Anodic Half-cell Research Articles

Enhanced performance of sulfone-based electrolytes at lithium ion battery electrodes, including the LiNi0.5Mn1.5O4 high voltage cathode

In an extension of our previous studies of sulfone-containing electrolytes for lithium batteries, we report tests of sulfone–carbonate, and all-sulfone, electrolytes in a variety of anode and cathode half cells. While the all-sulfone electrolyte appears promising at the graphite anode in early cycles, it fails at the high voltage cathode and will not be further tested. On the other hand a sulfone–carbonate mixed solvent performs very well (97% capacity retention after 100 cycles with 99–100% coulomb efficiency) at the LiNi0.5M1.5O4 (LNMO) cathode, and also at the Li4Ti5O12 (LTO) anode, both of which are being developed for high power applications.

Power generation from a hybrid biological fuel cell in seawater

A hybrid biological fuel cell (HBFC) comprised of a microbial anode for lactate oxidation and an enzymatic cathode for oxygen reduction was constructed and then tested in a marine environment. Shewanella oneidensis DSP-10 was cultivated in laboratory medium and then fixed on a carbon felt electrode via a silica sol–gel process in order to catalyze anodic fuel cell processes. The cathode electrocatalyst was composed of bilirubin oxidase, fixed to a carbon nanotube electrode using a heterobifunctional cross linker, and then stabilized with a silica sol–gel coating. The anode and cathode half-cells provided operating potentials of −0.44 and 0.48V, respectively (vs. Ag/AgCl). The HBFC maintained a reproducible open circuit voltage >0.7V for 9d in laboratory settings and sustained electrocatalytic activity for >24h in open environment tests.

Diffusion-Free Mediator Based Miniature Biofuel Cell Anode Fabricated on a Carbon-MEMS Electrode

We report on the functionalization of a micropatterned carbon electrode fabricated using the carbon-MEMS process for its use as a miniature diffusion-free glucose oxidase anode. Carbon-MEMS based electrodes offer precise manufacturing control on both the micro- and nanoscale and possess higher electron conductivity than redox hydrogels. However, the process involves pyrolysis in a reducing environment that renders the electrode surface less reactive and introduction of a high density of functional groups becomes challenging. Our functionalization strategy involves the electrochemical oxidation of amine linkers onto the electrode. This strategy works well with both aliphatic and aryl linkers and uses stable compounds. The anode is designed to operate through mediated electron transfer between 2,5-dihydroxybenzaldehyde (DHB) based redox mediator and glucose oxidase enzyme. The electrode was first functionalized with ethylene diamine (EDA) to serve as a linker for the redox mediator. The redox mediator was then grafted through reductive amination, and attachment was confirmed through cyclic voltammetry. The enzyme immobilization was carried out through either adsorption or attachment, and their efficiency was compared. For enzyme attachment, the DHB attached electrode was functionalized again through electro-oxidation of aminobenzoic acid (ABA) linker. The ABA functionalization resulted in reduction of the DHB redox current, perhaps due to increased steric hindrance on the electrode surface, but the mediator function was preserved. Enzyme attachment was then carried out through a coupling reaction between the free carboxyl group on the ABA linker and the amine side chains on the enzyme. The enzyme incubation for both adsorption and attachment was done either through a dry spotting method or wet spotting method. The dry spotting method calls for the evaporation of enzyme droplet to form a thin film before sealing the electrode environment, to increase the effective concentration of the enzyme on the electrode surface during incubation. The electrodes were finally protected with a gelatin based hydrogel film. The anode half-cell was tested using cyclic voltammetry in deoxygenated phosphate buffer saline solution pH 7.4 to minimize oxygen interference and to simulate the pH environment of the body. The electrodes that yielded the highest anodic current were prepared by enzyme attachment method with dry spotting incubation. A polarization response was generated for this anodic half-cell and exhibits operation close to maximum efficiency that is limited by the mass transport of glucose to the electrode.

Towards Alternatives to Anodic Water Oxidation: Basket‐Handle Thiolate FeIII Porphyrins for Electrocatalytic Hydrocarbon Oxidation

Selective electrocatalytic oxidation of hydrocarbons to alcohols, epoxides or other (higher value) oxygenates should in principal present a useful complementary anodic half-cell reaction to cathodic generation of fuels from water or CO(2) viz. an alternative to oxygen evolution. A series of new basket-handle thiolate Fe(III) porphyrins have been synthesised and shown to mediate anodic oxidation of hydrocarbons, specifically adamantane hydroxylation and cyclooctene epoxidation. We compare yields obtained by electrochemical and chemical oxidation of the thiolate porphyrins and benchmark their behaviour against that of Fe(III) tetraphenyl porphyrin chloride and its tetrapentafluorophenyl analogue.

Microbial fuel cell with a polypyrrole/poly(methylene blue) composite electrode

Microbial fuel cell with a polypyrrole/poly(methylene blue) composite electrode Jonathan M Godwin, Richard W Evitts, Glyn F KennellDepartment of Chemical and Biological Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, CanadaAbstract: Different configurations of anodic and cathodic half-cells were incorporated into a microbial fuel cell to determine the effectiveness of a composite electrode. This novel composite electrode consisted of poly(methylene blue) and polypyrrole electrodeposited onto a stainless steel electrode. The novel electrode/immobilized mediator was incorporated into a microbial cathodic half-cell that relied on the microalgae Chlorella vulgaris for photosynthesis, and was a net reducer of carbon dioxide. Similar microbial cathodic half-cells were also examined using electrodes fabricated from graphite and graphite deposited with methylene blue. Results from using these three different electrodes in the microbial cathodic half-cell were examined and compared with the results from others. The electrode using the novel immobilized mediator demonstrated the highest short circuit current density of 65 mA/m2 when compared with other C. vulgaris systems. Different anodic half-cells were also incorporated into the microbial fuel cell and tested. Anodic half-cells tested included a microbial half-cell containing Saccharomyces cerevisiae and one containing no microbial material and based on purely chemical constituents. In the case of the microbial anodic half-cell, different electrodes, including the novel immobilized mediator/electrode, were tested. It was found that the anodic half-cell performed better with a soluble mediator than an immobilized mediator/electrode. In the case of a fuel cell where both the anodic and cathodic half-cells are microbial, our results demonstrate better performance than previous systems by using a soluble mediator in the anodic half-cell with an immobilized mediator in the cathodic half-cell.Keywords: microbial fuel cell, biocathode, immobilized mediator, stainless steel electrode

The Effect of the Reference Electrode Position on the Measurement of Half Cell Polarization in Proton-Exchange Membrane Fuel Cells

In this experimental and numerical study we analyze the polarization of the electrodes in a PEM fuel cell system. In order to measure the anode and cathode potential with respect to the electrolyte potential, a dynamic hydrogen electrode (DHE) is used as reference electrode. Two fundamental configurations for integrating a DHE into the membrane electrode assembly (MEA) are investigated: In the first configuration, the DHE is contacted to the membrane within a circular gap in the cathode catalyst layer, which is called edge configuration. In the second configuration, the DHE is placed between two membrane layers, which is called sandwich configuration. Differences between the reference electrode setups can be ascribed to an inhomogeneous electrolyte potential distribution close to the edge of the electrodes as described in literature. Our 2D fuel cell model as published in an earlier article is used to investigate this effect. We show that it is not possible to detect the electrode polarization by use of a reference electrode in edge configuration. By use of the sandwich configuration, the polarization of the anode and cathode half cells can be measured independently.

Quantifying Individual Losses in a Direct Methanol Fuel Cell

Studying the performance of a direct methanol fuel cell (DMFC) is complicated by the complex interactions of kinetic and transport processes. As a result, changes in one aspect of the cell have consequences in other aspects, which are difficult to elucidate from full-cell polarization (i.e., voltage versus current) behavior. This study outlines a strategy to use current and voltage relationships from anode half-cells, cathode half-cells, and hydrogen pump coupled with methanol crossover data and a mathematical model. In this way, all the kinetic and transport processes have been quantified, and the cell voltage was deconstructed (i.e., individual voltage losses were quantified). This data analysis accounts for all of the voltage losses observed during the operation of the full cell. As expected, the anode and cathode overpotentials accounted for most of the losses (i.e., 92% on average). Also, the cathode flow rate has been shown to affect the methanol crossover by diffusion. Cells operated at constant stoichiometry or where the cathode flow rate is small can show a parabolic shape in the methanol crossover because the electroosmotic drag dominates over diffusion as the primary transport mechanism for methanol through the membrane. Decrease in the methanol crossover was observed for cells with high compression and thicker cathode electrodes. The one-dimensional model, developed previously (García et al., 2004, “Mathematical Model of a Direct Methanol Fuel Cell,” J. Fuel Cell Sci. Technol., 1(1), pp. 43–48), was improved by: (1) including methanol transport from the anode flow channel to the backing layer using a mass transfer resistance and (2) accounting for the unreacted methanol transport through the cathode. The model was able to reasonably predict the anode, cathode, full-cell polarization, and methanol crossover data for methanol concentrations between 0.05 M and 2 M at all operating currents.

Suspension Plasma Spray and Performance Characterization of Half Cells with NiO/YSZ Anode and YSZ Electrolyte

The use of a liquid feedstock carrier in suspension plasma spray (SPS) permits injection of fine powders, providing the possibility of producing sprayed coatings that are both thin and dense and have fine microstructures. These characteristics make SPS an attractive process for depositing highly efficient electrodes and electrolytes for solid oxide fuel cell (SOFC) applications. In this study, NiO-yttria stabilized zirconia (YSZ) anode and YSZ electrolyte half cells were successfully deposited on porous Hastelloy X substrates by SPS. The NiO-YSZ anode deposition process was optimized by design of experiment. The YSZ electrolyte spray process was examined by changing one parameter at a time. The results from the design-of-experiment trials indicated that the porosity of the as-deposited coatings increased with an increase of suspension feed rate while it decreased with an increase of total plasma gas flow rate and standoff distance. The deposition rate increased with an increase of total plasma gas flow rate, suspension feed rate, and standoff distance. The microstructure examination by SEM showed that the NiO and YSZ phases were homogeneously distributed and that the YSZ phase had a lamellar structure. It was observed that the density of the YSZ electrolyte layer increased as input power of the plasma torch increased. Electrochemical characterization of the fabricated cells indicated that an open cell voltage of 0.989 V at 500 °C and a peak power of 0.610 W/cm2 at 750 °C were reached.

Electrochemical Impedance Spectroscopy of Liquid Tin Anode Solid Oxide Fuel Cell

Solid oxide fuel cells (SOFCs) can convert the chemical energy stored in hydrocarbon fuels directly into electricity bypassing the many energy transfers that normally occur, (chemical→ heat (steam boiler)→ mechanical (turbine)→ electrical (generator)), when hydrocarbon fuels are combusted to produce electricity. CellTech Power has developed a liquid tin anode (LTA) SOFC that is not damaged by fuels that contain sulfur. This paper develops an analytical electrochemical impedance spectroscopy model from first principals for the the LTA-SOFC anode half cell. The model is in conjunction with experimental data to determine; the average Ohmic resistance, 8.81mΩ, average steady state concentration of tin oxide in liquid tin, 1.09E-9 mol/cm3, effective diffusion coefficient of tin oxide through liquid tin, 0.198 cm2/s, and the pre-exponential factor for the butler volmer equation 2.92E5 C*cm/mol/s.

Ni/YSZ anode – Effect of pre-treatments on cell degradation and microstructures

Anode supported (Ni/YSZ–YSZ–LSM/YSZ) solid oxide fuel cells were tested and the degradation over hundreds of hours was monitored and analyzed by impedance spectroscopy. Test conditions were chosen to focus on the Ni/YSZ anode degradation and all tests were operated at 750 °C, a current density of 0.75 A cm −2. Oxygen was supplied to the cathode and the anode inlet gas mixture had a high p(H 2O)/p(H 2) ratio of 0.4/0.6. Commercially available gasses were applied. The effect of different types of pre-treatments on the Ni/YSZ electrode degradation during subsequent fuel cell testing was investigated. Pre-treatments included operating at OCV (4% and 40% H 2O in H 2) prior to fuel cell testing, cleaning of the inlet H 2 gas at 700 °C and processing the anode half cell via multilayer tape casting. Analyses of impedance spectra showed that the increase in the charge transfer reaction resistance in the Ni/YSZ ( R Ni,TPB) was decreased to ¼ or less for the pre-treated and fuel cell tested cells when compared with a non-pre-treated reference tested cell; all operated at the same fuel cell test conditions. Scanning electron microscopy and image analyses for the non-pre-treated reference tested cell and selected pre-treated cells showed significant differences in the area fractions of percolating nickel both in the active anode and support layer.

Catalytic activity of Ni-YSZ anodes in a single-chamber solid oxide fuel cell reactor

The importance of heterogeneous catalysis in single-chamber solid oxide fuel cells (SC-SOFC) is universally recognized, but little studied. This work presents a thorough investigation of the catalytic activity of three Ni-YSZ half-cells in a well-described single-chamber reactor. One in-house electrolyte-supported and two commercially available anode-supported half-cells composed of anodes with thicknesses ranging from 50 μm to 1.52 mm are investigated. They are exposed to methane and oxygen gas mixtures within CH 4:O 2 flow rate ratios ( R in) of 0.8–2.0 and furnace temperatures of 600–800 °C. The conversion of methane always results in the formation of syngas species (H 2 and CO). However, their yields vary considerably based on the individual anode, the operating temperature, and R in. The SC-reactor design and the presence of hot-spots at the reactor entrance bring the methane and oxygen conversion rates well above the limit expected from experiments carried out with anode half-cells only. Major variations in the H 2/CO ratio are observed. In lowering the temperature from 800 °C to 600 °C, it spreads from well below to well above the stoichiometric value of 2.0 expected for the partial oxidation reaction. To optimize the SC-SOFC any further, the findings stress the need to undertake even more catalytic studies of its electrode materials under actual structure and morphology as well as final reactor configuration.

A Microbial Fuel Cell with a Photosynthetic Microalgae Cathodic Half Cell Coupled to a Yeast Anodic Half Cell

A recently developed photosynthetic cathodic half cell has been coupled to a fermentative anode to produce a complete microbial fuel cell. The photosynthetic organism Chlorella vulgaris was employed as the electron acceptor in the cathodic half cell with the yeast strain Saccharomyces cerevisiae serving as the electron donor in the anodic half cell. Maximum power was observed at 90 mV and a load of 5000 Ω, giving a power density of 0.95 mW/m2 of electrode surface area. The effect of changing culture conditions on fuel cell operation is reported. A maximum open circuit voltage of 315 mV was achieved with the addition of supplemental glucose to the anodic half cell. Enriching the feed air bubbled into the cathode half cell with 10% CO2 increased the open circuit voltage by a factor of 1.5 compared to using pure air as the feed gas. Since photosynthetic microbial growth at the cathode of the MFC consumes CO2, this complete microbial fuel cell is CO2 neutral and produces both electricity and ethanol as valuable energy products.

Glucose Driven Nanobiopower Cells for Biomedical Applications

Power supply is an important aspect of micronanobiomedical devices. Implantable devices are required to stay inside of the body for longer period of time to provide continuous monitoring, detection, and therapeutics. The constricted areas of the human body, accessed by these devices, imply that the power source should not increase the payload significantly. Conventional on-board power sources are big, as compared with the device themselves, or involve wire-outs. Both provisions are liable to develop complications for sensor/actuator implant packaging. A plausible approach can be innovative solutions for sustainable bio-energy harvesting. Research studies have reported feasibility of miniature power sources, running on redox reactions. The device design, reported in this study, is a combination of nano-engineered composites and flexible thin film processing to achieve high density packaging. Of which, the end goal is production of energy for sensor applications. Both the bio-electrodes were successfully functionalized by amide bond cross-linkage between the carbon nanotube surface and the enzyme molecules: catalase and glucose oxidase for cathode and anode, respectively. The nanocomposite based biopower cell was evaluated as a steady power supply across the physiological range of glucose concentration. The power cell was able to deliver a steady power of 3.2 nW at 85 mV for glucose concentrations between 3 mM and 8 mM. Electron microscopy scanning of the functionalized electrode surface and spectroscopic evaluation of nanotube surface were used for evaluation of the biofunctionalization technique. Cyclic voltametric (CV) scans were performed on the cathodic and anodic half cells to corroborate bioactivity and qualitatively evaluate the power cell output against the redox peaks on the CV scans. The importance of these results has been discussed and conclusions have been drawn pertaining to further miniaturization (scale down) of the cell.

Outward electron transfer by Saccharomyces cerevisiae monitored with a bi‐cathodic microbial fuel cell‐type activity sensor

A Janus head-like bi-cathodic microbial fuel cell was constructed to monitor the electron transfer from Saccharomyces cerevisiae to a woven carbon anode. The experiments were conducted during an ethanol cultivation of 170 g/l glucose in the presence and absence of yeast-peptone medium. First, using a basic fuel-cell type activity sensor, it was shown that yeast-peptone medium contains electroactive compounds. For this purpose, 1% solutions of soy peptone and yeast extract were subjected to oxidative conditions, using a microbial fuel cell set-up corresponding to a typical galvanic cell, consisting of culture medium in the anodic half-cell and 0.5 M K(3)Fe(CN)(6) in the cathodic half-cell. Second, using a bi-cathodic microbial fuel cell, it was shown that electrons were transferred from yeast cells to the carbon anode. The participation of electroactive compounds in the electron transport was separated as background current. This result was verified by applying medium-free conditions, where only glucose was fed, confirming that electrons are transferred from yeast cells to the woven carbon anode. Knowledge about the electron transfer through the cell membrane is of importance in amperometric online monitoring of yeast fermentations and for electricity production with microbial fuel cells.

An impedance study of an operating direct methanol fuel cell

An electrochemical impedance spectroscopy (EIS) technique was developed to characterize a direct methanol fuel cell (DMFC) under various operating conditions. A silver/silver chloride electrode was used as an external reference electrode to probe the anode and cathode during fuel cell operation and the results were compared to the conventional anode or cathode half-cell performance measurement using a hydrogen electrode as both the counter and reference electrode. The external reference was sensitive to the anode and the cathode as current was passed in a working DMFC. The impedance spectra and DMFC polarization curves were systematically investigated as a function of air and methanol flow rates, methanol concentration, temperature, and current density. Water flooding in the cathode was also examined.

Highly efficient CO 2 bubble removal on carbon nanotube supported nanocatalysts for direct methanol fuel cell

In this paper, we investigate the CO 2 microbubble removal on carbon nanotube (CNT)-supported Pt catalysts in direct methanol fuel cells (DMFCs). The experiments involve the incorporation of near-catalyst-layer bubble visualization and simultaneous electrochemical measurements in a DMFC anodic half cell system, in which CH 3OH electro-oxidation generate carbon dioxide (CO 2) microbubbles. We observe rapid removal of smaller CO 2 bubble sizes and less bubble accumulation on a Pt-coated CNT/CC (Pt/CNT/CC, CC means carbon cloth) electrode. The improved half cell performances of the high CO 2 microbubble removal efficiency on the CNT-modified electrode (Pt/CNT/CC) were 34% and 32% higher than on Pt/CC and Pt/CP electrodes, respectively.

Low Temperature Electrochemical Production of Hydrogen from the Hybrid Copper-Chlorine Thermochemical Cycle

Electrolysis of cuprous chloride is a critical step in the copperchlorine thermochemical cycle for hydrogen production, a novel process with the advantage of mild operating conditions and capability of recovery of low grade heat from nuclear reactors. This step can be achieved in solid polymer electrolyte reactor with either Nafion membrane or anion exchange membrane. In this paper, cell polarization experiments show that the reactor with Nafion 115 has a higher thermal stability than that of the AMX membrane for the bulk electrolysis. In the anode half cell reaction, effects of catalysts and mass transfer were studied on the thin film electrode on the rotating disk electrode (RDE). It was found that the active carbon Vulcan XC 72 has comparable activity towards the cuprous chloride oxidation with conventional electro- catalysts, such as Pt black, Pt/C and RuO2. Also, mass transfer was serious in the rate process in the anode.

Characterisation and Performance of SOFC Components made by Reactive Spray Deposition Technology

The paper presents an overview of the results obtained by using a newly developed flame based deposition technique to fabricate SOFC components. Gadolinia doped ceria (20% mol gadolinia), yttria stabilised zirconia (8% mol yttria) and samarium strontium cobaltite (50% at Sm) ceramics have been deposited on various substrates, including SOFC anode materials and half cells. Thin and dense electrolyte layers having thicknesses in the range of 100 nm to 2 mm have been successfully fabricated. Porous cathode layers deposited on half cell substrates have shown a 25-30% increase in performance compared to samaria doped ceria - samarium strontium cobaltite screen printed cathodes tested in the same conditions.

Economic assessment of an integrated bioethanol–biodiesel–microbial fuel cell facility utilizing yeast and photosynthetic algae

A strategy for the integration of a novel CO 2 photosynthetic culture and power generation system into a commercial bioethanol plant is presented. Photosynthetic microalgae column photobioreactors, acting as cathodic half cells, are coupled with existing yeast fermentors at a bioethanol plant, acting as anodic half cells, to create coupled microbial fuel cells. The microalgae photobioreactors also sequester CO 2 emitted by the yeast fermentors. Incorporating microbial fuel cells into an existing bioethanol plant generates some of the power used in bioethanol production and the microalgae species Chlorella vulgaris contains oil, which acts as a byproduct for the production of biodiesel. The goal of the study is to determine the required design specifications of novel, airlift PBR cathodes to make the integrated system economically feasible at an existing bioethanol plant. Data from previous experimental studies was used to develop the optimum integration strategy. The reported parameters include PBR size, number of integrated MFCs, fuel cell outputs, oil (for biodiesel) production rate, and CO 2 consumption rate.

Carbon anode in direct carbon fuel cell

Direct carbon fuel cell (DCFC) is a kind of high temperature fuel cell using carbon materials directly as anode. Electrochemical reactivity and surface property of carbon were taken into account in this paper. Four representative carbon samples were selected. The most suitable ratio of the ternary eutectic mixture Li 2CO 3–K 2CO 3–Al 2O 3 was determined at 1.05:1.2:1(mass ration). Conceptual analysis for electrochemical reactivity of carbon anode shows the importance of (1) reactive characteristics including lattice disorder, edge-carbon ratio and the number of short alkyl side chain of carbon material, which builds the prime foundation of the anodic half-cell reaction; (2) surface wetting ability, which assures the efficient contact of anode surface with electrolyte. It indicates that anode reaction rate and DCFC output can be notably improved if carbon are pre-dispersed into electrolyte before acting as anode, due to the straightway shift from cathode to anode for CO 3 2− provided by electrolyte soaked in carbon material.