Platinum anodic films with oxygen

Ruthenium trichloride catalyzes the production of oxygen at a platinum anode via higher oxidation state species, whilst one of the most effective catalysts for oxygen or chlorine evolution is formed by reduction of a solution containing [Fe2(S04)3] and K3[Ru(CN)6]. This leads to a film on the electrode of ruthenium purple, Fe4[Ru(CN)6]3, with a structure analogous to that of Prussian blue. Oxygen can then be produced at 0.2 V vs. 

The best-known example of a membrane-covered electrode is the Clark electrode for determination of dissolved oxygen (Fig. 14.49,10). A membrane (usually PTFE) with pores of a size that lets only oxygen diffuse through is placed over a thin film of electrolyte on top of a platinum or gold electrode, the potential of this being controlled so as to reduce oxygen. The anode is usually a silver disc that acts simultaneously as reference electrode. It can be used for oxygen determination in gas or liquid phases. 

---