Direct current proton flow

Figure 7.4. The anode and cathode bi-polar plates, the gas plenums, the membrane, and the gas diffusion layer. The Plenums are slowly replenished from an external feed. The black arrows indicate direction of electron flow and of proton counterflow. The external circuit between anode and cathode is completed through a load bank with variable resistance Rg. The voltage between anode and cathode plates is denoted by V and the external current by 7. ...

High frequency resistance measurements, usually done to measure the membrane resistance for direct current, will see this effective conductivity. At low frequency and DC current, only protons flow with the conductivity Oh-The effective conductivity is only uniform across the membrane when no current is flowing and X is uniform. The high and low frequency resistances are... 

On the same principle as the routine measurement of electronic resistivity, Ohm s law is used to analyze the resistivity of a proton-conductive membrane against the flow of either alternating current (AC) or direct current (DC). The proton conductivity can be calculated according to Eqn (5.1) ... 

A pH meter is another way to measure the exact pH of a substance. Of all the ways to measure pH, using a pH meter is the most precise. A pH meter sends an electrical current through the sample being tested. Because electricity is a flow of negatively charged electrons, the force of the electron current is directly proportional to the hydrogen ion content of the sample. In other words, the more current (or electrons) carried though the sample, the more protons... 

If water movement in the membrane is also to be considered, then one way to do this is to again use the Nernst—Planck equation. Because water has a zero valence, eq 29 reduces to Pick s law, eq 17. However, it is also well documented that, as the protons move across the membrane, they induce a flow of water in the same direction. Technically, this electroosmotic flow is a result of the proton—water interaction and is not a dilute solution effect, since the membrane is taken to be the solvent. As shown in the next section, the electroosmotic flux is proportional to the current density and can be added to the diffusive flux to get the overall flux of water... 

The currents flowing within the Y-system set up a magnetic field which may be experienced directly by the proton hi the X—H bond. 

Here, the electroosmotic flow is proportional to the proton current density jp with a drag coefficient n (wx). D Arcy flow as the mechanism of water backflow proceeds in the direction of the negative gradient of liquid pressure, which (for A P% = 0) is equal to the gradient of capillary pressure. The density of water, cw, and the viscosity, /1, are assumed to be independent of w. The transport coefficient of D Arcy flow is the hydraulic permeability K wx). 

In the presence of the magnetic field, the electron circulates in anticlockwise direction to Bq. The motion of the electron is similar to an electric current flowing in a closed loop, and as such, it is associated with a secondary magnetic field that opposes the applied field Bq. Thus, the observed resonance frequency of a proton appears to be slightly less than that predicted from the value of Bq and the gyromagnetic ratio of a proton (Fig. 16.9). 

Hydrogen-powered cars are based on fuel cells that store hydrogen, or H2 gas, inside a material called a polymer exchange membrane. The fuel cell contains two electrodes an anode (negative side) and a cathode (positive side). At the anode, the H2 molecules are split into protons and electrons. The protons pass through a polymer exchange membrane, while the electrons are unable to pass through this membrane and thus have to flow in a different direction. This creates a current of electricity by which the car is powered. 

It will become obvious from the following outline that an important fact to remember when looking at polymer membrane is the hydration of protons in the aqueous medium. The protons always exist in the form of species H" " nHjO. During discharge of the cell, when current flows, the hydrated protons migrate in the membrane from the anode toward the cathode, each proton dragging along n water molecules in the same direction. 

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