In this work, nanoporous nickel hydroxide (Ni(OH)(2)) films were rationally synthesized by a facile and cost-effective one-pot route. Hydrogen (H-2) bubbles and hydroxide (OH-) ions simultaneously generated from water electrolysis at the cathode at appropriate potentials play a critical role of producing in-situ porous Ni(OH)(2) films in a solution of nickel salt. The induced H-2 bubbles served as dynamic templates to create porosity and OH-ions as a precipitant to crystallize Ni(OH)(2). At optimal conditions, porous Ni(OH)(2) films with pores as small as similar to 2 nm were directly formed, as verified by N-2 adsorption/desorption measurements. The as-obtained nanoporous Ni(OH)(2) films exhibit high specific capacity > 739 C/g at the charge/discharge current density of 1 A/g and mass loading of 0.6 mg/cm(2) in three-electrode configuration; and energy and power densities as high as 152 Wh/kg and 13.5 kW/kg at current density of 15 A/g in two-electrode asymmetric supercapacitor. This straightforward, low-cost, and highly-efficient synthesis of nanoporous Ni(OH)(2) films is potentially useful for capacitor industry as well as other application fields. In addition, the water electrolysis method may be applied to the direct formation of other porous metal hydroxides. (C) 2019 The Electrochemical Society.