Hydrogen evolution method

Zinc is determined quantitatively by titration of the acid solubilized material with K ferro-cyanide, the endpoint being indicated when a drop of uranyl nitrate produces on a porcelain plate a brown tinge with a drop of titrated mixt. Metallic Zn is determined by the hydrogen evolution method using a gas burette (Ref 8)... 

TABLE 3.7. Polarization Data for the Hydrogen Evolution Method... 

The hydrogen evolution method has several advantages over the traditional weight loss measurement in estimating corrosion damage or corrosion rate of a Mg alloy ... 

The hydrogen evolution method is also superior to the estimation of corrosion rate from polarization curve in terms of measurement accuracy. The application of the traditional Tafel extrapolation in estimating the corrosion rates of Mg and its alloys is actually questionable and in many cases can lead to a misleading result, although it has been employed to investigate or evaluate the corrosion performance of Mg and its alloys in some studies (Bonora et al, 2000 Eliezer et al, 2000 Hallopeau et al., 1997 Krishnamurthy et al., 1988 Mathieu et al., 2000). 

Song G.-L, Atrens A., StJohn D. (2001), An hydrogen evolution method for the estimation of the corrosion rate of magnesium alloys , in J. Hryn (ed.). Magnesium Technology 2001, TMS, pp 255-262. 

Hydrogen evolution method Electrochemical measurements (linear polarization, EIS)... 

An alternative test is the hydrogen evolution method (Kray, 1934). This test is based on the fact that during Mg dissolution an equal part of hydrogen is produced (equation 10.7). By collecting the evolving hydrogen gas the corrosion rate can be determined easily and rapidly (Song and Atrens, 2003) with material available in most laboratories (Fig. 10.7). 

Schematic drawing of the setup for measuring corrosion rates by the hydrogen evolution method. The Mg sample is immersed below a funnel which is directing the gas bubbles into a burette which is filled with a solution. 

Kray, R. H. (1934) Modified hydrogen evolution method for metallic magnesium, aluminum, and zinc. Ind Engi Chem Anall Edn, 6, 250-51. 

Until the advent of modem physical methods for surface studies and computer control of experiments, our knowledge of electrode processes was derived mostly from electrochemical measurements (Chapter 12). By clever use of these measurements, together with electrocapillary studies, it was possible to derive considerable information on processes in the inner Helmholtz plane. Other important tools were the use of radioactive isotopes to study adsorption processes and the derivation of mechanisms for hydrogen evolution from isotope separation factors. Early on, extensive use was made of optical microscopy and X-ray diffraction (XRD) in the study of electrocrystallization of metals. In the past 30 years enormous progress has been made in the development and application of new physical methods for study of electrode processes at the molecular and atomic level. 

The isotope effect (i.e. the difference in the rates of evolution of hydrogen from H20 and D20) on hydrogen evolution is very important for theoretical and practical reasons. The electrolysis of a mixture of H20 and D20 is characterized, like in other separation methods, by a separation factor... 

Classically, processes involving surface intermediates were investigated primarily by methods (2) (4) above and in particular by measuring current as a function of concentration of reagents and electrode potential. A familiar example is the hydrogen evolution reaction, which may proceed by one of two possible mechanisms, both of which share a common first step ... 

Cationic ions and polyelectrolytes can stabilize the formation of the PS I monolayers at the air-water interface. These complex monolayers can be transferred onto the hydrophobic substrate surfaces by horizontal lifting method. The PS I/polyelectrolyte complex film may be used for the development of a biosystem for the studies on photoinduced electron transfer and for hydrogen evolution. 

There are several variants of this method for more complicated reactions. If the reacting species is produced by a preceding chemical reaction, deviations from Eq. (14.6) may be observed for large in, when the reaction is slower than mass transport. From these deviations the rate constant of the chemical reaction can be determined. As an example we consider hydrogen evolution from a weak acid HA, where the reacting protons are formed by a preceding dissociation reaction ... 

In addition to the development of new methods, new applications of molecular dynamics computer simulation are also needed in order to make comparisons with experimental results. In particular, more complicated chemical reactions, beyond the relatively simple electron transfer reaction, could be studied. Examples include the study of chemical adsorption, hydrogen evolution reactions, and chemical modification of the electrode surface. All of the above directions and opportunities promise to keep this area of research very active ... 

Less investigated as potential methods for hydrogen bioproduction, in vitro systems make exclusively use of the enzymatic component responsible for hydrogen evolution... 

As the name indicates alkaline electrolyzers use high pH electrolytes like aqueous sodium hydroxide or potassium hydroxide. This is the oldest, most developed and most widely used method of water electrolysis. Hydrogen evolution takes place at the cathode, and oxygen evolution takes place at the anode. The cathodic reaction can be represented by the following steps [26,27]... 

The overall effect is the decomposition of water. An advantage of this method is that only a low light energy input, about one quantum/H2, is required for hydrogen evolution [179]. During... 

---