Cobalt nanoparticles on an amorphous Si3N4 matrix were synthesized by direct ball-milling of Co and Si3N4 powders for an improvement of their electrochemical performance. The microstructure, morphology and chemical state of the ball-milled Co-Si3N4 composites are characterized by Xray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The electrochemical performance of Co-Si3N4 composites was investigated by galvanostatic charge-discharge process and cyclic voltammetry (CV) technique. It is found that metallic Co nanoparticles of 10-20 nm in size are highly dispersed on the amorphous inactive Si3N4 matrix after the ball-milling. The composite with a Co/Si molar ratio of 2/1 shows the optimized electrochemical performance, including discharge capacity and cycle stability. The formation of Co nanoparticles with a good reaction activity is responsible for the discharge capacity of the composites. The reversible faradic reaction between Co and beta-Co(OH)(2) is dominant for ball-milled Co-Si3N4 composite. The surface modification of the hydrogen storage PrMg12-Ni composites using CO-Si3N4 composites can enhance the initial discharge capacity based on the hydrogen electrochemical oxidation and Co redox reaction. (C) 2608 Elsevier B.V. All rights reserved.