Potential of gas electrodes in equilibrium

Gas electrodes may also be regarded as electronic-and-ionic electrodes covered with a gaseous film. The electron transfer occurs between the electrode and the gaseous film (2 + 2 eoii H2( ) and the ion transfer occurs between the 

For the hydrogen electrode, the interfadal potential between the electrode metal and the hydrogen gas film is determined by the electron transfer equilibrium and the interfacial potential between the hydrogen gas film and the aqueous 

As described in Sec. 2.11, the electron level in the normal hydrogen electrode (gaseous hydrogen molecules at unit fiigacity and hydrated protons at unit activity) is -4.5 eV (or - 4.44 eV in the lUPAC report [Trasatti, 1986]). We, then, obtain the equilibrium potential of the normal hydrogen electrode nhe (= in Eqn. 4-32) as shown in Eqn. 4-34  

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