Polarization Characteristics of Porous Electrode Systems with Adsorbed Intermediates Participating in the Electrode Reaction

Current-potential relationships are derived for porous electrode systems following a homogeneous model and whenadsorbed intermediates participate in the electrode reaction. Limiting Tafel slopes were deduced and compared with thecorresponding behavior on planar electrode systems. The theoretical results showed doubling of Tafel slopes when theslow-step is a charge-transfer reaction and a nonlogarithmic current-voltage behavior when the slow-step is a chemical reaction.Comparison of the experimental results with theory for the case of oxygen reduction on carbon surfaces in alkalinemedia indicates that a slow chemical reaction following the initial charge-transfer reaction to be the likely rate-controllingstep. Theoretical relationships are utilized to determine the exchange current density and the surface coverage by the adsorbedintermediates during the course of oxygen reduction from alkaline solutions on "carbon." Tafel slope measurementson planar and porous electrodes for the same reaction are suggested as one of the diagnostic criteria for elucidatingthe mechanistic pathways of electrochemical reactions.

An electrochemically impregnated sintered-nickel electrode

An electrochemically impregnated sintered-nickel porous electrode with a capacity of 225 +/- 10 mAh per g of active material has been developed. This capacity is comparable with any state-of-the-art nickel hydroxide electrode reported in the literature, such as the stabilized alpha-nickel hydroxides that contain aluminium, iron and other trivalent cations. A technical update on various types of nickel positive electrodes is given.

Fractional-factorial design of a porous-carbon fuel-cell electrode

The use of fractional-factorial methods in the optimization of porous-carbon electrode structure is discussed with respect to weight-loss of carbon during gas treatment, weight and mixing time of binder, compaction temperature, time and pressure, and pressure of feed gas. The experimental optimization of an air electrode in alkaline solution is described.

Polymer template-assisted microemulsion synthesis of large surface area, porous Li2MnO3 and its characterization as a positive electrode material of Li-ion cells

Lithium-rich manganese oxide (Li2MnO3) is prepared by reverse microemulsion method employing Pluronic acid (P123) as a soft template and studied as a positive electrode material. The as-prepared sample possesses good crystalline structure with a broadly distributed mesoporosity but low surface area. As expected, cyclic voltammetry and charge-discharge data indicate poor electrochemical activity. However, the sample gains surface area with narrowly distributed mesoporosity and also electrochemical activity after treating in 4 M H2SO4. A discharge capacity of about 160 mAh g(-1) is obtained. When the acid-treated sample is heated at 300 A degrees C, the resulting porous sample with a large surface area and dual porosity provides a discharge capacity of 240 mAh g(-1). The rate capability study suggests that the sample provides about 150 mAh g(-1) at a specific discharge current of 1.25 A g(-1). Although the cycling stability is poor, the high rate capability is attributed to porous nature of the material.

Polymer Template Assisted Synthesis of Porous Li1.2Mn0.53Ni0.13Co0.13O2 as a High Capacity and High Rate Capability Positive Electrode Material

A porous layered composite of Li2MnO3 and LiMn1/3Co1/3Ni1/3O2 (composition: Li1.2Mn0.53Ni0.13Co0.13O2) is prepared by reverse microemulsion method employing a soft polymer template and studied as a positive electrode material. The precursor is heated at several temperatures between 500 and 900 degrees C. The product samples possess mesoporosity with broadly distributed pores of about 30 nm diameters. There is a decrease in pore volume as well as in surface area by increasing the temperature of preparation. Nevertheless, the electrochemical activity of the composite increases with an increase in temperature. The discharge capacity values of the samples prepared at 800 and 900 degrees C are about 250 mAh g(-1) at a specific current of 40 mA g(-1) with an excellent cycling stability. A value of 225 mAh g(-1) is obtained at the end of 30 charge-discharge cycles. Both these composite samples possess high rate capability, but the 800 degrees C sample is marginally superior to the 900 degrees C sample. A discharge capacity of 100 mAh g(-1) is obtained at a specific current of 1000 mA g(-1). The high rate capability is attributed to porous nature of the composite samples. (C) 2013 The Electrochemical Society. All rights reserved.

Preparation and electrochemical performance of porous hematite (alpha-Fe2O3) nanostructures as supercapacitor electrode material

Porous alpha-Fe2O3 nanostructures have been synthesized by sol-gel route. The effect of preparation temperature on the morphology, structure, and electrochemical stability upon cycling has been studied for supercapacitor application. The discharge capacitance of alpha-Fe2O3 prepared at 300 A degrees C is 193 F g(-1), when the electrodes are cycled in 0.5 M Na2SO3 at a specific current of 1 A g(-1). The capacitance retention after 1,000 cycles is about 92 % of the initial capacitance at a current density of 2 A g(-1). The high discharge capacitance as well as stability of alpha-Fe2O3 electrodes is attributed to large surface area and porosity of the material. There is a decrease in specific capacitance (SC) on increasing the preparation temperature. As iron oxides are inexpensive, the synthetic route adopted for alpha-Fe2O3 in the present study is convenient and the SC is high with good cycling stability, the porous alpha-Fe2O3 is a potential material for supercapacitors.

Porous lithium rich Li1.2Mn0.54Ni0.22Fe0.04O2 prepared by microemulsion route as a high capacity and high rate capability positive electrode material

A porous layered composite of Li2MnO3 and LiMn0.35Ni0.55Fe0.1O2 (composition:Li1.2Mn0.54Ni0.22Fe0.04O2) is prepared by inverse microemulsion method and studied as a positive electrode material. The precursor is heated at several temperatures between 500 and 900 degrees C. The X-ray diffraction, scanning electron microscopy, and transmission electron microscopy studies suggested that well crystalline submicronsized particles are obtained. The product samples possess mesoporosity with broadly distributed pores around 10 similar to 50 nm diameter. Pore volume and surface area decrease by increasing the temperature of preparation. However, the electrochemical activity of the composite samples increases with an increase in temperature. The discharge capacity values of the samples prepared at 900 degrees C are about 186 mAh g(-1) at a specific current of 25 mA g(-1) with an excellent cycling stability. The composite sample also possesses high rate capability. The high rate capability is attributed to the porous nature of the material. (C) 2014 Elsevier Ltd. All rights reserved.

Hierarchically porous Li1.2Mn0.6Ni0.2O2 as a high capacity and high rate capability positive electrode material

Layered composite samples of lithium-rich manganese oxide (Li1.2Mn0.6Ni0.2O2) are prepared by a reverse microemutsion route employing a soft polymer template and studied as a positive electrode material. The product samples possess dual porosity with distribution of pores at 3.5 and 60 nm. Pore volume and surface area decrease on increasing the temperature of preparation. Nevertheless, the electrochemical activity of the composite increases with an increase in temperature. The discharge capacity value of the samples prepared at 800 and 900 degrees C is about 240 mA h g(-1) at a specific current of 25 mA g(-1) with a good cycling stability. The composite sample heated at 900 degrees C possesses a high rate capability with a discharge capacity of 100 mA h g(-1) at a specific current of 500 mA g(-1). The high rate capability is attributed to porous nature of the composite sample.

Open-circuit potential—time transients of alkaline porous iron electrodes at various states-of-charge

Open-circuit potential—time transients during the discharge of alkaline porous iron electrodes at various states-of-charge have been studied. From this, it has been possible to arrive at a correlation between the parameters of self-discharge kinetics of the electrode and observed open-circuit potential—recovery time constants. The study provides a method of estimate the state-of-charge of the rechargeable iron electrodes. As a hydrogen evolution reaction inevitably occurs on alkaline iron electrodes, the kinetics of the reaction have also been investigated.

Synthesis of zinc oxide porous structures by anodization with water as an electrolyte

We report a simple, reliable and one-step method of synthesizing ZnO porous structures at room temperature by anodization of zinc (Zn) sheet with water as an electrolyte and graphite as a counter electrode. We observed that the de-ionized (DI) water used in the experiment is slightly acidic (pH=5.8), which is due to the dissolution of carbon dioxide from the atmosphere forming carbonic acid. Porous ZnO is characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and photoluminescence (PL) studies. The current-transient measurement is carried out using a Gamry Instruments Reference 3000 and the thickness of the deposited films is measured using a Dektak surface profilometer. The PL, Raman and X-ray photoelectron spectroscopy are used to confirm the presence of ZnO phase. We have demonstrated that the hybrid structures of ZnO and poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS) exhibit good rectifying characteristics. The evaluated barrier height and the ideality factor are 0.45 eV and 3.6, respectively.

Morphology Controlled Growth of Meso-Porous Co3O4 Nanostructures and Study of Their Electrochemical Capacitive Behavior

The morphology of nanocrystalline Co3O4 synthesized through microwave irradiation of a solution of a cobalt complex is found to depend reproducibly on the conditions of synthesis and, in particular, on the composition of the solvent used. Despite the rapidity of the process, oriented aggregation occurs under certain conditions, depending on solvent composition. Annealing the oriented samples leads to microstructures with significant porosity, rendering the material suitable as electrodes for electrochemical capacitors. Electrochemical analysis of the oxide samples was carried out in 0.1M Na2SO4 electrolyte vs. Ag/AgCl electrode. A stable specific capacitance of 221 F/g was measured for a meso-porous sample displaying oriented aggregation. Stability of these oxide materials were checked for longer charge-discharge cycling. (C) 2012 The Electrochemical Society. DOI: 10.1149/2.002210jes] All rights reserved.

Vertical electric field stimulated neural cell functionality on porous amorphous carbon electrodes

We demonstrate the efficacy of amorphous macroporous carbon substrates as electrodes to support neuronal cell proliferation and differentiation in electric field mediated culture conditions. The electric field was applied perpendicular to carbon substrate electrode, while growing mouse neuroblastoma (N2a) cells in vitro. The placement of the second electrode outside of the cell culture medium allows the investigation of cell response to electric field without the concurrent complexities of submerged electrodes such as potentially toxic electrode reactions, electro-kinetic flows and charge transfer (electrical current) in the cell medium. The macroporous carbon electrodes are uniquely characterized by a higher specific charge storage capacity (0.2 mC/cm(2)) and low impedance (3.3 k Omega at 1 kHz). The optimal window of electric field stimulation for better cell viability and neurite outgrowth is established. When a uniform or a gradient electric field was applied perpendicular to the amorphous carbon substrate, it was found that the N2a cell viability and neurite length were higher at low electric field strengths (<= 2.5 V/cm) compared to that measured without an applied field (0 V/cm). While the cell viability was assessed by two complementary biochemical assays (MTT and LDH), the differentiation was studied by indirect immunostaining. Overall, the results of the present study unambiguously establish the uniform/gradient vertical electric field based culture protocol to either enhance or to restrict neurite outgrowth respectively at lower or higher field strengths, when neuroblastoma cells are cultured on porous glassy carbon electrodes having a desired combination of electrochemical properties. (C) 2013 Elsevier Ltd. All rights reserved.

Synthesis, characterisation and application of an exfoliated graphite-diamond composite electrode in the electrochemical degradation of trichloroethylene

A composite electrode made up of exfoliated graphite (EG) and diamond was prepared for the electrochemical oxidation of trichloroethylene (TCE). The SEM images of the EG-diamond material showed that diamond powders were dispersed on the surface of EG materials. The N-2 adsorption-desorption isotherm of EG-diamond material resulted in a poor adsorption capability due to the insertion of diamond powders into the porous matrix of EG. Raman spectroscopy revealed the presence of characteristic sp(3) bands of diamond confirming good interaction of diamond with EG. Electrochemical characterisation of EG-diamond in 0.1 M Na2SO4 resulted in an enhanced working potential window. The EG-diamond electrode was employed for the electrochemical oxidation of trichloroethylene (0.2 mM) in a Na2SO4 supporting electrolyte. The EG-diamond, in comparison to the pristine EG electrode, exhibited a higher removal efficiency of 94% (EG was 57%) and faster degradation kinetics of 25.3 x 10(-3) min(-1) showing pseudo first order kinetic behaviour. Under the optimised conditions, 73% total organic content (TOC) removal was achieved after 4 h of electrolysis. The degradation of TCE was also monitored with gas chromatography-mass spectrometry. Dichloroacetic acid (DCAA) was identified as a major intermediate product during the electrochemical oxidation of TCE. The electrochemical degradation of TCE at the EG-diamond electrode represents a cost effective method due to the ease of preparation of EG-diamond composite material without the necessity of diamond activation which is normally achieved through doping.

High specific surface area alpha-Fe2O3 nanostructures as high performance electrode material for supercapacitors

Porous alpha-Fe2O3 nanostructures have been synthesized by a simple sol-gel route. The alpha-Fe2O3 nanostructures are poorly crystalline and porous with BET surface area of 386 m(2) g(-1). The high discharge capacitance of alpha-Fe2O3 electrodes is 300 F g(-1) when the electrodes are cycled in 0.5 M Na2SO3 at a current density of 1 A g(-1). The capacitance retention after 1000 cycles is about 73% of the initial capacitance at a current density of 2 A g(-1). The high discharge capacitance of alpha-Fe2O3 in comparison with the literature reports are attributed to high surface area and porosity of the iron oxide prepared in the present study. As the iron oxides are inexpensive, the capacity of alpha-Fe2O3 is expected to be of potential use for supercapacitor application. (C) 2014 Elsevier B.V. All rights reserved.

Electrospun SnSb Crystalline Nanoparticles inside Porous Carbon Fibers as a High Stability and Rate Capability Anode for Rechargeable Batteries

In an electrochemical alloying reaction, the electroactive particles become mechanically unstable owing to large volume changes occurring as a result of high amounts of lithium intake. This is detrimental for long-term battery performance. Herein, a novel synthesis approach to minimize such mechanical instabilities in tin particles is presented. An optimal one-dimensional assembly of crystalline single-phase tin-antimony (SnSb) alloy nanoparticles inside porous carbon fibers (abbreviated SnSb-C) is synthesized for the first time by using the electrospinning technique (employing non-oxide precursors) in combination with a sintering protocol. The ability of antimony to alloy independently with lithium is beneficial as it buffers the unfavorable volume changes occurring during successive alloying/dealloying cycles in Sn. The SnSb-C assembly provides nontortuous (tortuosity coefficient, =1) fast conducting pathways for both electrons and ions. The presence of carbon in SnSb-C completely nullifies the conventional requirement of other carbon forms during cell electrode assembly. The SnSb-C exhibited remarkably high electrochemical lithium stability and high specific capacities over a wide range of currents (0.2-5Ag(-1)). In addition to lithium-ion batteries, it is envisaged that SnSb-C also has potential as a noncarbonaceous anode for other battery chemistries, such as sodium-ion batteries.