Porous-electrode theory

Newman J., Teedemann W. Porous-Electrode Theory with Battary Application. A.I. Ch. Journal. 1975 21 25-41. 

Zheng G., Popov B.N. and White R. E. Application of Porous Electrode Theory on Metal-Hydride Electrodes in Alkaline Solution. J. Electrochem Soc. 1996 143 435-41. 

K. Kordesch, J. Gsellmann, S. Jahangir, M. Schautz, in Proceedings of the Symposium on Porous Electrodes Theory and Practice, Edited by H.C. Maru, T. Katan, M.G. Klein, The Electrochemical Society, Inc., Pennington, NJ, p. 163, 1984. 

The beginning of modeling of polymer-electrolyte fuel cells can actually be traced back to phosphoric-acid fuel cells. These systems are very similar in terms of their porous-electrode nature, with only the electrolyte being different, namely, a liquid. Giner and Hunter and Cutlip and co-workers proposed the first such models. These models account for diffusion and reaction in the gas-diffusion electrodes. These processes were also examined later with porous-electrode theory. While the phosphoric-acid fuel-cell models became more refined, polymer-electrolyte-membrane fuel cells began getting much more attention, especially experimentally. 

Porous-Electrode Models. The porous-electrode models are based on the single-pore models above, except that, instead of a single pore, the exact geometric details are not considered. Euler and Nonnenmacher and Newman and Tobias were some of the first to describe porous-electrode theory. Newman and Tiedemann review porous-electrode theory for battery applications, wherein they had only solid and solution phases. The equations for when a gas phase also exists have been reviewed by Bockris and Srinivasan and DeVidts and White,and porous-electrode theory is also discussed by New-man in more detail. 

Figure 10. Resistor-network representation of porous-electrode theory. The total current density, i, flows through the electrolyte phase (2) and the solid phase (1) at each respective end. Between, the current is apportioned on the basis of the resistances in each phase and the charge-transfer resistances. The charge-transfer resistances can be nonlinear because they are based on kinetic expressions.

Porous Electrodes Theory and Practice, 1984. (Ed. H, Maru, T, Katan and M, Klein.)... 

Porous electrode theory assumes that medium is a superposition of continuous solid and electrolyte phases with a known vo-Inme fraction. The solid phase potential of the positive electrode is because of electronic conduction ... 

Most of the batteries use porous electrodes. Hence, the material and energy balance should consider the use of porous electrode theory. Botte et al. [26] present a review of the different approaches that have been used for porous electrode theory. 

Consider a linear electrochemical reaction inside a porous electrode. [15] [16] The dimensionless solid phase potential (d>i) and electrolyte potential (O2) are governed by the macroscopic porous electrode theory ... 

Newman, J., Tiedemann, W. Porous-electrode Theory with Battery Applications. AIChE Journal 21(1), 25 1 (1975)... 

The porous electrode theory was developed by several authors for dc conditions [185-188], bnt the theory is usually applied in the ac regime [92,100,101,189-199], where mainly small signal frequency-resolved techniques are used, the best example of which are ac theory and impedance spectra representation, introdnced in the previons section. The porous theory was first described by de Levi [92], who assumed that the interfacial impedance is independent of the distance within the pores to obtain an analytical solution. Becanse the dc potential decreases as a fnnction of depth, this corresponds to the assnmption that the faradaic impedance is independent of potential or that the porons model may only be applied in the absence of dc cnrrent. In snch a context, the effect of the transport and reaction phenomena and the capacitance effects on the pores of nanostructured electrodes are equally important, i.e., the effects associated with the capacitance of the ionic donble layer at the electrode/electrolyte-solntion interface. For instance, with regard to energy storage devices, the desirable specifications for energy density and power density, etc., are related to capacitance effects. It is a known fact that energy density decreases as the power density increases. This is true for EDLC or supercapacitors as well as for secondary batteries and fnel cells, particnlarly due to the distributed nature of the pores... 

Porous-electrode theory has been used to describe a variety of electrochemical devices including fuel cells, batteries, separation devices, and electrochemical capacitors. In many of these systems, the electrode contains a single solid phase and a single fluid phase. Newman and Tiedemann reviewed the behavior of these flooded porous electrodes [23]. Many fuel-cell electrodes, however, contain more than one fluid phase, which introduces additional complications. Typical fuel cell catalyst layers, for example, contain both an electrolytic phase and a gas phase in addition to the solid electronically conducting phase. An earher review of gas-diffusion electrodes for fuel cells is provided by Bockris and Srinivasan [24]. 

Even among the models that employ porous-electrode theory, there have been differences in how the various models choose to describe the electrode. For example, consider the catalyst layer in a state-of-the-art PEM fuel cell containing a supported-platinum-on-carbon (or platinum-alloy-on-carbon) catalyst, a polymeric membrane material, and, in some cases, a void volume. Whether this void volume is considered explicitly, or whether gas- and liquid-phase transport is simply described via permeability through the ionomer is one of the key differences between the various models. 

J. Newman and W. Tiedemann, Porous-Electrode Theory with Battery Applications, AIChE J., 21,41 (1975). 

Based on Newman s well-known modelling approach [8 10] the impedance of a commercial cell is described. This approach combines concentrated solution theory, porous electrode theory and Butler-Volmer kinetics to form a set of coupled partial differential equations. 

Newman, J. and Tiedemann, W. (1975) Porous-electrode theory with battery applications. AIChE J., 21, 25-41, and references therein. 

Porous Electrode Theory for Membrane-CDl with an Ion-Selective Blocking... 

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