A reference half-cell for application in an electrochemical sensor, comprising a housing, in which a chamber containing a reference electrolyte is formed, wherein the reference electrolyte (5, 105) is in contact with a medium surrounding the housing via a liquid junction arranged in a wall of the housing, wherein the liquid junction comprises a porous diaphragm, especially a porous ceramic diaphragm, and wherein the diaphragm has, at least partially, a coating, which comprises at least one metal.