Platinum is used as the inert electrode in the standard hydrogen electrode.
The standard hydrogen electrode, or SHE, is assigned a standard electrode potential of exactly 0 volts. It consists of hydrogen gas at standard pressure, hydrogen ions in solution under standard conditions, and a platinum electrode that provides a conductive surface for the reaction.
Platinum is suitable because it is chemically resistant and can catalyze the hydrogen oxidation and reduction reactions without being consumed as a reactant. The platinum is often coated with finely divided platinum, called platinum black, to increase surface area and improve catalytic behavior.
The electrode does not measure an absolute voltage by itself. Instead, other half-cells are connected to it so their electrode potentials can be compared with the zero-volt reference. The standard hydrogen electrode is therefore a reference system in electrochemistry, not a typical battery electrode used for household power.