallinity, morphology, surface and porosity characteristics, chemical composition and optical properties in more detail. The pseudocapacitive behavior of the NiO samples was investigated by cyclic voltammograms (CV) and galvanostatic charge-discharge tests in 2M KOH. The results analysis reveals that both specific capacitance and surface area decrease with the increase of calcination temperatures. Among the NiO samples, the NiO-400 nanoflakes calcinated at 400°C possess the highest specific capacitance of 381Fg−1 at a current density of 2Ag−1, but much lower than the Ni(OH)2 sample. In addition, the UV–vis analysis shows that there is a red shift of absorption peak for the three NiO samples with the increasing temperature and the NiO-400 has a broad band gap of 3.3eV, which renders the material highly interesting for application in photocatalyst.

Polarography of Te (IV) Anions in Neutral Solutions in Presence of 2,2'- Dipyridyl and Fe(dipy)3 2+ - Complexes

<p>The electroreduction of Te (IV) ions in neutral non-buffer solutions containing 2,2'-dipyridyl (4⋅10<sup>-5</sup>- 4⋅10<sup>-3</sup> M) or tris-dipyridyl iron (II) complexes is studied by the polarographic method. NaF (0.01-0.5 M) or NaNO<sub>3</sub> (0.1-1 M) are used as supporting electrolytes. The mechanism of electrochemical reactions of Te (IV) anions on mercury electrodes in the presence of the additives is discussed. The electroreduction of Te (IV) anions is shown to proceed through electron transfer and proton addition. The obtained results point to a considerable influence of electric double layer structure on electrochemical reactions of Te (IV) ions in the presence of inorganic and specifically adsorbed organic compounds in the electrolyte. It is shown, that 2,2'-dipyridyl does not form complexes with Te (IV) anions. Having been adsorbed on the surface of mercury electrode, 2,2'-dipyridyl complexes increase negative <em>Ψ</em>'-potential that results in a shift of Te (IV) electroreduction wave to more negative potentials and decrease in the current of Te (IV) wave and peak at -1.19 V. It is shown that 2,2'-dipyridyl molecules at <em>ε</em> > 0, (<em>ε</em> – charge of an electrode) are adsorbed in plane orientation, and at ε < 0, plane or vertical. Vertically adsorbed molecules cause a significant decrease in the double layer capacitance. At negative potentials orientation of 2,2'-dipyridyl molecules changes from plane to vertical with the increasing 2,2'-dipyridyl concentration. This change of orientation results in a typical maximum capacitance emerging in the potential range of -0.7 to -1.2 V. It is shown that the supporting electrolyte, 2,2'-dipyridyl and Fe(dipy)<sub>3</sub> <sup>2+</sup> have influence on the electroreduction of Te (IV) anions in neutral non-buffer solutions through a change in the <em>Ψ</em>'-potential of mercury electrode.</p>

Synthesis of mesoporous reduced graphene oxide by Zn particles for electrodes of supercapacitor in ionic liquid electrolyte

Abstract Mesoporous reduced graphene oxide ( m -rGO) was synthesized by mixing Zn and graphene oxide in acidic conditions followed by ultrasonication and was investigated as a supercapacitor electrode in a 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) electrolyte. m -rGO shows a specific capacitance of 104.3 F g −1 at 1 A g −1 and a decrease in capacitance of 3% after 5000 cycles. The high performance is attributed to the significant mesopores, facilitating mass transport of the electrolyte. Thus, we report the facile synthesis of m -rGO with enhanced capacitance and durability in an ionic liquid electrolyte that has great potential for electrochemical energy storage applications.

Architectural modifications for flexible supercapacitor performance optimization

We have developed material and architectural alternatives for flexible supercapacitors and investigated their effect on practical performance. The substrate alternatives include paperboard as well as various polyethylene terephthalate (PET) films and laminates, with aqueous NaCl electrolyte used in all devices. In all the supercapacitors, activated carbon is used as the active layer and graphite ink as the current collector, with various aluminium or copper structures applied to enhance the current collectors’ conductivity. The capacitance of the supercapacitors was between 0.05 F and 0.58 F and their equivalent series resistance (ESR) was from <1 Ω to 14 Ω, depending mainly on the current collector structure. Furthermore, leakage current and selfdischarge rates were defined and compared for the various architectures. The barrier properties of the supercapacitor encapsulation have a clear correlation with leakage current, as was clearly shown by the lower leakage in devices with an aluminium barrier layer. A cycle life test showed that after 40000 charge-discharge cycles the capacitance decreases by less than 10%.

Supercapacitor Degradation Assesment by Power Cycling and Calendar Life Tests

Abstract Degradation of Supercapacitors (SC) is quantified by accelerated ageing tests. Energy cycling tests and calendar life tests are used since they address the real operating modes. The periodic characterization is used to analyse evolution of the SC parameters as a whole, and its Helmholtz and diffusion capacitances. These parameters are determined before the ageing tests and during 3 × 105 cycles of both 75% and 100% energy cycling, respectively. Precise evaluation of the capacitance and Equivalent Series Resistance (ESR) is based on fitting the experimental data by an exponential function of voltage vs. time. The ESR increases linearly with the number (No) of cycles for both 75% and 100% energy cycling, whereas a super-linear increase of ESR vs. time of cycling is observed for the 100% energy cycling. A decrease of capacitance in time had been evaluated for 2000 hours of ageing of SC. A relative change of capacitance is ΔC/C0 = 16% for the 75% energy cycling test and ΔC/C0 = 20% for the 100% energy cycling test at temperature 25°C, while ΔC/C0 = 6% for the calendar test at temperature 22°C for a voltage bias V = 1.0 Vop. The energy cycling causes a greater decrease of capacitance in comparison with the calendar test; such results may be a consequence of increasing the temperature due to the Joule heat created in the SC structure. The charge/discharge current value is the same for both 75% and 100% energy cycling tests, so it is the Joule heat created on both the equivalent series resistance and time-dependent diffuse resistance that should be the source of degradation of the SC structure. The diffuse resistance reaches a value of up to 30Ω within each 75% energy cycle and up to about 43Ω within each 100% energy cycle.

Accelerated Durability Tests for Pt-Nanoclusters Modified Carbide Derived Carbons Catalysts in Acidic Solution

Pt-nanoparticles activated porous carbon composite catalysts are widely used in PEMFC applications. The instability of these catalysts in harsh fuel cell working conditions is the main problem hindering the large-scale application of the fuel cell technology in commercial and energy recuperation systems [1]. Hierarchical microporous-mesoporous carbon supports C(Mo2C) were prepared from molybdenum carbide using high temperature chlorination method at different synthesis temperatures from 600 °C to 1000 °C. The Pt-nanoparticles were deposited onto the carbon support using the NaHB4method [2,3]. The X-ray diffraction, low temperature nitrogen sorption, thermogravimetric analysis (TGA) and high-resolution scanning electron microscopy (HRSEM) methods were used to characterize the catalysts materials. The medium size of the Pt-nanoparticles deposited was 4.5±0.6 nm. Corrosion of the Pt-C(Mo2C) catalysts were evaluated using an accelerated durability test (ADT) method (in oxygen (99.999%, AGA) saturated 0.5 M H2SO4 aqueous solution, from 0.58 V to 0.98 V vs SHE, at potential scan rate 50 mV s−1) [4]. The oxygen electroreduction reaction kinetics and the value of electrochemically active surface area (ECA) of the catalysts were determined after 10, 100, 1000, 3000, 10 000, 20 000 and 30 000 cycles. Electrochemical impedance spectra were obtained at 0.9 V vs SHE within ac frequencies from 0.01 to 10 000 Hz to determine the changes of the electrolyte resistance and capacitance values during the ADT. The results show that only 20% decrease in electrode capacitance and 15% increases in series resistance takes place during 30,000 potential cycles. The values of ECA were estimated in the solution saturated with nitrogen (99.999%, AGA) using the cyclic voltammetry at different potential scan rates from 30 to 1000 mV s−1. The rotating disc electrode method was used to evaluate the oxygen electroreduction kinetics in solution saturated with oxygen at rotation rate 1600 rev min−1 and at potential scan rate 20 mV s−1within the region of potentials from 1.03 V to 0.03 V vs SHE. Based on the cyclic voltammetry and rotating disk electrode data the main decrease in ECA took place during the first 1000 cycles and thereafter the ECA value stabilized. The half wave potential values depend weakly on the number of cycles (up to 30,000) measured. The content of Pt in the catalyst was determined before and after the ADT using the electrochemical dissolution of platinum from the electrode in 6 M HCl solution. The average weight percentage of Pt in different catalyst materials was 71.8±1.7. The content of Pt in the catalysts before the ADT was in a good agreement with the TGA data.

(Invited) Present and Future of LTPS Technology

Japan Display Inc. has developed excellent quality TFT-LCD displays based on precise LTPS technology and progressive LCD-cell technology [1]. Their advantages are less than half the power consumption and a contrast ratio of 2000:1 using unique RGBW technology, photoalignment technology, and an in-cell touch panel technology with 1mmΦstylus input simultaneously. We have recently developed two high resolution displays with more than 500-ppi which one can realize higher response rate with higher frame rate driving and another can reduce the power consumption by 30% with a lower frame rate driving. One is the 17.3-inches 8K4K display with 550ppi and 120-Hz frame rate driving and another is the 8-inches 4K2K with 510-ppi with 30-Hz frame rate driving. We adopted two technologies for the LTPS backplanes, one was a 1.5-µm high resolution process, and the other was an increase of the pixel capacitance. Figure 1 shows the cross sectional SEM image of a poly-Si layer. I-line photolithography was adopted and the dry etching condition of the poly-Si patterning process was optimized in order to obtain poly-Si islands 1.5-µm wide with a good taper angle. In addition, a thinner insulator for the storage capacitance Cs was fabricated almost by half to increase the CSvalue with care in terms of coverage over other layers. The adoption of a 1.5-µm short channel LTPS process and thinner insulator thickness can contribute two benefits. One is a decrease in load capacitance which is considerably increased as the number of pixels increase up to 8K4K. Another is a decrease in feed through voltage ΔVth which is described by equation (1), which causes cross talk especially on higher resolution display. The developed 17.3-inches 8K4K LTPS-LCD with 510-ppi resolution in collaboration with NHK is shown in Figure 2 [2]. We realized uniform transmittance distribution and sufficiently small cross talk much less than 2% on this prototype display which attributes its small load capacitance and small feed through voltage. We also developed 8-inches 4K2K display with 510-ppi. By adopting the same LTPS technologies, we also realized 30-Hz frame rate driving with acceptable flicker level which is defined as the range of the maximum and minimum liminance. We could decrease the total power consumption for drinving by 32% adopting 30-Hz frame rate driving as shown in Figure 3. Reference: [1] T. Kaneko, et al., "Innovative 5-inch FHD and 7-inch WQXGA Displays for Next Generation Smartphones and Tablets", Proc. SID'13, 2013, pp693-296. [2] K. Mochizuki, et al., "A 510-ppi 8K4K LTPS TFT-LCD with 120-Hz Frame Rate Driving" SID'16, Digest paper, 67.2, 2016 Figure 1

Resolving the Effects of Surface Area and Porosity on the Capacitance of Activated Carbon

Electrochemical double-layer capacitors (EDLCs) store energy at the interface of the electrode and electrolyte, known as the electrical double layer. One of the challenges facing EDLC technology is their moderate energy density compared to batteries and fuel cells. Therefore, improving EDLC performance requires identification of the key electrode and electrolyte parameters that affect energy density. Some of the key parameters that are known to impact the energy density of an electrode material are the material’s specific surface area (SSA), its pore size distribution, the macroscopic morphology, and the material’s chemical composition, relating to the wettability of the material and the faradaic reactions that may occur during charging. However, published research to date has not isolated the intercoupled relationship between specific surface area and pore size distribution. While high surface area materials often have high microporosity (pores less than 2 nm in diameter) due to the high surface to volume ratio of these small pores, as the pore size is increased into the mesopores range (2-50 nm diameter pores), the material’s SSA tends to decrease, since mesopores have a lower surface to volume ratio [1, 2]. As such, there remains an ongoing unresolved debate as to the relationship between pore size and SSA-normalized capacitance [2], with some researchers demonstrating an increased SSA-normalized capacitance in pores with diameters less than 1 nm [3], some researchers suggesting that there is no correlation between pore size and SSA-normalized capacitance [4], and some researchers demonstrating that there is a relationship between SSA-normalized capacitance and pores greater than 2 nm in diameter [5]. One of the main challenges to unravel the correlation between pore size and SSA-normalized capacitance is the variation in a material’s structural features, including total SSA, and its chemical composition. This makes it challenging to determine the effect of a single parameter [2]. In order to investigate the effect of pore size on SSA-normalized capacitance, the ideal materials for comparison would be those of similar specific surface area, and chemical composition, but differing pore size distribution. This approach ensures that the effects of the material’s total SSA are constant. When materials have different total SSA values, it is difficult to determine if the variations in performance are associated to differing pore size or differing surface area. Additionally, the relationship is more complicated in a sample with multiple pore sizes, which is common in activated carbon materials. It is critical to determine the relationship between pore size and capacitance in materials with narrow pore size distributions, and materials that have broad pore size distributions. By identifying the key structural features that improve the energy density of a material, the overall performance of EDLCs may also be improved. This study investigates the relationship between SSA-normalized capacitance and pore size distribution. Activated carbon materials were prepared with various pore size, but with similar specific surface area and chemical composition. The relationship between pore size and both SSA-normalized capacitance and gravimetric capacitance as well as the rate performance of the activated carbon materials is reported. Finally, the dependence of capacitance on maximum operating voltage is discussed in order to better elucidate the relationship between porosity and capacitance. Initial results have demonstrated that as the pore size increases, the SSA-normalized capacitance decreases. However, a similar decrease was not observed in the gravimetric capacitance. This indicates that the variation in bulk density of broad pore size distribution carbon materials may mask the effects of enhanced SSA-normalized capacitance in sub-nanometer pores. The results suggest that there may be a critical pore size distribution that will maximize both SSA-normalized capacitance and gravimetric capacitance.

Accelerated Durability Tests for Pt-Nanoclusters Modified Carbide Derived Carbons Catalysts in Acidic Solution

The accelerated durability test (ADT) of carbide derived carbon (CDC) electrodes activated with Pt-nanoparticles were performed for 30,000 cycles in 0.5 M H2SO4 aqueous solution. Hierarchical microporous-mesoporous carbon supports C(Mo2C) were prepared from molybdenum carbide using high temperature chlorination method at different fixed synthesis temperatures from 600 °C to 1000 °C. The Pt-nanoparticles were deposited onto the C(Mo2C) using the NaHB4 method. The X-ray diffraction, low temperature nitrogen combined with CO2 sorption, thermogravimetric analysis and high-resolution scanning electron microscopy methods were used to characterize the catalysts materials. For detailed understanding of the Pt-nanoparticles degradation mechanism the particle size distribution analysis was performed. It was found that the main decrease in electrochemical surface area took place after 1,000 polarization cycles. During the ADT the half wave potential values depend weakly on the number of cycles and electrochemical impedance results show that only 20% decrease in the electrode capacitance has been observed.

Skin Hydration Sensor for Customizable Electronic Textiles

This paper introduces the design and simulated operation of a capacitive hydration sensor for integration into textile-based electronics. The multilayer patch is composed of a textile layer and an attached series of serpentine-interdigitated electrodes. The model used for simulations incorporated this design onto a representative model of skin. The serpentine-interdigitated electrodes are electrodes for capacitive measurement of skin hydration. In this study, the capacitance change relative to skin hydration was simulated using finite element analysis. The simulation results suggest the fabric layer had little effect on the capacitance of the sensor. Furthermore, the frequency domain simulations indicated that the capacitance of the sensor decreased with increasing frequency, and the decrease in capacitance was more significant for the dry skin compared to the wet skin. Therefore, the variation in the capacitance value of the serpentine-interdigitated electrodes can be employed for continuous skin hydration detection.

Hybrid α-Fe2O3@Ni(OH)2 nanosheet composite for high-rate-performance supercapacitor electrode.

In this study, we report a facile fabrication of ultrathin two-dimensional (2D) nanosheet hybrid composite, α-Fe2O3 nanosheet@Ni(OH)2 nanosheet, by a two-step hydrothermal method to achieve high specific capacitance and good stability performance at high charging/discharging rates when serving as electrode material of supercapacitors. The α-Fe2O3@Ni(OH)2 hybrid electrode not only has a smooth decrease of the specific capacitance with increasing current density, compared with the sharp decline of single component of Ni(OH)2 electrode, but also presents excellent rate capability with a specific capacitance of 356 F/g at a current density of 16 A/g and excellent cycling stability (a capacity retention of 93.3% after 500 cycles), which are superior to the performances of Ni(OH)2 with a lower specific capacitance of 132 F/g and a lower capacity retention of 81.8% at 16 A/g. The results indicate such hybrid structure would be promising as excellent electrode material for good performances at high current densities in the future.

Experimental and theoretical approach studies for melatonin drug as safely corrosion inhibitors for carbon steel using DFT

The inhibitory action of melatonin drug on the corrosion of carbon steel in 0.5M H2SO4 solution was investigated using galvanostatic polarization, electrochemical impedance spectroscopy, potentiodynamic anodic polarization techniques and density functional theory (DFT). It has been found that as the concentration of melatonin drug increases the values of corrosion current density and the values of double layer capacitance decreases, while the values of charge transfer resistance and the percentage of inhibition efficiency increase. This donates that the inhibiting effect of melatonin drug. Polarization date proves that the melatonin drug acts as mixed inhibitor. Melatonin drug inhibits the pitting corrosion of carbon steel in chloride containing solution by shifting the pitting corrosion to more noble direction. The adsorption of melatonin on the carbon steel surface obeys Langmuir adsorption isotherm. The relevancy of quantum chemical descriptors to the performance of melatonin as corrosion inhibitors was investigated.

A new shape memory alloy film/p-Si solar light four quadrant detector for solar tracking applications

Shape memory alloys (SMAs) are promising materials for industrial and electronic actuators applications. The Cu-Al-Mn-Ni shape memory alloy was coated as a Schottky contact on p-Si substrate to fabricate a four quadrant sensor using a vacuum coating system. A front illuminated shape memory film-p-type silicon -based four-quadrant solar light Schottky sensor was fabricated using the various metal contact masks. The electrical and photoresponse properties of Cu-Al-Mn-Ni/p-Si diode were investigated. These properties of the diode were analyzed under in a wide range of frequencies and illumination intensities. The reverse current of the diode increases with increasing illumination intensities. This result confirms that the diode exhibits both photoconducting and photovoltaic behavior. The forward bias current of the diode increases exponentially with voltage confirming rectification behavior. Electronic parameters such as ideality factor, barrier height and series resistance of the diode were determined from I-V characteristics and Cheung’s functions. The transient photocurrent, photocapacitance and photoconductance measurements indicate that the diode is very sensitive to illumination. Also, the admittance measurements of the diode exhibited a decrease in capacitance and increase in conductance with increasing frequency. The frequency dependence of capacitance and conductance is attributed to the presence of interface states. It is evaluated that Cu-Al-Mn-Ni/p-Si shape memory alloy film/p-Si based four quadrant detector can be used in solar tracking applications.

Micron dimensioned cavity array supported lipid bilayers for the electrochemical investigation of ionophore activity

Microcavity supported lipid bilayers, MSLBs, were applied to an electrochemical investigation of ionophore mediated ion transport. The arrays comprise of a 1cm2 gold electrode imprinted with an ordered array of uniform spherical-cap pores of 2.8μm diameter prepared by gold electrodeposition through polystyrene templating spheres. The pores were pre-filled with aqueous buffer prior to Langmuir-Blodgett assembly of a 1,2-dioleoyl-sn-glycero-3-phosphocholine bilayer. Fluorescence lifetime correlation spectroscopy enabled by the micron dimensions of the pores permitted study of lipid diffusion across single apertures, yielding a diffusion coefficient of 12.58±1.28μm2s−1 and anomalous exponent of 1.03±0.02, consistent with Brownian motion. From FLCS, the MSLBs were stable over 3days and electrochemical impedance spectroscopy of the membrane with and without ionic gradient over experimental windows of 6h showed excellent stability. Two ionophores were studied at the MSLBs; Valinomycin, a K+ uniporter and Nigericin, a K+/H+ antiporter. Ionophore reconstituted into the DOPC bilayer resulted in a decrease and increase in membrane resistance and capacitance respectively. Significant increases in Valinomycin and Nigericin activity were observed, reflected in large decreases in membrane resistance when K+ was present in the contacting buffer and in the presence of H+ ionic gradient across the membrane respectively.

Stability studies of polypyrole- derived carbon based symmetric supercapacitor via potentiostatic floating test

This work present the synthesis and electrochemical performance of mesoporous carbon material derived from the activation and carbonisation of polypyrole (PPY). Electrochemical performance of the PPY derived carbon was investigated in a two electrode cell in a 6M KOH alkaline electrolyte. The symmetric device was subjected to floating test (voltage holding) for ∼200h at a voltage of 1.2V and the specific capacitance as well as the resistance of device was determined after every 10h of floating. The device exhibited a specific capacitance of 179Fg−1 at 0.5Ag−1 and 158Fg−1 at 10Ag−1. In addition, after floating for ∼120h the resistance was constant with a very slow decrease in capacitance. Beyond ∼120h, a quick decrease in capacitance was observed with a corresponding increase in resistance, indicating a possible deterioration to the electrodes. Remarkably, at the end of floating, the specific capacitance calculated at 5Ag−1 was 120Fg−1 (∼25% decay in capacitance from the initial value 160.5Fg−1 at 5Ag−1) suggesting good stability of the device over a long period of time (∼8 days).

Electrochemical and theoretical investigation of the inhibitory effect of two Schiff bases of benzaldehyde for the corrosion of aluminium in hydrochloric acid

The corrosion inhibition effect of o-Aminophenol-N-Benzylidene (o-AmphNB) and o-Anisidene-N-Benzylidene (o-AnsNB) for pure Aluminium in 1 M HCl at different concentrations of two different inhibitors were investigated by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The values of ΔGadso revealed that the adsorption mechanism of these molecules on aluminium surface is competitive phenomenon between chemical and physical adsorption. Potentiodynamic polarization parameters revealed the mixed mode of inhibition with predominance of cathodic inhibition. The impedance results showed that with increase in concentration of inhibitor, charge transfer resistance increases while double layer capacitance decreases. Quantum chemical calculations based on density functional theory (DFT) method were performed on o-AmphNB and o-AnsNB to determine the relationship between molecular structures and their inhibition efficiencies. Correlation analysis concluded that the inhibition effect of inhibitors could be explained in terms of electronic properties.

A novel 4H-SiC MESFET with double upper gate and recessed p-buffer

A novel structure named 4H-SiC metal semiconductor field effect transistor with double upper gate and recessed p-buffer (DURP MESFET) is proposed and simulated in this paper. The increase in the saturation drain current and the breakdown voltage, and the decrease in the gate-source capacitance are achieved compared with those of DR MESFET, which are result from the reduction of the depletion region under the gate by the introduction of a double upper gate. The negative influence of the double upper gate on trans-conductance is suppressed by employing a recessed p-buffer. With the optimal size, the height of the upper gate Z = 0.10 μm, the depth and width of the recessed p-buffer of 0.05 μm and 0.35 μm, superior DC and RF characteristics for the proposed structure can be obtained, such as a 22.5% increase in the saturation drain current and a 17.9% increase in the breakdown voltage compared to the DR MESFET. The gate-source capacitance is 0.439 pF/mm compared to 0.573 pF/mm of DR MESFET by reference to simulated results, which would lead to the DURP MESFET has excellent RF performance.

Corrosion Inhibition of Carbon Steel in 1 M Hydrochloric Acid Solution by Aqueous Extract of Thevetia peruviana

The inhibitive effect of Thevetia peruviana on the corrosion behavior of carbon steel in 1 M HCl was studied using the weight loss method, polarization, AC electrochemical impedance spectroscopy and electrochemical frequency modulation techniques. The inhibition efficiency was found to depend on the concentration of the extract and the temperature of the medium. Results showed that this extract acts as a mixed-type inhibitor. The charge transfer resistance increases but the double layer capacitance decreases by increasing the extract concentration. It was found that the investigated extract acts via adsorption on the carbon steel surface and obeys the Temkin adsorption isotherm. The effect of temperature on the corrosion rate in the absence and presence of the extract was investigated, some activated, and the adsorption parameters were calculated. The results of the electrochemical methods were in good agreement with the weight loss measurement results.

Comparative study of Levofloxacin and its amide derivative as efficient water soluble inhibitors for mild steel corrosion in hydrochloric acid solution

The influence of 8-fluoro-3-methyl-9-(4-methyl-piperazin-1-yl)-6-oxo-2,3-dihydro-6H-1-oxa-3a-aza-phenalene-5-carboxylic acid or levofloxacin (P1) and newly synthesized 8-fluoro-3-methyl-9-(4-methyl-piperazin-1-yl)-6-oxo-2,3-dihydro-6H-1-oxa-3a-aza-phenalene-5-carboxylic acid-(5-methyl-pyridin-2-yl)-amide (P2) on corrosion inhibition of mild steel in 0.5 M hydrochloric acid solution was studied using weight loss and electrochemical techniques. Inhibition efficiency of P1 and P2 increased with concentration and decreased with temperature in the concentration range 0.14–0.35 mM in the temperature range 303–333 K. Thermodynamic parameters for dissolution and adsorption process were studied. Increase in energy of activation after the addition of inhibitors indicated formation of barrier film which prevents charge and mass transfer. Free energy of adsorption showed that the type of adsorption was neither physical nor chemical but comprehensive. The adsorption of the P1 and P2 on the mild steel surface was found to obey the Langmuir isotherm. Impedance measurement showed that there is increase in the polarization resistance and decrease in double layer capacitance after the addition of inhibitors. From polarization study as the shift in corrosion potential is more than 85 mV, both P1 and P2 are anodic type of inhibitors. Scanning electron microscope images confirm the formation of inhibitory film on mild steel surface. Quantum chemical calculation results well correlated with experimental results. Lower values of energy gap, ionization potential and hardness, higher value of softness make P2 better inhibitor compared to P1.

Preparation of Nano-Porous Activated Carbon Aerogel Using a Single-Step Activation Method for Use as High-Power EDLC Electrode in Organic Electrolyte.

Carbon aerogel was chemically activated with KOH using two different activation methods (conventional activation method and single-step activation method) to yield the nano-porous activated carbon aerogel. Both nano-porous activated carbon aerogels exhibited a better capacitive behavior than carbon aerogel in organic electrolyte. However, a drastic decrease in the specific capacitance with increasing current density was observed in the ACA_C (activated carbon aerogel prepared by a conventional activation method), which is a general tendency of carbon electrode for EDLC in organic electrolyte. Interestingly, the specific capacitance of ACA_S electrode (activated carbon aerogel prepared by a single-step activation method) decreased slowly with increasing current density and its CV curve maintained a rectangular shape well even at a high scan rate of 500 mV/s. The enhanced electrochemical performance of ACA_S at a high current density was attributed to its low ionic resistance caused by the well-developed pore structure with appropriate pore size for easy moving of organic electrolyte ion. Therefore, it can be concluded that single-step activation method could be one of the efficient methods for preparation of nano-porous activated carbon aerogel electrode for high-power EDLC in organic electrolyte.