The electrochemical formation of Pr-Ni alloys was investigated in a molten LiCl-KCl-PrCl3 (0.50 mol %) system at 723 K. A coherent and dense PrNi2 film was rapidly formed on a Ni electrode by potentiostatic electrolysis at 0.50 V. When a thin Ni electrode (50 mu m) was used, PrNi was formed at 0.50 V after the whole electrode became PrNi2. The formed PrNi2 electrodes were transformed to other phases, i. e., PrNi3, Pr2Ni7, PrNi5, and Ni, by electrochemical displantation. The formation reactions of the alloys and the corresponding equilibrium potentials were clarified. From morphological and crystallographic investigations using transmission electron microscopy and electron diffraction, it has been suggested that the rapid PrNi2 formation is due to the high Pr diffusivity in and near the grain boundaries. (c) 2005 The Electrochemical Society. All rights reserved.