A novel.electrolytic cell with Pt,O-2(air)vertical bar ZrO2 used as reference electrode was constructed integrally by using a one-end-closed magnesia partially stabilized zirconia solid electrolyte tube. Various electrochemical measurement techniques such as cyclic voltammetry (CV), chronopotentiometry (CP) and chronoamperometry (CA) were applied, and thermodynamic software Factsage was combined to study the effects of NiO concentration and temperature on electrochemical behavior of Ni ion in SiO2-CaO-MgO-Al2O3 molten slag at temperatures not less than 1673 K. The results indicate that Ni in molten slag is in stable form of Ni2+ instead of Ni3+; reduction of Ni2+ in molten slag is a diffusion control reaction process with a single step; smaller concentration of NiO and higher temperature lead to better reversibility of Ni2+ reduction reaction; with CV, CP and CA electrochemical measurement techniques, diffusion coefficients of Ni2+ at 1723K are derived, respectively. Further, diffusion activation energy of Ni2+ from data corresponding to CV and CA techniques is derived from Arrhenius equation factored in diffusion coefficient and temperature. (C) 2015 The Electrochemical Society. All rights reserved.