Electrode Pore Size Research Articles

Tailoring Electrode/Electrolyte Interfacial Properties in Flexible Supercapacitors by Applying Pressure

AbstractElectrode/electrolyte interfacial properties of flexible supercapacitors assembled with nanostructured activated carbon fabric (ACF) electrodes can be tailored by applying a pressure and tuning electrolyte ion size relative to electrode pore size. Experimental results reveal that increasing pressure between the supercapacitor electrodes can significantly improve capacitive performance. The ratio of solvated ion size in the electrolyte to the pore size on the electrodes determines the minimum pressure necessary to achieve an optimum performance. For a specific electrode material, this minimum pressure for optimum performance is primarily governed by the size of the larger solvated ions (either the anions or cations), and is lower (∼689 KPa) when the ratio of the solvated ion size to the pore size is higher than 0.6, and is higher (at least 1379 KPa) when the ratio is lower than 0.6. An analytical model capable of predicting the experimental performance data has been developed. These results together provide a fundamental understanding of pressure dependence of electrode/electrolyte interfacial properties and pave the way for practical applications of flexible supercapacitors.

Optimization of physical parameters of solid oxide fuel cell electrode using electrochemical model

To enhance the performance of anode-supported solid oxide fuel cell (SOFC), an electrochemical model has been developed in this study. The Butler-Volmer equation, Ohm’s law and dusty-gas model are incorporated to predict the activation, ohmic and concentration overpotentials, respectively. The optimal cell microstructure and operating parameters for the best current-voltage (J-V) characteristics have been sought from the information of the exchange current density and gas diffusion coefficients. As the cell temperature rises, the activation and ohmic overpotentials decrease, whereas the concentration overpotential increases due to the considerable reduction of gas density at the elevated temperature despite the increased diffusion coefficient. Also, increasing the hydrogen molar fraction and operating pressure can further augment the maximum cell output. Since there exists an optimum electrode pore size and porosity for maximum cell power density, the graded electrode has newly been designed to effectively reduce both the activation and concentration overpotentials. The results exhibit 70% improved cell performance than the case with a non-graded electrode. This electrochemical model will be useful to simply understand overpotential features and devise the strategy for optimal cell design in SOFC systems.

Confinement of Symmetric Tetraalkylammonium Ions in Nanoporous Carbon Electrodes of Electric Double-Layer Capacitors

We present a study on electric double-layer capacitors in organic electrolytes based on symmetrical bulky tetraalkylammonium cations, using activated carbons with adjusted pore size distribution. The results reveal that a close fit of electrode pore size distribution to the size of electrolyte ions can lead to a saturation of the active surface, observable as a decrease in capacitive current beyond the saturation point. This effect arises because of maximum cation loading being reached within the electrolyte voltage window following the trend: the longer the alkyl substituent, the lower the saturation voltage. In contrast, if the pore size distribution presents mostly pores significantly larger than the ion size, the saturation effect is not observed at the expense of the lower surface charge storage. The good correspondence between the maximum charge calculated on the basis of a distorted configuration of cations, Qmax, and the measured one, Qexp, suggests that cations use a wider range of pore sizes than would be possible at their unconfined and undistorted geometries. The saturation of the electrode porosity limits the usable voltage of a supercapacitor system and consequently the deliverable energy and power. In view of optimizing the electrochemical performance, the possibility of such an effect should be considered in adapting the sizes of electrode pores and electrolyte ions.

Parametric study of solid oxide fuel cell performance

Abstract An electrochemical model was developed to study the current–voltage ( J – V ) characteristics of a solid oxide fuel cell (SOFC). The Butler–Volmer equation, Fick’s model and Ohm’s law were used to determine the activation, concentration and ohmic overpotentials, respectively. One important feature of this model is that both the exchange current density and gas diffusion coefficients were dependent on the cell microstructures (porosity and pore size) and operational parameters (temperature, pressure and gas composition). The simulation results were compared with experimental data from the literature, and good agreement was obtained. The subsequent parametric modeling analyses determined how individual overpotentials were related to the geometric and operational parameters. It was found that there existed optimal values of electrode pore size and porosity for maximum cell performance. Both the activation and ohmic overpotentials decreased significantly with increasing temperature. However, the concentration overpotential was found to increase with increasing temperature. This unexpected phenomenon was caused by the reduced gas density at elevated temperature despite the increase in diffusion coefficient with increasing temperature. Besides, increasing the hydrogen content in the fuel stream and increasing the operating pressure were possible ways to enhance the SOFC power output. The parametric analyses provided insights in the operation of SOFCs and clarified some ambiguous understanding of SOFC overpotentials. The present model could also serve as a valuable tool for SOFC optimization design.

A reticulated vitreous carbon spectroelectrochemical detector for flow injection analysis and liquid chromatography

AbstractA spectroelectrochemical detector for flow injection and liquid chromatography is described. The detector design has dimensions of a standard 1 cm sample cuvette with a replaceable reticulated vitreous carbon working electrode. No special cell holder or modifications to the spectrophotometer are required to use the detector. Chronocoulometry is used to indicate a trend from thin‐layer behavior toward semi‐infinite diffusion behavior as the electrode pore size increases. Ferro‐/ferricyanide solutions were used to evaluate the flow injection characteristics of the detector. A sampling rate of 180 injections per hour was used. Linear calibration curves in the micromolar range were achieved with a reproducibility of 2–7%. A mixture of phenol, chlorophenols, and nitrophenols was used to investigated the simultaneous electrochemical and optical response for liquid chromatography.

Ionic diffusion in voltage-clamped isolated cardiac myocytes. Implications for Na,K-pump studies

The whole-cell voltage-clamp technique employing electrolyte-filled micro-pipette suction electrodes is widely used to investigate questions requiring an electrophysiological approach. With this technique, the ionic composition of the cytosol is assumed to be strongly influenced (as result of diffusion) by the ionic composition of the solution contained in the electrode. If this assumption is valid for isolated cardiac myocytes, the technique would be particularly powerful for studying the dependence of their Na,K-pump on the intracellular [Na+]. However, the relationship between the concentrations of ions in the solution filling the electrode and those in the cytosol has not been established. The relationship was investigated to determine in particular whether the [Na+] at the intracellular cation ligand binding sites for the Na-pump ([ Na+]ps) can be set and clamped by [Na+] in the pipette electrode ([ Na+]pip). If [Na+]pip can set and clamp [Na+]ps, this would provide a means for defining the dependence of the Na,K-pump on intracellular [Na+]. The relationship between [Na+]pip and [Na+]ps was analyzed using two approaches. First, a mathematical model of three-dimensional ionic diffusion within a whole-cell patch-clamped myocyte was developed and the effects of experimental parameters on mean [Na+]ps were investigated. When typical experimental values were simulated, the time course to achieve steady state mean [Na+]ps was found to be most sensitive to variations in electrode pore size, cell length and the Na+ pumping rate, but at steady state, mean [Na+]ps varies from [Na+]pip by 5% or less depending on pump rate. Second, to provide experimental support for the validity of the simulations, isolated ventricular myocytes were voltage-clamped and the reversal potential for the Na current was determined in order to estimate steady state intracellular [Na+]. The results of the mathematical and experimental analyses suggest that steady state [Na+]ps can be regulated by the [Na+] in suction pipette electrodes. These findings, while also having a broader significance, indicate for isolated cardiac myocytes that whole-cell suction micro-electrodes can provide a means to assess the dependence of the Na,K-pump on [Na+]ps.