Solid reference electrode, effect electrolytes

The measurement of potentials in electrolytes is not as easy as it is for solid-state devices. Depending on the composition of the electrolyte and the electrode material a monolayer of adsorbates or a thin passivation layer may be formed on the electrode, and can significantly shift the electrode potential. These effects have to be taken into account for the working as well as for the counter electrode. The potential at the latter becomes irrelevant if a reference electrode is used. The reference electrode should be placed as close as possible to the Si electrode or it can access the Si electrode via a capillary. The size of the reference electrode is not rel-... 

Ion-selective electrodes are systems containing a membrane consisting basically either of a layer of solid electrolyte or of an electrolyte solution whose solvent is immiscible with water. The membrane is in contact with an aqueous electrolyte solution on both sides (or sometimes only on one). The ion-selective electrode frequently contains an internal reference electrode, sometimes only a metallic contact, or, for an ion-selective field-effect transistor (ISFET), an insulating and a semiconducting layer. In order to understand what takes place at the boundary between the membrane and the other phases with which it is in contact, various types of electric potential or of potential difference formed in these membrane systems must first be defined. 

The first term on the RHS of Equation 25.28 represents the heat generation effect due to electrode reactions the second and third terms correspond to the joule heating in the solid active material and electrolyte phases, respectively. The subscript n refers to the anode and cathode electrodes. 

In this section the use of amperometric techniques for the in-situ study of catalysts using solid state electrochemical cells is discussed. This requires that the potential of the cell is disturbed from its equilibrium value and a current passed. However, there is evidence that for a number of solid electrolyte cell systems the change in electrode potential results in a change in the electrode-catalyst work function.5 This effect is known as the non-faradaic electrochemical modification of catalytic activity (NEMCA). In a similar way it appears that the electrode potential can be used as a monitor of the catalyst work function. Much of the work on the closed-circuit behaviour of solid electrolyte electrochemical cells has been concerned with modifying the behaviour of the catalyst (reference 5 is an excellent review of this area). However, it is not the intention of this review to cover catalyst modification, rather the intention is to address information derived from closed-circuit work relevant to an unmodified catalyst surface. 

Most commonly, such substrate effects are expected to arise from variations in the work terms w and w, in this relation where the subscript p and s refer to precursor and successor states. For outer-sphere reactions, w and w will be determined at least in part by <() and [Eq. (a) in 12.3.7.3]. Because 4> depends upon both q" and q, substantial variations in k (up to 10- to 100-fold) may arise from this source. For solid electrodes there can be considerable uncertainties in , because the extent of specific ionic adsorption of the supporting electrolyte often is unknown. However, this difficulty can be minimized by employing uncharged or singly charged reactants. 

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