Electrocatalytic reaction and electrocatalyst

3 Electrocatalytic ammonia synthesis at normal pressure 10.2.3.1 Electrocatalytic reaction and electrocatalyst 

The electrochemical reaction, also called as the electrode reaction, takes place in electrolyte. The electrode reaction will occur when two metals or semiconductors called electrodes are inserted into aqueous electrol3des solution etc. and voltage is added between electrodes. In a broad sense, the electrode which is capable of inducing electrode reaction can be defined as an electrocatalyst. However, it is well-known that the variation of electrode type often leads to significant change in rate and selectivity in many cases. In fact, only such an electrode can be defined as an electrocatalyst, and this reaction is an electrocatal3dic reaction. The formation of 

Another difference between an electrochemical reaction and a catalytic reaction is that a so-called electrical double layer will form as the appearance of electrostatic potential gradient in the interface of electrolyte solution and electrode (conductor). Graham summarized in more detail the electrical double layer in 1947. He considered that this electrostatic potential, i.e. the double layer potential, is different from the electrode potential. He also discussed and observed in detail the double layer potential of Hg-electrode-water solution system. He found that it could not observe such potential when electrode reaction occurred while the ideal polarization happened in a wide range of electrode potential if there was no electrode reaction. Hg is a liquid and it is thus easy to observe its surface tension and calculate the relationship between surface tension and double layer potential. Therefore, its structure is clearer. The structure of electrical double layer is composed of Helmholz layer and diffusion layer. The Helmohloz face is located between Helmholz layer and diffusion layer. The external of Helmohloz face is diffusion double layer. The model of Helmholz electrical double layer corresponds to simple parallel-plate capacitor. According to its equation, it can quantitatively describe the structure of diffusion double layer. 

In electrochemistry, electrode potential is an important parameter for the activity of electrode. The measurement of electrode potential is to determine the ffowing electron between two electrodes. Oxidation reaction takes place on one electrode and reduction reaction takes place on the other electrode. The electrode reaction can be expressed as  

The calculation of electrode potential E) from Eq. (10.9) requires a series of standard electrode potential (Eq) data. It is well accepted that the standard hydrogen potential is standard electrode potential in the world. Its electrode reaction is  

---