Potential-pH Pourbaix Diagram

Marcel Pourbaix (1904-1998) was a Belgian physical chemist who is known for inventing the (electric) potential-pH, better known as Pourbaix, diagrams in the 1930s. In 1963, Pourbaix produced the Atlas of Electrochemical Equilibria, which contained potential-pH diagrams for all elements known at that time. 

Inzelt, and F. Scholz, Electrochemical Dictionary, Springer, Berlin, Germany, 2008. 

To construct this diagram, the following steps should be taken  

The lower dash line (2) corresponds to the Nernst equation, EfpH) for the H+(aq)/H2(g) half-reaction, 2H+(aq) + 2e = H2(g), with the following Nemst equation  

Any vertical line corresponds to a reaction without electrons involved. For example, line (3) corresponds to a hydrolysis reaction  

---

Figure 2. The potential-pH (Pourbaix) diagram for aluminum in aqueous medium, defining regions of thermodynamic stability of the different species.

A large number of publications deal with the construction and interpretation of potential -pH (Pourbaix) diagrams, and some of these have been included in Table HJ. Most of these studies avoid the question of activity coefficients because the stability fields are calculated for arbitrarily specified activities of the species in solution. 

Fig. 14.2 A potential-pH (Pourbaix) diagram for manganese. IModified from C. C. Liang In Encyclopedia of Electrochemistry of the Elements Bard,...

The concept of CP can be understood through potential-pH (Pourbaix) diagrams... 

A potential-pH (Pourbaix) diagram for a 2.5 M ZnBra primary electrolyte solution was constmcted using OLl Studio software (version 9.2, OLl Systems, Inc.) and is presented in Fig. 2.2. 

Corrosion test methods can be divided into electrochemical and non-electrochemical methods. Among the electrochemical techniques that have been used successfully for corrosion prediction are potentiodynamic polarization scans, electrochemical impedance, corrosion current monitoring, controlled potential tests for cathodic and anodic protection, and the rotating cylinder electrode for studies of velocity effects [3i,32]. Though not literally a test, potential-pH (Pourbaix) diagrams have been used as road maps to help understand the results of other tests. 

The main objective of this chapter is to introduce students to one of the most important subjects of the book, equilibrium electrochemistry, which is mainly based on equilibrium thermodynamics. Equilibrium electrochemistry is usually the first and required step in analyzing any electrochemical system. How to estimate the equilibrium potential of a half-reaction and the electric potential difference of an electrochemical cell are described in this chapter. One of the most fundamental equations of electrochemical science and engineering, the Nemst equation, is introduced and anployed for composing the potential-pH (Pourbaix) diagrams. Temperature dependence of the electrode potential and the cell potential difference is also described. 

Potential-pH (Pourbaix) diagram shows the thermodynamic stability of a metal. A region of corrosion immunity can be defined using this diagram. The Pourbaix diagram of A1 is discussed in detail. 

Potential-pH (Pourbaix) diagrams for iron and ruckel in aqueous solutions above the critical temperature of water ate shown in Figs. 4A and 4B, respectively. " The lack of detail, compared to their ambient temperature coimterparts, reflects the lack of thermodynamic data for species at supercritical temperatures, particularly for hydrolyzed iottic species, and the lack of stability of dissolved iottic species in the low dielectric constant supercritical medium. 

The principle of potential-pH (Pourbaix) diagrams has been extended to the case of bidi-mensional layers of elements adsorbed on metal surfaces [44,45]. It allows us to predict the conditions of stability of adsorbed sulfur on metals immersed in water containing... 

---