Bowden and Rideal

FIGURE 1.2 Tafel plots as electrode potential, E, versus the logarithm of the current density, logy, for mercury ( - ), platinized mercury to 1% (o-o), platinized mercury as thin film (a-a), fresh etched silver ( - ), aged etched silver (O-O), polished silver ( - ), bright platinum (H—h), and spongy platinum electrodes (c-c). 

Using liquid mercury, the Cambridge workers assumed that the area of the electrocatalyst was what it seemed to be no invisible roughness. The capacity (around 20 pP cm 2) was then taken by Bowden and Rideal to be the real capacity of the double layer. (By real, they meant unaffected by invisible micro-roughness. ) 

Bowden and Rideal s work was decidedly electrocatalytic in nature. They measured the rate of hydrogen evolution on several electrode materials. Taking into account the real area, that is, the geometric (apparent) area, decided by the ratio of CM/C , they found a tme, substantial, difference in rates of the hydrogen evolution on various different metals of the same real area. 

It is remarkable that the erudite Rideal (a specialist in catalysis) did not introduce the term electrocatalysis in 1928. The reason, I think, was that electrochemistry in 1928 was generally focused on the electrode potential at a constant current and not the current (= rate) at a constant 

if you know the current density, the current per unit area, for example, per square centimeter, when the square centimeter is real, one is also measuring the rate of the electrode reaction in moles per square centimeter (mol cm-2) of the product. It is 79 years since Bowden and Rideal, but electrochemists still talk in terms of amperes (A) or milliamperes per square centimeter (mA cm-2) and in a sense diminished the chance of a linkup with the general field of catalysis in chemistry, where, of course, results are expressed in gram moles per square centimeter per second (g mol cm-2 s-1). 

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Butler in 1924 developed the idea that the Nemst equilibrium potential for an electrochemical process is the potential at which the forward and back reactions proceed at the same rate [37]. Following this, Bowden and Rideal [38] introduced the term jo as the value of the forward and back current density at the reversible Nemst potential and wrote the Tafel equation in the form of Equation 1.6. 

The account of transient (i.e., rapid, or short-time measurements marks one of the areas in which electrochemists had priority. Thus, physical electrochemists (Bowden and Rideal. 1928 Butler and Armstrong, 1936) were making measurements in the submillisecond range long before measurements in such time domains were made in chemistry (by Norrish and Porter, and Eigen, all of whom independently received Nobel prizes). 

Both these difficulties depend on changes in the catalytic surface of the electrode, and such changes take time. The idea of making electrode kinetic measurements at short times ( transients ) had been introduced by Bowden and Rideal in 1928, but their aim was less to overcome undesired surface changes and more to make use of... 

This is the transient method for which most experience is available. It was introduced by Bowden and Rideal (1928). The name comes from that of Galvani4 and means, in fact, current. Thus, Galvanostatic transient means short-term constant current. The circuitry is simple. It consists of nothing more than a measurement cell in series with an adjustable resistance much larger in value than the resistance of the cell, a power source, a rapid action switch, and a cathode ray oscilloscope to record the variation in the potential of the working electrode with time. A typical potentialtime relation is shown in Fig. 8.6. 

Closely connected with the rate of passage of current at a steady overpotential is the rate of decay of overpotential after the current has been suddenly cut off. Apart from the observation of Bowden and Rideal that the rate of decay is enormously accelerated by dissolved oxygen, the data seem insufficient for generalization. Baars gave the equation for decay, Es — a —b log t, b being the same constant as the b in Tafel s equation but his own data do not bear this out very exactly Bowden and Rideal gave the equation... 

These figures are not the same as Bowden and Rideal s estimate of 1/3000 of a monolayer of ions, assuming a diameter for the hydrogen ion of 1 A but the value for the capacity used here is three times theirs. The difference is not very important they were the first to show that the layer of ions giving rise to the overpotential is very far from closely packed. 

Fig. 118. Variation of overvoltage with current density (Bowden and Rideal)...

The results recorded below for the variation of the overvoltage with current density at a mercury cathode in dilute sulfuric acid at 25 have been estimated from the data of Bowden and Rideal [ Proc. Roy. Soc. 120A, 59 (1928)]. 

The term electrocatalysis was first introduced by Grubb in 1963 [1] in connection with the anodic and cathodic charge-transfer reactions in fuel cells. However, the first systematic experimental investigations of various electrocatalysts had been carried out in the 1920s by Bowden and Rideal [2] and the concept and first interpretation of electrocatalysis had been introduced in the 1930s by Horiuti and Polanyi [3]. Their theory and its extensions and improvements have been analyzed lucidly by Bockris [4-6]. Recent reviews of progress in electrocatalysis can be found in more general [6-8] or specialized books [9-11]. 

Fig-1 Some of the first published comparative current-potential (Tafel) plots obtained by Bowden and Rideal [2, 4]. I. Mercury. II. Platinized mercury, 1/100 covered. III. Platinized mercury, thin film of Pt. IV. Etched silver, new. V. Etched silver, old. VI. Polished silver. VII. Bright platinum. 

Bowden and Rideal achieved two things with the new equipment. The double-layer charging part of the graph in Figure 1.1 can be represented by... 

This technique, being able to measure the real surface area, was relevant to the as yet unrealized catalytic properties of the surface, for Bowden and Rideal claimed that to compare the electro-catalytic properties of various metals one had to first eliminate any difference in real areas for the comparison of reaction rates (measured later when the potential no longer varied with time [Figure 1.2] on the same area). 

The term catalysis was coined by Berzelius in 1835 and is derived from the Greek kata (go down) and lysis or lyein (letting). The first authors to introduce the term catalytic electrode reactions were Bowden and Rideal in 1928 [1], who observed the different currents that appear for a certain reaction on distinct electrode surfaces but under the same electrode potentials. There is still some controversy over the first use of the term electrocatalysis. It seems from the literature that the Soviets were the pioneers in the field of electrocatalysis since 1934 [2]. The first reported work in electrocatalysis was on fuel cell processes by Grubbs in the 1950s [3]. 

Historically, it should be noted that double-layer capacitance measurements were first reliably made (at Hg) by Bowden and Rideal [1928] using the dc charging-current method and by Proskumin and Frumkin [1935] by means of ac modulation. Randles [1947,1952] pioneered the examination of impedance of an electrode process (e.g. redox reactions), using phase-sensitive detector instrumentation to record the frequency dependence of the separated real and imaginary components of Z. Under diffusion-control, the dependence of Z" and Z were found due to the Warburg impedance element. 

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