Potentiodynamic conditions

The kinetics and mechanism of the growth of anodic silver sulfide films on silver metal in aqueous sulfide solutions has been studied under potentiodynamic conditions [162], The Ag2S film formation was presumed to proceed as... 

Yeh LSR, Hudson PG, Damjanovic A (1982) Anodic formation of thin CdS films. I. Kinetics and mechanisms under galvanostatic and potentiodynamic conditions. J Appl Electrochem 12 153-162... 

Typical anodization curves of silicon electrodes in aqueous electrolytes are shown in Fig. 5.1 [Pa9]. The oxidation can be performed under potential control or under current control. For the potentiostatic case the current density in the first few seconds of anodization is only limited by the electrolyte conductivity [Ba2]. In this respect the oxide formation in this time interval is not truly under potentiostatic control, which may cause irreproducible results [Ba7]. In aqueous electrolytes of low resistivity the potentiostatic characteristic shows a sharp current peak when the potential is switched to a positive value at t=0. After this first current peak a second broader one is observed for potentials of 16 V and higher, as shown in Fig. 5.1a. The first sharp peak due to anodic oxidation is also observed in low concentrated HF, as shown in Fig. 4.14. In order to avoid the initial current peak, the oxidation can be performed under potentiodynamic conditions (V/f =const), as shown in Fig. 5.1b. In this case the current increases slowly near t=0, but shows a pronounced first maximum at a constant bias of about 19 V, independently of scan rate. The charge consumed between t=0 and this first maximum is in the order of 0.2 mAs cnT2. After this first maximum several other maxima at different bias are observed. 

Biogenic amines, such as histamine [131], adenine [132], dopamine [133] and melamine [134], have been determined using chemosensors combining MIP recognition and PM transduction at QCM. Electronically conducting MIPs have been used in these chemosensors as recognition materials. Initially, functional electroactive bis(bithiophene)methane monomers, substituted either with the benzo-18-crown-6 or 3,4-dihydroxyphenyl, or dioxaborinane moiety, were allowed to form complexes, in ACN solutions, with these amines as templates. Subsequently, these complexes were oxidatively electropolymerized under potentiodynamic conditions. The resulting MIP films deposited onto electrodes of quartz resonators were washed with aqueous base solutions to extract the templates. 

In situ polymerization, and electrochemical polymerization in particular [22], is an elegant procedure to form an ultra thin MIP film directly on the transducer surface. Electrochemical polymerization involves redox monomers that can be polymerized under galvanostatic, potentiostatic or potentiodynamic conditions that allow control of the properties of the MIP film being prepared. That is, the polymer thickness and its porosity can easily be adjusted with the amount of charge transferred as well as by selection of solvent and counter ions of suitable sizes, respectively. Except for template removal, this polymerization does not require any further film treatment and, in fact, the film can be applied directly. Formation of an ultrathin film of MIP is one of the attractive ways of chemosensor fabrication that avoids introduction of an excessive diffusion barrier for the analyte, thus improving chemosensor performance. This type of MIP is used to fabricate not only electrochemical [114] but also optical [59] and PZ [28] chemosensors. 

The presented electrochemical measurements prove that formation conditions sensitively affect the electronic film properties. Consequently, the formation conditions can be used for an adjustment and control of electronic properties to a certain extent. For instance, in the case of Ti/Ti02 changing from potentiody-namic to potentiostatic formation, conditions allows for significant reduction of the donor defect state concentration. Moreover, under potentiodynamic conditions, a pronounced texture dependence of oxide growth is observed, which can be significantly suppressed by potentiostatic formation. The texture dependence itself... 

Calandra et al. [44] adapted Muller s model to potentiodynamic conditions. Mac Donald [45] corrected a typographical error found in the mathematical expressions in the article. Devilliers et al. [46] developed a general model for the formation of low-conductivity films, considering a process controlled by the solution resistance in the pores of the film. The authors simulated the potentiodynamic curves for the following particular cases constant film thickness (bidimensional growth), three-dimensional growth, and a decomposition/dissolution process coupled to the electrochemical reaction. The potentiodynamic curves simulated for constant thickness are identical to those obtained by Calandra et al. [44]. 

Srinivasan and Gileadi [47] described the formation of a new phase under potentiodynamic conditions in terms of an adsorption process. The validity of the Langmuir isotherm was assumed for the following adsorption process ... 

As it was mentioned in Section 8.1, an experiment is included in order to illustrate the selection procedure. Each model was developed for specific experimental conditions. Sometimes, a description can be modified, extended, and corrected in order to cover other experimental conditions. Thus, a model initially developed with the purpose of describing a film formed under potentiostatic conditions can be adapted, via mathematical derivations, to potentiodynamic conditions. In the present experiment, the film considered was generated under potentiodynamic conditions by the use of voltammetric techniques. As a consequence, only the models developed for potentiodynamic conditions were considered [56-58]. 

The hrst step considered in the selection procedure corresponds to the verification of the mathematical relationships resulting from the models. For this purpose, the experimental data is analyzed according to the mathematical relationships of the most suitable theoretical models. Table 8.1 will be very useful as it collects the mathematical relationships satisfied by models developed for potentiodynamic conditions. 

Diagnostic Parameters Criteria for the Different Growth Models Nucleation-Growth-Overlap (I) [39] Miiller-Calandra (II) [43,44] and Srinivasan-Gileadi (III) [47] under Potentiodynamic Conditions... 

The nucleation theories for potentiodynamic conditions [44] lead mainly an instantaneous or progressive nucleation also for reversible and irreversible limiting conditions. The following dependences of 7p, Ep, and AE /2 with v can be obtained for four limiting cases. 

On the other hand, it was verified that the half-peak width AEy2 varies linearly with scan rate (Figure 8.12). This linear relationship together with those observed in Figures 8.10 and 8.11 are predicted by the nucleation-growth model for potentiodynamic conditions [39] when the nucleation process is fast and irreversible. 

Pettit, C.M., Goonetilleke, P.C., Roy, D., 2006. Measurement of differential capacitance for faradaic systems under potentiodynamic conditions considerations of Fourier transform and phase-selective techniques. J. Electroanal. Chem. 589, 219—231. 

There was an attempt to construct a BHJ SC with controlled morphology of an active layer using a layer-by-layer assembling with consecutive electropolymerization of the resulting layers to form a covalently linked D-A active material of precisely controllable thickness [116]. Electropolymerization was performed under potentiodynamic conditions by coupling IV-alkylcarbazole moieties of both D and A units. A photoactive layer was composed of three carbazol-derivatized components, i.e., [Ceolfullerene, ZnP, and oligofluorene derivatives (Scheme 53). The PCE of... 

Ahluwalia RK, Arisetty S, Wang X et al (2013) Thermodynamics and kinetics of platinum dissolution from carbon-supported electrocatalysts in aqueous media under potentiostatic and potentiodynamic conditions. J Eletrcochem Soc 160 F447-F455... 

Harris, L. B. and Damjanovic, A. 1975. Initial anodic growth of oxide film on platinum in 2NH2SO4 under galvanostatic, potentiostatic, and potentiodynamic conditions The question of mechanism. 122, 593-600. 

Interestingly, Pt dissolution imder potentiodynamic conditions is faster compared with potentiostatic conditions [37,38], In addition, cathodic dissolution of Pt, according to ... 

---