The electrochemical performance of amorphous NixB nanoparticles was examined by powder microelectrode, cyclic voltammetry, and chronopotentiometry techniques. Results show the adsorption and desorption of hydrogen, which was observed on cyclic voltammograms. Namely during charge, water is electrolyzed to hydrogen, which adsorbs, absorbs, diffuses into the NixB particles, and probably forms hydride NixBHz and vice versa. Nevertheless if the anodic switching potential is more positive than -0.5 V vs. HgO/Hg, the structure and composition of NixB particles will be destroyed irreversibly during cycling. The initial discharge capacity of the NixB nanoparticles can attain 333 mAh g(-1), which shows their potential for practical uses. (C) 2004 The Electrochemical Society.