Application of activated carbon/DNA composite electrodes to aqueous electric double layer capacitors

A novel capacitor electrode auxiliary, deoxyribonucleic acid (DNA), is applied to an electric double layer capacitor (EDLC) containing an aqueous 3.5 M NaBr electrolyte. The present electrode is composed of activated carbon (95 wt.%) and DNA (2.5 wt.%) with polytetrafluoroethylene (PTFE) as a binder (2.5 wt.%). An EDLC cell with the DNA-loading electrodes exhibits improved rate capability and discharge capacitance. An EDLC cell with DNA-free electrodes cannot discharge above a current density of 3000 mA g⁻¹ (of the electrode), while a cell with the DNA-loading electrodes can work at least up to 6000 mA g⁻¹. Moreover, an open-circuit potential (OCP) of the DNA-loading electrode sifts negatively with ca. 0.2 V from an OCP of the corresponding electrode without DNA. It is noteworthy that a small amount of DNA loading (2.5 wt.%) to the activated carbon electrode not only improves the rate capability but also adjusts the working potential of the electrode to a more stable region.     

Mesoporous activated carbon fiber as electrode material for high-performance electrochemical double layer capacitors with ionic liquid electrolyte

Activated carbon fibers (ACFs) with super high surface area and well-developed small mesopores have been prepared by pyrolyzing polyacrylonitrile fibers and NaOH activation. Their capacitive performances at room and elevated temperatures are evaluated in electrochemical double layer capacitors (EDLCs) using ionic liquid (IL) electrolyte composed of lithium bis(trifluoromethane sulfone)imide (LiN(SO₂CF₃)₂) and 2-oxazolidinone (C₃H₅NO₂). The surface area of the ACF is as high as 3291 m² g⁻¹. The pore volume of the carbon reaches 2.162 cm³ g⁻¹, of which 66.7% is the contribution of the small mesopores of 2-5 nm. The unique microstructures enable the ACFs to have good compatibility with the IL electrolyte. The specific capacitance reaches 187 F g⁻¹ at room temperature with good cycling and self-discharge performances. As the temperature increases to 60 °C, the capacitance increases to 196 F g⁻¹, and the rate capability is dramatically improved. Therefore, the ACF can be a promising electrode material for high-performance EDLCs.     

Molecular dynamics of the generation process of double‐walled carbon nanotubes from peapods

The generation process of a double‐walled carbon nanotube (DWNT) from a “peapod” was studied by classical molecular dynamics simulation. Starting from a peapod structure, defined by five C₆₀ molecules inside a (10,10) single‐walled carbon nanotube (SWNT), polymerized fullerenes, a peanut‐like structure and an almost nanotube‐like structure were obtained under suitable conditions of temperature control. The mean distance between the two layers of the DWNT agreed with an experimental report that it is larger than the interlayer spacing found in multi‐walled carbon nanotubes (MWNTs). In addition, the chirality dependence of the potential energy of a DWNT on the relative chirality of its constituent tubes was examined using a 6‐12 Lennard‐Jones potential. It was found that the potential energy depends only on the distance between the two layers, not on the relative chiralities. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(4): 254–264, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20115     

Effect of treatment of activated carbon fiber cloth electrodes with cold plasma upon performance of electric double-layer capacitors

Charge/discharge behavior of electric double-layer capacitors composed of activated carbon fiber cloth (ACFC) electrodes and an organic electrolyte was investigated. The modification of the ACFC electrodes was performed using cold plasma generated in argon-oxygen atmosphere. The effect of the cold plasma treatment of the ACPC electrodes on the capacitor performance was discussed on the basis of the physical and chemical properties of the ACFC surface such as pore radius distribution and surface atom concentration.     

Converting rice husk activated carbon into active material for capacitor using three-dimensional porous current collector

We have successfully applied rice husk activated carbon (RHAC) as an active material for the electric double layer capacitor using a three-dimensional (3D) porous current collector. The capacity and cycle stability were evaluated in a 1.0 mol dm⁻³ tetraethylammonium tetrafluoroborate/propylene carbonate solution in the range of 0-2.5 V. The specific capacity of the RHAC was about 14 mAh g⁻¹ at the 50 mA g⁻¹ discharge rate, corresponding to 19 F g⁻¹ under the present conditions. The RHAC cell using the 3D porous current collector possessed a lower internal resistance and better high-rate discharge properties than the RHAC cell using a conventional aluminum (Al) foil collector. After 5000 cycles of charging and discharging, the RHAC cell with the 3D current collector maintained 95% of its initial capacity, while the capacity of the one with the Al foil collector dropped to only 30%.     

Evaluation of Mg‐MOF‐74 for post‐combustion carbon dioxide capture through pressure swing adsorption

This paper presents a computational study of an energy‐efficient technique for post‐combustion CO₂ capture using novel material, namely, Mg‐MOF‐74, using pressure swing adsorption (PSA) processes. A detailed one‐dimensional, transient mathematical model has been formulated to include the heat and mass transfer, the pressure drop and multicomponent mass diffusion. The PSA model has been further extended by incorporating a heat regenerating process to enhance CO₂ sequestration. The heat dissipated during adsorption is stored in packed sand bed and released during desorption step for heating purpose. The model has been implemented on a MATLAB program using second‐order discretization. Validation of the model was performed using a complete experimental data set for CO₂ sequestration using zeolite 13X. Simulation of the PSA experiment on fixed bed has been carried out to evaluate the capacity of Mg‐MOF‐74 for CO₂ capture with varying feed gas temperature of 28 and 100 °C, varying pressurization and purge times and heat regeneration. It was discovered that the PSA process with heat regeneration system might be advantageous because it achieves equivalent amount of CO₂ sequestration in fewer PSA cycles compared with PSA without heat regeneration system. Based on the simulated conditions, CO₂ recovery with Mg‐MOF‐74 gives high percentage purity (above 98%) for the captured CO₂. Copyright © 2015 John Wiley & Sons, Ltd.     

Pt‐Rh/TiO2/activated carbon as highly active and stable HI decomposition catalyst for hydrogen production in sulfur‐iodine (SI) process

Pt‐TiO₂ loaded on activated carbon was studied as an active and stable catalyst to HI decomposition for H₂ formation in the sulfur‐iodine process. Although the activity of TiO₂‐loaded catalyst was slightly lower HI conversion than that of CeO₂ loaded one, the higher stability against HI decomposition reaction was achieved and almost equilibrium conversion was sustained over ~65 h examined. Moreover, effects of Rh or Ir addition on HI conversion were studied and it was found that Pt‐Rh bimetallic system was highly active and stable to HI decomposition. Scanning transmission electron micrograph observation suggested that the increased HI decomposition activity was assigned to the increased dispersion of Pt particles. High dispersion state of Pt was sustained after HI decomposition at 773 K by addition of Rh. Since the formation of PtI₄ was suggested by X‐ray photoelectron spectroscopy measurement during HI decomposition, increased stability by addition of Rh seems to be assigned to the high chemical stability of Rh against iodine. Almost the equilibrium HI conversion on Pt‐Rh‐TiO₂/M563 was sustained over 300 hours at 673 K.     

Fabrication of microporous and mesoporous carbon spheres for high‐performance supercapacitor electrode materials

Microporous and mesoporous carbon spheres (CSs) were fabricated using resorcinol and formaldehyde as precursors in the presence of Pluronic F127 as porogen and KOH as the active agent. The textural characteristic and morphology were characterized by scanning electron microscopy, transmission electron microscopy, and N₂ adsorption/desorption techniques. Pluronic F127 played an important role for generating mesopores, while KOH activation brought abundant micropores and resulted in a combined microporous and mesoporous structure of the CSs. The results showed that a typical sample (denoted as CS‐F‐K) possessed a spherical shape, with a high specific surface area of 735.4 m²/g, large pore volume of 0.622 cm³/g, and combined microporous and mesoporous structure, which endowed CS‐F‐K good electrochemical performance with a specific capacitance of 182 F/g under a current density of 0.5 A/g, remarkable rate performance, and long‐term cycling stability. After 1000 cycles at 3 A/g, CS‐F‐K electrode can still remain the specific capacitance of 154.8 F/g with a retention of 98.9%. The excellent electrochemical performance of CS‐F‐K was mainly attributed to the micro‐mesoporous structure, which promoted the ion accumulation on the electrode surface and facilitated fast ion transportation. Copyright © 2015 John Wiley & Sons, Ltd.     

Combination effect of ZnO and activated carbon for solar assisted photocatalytic degradation of Direct Blue 53

The degradation efficiency of AC–ZnO composite photocatalyst was evaluated with solar light using an azo dye Direct blue 53 (DB53) at room temperature. Activity measurements performed under solar radiation have shown good results for the photodegradation of DB53. The synergistic effect observed was ascribed to an extended adsorption of DB53 on activated carbon followed by its transfer to ZnO where it was photocatalytically degraded. The enhanced photocatalytic activity of AC–ZnO when compared to ZnO is found to be due to this synergistic effect. A study on the effects of various parameters like concentration of dye, amount of catalyst and initial pH on the photodegradation of DB53 has been carried out to find optimum conditions.     

Thermodynamic analysis of double‐stage biomass fired Organic Rankine Cycle for micro‐cogeneration

A biomass fired double‐stage Organic Rankine Cycle (ORC) for micro‐cogeneration is studied. Focus is laid on optimizing thermal efficiency in summer mode by appropriate working fluid and pressure level selection. Simulation and thermodynamic analysis show that in double‐stage ORC, the working fluid in the low‐temperature circuit (LTC) effects total efficiency more than the working fluid in the high‐temperature circuit (HTC). Within the chosen boundary conditions, isopentane gives best thermal efficiency, whereas R227ea is the least efficient in the LTC. Among the working fluids for the HTC, maximum total efficiency is similar for several working fluids. Simulations demonstrate that a prediction of thermal efficiencies with respect to physico‐chemical characteristics of different working fluids is only feasible within certain chemical classes. In the HTC, low critical temperature, low molar mass, and high critical pressure increase the efficiency, whereas in the LTC, condensation pressure is most crucial for high efficiency. Constructional analysis indicate that in the majority of cases, an increase in thermal efficiency is connected with high‐volume flow rates at the outlet of the turbine, which leads to voluminous expansion units and high investment costs, respectively. Appropriate working fluid combinations within a double‐stage ORC reach total efficiencies of up to 35% at flue gas temperatures from 950 to 150 °C. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel Cu–carbon nanofiber composites for the counter electrodes of dye‐sensitized solar cells

Copper (Cu)‐catalyzed carbon nanofibers (CNFs) were used as an alternative of the conventional platinum‐noble‐metal‐based catalyst at the counter electrode (CE) of a dye‐sensitized solar cell (DSSC). The CNFs were grown on activated carbon microfiber powder (PACF) using chemical vapor deposition (CVD) and the Cu nanoparticles (NPs). The Cu NPs served simultaneous roles: (i) as the CVD catalyst for the growth of the CNFs; (ii) as an enhancer of the electrode conductivity; and (iii) as a catalyst for the reduction reaction. The Cu‐CNF composite was applied as a thin layer on the fluorine‐doped tin oxide glass using the simple doctor blade method. The prepared Cu‐NP‐dispersed PACF/CNF composite was characterized using various spectroscopic techniques, including scanning electron microscopy, Fourier transform infrared ray, X‐ray diffraction, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests showed that the Cu‐PACF/CNFs had a high electrocatalytic activity and low charge transfer resistance (1.26 Ω cm²), using the cyclic voltammetry and electrochemical impedance spectroscopy measurements. The DSSC fabricated with Cu‐PACFs/CNFs exhibited a power conversion efficiency value of 4.36%, open circuit voltage of 0.75 V, short circuit current density of 11.12 mA cm^?2, and fill factor of 54%. The prepared transition metal–CNF composite was simple to develop and can potentially be used as an efficient catalyst at the CE of DSSCs. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of carbon nanomaterials for dye‐sensitized solar cells

In this paper, it was demonstrated that Na₂O can react with CO to produce carbon nanofibers at 500 °C and carbon nanosheets at 550 °C. Furthermore, the nanosheets exhibited excellent performance as a counter electrode for a dye‐sensitized solar cell (DSSC), leading to a high power conversion efficiency of 7.57%. The efficiency is larger than that (4.72%) of a DSSC with the carbon nanofiber counter electrode and even comparable with that of an expensive Pt‐based DSSC. Copyright © 2015 John Wiley & Sons, Ltd.     

Energy‐efficient design of greenhouse for Canadian Prairies using a heating simulation model

Greenhouses in northern climates require a large amount of supplemental heating for growing crops in winter seasons, so energy‐efficient design of greenhouses based on local climate is important to minimize the heating demand. In this study, greenhouse design parameters including shape, orientation, the angle of the roof, and width of the span have been studied for the conceptual design of conventional greenhouses for Canadian Prairies using a heating simulation model. Five different shapes of greenhouses including even‐span, uneven‐span, modified arch, vinery, and quonset shape have been selected for the study. The simulation results proved that the uneven‐span gable roof shape receives the highest solar radiation, whereas the quonset shape receives the lowest solar radiation. However, the quonset shape greenhouse requires about 7.6% less annual heating as compared to the gable roof greenhouse, but the quonset would not be adopted as multispan greenhouses. Therefore, the gable roof greenhouse is considered as energy efficient for the multispan gutter connected greenhouses whereas quonset shape as a free‐standing single‐span greenhouses. In high northern latitudes, the greenhouse with east‐west orientation is more energy efficient from heating and cooling point of view when the length‐width ratio of the greenhouse is more than 1. The heating energy saving potential of the large span width in single‐span greenhouses is relatively higher as compared to the multispan greenhouses.     

Synthesis and characterization of PVDF‐coated cotton‐derived hard carbon for anode of Li‐ion batteries

A carbonized cotton that is coated by pyrocarbon of Polyvinylidene Fluoride (PVDF) (HC/P) was synthesized by a facile method. Its microstructure and electrochemical performances as anode for Li‐ion batteries were characterized by X‐Ray Diffraction (XRD), Raman, X‐ray photoelectron spectrometer (XPS), Scanning Electron Microscope (SEM), and other means. It is found that coating process does not affect the phase structure but influences the morphology, specific area, and electrochemical performances. HC/P series have abundant pores with diameter of 2 to 5 nm and small‐size particles; thus, they have much more lithium storage position or charge/discharge capacity than pristine hard carbon (HC). Besides, Cyclic Voltammetry (CV) curves of HC/P‐2 proved that the irreversible side reactions of Li⁺ with surface functional groups were reduced, which can explain the advancement of initial coulomb efficiency. Among three HC/P samples, HC/P‐2 owns the best electrochemical performances. It delivered 520 mAh/g under current density of 20 mA/g and kept 95.9% retention rates of capacity after 100 cycles under 200 mA/g of current density.     

Morphology‐dependent electrochemical performance of nitrogen‐doped carbon dots@polyaniline hybrids for supercapacitors

In this work, the binary N‐CDs@PANI hybrids were fabricated by introducing zero‐dimensional nitrogen‐doped carbon dots (N‐CDs) into reticulated PANI. Firstly, N‐CDs were prepared by one‐pot microwave method, and then, the N‐CDs were introduced into in situ oxidative polymerization of aniline (ANI) monomer. The N‐CDs with abundant functional groups and high electronic cloud density played a significant role in guiding the polyaniline‐ordered growth into intriguing morphologies. Moreover, morphology‐dependent electrochemical performances of N‐CDs@PANI hybrids were investigated and N‐CDs improve static interaction and enhance the special capacitances in the N‐CDs@PANI hybrids. Especially, the specific capacitance of PC4 hybrid can reach 785 F g^?1, which exceed that of pure PANI (274 F g^?1) at current density of 0.5 A g^?1 according to three‐electrode measurement. And the capacitance retention of the PC4 hybrid still keeps 70% after 2000 cycles of charge and discharge. The N‐CDs@PANI hybrids can have potential applications in electrode materials, supercapacitors, nonlinear optics, and microwave absorption.     

Investigation of catalyst layer defects in catalyst‐coated membrane for PEMFC application: Non‐destructive method

The commercialization of polymer electrolyte membrane fuel cells has been hindered by durability problems caused by defects in the manufacturing process. We demonstrate for the first time a non‐destructive, non‐contact method that uses optical microscopy and image analysis to identify defects that may lead to failure in catalyst‐coated membranes (CCMs) of polymer electrolyte membrane fuel cells. This method is applied to 2 commercial CCMs produced by the decal transfer technique. Defects in the catalyst layer (CL) at the beginning‐of‐life (BOL) are characterized in terms of their initial size and shape, and their propagation is tracked as the CCMs are aged in a non‐reactive environment. The defected area in one of the commercial CCMs increases from approximately 2.4% of the total CL area at BOL to 10.5% by end‐of‐life (EOL). BOL defects in the CL are found to propagate faster in the CCMs stored for 2 years under atmospheric conditions compared with freshly manufactured CCMs with narrow CL defects. Image analysis of another commercial CCM shows the presence of pores with diameters between 5 and 25 μm that comprise 52% of the total pore area in the CL. Other defects such as scratches and missing/empty catalyst areas are identified and characterized, providing a framework for quality control applications. Finally, the effect of defects on fuel cell performance is characterized by measurement of the open‐circuit voltage (OCV). These experiments show that CCMs with a large number of cracks in the CL exhibit a voltage loss of 2.55 mV/hr, whereas CCMs with thin/missing/empty CL defects show a loss of 1.12 mV/hr.     

Electrokinetically modulated flow of couple stress magneto‐nanofluids in a microfluidic channel

In the present article, the theoretical investigation is presented for the mixed electrokinetic and pressure‐driven transport of couple stress nanoliquids in a microchannel with the effect of magnetic field and porous medium. This topic has gained a remarkable scope in nanoscale electro‐osmotic devices. The formulation of the present mathematical problem is simplified using the Debye‐Hückel linearization assumption. The merging model has important features such as the thermal Grashof number, solutal Grashof number, Joule heating, Helmholtz‐Smoluchowski velocity. The analytical solutions are presented for the axial velocity, temperature, and solute concentration. The expressions for the heat transfer rate, solute mass transfer rate, and surface shear stress function at the walls are also presented. The results display that, the velocity of the couple stress nanofluid is less in the case of pure electro‐osmotic flow as compared to that of combined electro‐osmotic and pressure‐driven flow. When the Joule heating parameter vanishes, the temperature and solute concentration profiles are linear, otherwise nonlinear. The shear stress function is larger in the case of pure electro‐osmotic flow and it is smaller for the combined effects of electro‐osmotic and pressure gradient. The present analysis places a significant observation that the various zeta potential plays an influential role in heartening fluid velocity. The analysis is relevant to electrokinetic hemodynamics and microfluidics.     

Determining photosensor settings for optimum energy saving of suspended lighting systems in a small double‐skinned office

A photoelectric dimming control system applied to a suspended direct/indirect and indirect lighting system was analyzed to determine effective control options in a small office with double‐skin envelope. Computer simulations were performed for photosensors positioned at three different locations with three specific configurations under three Commission Internationale de l'Élairage standard sky types. Optimum ideal dimming level was determined for each combination of room orientation, photosensor configurations and positions. In general, fully shielded photosensors achieved better control performance among other configurations used for the photosensors on the ceiling and the back wall. The effect of photosensor configurations on dimming system performance was as significant as the photosensor positions. As the penetration of daylight decreased due to the shaded area on the internal envelope, the control system performance deteriorated. The correlation between the photosensor signals and the desktop illuminance levels due to daylight was not significantly meaningful under the lighting systems. Lighting energy savings were determined for the best and good system control performance. Copyright © 2009 John Wiley & Sons, Ltd.     

One‐pot synthesis of Pd‐MoO2/C by microwave sintering as an efficient electrocatalyst for ethanol oxidation reaction

The composite catalysts of Pd‐MoO₂/C for ethanol oxidation reaction (EOR) were prepared by microwave sintering. MoO₃ was thermally reduced to MoO₂ by carbon black in the preparing process of the Pd‐MoO₂/C material. The TEM analysis showed that Pd‐MoO₂ was well polymerized. Chronoamperometric, cyclic voltammetry, and electrochemical impedance spectra methods were applied to reveal the performance for EOR at room temperature. The Pd‐MoO₂/C electrode exhibited considerable high activity and stability. MoO₂ as a co‐catalyst significantly improved the catalytic activity of Pd‐MoO₂/C for EOR.