Platinum hydrogen electrode

Abstract The primary method for pH is based on the measurement of the potential difference of an electrochemical cell containing a platinum hydrogen electrode and a silver/silver chloride reference electrode, often called a Harned cell. Assumptions must be made to relate the operation of this cell to the thermodynamic definition of pH. National metrology institutes use the primary method to assign pH values to a limited number of primary standards (PS). The required comparability of pH can be ensured only if the buffers used for the calibration of pH meter-electrode assemblies are traceable to... 

Secondary pH reference materials can be derived from the PS buffer solutions by different measurement procedures, which provide results for pH(SS) of the same nominal composition as pH(PS) pH(SS) of different composition pH(SS) not compatible with platinum hydrogen electrodes. 

In the preliminary stages of this study, some difficulty was experienced in obtaining stable potentials with the silver-silver chloride electrode in H20/NMA mixtures at a mole fraction of NMA of 0.5. However, the emf of cells with platinized platinum-hydrogen electrodes and silver-silver bromide electrodes reached values which were constant over a period of at least 4 to 5 hr, making this cell appear suitable for a study of the thermodynamics of HBr in H20/NMA mixtures with mole fraction NMA (x2) up to at least 0.50. 

The palladised-platinum hydrogen electrode is used to reduce the catalytised chemical reduction of the phthalate by hydrogen gas. The calculation involves a non-thermodynamic assumption, the Bates-Guggenheim Convention, for the single ion activity of the chloride ion - as... 

In a certain case of a platinum hydrogen electrode, on which the equilibrium Hads -O H+ + e is established, at /xy = const,... 

The most cited reference electrode is the platinum-hydrogen electrode, and electrode DC potentials are often given relative to such an electrode. It is an important electrode for absolute calibration, even if it is impractical in many applications. The platinum electrode metal is submerged in a protonic electrolyte solution, and the surface is saturated with continuously supplied hydrogen gas. The reaction at the platinum surface is a hydrogen redox reaction H2 2H (aq) + 2e, of course with no direct chemical participation of the noble metal. Remember that the standard electrode potential is under the condition pH = 0 and hydrogen ion activity 1 mol/L at the reference electrode. Thus the values found in tables must be recalculated for other concentrations. Because of the reaction it is a hydrogen electrode, but it is also a platinum electrode because platinum is the electron source or sink, and perhaps a catalyst for the reaction. 

Frumkin AN, Petrii OA, Marvet RV (1966) The dependence of the double layer charge on the platinum hydrogen electrode surface upon the potential. J Electroanal Chem 12 204... 

Thus, the chemical cell, consisting of an aqueous solution of hydrogen chloride (activity a, concentration c), a platinum-hydrogen electrode (partial pressure of hydrogen p), and a silver-silver chloride electrode, both with copper terminals, is represented by the diagram... 

The classical platinum hydrogen electrode consists of a platinum wire connected with a platinum flag of 1 cm. In order to increase the effective surface finely divided platinum, so-called platinum black, is electrochemically precipitated on the platinum sheet. 

The hydrogen electrode is still the basis for all pH measurements to date. The pH of the standard buffers used to calibrate pH electrodes is traced back to primary buffer solutions [11]. The primary method for pH is based on the measurement of the potential of an electrochemical cell without liquid junction, involving a selected buffer solution, a platinum hydrogen electrode, and a silver/silver chloride reference electrode. The standard potential of the silver/silver chloride electrode in hydrochloric acid at a molality of 0.01 mol kg is determined simultaneously. 

The primary procedure for pH is based on the measurement of the potential difference of a electrochemical cell without liquid junction, involving a selected buffer solution, a platinum hydrogen electrode, and a silver/silver chloride reference electrode, in cell I [15] ... 

Fig. 5.1.2 Schematic representation of the platinum hydrogen cell (Hamed cell). (1) Platinum hydrogen electrode, (2) inlet bubbler,...

The widely used buffer solution potassium hydrogen phthalate (pH = 4.1 at 25 °C) cannot be measured by the platinum hydrogen electrode due to reduction of the phthalate. In this case a palladium electrode is used. 

Using a similar concept, Sue et al." designed another flowthrough external pressure balanced reference electrode using a platinum/hydrogen electrode instead of Ag/AgCl electrode. The cell they developed can be depicted by ... 

Electrochemical series The relationship of materials as to their electrode potential (tendency to lose electrons as related to a platinum/hydrogen electrode i.e., electrode potential). Also called the Electromotive series. 

Electrode potential The voltage generated when a material is immersed in an electrolyte usually referred to a standard platinum/hydrogen electrode used as the zero potential. See also Electrochemical series. 

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