Rotating disk electrode electrolyte solutions

A standard rotating disk electrode (RDE) setup with a gas-tight Pyrex cell was used for the experiment on CO adsorption and the HOR. A Pt wire was used as counterelectrode. A reversible hydrogen electrode, RHE(t), kept at the same temperature as that of the cell (t, in °C), was used as the reference. All the electrode potentials in this chapter will be referenced to RHE(f). The electrolyte solution of 0.1 M HCIO4... 

Hydrodynamic voltammetry — is a voltammetry technique featuring an electrolyte solution which is forced to flow at a constant speed to the electrode surface. -> mass transport of a redox species enhanced in this way results in higher current. The forced flow can be accomplished either by agitation of the solution (solution stirring, or channel flow), or the electrode (electrode rotation, see -> rotating disk electrode or vibration,... 

Example 2.2 Convective Diffusion Equation The material balance equation near a rotating disk electrode in an electrolyte solution where the migration can be neglected can be written as... 

The anodic dissolution experiments of zinc rotating disk electrode were carried out in alkaline electrolyte [278] and in solution at pH 5.5 containing NH4CI and NH4CI +- ZnCb [279], NH4CI -I- NiCb, and NH4CI - NiCh-h ZnCb [280, 281]. The zinc electrode was covered by a porous film composed of a mixture of metallic zinc and zinc hydroxide [279]. In Ni-containing solutions, the passivation of Zn was a result of Zn-Ni alloy formation and Zn(OH)2 precipitation [280]. 

On the other hand, Fig. 12a evidences the inertness of the reorganization of the tetracoordinated Cu(II) rotaxane. Thus, a total conversion of tetracoordinated 13 to tetracoordinated 13 was performed by preparative electrolysis and the subsequent rearrangement of tetracoordinated 13 into pentacoordinated 13 i was followed by monitoring the current (vs. time) flowing through a rotating disk electrode polarized at +0.3 V. Indeed, at that potential, the cathodic current observed is representative of the presence and concentration of 13, the tetracoordinated Cu(II) complex only. This remains true even if the electrolytic solution contains tetracoordinated 13 which will be electro chemically silent in the potential range used. 

In electrochemistry an electrode is an electronic conductor in contact with an ionic conductor. The electronic conductor can be a metal, or a semiconductor, or a mixed electronic and ionic conductor. The ionic conductor is usually an electrolyte solution however, solid electrolytes and ionic melts can be used as well. The term electrode is also used in a technical sense, meaning the electronic conductor only. If not specified otherwise, this meaning of the term electrode is the subject of the present chapter. In the simplest case the electrode is a metallic conductor immersed in an electrolyte solution. At the surface of the electrode, dissolved electroactive ions change their charges by exchanging one or more electrons with the conductor. In this electrochemical reaction both the reduced and oxidized ions remain in solution, while the conductor is chemically inert and serves only as a source and sink of electrons. The technical term electrode usually also includes all mechanical parts supporting the conductor (e.g., a rotating disk electrode or a static mercury drop electrode). Furthermore, it includes all chemical and physical modifications of the conductor, or its surface (e.g., a mercury film electrode, an enzyme electrode, and a carbon paste electrode). However, this term does not cover the electrolyte solution and the ionic part of a double layer at the electrode/solution interface. Ion-selective electrodes, which are used in potentiometry, will not be considered in this chapter. Theoretical and practical aspects of electrodes are covered in various books and reviews [1-9]. 

The rotating disk electrode is becoming one of the most powerful methods for studying both diffusion in electrolytic solutions and the kinetics of moderately fast electrode reaction because the hydrodynamics and the mass-transfer characteristics are well understood and the current density on the disk electrode is supposed to be uniform. Levich [179] solved the family of equations and provided an empirical relationship between diffusion limiting current (id) and rotation rate ( >) as shown in Eq. (9.42). In particular applications in fuel cells, the empirical relationship which is given by Levich was also used in linear scan voltammetry (LSV) experiment performed on a RDE to study the intrinsic kinetics of the catalyst [151,159,180-190]. However, it is more appropriate to continue the discussion later in detail in the LSV section. 

---