Dealloying is a facile method to prepare nanoporous metals. Normally, the formation of nanoporous structure during dealloying is accompanied by a macroscopic volume reduction, which is utilized herein to prepare homogeneous nanoporous Ni (np-Ni) particles by ultrasonic-assisted dealloying Mg-Ni-La metallic glass ribbons in (NH4)(2)SO4 aqueous solution. Particles with different shapes can be fabricated by adjusting the thickness of the metallic glass ribbons. The np-Ni particles exhibit a ligament-pore structure with a high specific surface area of 53 m(2) g(-1). The process for particle formation and the ligament structure are discussed. The np-Ni can be applied as an efficient electrocatalyst for hydrogen evolution reaction (HER). To reach a high current density of 100 mA cm(-2), it requires merely 46 mV with a small Tafel slope of 21 mV dec(-1). Furthermore, the np-Ni particles have a good catalytic stability during water electrolysis without any increase of overpotential for at least 20 h, which may be attributed to the chemical stability of Mg and La in alkaline media and the firm support of the ligament-pore structure. It is expected that the current catalyst can enable the manufacturing of affordable water splitting systems. (C) 2018 The Electrochemical Society.