Cathodic regime

The OCP etch rate of p-type and highly doped n-type Si electrodes in HF-HNO3 mixtures increases by an order of magnitude under sufficiently anodic bias [Le20]. In the cathodic regime significant dark-currents are observed for p-type electrodes, as shown in Fig. 4.12. This is ascribed to hole injection from the electrolyte [Kol4]. Note that hole injection is not observed in aqueous HF free of oxidants. 

While the electrochemical reaction in the cathodic regime is similar for most commonly used aqueous electrolytes, the anodic reaction depends on composition and pH of the electrolyte. 

In the cathodic regime the silicon atoms of the electrode do not participate in the chemical reaction. Therefore, an n-type or a strongly illuminated p-type silicon electrode behave like a noble metal electrode and hydrogen evolution or metal plating reactions are observed. For the case of an aqueous electrolyte free of metal ions the main reaction is electrochemical hydrogen evolution according to ... 

If [BMIMJPFg ionic liquid is saturated with GeCLj (Figure 6.2), two main reduction processes (Pi and P2) are observed in the cathodic regime [42], The first reduction peak, with a minimum at +500 mV vs. Ge (Pi) is attributed to the reduction of Ge(IV) to Ge(II). At potentials below 0 mV (P2) the bulk deposition of Ge from Ge(II) sets in, as can be seen with the naked eye. The rising cathodic current at about —1000 mV vs. Ge is attributed to the irreversible reduction of the organic cation. If only Pi is passed, an oxidation process is not observed. If Ge deposition is performed an oxidation peak at 1000 mV is observed, which means that this peak must be correlated to Ge electrooxidation. A series of oxidation peaks above +1500 mV is also observed if the electrode potential is cycled between +1000 and... 

Bias-dependent measurements were performed in order to check to what extent the mechanism depends on the electrical operation conditions. Fig. 43 shows double-logarithmic plots of the electrode polarization resistance (determined from the arc in the impedance spectrum) versus the microelectrode diameter observed at a cathodic bias of —300 mV and at an anodic bias of +300 mV respectively. In the cathodic case the electrode polarization resistance again scales with the inverse of the electrode area, whereas in the anodic case it scales with the inverse of the microelectrode diameter. These findings are supported by I-V measurements on LSM microelectrodes with diameters ranging from 30-80 pm the differential resistance is proportional to the inverse microelectrode area in the cathodic regime and comes close to an inverse linear relationship with the three-phase boundary (3PB) length in the anodic regime [161]. 

Figure C2.8.4. The solid line shows a typical semilogarithmic polarization curve (logj against U) for an active electrode. Different stages of reaction control are shown in the anodic and cathodic regimes the linear slope according to an exponential law indicates activation control at high anodic and cathodic potentials the current becomes independent of applied voltage, indicating diffusion control.

Sodium and lithium Both sodium [15] and lithium [16] electrodeposition was successful in neutral chloroaluminate ionic liquids that contained protons. These elements are interesting for Na- or Li-based secondary batteries, where the metals would serve directly as the anode material. The electrodeposition is not possible in basic or acidic chloroaluminates, only proton-rich NaQ or LiQ buffered neutral chloroaluminate liquids were feasible. The protons enlarged the electrochemical window towards the cathodic regime so that the alkali metal electrodeposition became possible. For Na the proton source was dissolved HQ that was introduced via the gas phase or via 1-ethyl-3-methylimidazolium hydrogen dichloride. Triethanolamine hydrogen dichloride was employed as the proton source for Li electrodeposition. For both alkali metals, reversible deposition and stripping were reported on tungsten and stainless steel substrates, respectively. 

The most intriguing feature of boron-doped diamond electrodes is represented by the unusually wide electrochemical window [1, 2]. In aqueous media, the overpotential for the evolution of molecular oxygen is higher than on every other common anode material and in the cathodic regime comparable to mercury. Consequently, these tmique properties might lead to the replacement of either very costly noble metals... 

So, the best guideline for the cathodic electrografting of vinyl monomers to be successful is a scale of donidty of monomers and organic solvents stable in the cathodic regime. However,... 

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