The synergistic influences of the OH- concentration and electrolyte conductivity on the redox behavior of NiOOH/Ni(OH)(2) for nickel oxide-coated graphite electrodes are clearly demonstrated by voltammetric and impedance analyses. The increase in the OH-concentration and electrolyte conductivity effectively promote the utilization of active nickel species and the electrochemical reversibility of NiOOH/Ni(OH)(2), indicating the simultaneous involvement of OH- and cations in the redox transition. The upper limit for utilizing Ni oxyhydroxides is mainly determined by the OH-concentration, which is facilely reached by increasing the electrolyte conductivity (adding Na2SO4). The synergistic phenomena could be very important in the applications of Ni oxide-based batteries, supercapacitors, sensors, electrochromic devices, and organic synthesis. (C) 2008 The Electrochemical Society.