Electrochemical membranes

In addition to their use as reference electrodes in routine potentiometric measurements, electrodes of the second kind with a saturated KC1 (or, in some cases, with sodium chloride or, preferentially, formate) solution as electrolyte have important applications as potential probes. If an electric current passes through the electrolyte solution or the two electrolyte solutions are separated by an electrochemical membrane (see Section 6.1), then it becomes important to determine the electrical potential difference between two points in the solution (e.g. between the solution on both sides of the membrane). Two silver chloride or saturated calomel electrodes are placed in the test system so that the tips of the liquid bridges lie at the required points in the system. The value of the electrical potential difference between the two points is equal to that between the two probes. Similar potential probes on a microscale are used in electrophysiology (the tips of the salt bridges are usually several micrometres in size). They are termed micropipettes (Fig. 3.8D.)... 

This chapter will deal with the basic properties of electrochemical membranes in general and the membrane aspects of bioelectrochemistry in particular. A number of bioelectrochemical topics was discussed in Sections 1.5.3 and 3.2.5. 

Membranes exhibiting selectivity for ion permeation are termed electrochemical membranes. These membranes must be distinguished from simple liquid junctions that are often formed in porous diaphragms (see Section 2.5.3) where they only prevent mixing of the two solutions by convection and have no effect on the mobility of the transported ions. It will be seen in Sections 6.2 and 6.3 that the interior of some thick membranes has properties analogous to those of liquid junctions, but that the mobilities of the transported ions are changed. 

A characteristic property of electrochemical membranes is the formation of an electric potential difference between the two sides of the membrane,... 

An electrochemical membrane process can, in principle, perform the entire sequence in a single step while enriching the process gas slightly with H2. If the H2S could be electronated at a suitable cathode ... 

The theoretical minimum work for electrochemical membrane separation is precisely... 

Fig. 4.1. Cellular model illustrating cell types in vascular wall involved in vasorelaxation induced by SERMs. Putative targets of SERMs are indicated within cyan tags. SERMs directly affect L-type VDCC, BK fil subunit in smooth muscle cells, and ER in endothelial cells. L-type VDCC L-type voltage-dependent calcium channel BK calcium-activated large conductance K+ channel PKG protein kinase G eNOS endothelial nitric oxide synthase GC soluble guanylate cyclase cGMP cyclic GM P V electrochemical membrane potential ER estrogen receptor. See text for further details...

Wimer, J.G. Williams, M.C. Archer, D.H. Osterle, J.F. Networking Electrochemical Membrane Separation Devices ... 

In physics, an elastic two-dimensional plate is tenned a membrane (Latin membram = parchment) but in chemistry the tenn denotes a body, usually thin, which serves as a phase separating two other bulk phases. If this body is penneable to the same degree for all components of the adjacent phases and does not affect their mobility, then its only function is to prevent rapid mixing of the two phases. This is then tenned a diaphragm. A real membrane must exhibit a certain selectivity, based on different penneability for the components of the two phases, and is then tenned a semipenneable membrane. Membranes separating two electrolytes that are not penneable to the same degree for all ions are called electrochemical membranes. It is with these that we are concerned here. 

Consider an electrochemical membrane formed of poorly soluble salt JA, separating two solutions with different concentrations of anion A", Cj and Ci. 

Finally, there is intensive and widespread activity on the development of electrochemical membrane reactors. Recent results of these investigations have been presented in [82-86]. 

Combustion reactions often cause extensive exergy loss. Exeigy calculations show that the entropy production can cause the loss of considerable potential work due to a reaction. An electrochemical membrane reactor or a fuel cell could reduce exergy loss considerably. 

Schmidt, D. S. Winnick, J. Electrochemical Membrane Flue-Gas Desulfurization K2SO4/V2O5 Electrolyte, Am. Inst. Chem. Eng. J. 1998, 44, 323-331. 

Nomura, M., Fujiwara, S., Ikenoya, K., Kasahara, S., Nakajima, H., Kubo, S., Hwang, G.-J., Choi, H.-S., and Onuki, K., Application of an electrochemical membrane reactor to the thermochemical water splitting IS process for hydrogen production, Journal of Membrane Science, 240, 221-226, 2004. 

McHenry D.J. and Winnick J., Electrochemical membrane process for flue gas desulfurization, AIChE J. 40 143 (1994). 

Hamakawa S, Hayakawa T, Suzuki K, Murata K, and Takehira K. Methane conversion with an electrochemical membrane reactor. Proceedings of ICIM 5 (Inorganic Membranes), Nagoya, Japan S. Nakao (ed.), 1998 350-353. 

Salema K, Sandeauxa J, Molenata J, Sandeauxa R, and Gavacha C. Elimination of nitrate from drinking water by electrochemical membrane processes. Desalination 1995 101(Suppl. 2) 123-131. 

The cathodic reduction of nitrate and electrochemical membrane technology... 

Figure 1. Principle of the hydrocarbon oxidation using an electrochemical membrane reactor.

Figure 2. Schematic diagram of the electrochemical membrane reactor.

Gas-phase electrochemical membrane transport is one of the techniques chosen by National Aeronautics and Space Administration or manned spacecraft C02 control (51). This technique, suggested by fuel cell development, has given rise to similar processes for S02 removal from flue gas and H20 removal from coal gas (52). 

The electrochemistry of nerves has been the subject of several decades of study. Ion transport across cell walls is a key element in the functioning of nerve cells, and a network of nerves can be viewed as a set of electrochemical, membrane-containing microcells that are coupled by chemical messengers. Interfaces between nerves and... 

Hamakawa et al. [2.66]) utilized exactly such a concept shown schematically in Figure 2.2. Hamakawa et al. [2.66], for example, used a SrCe0.95Yb0.05O2.95 membrane as a proton, solid oxide electrolyte with two porous Ag electrodes attached to it. CH4 was passed in the one compartment of the electrochemical membrane reactor (the anode) while Ar was flown into the other cell. C2 products (C2H4 and C2H6) were detected in the anode... 

Another partial oxidation reaction that is attracting industrial attention for the application of reactive separations is the production of synthesis gas from methane [Stoukides, 2.127]. The earlier efforts made use of solid oxide solutions as electrolytes. Stoukides and coworkers (Eng and Stoukides [2.200, 2.126], Alqahtany et al. [2.201, 2.202]), for example, using a YSZ membrane in an electrochemical membrane reactor obtained a selectivity to CO and H2 of up to 86 %. They found that a Fe anodic electrode was as active as Ni in producing synthesis gas from methane (Alqahtany et al. [2.201, 2.202]), and that electro-chemically produced O was more effective in producing CO than gaseous oxygen (no ef-... 

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