scholarly journals Ion Transport through Diffusion Layer Controlled by Charge Mosaic Membrane

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Akira Yamauchi
Keyword(s):  
Ion Transport ◽  
Current Density ◽  
Membrane Surface ◽  
Transition Time ◽  
Limiting Current ◽  
Water Dissociation ◽  
Limiting Current Density ◽  
Voltage Curve ◽  
Current Voltage Curve ◽  
Exchange Membrane

The kinetic transport behaviors in near interface of the membranes were studied using commercial anion and cation exchange membrane and charge mosaic membrane. Current-voltage curve gave the limiting current density that indicates the ceiling of conventional flux. From chronopotentiometry above the limiting current density, the transition time was estimated. The thickness of boundary layer was derived with conjunction with the conventional limiting current density and the transition time from steady state flux. On the other hand, the charge mosaic membrane was introduced in order to examine the ion transport on the membrane surface in detail. The concentration profile was discussed by the kinetic transport number with regard to the water dissociation (splitting) on the membrane surface.

Performance Enhancement in Proton-Exchange Membrane Fuel Cell for Cathode Pulsating Flow

2010 ◽  
Author(s):  
Yun Ho Kim ◽  
Hun Sik Han ◽  
Seo Young Kim ◽  
Gwang Hoon Rhee
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Proton Exchange Membrane ◽  
Performance Enhancement ◽  
Proton Exchange ◽  
Pulsating Flow ◽  
Limiting Current ◽  
Mean Flow ◽  
Limiting Current Density ◽  
Exchange Membrane

The effect of cathode flow pulsation on the performance enhancement of a 10-cell proton-exchange membrane fuel cell is investigated. We perform the experiment using two pulsation devices. One pulsation device, i.e., acoustic woofer, generates a pulsating flow, which is added to a unidirectional flow supplied from a compressed air tank. The other pulsation device is a crankshaft system that produces a pure oscillatory flow without mean flow. In the case of cathode pulsating flow with mean flow, the fuel cell power output and the limiting current density dramatically increase as pulsating frequency increases at given pulsating amplitude, while the fuel cell efficiency slightly decreases. This result is contributed that the pulsating flow enhances the dispersion inside the cathode channels, and then improving the oxygen and temperature distributions. This performance enhancement by cathode pulsating flow is more distinct at low cathode mean flow rates. In the case of cathode pulsating flow without mean flow, the fuel cell stack is operated despite cathode mean flow is absent. The limiting current density is extended as the pulsating frequency and swept distance (amplitude) increase. When the pulsating frequency and swept distance are 2.38Hz and 13.65mm respectively, the fuel cell performance is equal to that the cathode mean flow rate is 1.29 lpm. Also, the case of pulsating flow is more stable at the concentration loss region than the case of non-pulsating flow for the same performance conditions.

scholarly journals Noise spectra of K+ and NH4+ ions at over-limiting current in an electrochemical system with a cation exchange membrane

2013 ◽  
Vol 3 (3) ◽  
pp. 291-296
Author(s):  
K. Oulmi ◽  
K. E. Bouhidel ◽  
G. M. Andreadis
Keyword(s):  
Limiting Current ◽  
Electrical Noise ◽  
Singular Behaviour ◽  
Counter Ion ◽  
Power Spectral ◽  
Counter Ions ◽  
Voltage Curve ◽  
Current Voltage ◽  
Current Voltage Curve ◽  
Exchange Membrane

The present work investigates the effect of the counter ion nature on the noise of the over-limiting current (Iov). Moreover, the electrochemical methods, current voltage curve (I–V) and the chronopotentiometry (V–t) measurements are applied. The over-limiting current is always accompanied by a neat electrical noise. It is a well accepted experimental phenomenon. The study of this noise may contribute to a better understanding of the Iov and the feasibility of electrodialysis operation at this current in terms of energy consumption. The electrical noise depends directly on the counter ion nature. The power spectral density of the membrane's potential fluctuation was obtained via Fourier analysis of the time series recorded during the transport of counter ions (K+ and NH4+). The spectra are evaluated above the limiting current indicating the differences between the K+ and the NH4+. It is found that the cation NH4+ presents a singular behaviour and the noise is minimal.

scholarly journals Numerical Investigation of the Effect of Two-Dimensional Surface Waviness on the Current Density of Ion-Selective Membranes for Electrodialysis

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1397
Author(s):  
Andreas Gross ◽  
Arthur Morvezen ◽  
Pedro Castillo Gomez ◽  
Xuesong Xu ◽  
Pei Xu
Keyword(s):  
Surface Roughness ◽  
Current Density ◽  
Stokes Equations ◽  
Membrane Surface ◽  
Ion Concentration ◽  
Limiting Current ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Limiting Current Density ◽  
Selective Membranes

Ion-selective membranes are an important component of electrodialysis stacks for desalination. Manufacturing imperfections or slight inhomogeneity of the material can lead to minute membrane surface imperfections. Two-dimensional solutions of the coupled Poisson–Nernst–Planck and Navier–Stokes equations were sought for a perfectly smooth membrane and for membranes with well-defined small-amplitude harmonic surface roughness. The simulations were carried out with the validated rheoEFoam solver by Pimenta and Alves. In the overlimiting regime, the electric field is strong enough for an electrokinetic instability to occur. The instability leads to disturbance growth and the formation of electro-convection cells, which strongly increase the current density. The present simulations show that with an increasing ion concentration and applied voltage, the instability becomes stronger and the overlimiting regime is reached earlier. The limiting current density shows a noticeable dependence on the wavelength of the surface roughness. When the wavelength of the surface roughness is incommensurate with the wavelength of the naturally occurring instability, the limiting current density is increased. Since production membranes will always have some degree of surface roughness, this suggests that membrane surface treatments which favor certain wavelengths may have an effect on the overall membrane performance.

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