Reversible hydrogen electrode RHE

According to Sato et al.,6,9 the barrier-layer thickness is about 1.5 to 1.8 nm V-1, and increases to 3 nm around the oxygen-evolution potential. In Fig. 5, the scale of the electrode potential, Vrhe, is that of the reversible hydrogen electrode (RHE) in the same solution. The electrode potentials extrapolated from the linear plots of the potentials against the film thickness suggested that the potential corresponding to the barrier thickness equal to zero is almost equal to 0.0 V on the RHE scale, independent of the pH of the solution, and approximately agrees with the equilibrium potential for the oxide film formation of Fe or Fe. Therefore it is concluded that the anodic overpotential AE applied from the equilibrium potential to form the oxide film is almost entirely loaded with the barrier portion. 

For many electrodes it is fonnd that one H+ or OH ion is involved in the reaction per electron hence, the electrode potential becomes 0.059 V more negative when the pH is raised by 1 unit this is the same potential shift as found for the hydrogen electrode. For such electrodes a special scale of electrode potentials is occasionally employed These potentials, designated as E refer to the potential of a reversible hydrogen electrode (RHE) in the same solution (i.e., at the given pH). For the electrodes of the type considered, potentials in this scale are independent of solution pH. 

OHads formation has a clear voltammetric signature on a number of surfaces, including the (lll)-oriented surfaces of platinum group metals, Pt(lll) in alkaline and acid electrolytes of non-adsorbing anions [Markovic and Ross, 2002], and Au(lll), Au(lOO), and Ag(lll) in neutral and alkaline electrolytes [Savinova et al., 2002]. On these surfaces, the reaction has a reversible character. Anderson and co-workers calculated the reversible potential of Reaction (9.1) on Pt to be 0.62 V with respect to a reversible hydrogen electrode (RHE) [Anderson, 2002]. The Pt(lll)-OH bond energy has been estimated to be about 1.4 eV in an alkaline electrolyte [Markovic and Ross, 2002]. 

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... 

An important eonelusion was that the best catalyst is not the alloyed one as expected, nor the mixture of Pt/XC 72 and Ru/XC 72 powders, but one eonsisting of a dispersion of Pt colloid and Ru colloid on the same carbon support, i.e., the Pt + Ru/XC 72 eatalyst. The latter leads to higher current densities for the eleetro-oxidation of methanol than the other catalysts with the same atomic ratio for potentials lower than 0.5 V versus a reversible hydrogen electrode (RHE) (Fig. 11.3). This result... 

The reversible hydrogen electrode (RHE) consists of Pt in contact with hydrogen at 1 atmosphere in the same solution us that employed in the electrochemical cell. On the RHE scale, therefore, hydrogen evolution always occurs at 0 V. 

This is a thermodynamically reversible process that often serves as a standard reference electrode, known as the reversible hydrogen electrode (RHE), for all other electrochemical processes. 

Figure 12. (a) Cyclic voltammetric (CV) curve and mass spectrometric cyclic vol-tammetric (MSCV) curves of (b) at m/z = 78 (benzene) and of (c) m/z = 44 (CO2) for benzene chemisorbed on Au(332)-0.82ML-Pd surfaces in benzene-free 0.1 M H2SO4. The potential scans were initiated in the negative direction. Scan rate 10 mV/s. The potentials are referenced against the reversible hydrogen electrode (RHE). 

The conditions under which IGA occurs in Alloy 600 in high-temperature caustic solutions (20-25% NaOH, 290-320 °C) have been somewhat better defined, from an electrochemical viewpoint, in the work of Cayla et al. [38]. These workers employed an external Hg/HgO reference electrode that was calibrated to the reversible hydrogen electrode (RHE) scale at the pH and temperature of interest. However, even in this ease, it is not clear to whieh hydrogen partial pressure this scale refers (presumably/hj = 1), which again emphasizes the need for the nuclear corrosion community to settle on a single potential scale that is understood by everyone involved in this type of work. Nevertheless, Cayla et al. [38] found that IGA occurs in a limited range of potential close to (within 100 mV of) the reversible hydrogen potential. 

Titanium-supported Pt/Ti02 specimens characterized by cyclic voltammetry had an apparent (geometrical) area of 0.28 cm2. The measurements were carried out in an aq. 0.5 M NaHS0i,/0.5 M Na2S0t, solution kept at 20°C. The solution was saturated with Ar or CO under 1 atm. The potentials were monitored with respect to and are referred to the reversible hydrogen electrode (RHE) in the same solution. The cyclic-voltammetry procedure followed that conventionally employed with the potential swept, in general, at a rate of 0.1 V s-1. 

On bare Au(lll) [161] after injection of a dilute aqueous solution of TMPyP directly into the STM cell under potential control at 0.8 V (versus a reversible hydrogen electrode (RHE)) immediately spots appeared and covered the surface. 

The open-circuit potential (OCP) recorded immediately after bringing in contact the C0-c(4x2)/Ni(lll) specimen with the 0.1 M KOH electrolyte was found to be about 0.24 V vs DHE (The electrode potential of Che DHE in 0.1 M KOH vs Reversible Hydrogen Electrode (RHE) was calculated to be 0.06 V. All of the electrode potentials in this thesis are cited vs DHE)) drifting rapidly over about 2 minutes to a fairly stable value of 0,20 V. This behavior was found to be very reproducible, yielding for... 

Carbon dioxide is the main reaction product for < 1.1 V (vs reversible hydrogen electrode (RHE)) on pyrolytic graphite. For a pH between 1 and 9, the Tafel slope changes from 0.150 to 0.240 V per decade, depending on the solution composition and electrode preparation. 

Unless otherwise stated, all potentials are expressed vs. reversible hydrogen electrode, RHE. 

A mechanically polished tin disk immersed in 0.5 M citric acid was prepared following the procedure described in the literature [59]. Because high-scan-rate voltammetric curves were recorded, a calomel reference electrode is not recommended because of its slow response [60], The reversible hydrogen electrode (RHE) was used as the reference electrode at 25°C. The required materials and reagents are a three-compartment electrochemical cell with a platinized platinum auxiliary electrode and a 0.5 M (pH = 1.8) citric acid solution prepared with triple-distilled water. 

Fig. 2 Photocurrent-voltage plots for (a) a nanoparticulate P25 T102 film and (b) a compact, sol-gel derived anatase T102 electrode recorded in a 0.1 MNaOH aq. solution and after addition of 0.1 M methanol. The electrodes were irradiated with the full output of a 150 W Xe lamp. The applied potentials are expressed vs reversible hydrogen electrode (RHE) in the same solution. (Reproduced with permission of the Royal Society of Chemistry from [10])...

In the cell shown in Figure 5.8, there are three electrodes (1) the catalyst-coated disk-working electrode made of either GC or other stable metal materials such as Au, (2) the counterelectrode (e.g., Pt foil or net. For non-noble metrd catalysts, the normally used counterelectrode is made of carbon or Ti material to avoid possible Pt contamination), and (3) the reference electrode such as a normal hydrogen electrode (NHE), reversible hydrogen electrode (RHE), or saturated calomel electrode (SCE). Note that the NHE uses a large surface Pt-black as the metal electrode and 1.0 M H+ aqueous solution (such as 0.5 M H2SO4) as the electrolyte. Its electrode potential is defined as zero at 1.0 atm hydrogen gas, and any temperature. 

---