The potentials of copper and iron reference electrodes were measured in dehydrated melts of KF center dot 2HF, NH4F center dot KF center dot 4HF, and NH4F center dot 2HF against the hydrogen evolution potential on Pt. The potential of a fresh copper reference electrode was unstable for the initial 30 days and then became constant, whereas those of an anodically oxidized and a thermally fluorinated copper reference electrode became stable in a shorter time. The potential of the thermally fluorinated copper reference electrode obtained experimentally in the KF center dot 2HF melt was 0.402 +/- 0.003 vs H-2 at 373 K, and the values for the three kinds of copper electrodes were close to one another. Theoretical electrode potentials calculated from thermodynamic data were 0.458 V for CuF2/Cu and 0.307 V for CuF/Cu against HF/H-2. Because the observed potentials on the copper electrodes existed between these values, it may be caused by coexistence of CuF and CuF2 on the surface. These copper electrodes, which should be denoted as CuF2+CuF/Cu or CuFx(1 < x < 2)/Cu, are useful as reference electrodes for electrochemical measurements in fluoride melts containing HF. The observed potentials of the fresh iron and the thermally fluorinated iron electrodes in the KF center dot 2HF melt at 373 K were -0.147 +/- 0.004 and -0.195 +/- 0.003 V vs H-2, respectively, and were not in agreement with each other. Both iron electrodes after immersion in the melt were covered with the film composed of FeF3 and FeF2; however, the theoretical potentials [E(FeF3/Fe)(373)=-0.355 V and E(FeF2/Fe)(373)=-0.434 V vs E(HF/H-2)(373)] were fairly lower than the experimentally observed values. These results suggested that the potential of iron electrodes was determined by other minor species on the surface and therefore, they cannot be used as reference electrodes in fluoride melts containing HF. (c) 2006 The Electrochemical Society.