What gas is used in a standard hydrogen electrode?

The standard hydrogen electrode (SHE) is a reference electrode that is crucial in electrochemistry for measuring the standard electrode potentials of other half-reactions. Hydrogen gas is the specific gas used in this electrode.

In a standard hydrogen electrode, hydrogen gas is bubbled over a platinum electrode immersed in a solution that typically contains (1 , \text{M}) hydrogen ions ((H^+)). The half-reaction that occurs at the hydrogen electrode can be represented as follows:

[ 2H^+ + 2e^- \leftrightarrow H_2(g) ]

By convention, this half-reaction is assigned a standard electrode potential of (0 , \text{V}) at all temperatures. This makes the SHE an essential reference point against which the electrode potentials of other electrochemical cells can be compared. Using hydrogen allows for a consistent and standardized measure, making it integral in electrochemical measurements and calculations.

Considering other options, gases like oxygen, nitrogen, and carbon dioxide do not serve this purpose because they do not participate in the standard electrode reactions of the same nature as hydrogen does. They do not interact to form a standard potential as defined for the SHE. Hence, hydrogen is uniquely suited for