ReNi2.6-xMnxCo0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloys were prepared by induction melting. The effects of partially substituting Mn for Ni on the phase structure and electrochemical properties of the alloys were investigated systematically. In the alloys, (La, Ce)(2)Ni-7 phase with a Ce2Ni7-type structure, (Pr, Ce)Co-3 phase with a PuNi3-type structure, and (La, Pr)Ni-5 phase with a CaCu5-type structure were the main phases. The (La,Pr)Ni phase appeared when x increased to 0.45, and the (La, Pr)Ni-5 phase disappeared with further increasing x (x > 0.45). The hydrogen-storage capacity of the ReNi2.6-xMnxCo0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloys initially increased and reached a maximum when Mn content was x = OAS, and then decreased with further increasing Mn content. The ReNi2.6-xMnxCo0.9 (x = 0.0, 0.225, 0.45, 0.675, 0.90) alloy exhibited a hydrogen- storage capacity of 0.81, 0.98, 1.04, 0.83 and 0.53 wt.%, respectively. Electrochemical studies showed that the maximum discharge capacity of the alloy electrodes initially increased from 205 mAh/g (x 0.0) to 352 mAh/g (x = 0.45) and then decreased to 307 mAh/g (x = 90). The hydrogen absorption rate first increased and then decreased with addition of Mn element. The ReNi2.15Mn0.45Co0.9 alloy showed faster hydrogen absorption kinetics than that of the other alloys. The presence of Mn element slowed hydrogen desorption kinetics. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.