Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without theAbstract: The definition of a "primary method of measurement" [1] has permitted a full consideration of the definition of primary standards for pH, determined by a primary method (cell without transference, Harned cell), of the definition of secondary standards by secondary methods, and of the question whether pH, as a conventional quantity, can be incorporated within the internationally accepted system of measurement, the International System of Units (SI, Système International d'Unités). This approach has enabled resolution of the previous compromise IUPAC 1985 Recommendations [2]. Furthermore, incorporation of the uncertainties for the primary method, and for all subsequent measurements, permits the uncertainties for all procedures to be linked to the primary standards by an unbroken chain of comparisons. Thus, a rational choice can be made by the analyst of the appropriate procedure to achieve the target uncertainty of sample pH. Accordingly, this document explains IUPAC recommended definitions, procedures, and terminology relating to pH measurements in dilute aqueous solutions in the temperature range 5-50 °C. Details are given of the primary and secondary methods for measuring pH and the rationale for the assignment of pH values with appropriate uncertainties to selected primary and secondary substances.

In this work the oxidation states assumed by Ir in oxide systems used as heterogeneous catalysts for water oxidation are determined by means of in situ X-ray Absorption Spectroscopy (XAS). Using a highly hydrated iridium oxide film allows the maximum number of Ir sites to be involved in the electrochemical processes occurring at the catalysts during water oxidation (oxygen evolution reaction, OER). X-ray Absorption Near Edge Structure (XANES) spectra clearly indicate the co-existence of Ir(III) and Ir(V) at the electrode potentials where OER occurs. This represents a fundamental step both in the understanding of the water oxidation mechanism catalysed by heterogeneous Ir oxide systems, and in the possible tailoring of electrocatalysts for OER.

The construction and use of ''dynamic potential-pH diagrams'' (DPPDs), that are intended to extend the usefulness of thermodynamic Pourbaix diagrams to include kinetic considerations is described. As an example, DPPDs are presented for the comparison of electrocatalysts for water oxidation, i.e., the oxygen evolution reaction (OER), an important electrochemical reaction because of its key role in energy conversion devices and biological systems (water electrolyses, photoelectrochemical water splitting, plant photosynthesis). The criteria for obtaining kinetic data are discussed and a 3-D diagram, which shows the heterogeneous electron transfer kinetics of an electrochemical system as a function of pH and applied potential is presented. DPPDs are given for four catalysts: IrO 2 , Co 3 O 4 , Co 3 O 4 electrodeposited in a phosphate medium (Co-Pi) and Pt, allowing a direct comparison of the activity of different electrode materials over a broad range of experimental conditions (pH, potential, current density). In addition, the experimental setup and the factors affecting the accurate collection and presentation of data (e.g., reference electrode system, correction of ohmic drops, bubble formation) are discussed.

Aiming to deeply understand the electrocatalytic mechanism of silver on reduction of benzyl chloride, we carried out an in situ electrochemical surface-enhanced Raman spectroscopic study to characterize various surface species in different electrode potential regions. A further analysis with DFT calculation reveals that the benzyl radical and its anionic derivate bonded on a silver electrode are the key intermediates, implying that the pathway could drastically differ from the outer sphere concerted electron reduction at inert electrodes.

In this paper, we present a comprehensive study on low hydration Ir/IrO 2 electrodes, made of an Ir core and an IrO 2 shell, that are designed and synthesized with an innovative, green approach, in order to have a higher surface/bulk ratio of Ir−O active centers. Three materials with different hydration degrees have been deeply investigated in terms of structure and microstructure by means of transmission electron microscopy (TEM) and synchrotron radiation techniques such as high-resolution (HR) and pair distribution function (PDF) quality Xray powder diffraction (XRPD), X-ray absorption spectroscopy (XAS), and for what concerns their electrochemical properties by means of cyclic voltammetry and steady-state I/E curves. The activity of these materials is compared and discussed in the light of our most recent results on hydrous IrO x . The main conclusion of this study is that the Ir core is noninteracting with the IrO x shell, the latter being able to easily accommodate Ir in different oxidation states, as previously suggested for the hydrated form, thus explaining the activity as electrocatalysts. In addition, in operando XAS experiments assessed that the catalytic cycle involves Ir(III) and (V), as previously established for the highly hydrated IrO x material.