Platinum electrodes hydrogen adsorption

Separation of bismuth and polonium from lead can also be achieved by Immersing a hydrogen soaked platinum electrode In a 0.1 M hydrochloric acid solution of the tracer lead, bismuth and polonium (E6). Nitric acid, bromine or other substances which might poison the platinum electrode for adsorption, of hydrogen must be absent. This has been used for separation of RaD from RaE and RaF (E6)(H5)- This method does not introduce nickel or silver contamination Into the RaD solution or In the RaE or RaP when these are dissolved from the electrode. 

Adsorption of Reaction Components In many cases, adsorption of a reactant is one of the hrst steps in the electrochemical reaction, and precedes charge transfer and/or other steps of the reaction. In many cases, intermediate reaction products are also adsorbed on the electrode s snrface. Equally, the adsorption of reaction products is possible. The example of the adsorption of molecular hydrogen on platinum had been given earlier. Hydrogen adsorption is possible on the platinum electrode in aqueons solntions even when there is no molecular hydrogen in the initial system at potentials more negative than 0.3 V (RHE), the electrochemical reaction... 

Cyclic voltammetry is perhaps the most important and widely used technique within the field of analytical electrochemistry. With a theoretical standard hydrogen electrode at hand, one of the first interesting and challenging applications may be to try to use it to make theoretical cyclic voltammograms (CVs). In following, we set out to do this by attempting to calculate the CV for hydrogen adsorption on two different facets of platinum the (111) and the (100) facets. 

Cyclic voltammetry studies of single-crystal platinum electrodes in acidic aqueous electrolytes showed that the two characteristic peaks of hydrogen adsorption/desorption on platinum (see Fig. 5.40) correspond in fact to reactions at two different crystal faces the peak at lower potential to Pt(100) and the other one to Pt(lll). 

The second most widely used noble metal for preparation of electrodes is gold. Similar to Pt, the gold electrode, contacted with aqueous electrolyte, is covered in a broad range of anodic potentials with an oxide film. On the other hand, the hydrogen adsorption/desorption peaks are absent on the cyclic voltammogram of a gold electrode in aqueous electrolytes, and the electrocatalytic activity for most charge transfer reactions is considerably lower in comparison with that of platinum. 

Electrode processes can be retarded (i.e. their overpotential is increased) by the adsorption of the components of the electrolysed solution, of the products of the actual electrode reaction and of other substances formed at the electrode. Figure 5.43 depicts the effect of the adsorption of methanol on the adsorption of hydrogen at a platinum electrode (see page 353). 

The authors found that as CO is more strongly adsorbed than hydrogen, the introduction of CO into the electrochemical cell was immediately accompanied by its adsorption at the platinum electrode. This was shown by the decrease in the charge under the hydride udsorption features, and ulso the appearance of the oxidative stripping peaks 1 and II. 

Hydrogen adsorption on platinum electrodes in perchloric acid solutions... 

Ruthenium was electrochemically deposited on platinum foil at a potential of 50 mV for 10 s. The cyclic voitammogram of this Pt—Ru electrode in 3 M H2SO4 is shown in Fig. 4—2. The voitammogram shows the hydrogen adsorption-desorption features from 50 mV to 200 mV and the oxidation and reduction current over 300 mV. The voltanunogram seemed stable when the upper limit potential was 800 mV. When the upper limit was higher than 800 mV, the voitammogram became slowly like pure... 

Potentiodynamic Technique. Adsorption of methanol on Pt in acid solution was studied by Breiter and Gilman (3) using a potentiostatic technique. The anodic sweep, with a sweep rate of 800 V/s, was started at rest potential and extended to 2.0 V with respect to a hydrogen reference electrode in the same solution. As shown in Figure 10.8, the current was recorded as a function of potential (time) in the absence (curve A) and in the presence (curve B) of methanol. The increase in current in curve B is due to oxidation of the adsorbed methanol on the platinum electrode. Thus, shaded area 2 minus shaded area 1 (Fig. 10.8) yields the change 2m (C/cm ) required for oxidation of the adsorbed methanol ... 

It was established that for the interpretation of phenomena occurring at a platinum electrode, the competitive adsorption of hydrogen and the anions (involving the reacting ones) should be taken into consideration [13-15]. 

An analog of the platinized platinum electrode is the black or gray nickel electrode, which under certain experimental conditions can be used as the hydrogen electrode instead of the platinum electrode [65]. This electrode can be obtained by electrochemical deposition of nickel under the experimental conditions described in [65]. The real surface areas of these electrodes significantly surpass their geometric surface areas. In addition, potential-dependent adsorption of hydrogen occurs on the nickel surface and the measurement of the hydrogen capacity of the electrode in alkaline medium offers a tool for the determination of the real surface area [66]. 

Platinum electrodes are widely used as an inert electrode in redox reactions because the metal is most stable in aqueous and nonaqueous solutions in the absence of complexing agents, as well as because of its electrocatalytic activity. The inertness of the metal does not mean that no surface layers are formed. The true doublelayer (ideal polarized electrode) behavior is limited to ca. 200-300 mV potential interval depending on the crystal structure and the actual state of the metal surface, while at low and high potentials, hydrogen and oxygen adsorption (oxide formation) respectively, occur. 

It was demonstrated that the radiotracer method, using labeled anions, is an adequate tool to follow anion adsorption in the course of voltammetric measurements and to gain simultaneous information on hydrogen and anion adsorption [163]. Coupling voltammetric and radiometric measurements in the study of platinized platinum electrodes gave insight in the anion-hydrogen atom coadsorption process. 

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