The Electrochemistry of Gold: I The Redox Behaviour of the Metal in Aqueous Media

Gold is frequently regarded as the ideal metal for the investigation of solid electrode behaviour, which in aqueous media is often considered in very simplistic terms as being that of a metal which is highly resistant to dissolution. Gold possesses very weak chemisorbing properties and an extensive double layer region that in the presence of most pure electrolytes is often assumed to be totally free of Faradaic behaviour, and exhibits a monolayer (or AU(2)O(3)) oxide formation/removal reaction at quite positive potentials. However, recent investigations have revealed that the electrochemistry of polycrystalline gold in aqueous solution is considerably more complex. Two significantly different types of oxide deposits, monolayer (or a) and hydrous (or beta), may be produced on the metal and the behaviour of the beta-deposit is quite unusual. It is suggested that not only the behaviour of the beta-oxide but, far more important from a practical viewpoint, the catalytic and electrocatalytic behaviour of gold (which will be discussed in more detail in Part II) may be rationalized in terms of the active state (or states) of gold. This active state (frequently present only at very low coverage) reacts in a manner that is quite different from that of stable gold. The nature of the active state of gold deserves far more attention than it has received to date.