Platinum black

Platinum black is a fine powder of platinum with good catalytic properties. The name of platinum black is due to its black color.

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Platinum black is widely used as a thin film covering solid platinum metal, forming platinum electrodes for applications in electrochemistry. The process of covering platinum electrodes with platinum black is called "platinization of platinum". The platinized platinum has a true surface area much higher than the geometrical surface area of the electrode and, therefore, exhibits catalytic action superior to that of shiny platinum.

Process of platinization

Before platinization, the platinum surface is cleaned by immersion in aqua regia (50% solution, i.e., 3 volumes of 12 mol/kg of HCl, 1 volume of 16 mol/kg HNO₃, 4 volumes of water)^[1].

Platinization is often conducted from water solution of 0.072 mol/kg of chloroplatinic acid and 0.00013 mol/kg of lead acetate, at a current density of 30 mA/cm² for up to 10 minutes. The process evolves chlorine at the anode; the interaction of the chlorine with the cathode is prevented by employing a suitable separation (e.g., a glass frit)^[1].

After platinization, the electrode should be rinsed and stored in distilled water. The electrode loses its catalytic properties on prolonged exposure to air.

See also

Standard hydrogen electrode

References