This investigation first proposed that open-circuit potential vs time (OCP-t) is a novel nonlinear potential step controlled by redox reaction and nucleation. A novel thermodynamic model of OCP-t is obtained for electroless deposition of Ni on Pd-activated p-type silicon (100). Thermodynamic transient properties such as capacity of double layer C, surface charge density q, interfacial tension gamma, and resistance of chemical reaction Rr are calculated. Results show that the variation of OCP is dependant on the interfacial double layer. The breakdown and rearrangement of the double layer causes surface charge density step, which triggers momentary nucleation of Ni on the substrate. Results also show that reductant pulses would be an effective way to speed nuclei growth. (c) 2006 The Electrochemical Society.