Co-S samples were synthesized by different methods and investigated as the negative materials for alkaline rechargeable batteries. The phase structure of the samples was characterized by XRD. Electrochemical measurements showed that the Co-S electrodes prepared by physical mixture displayed high discharge capacities and excellent cycle stability, while the CoS compound electrodes displayed poor discharge capacities. The reaction mechanism and the reasons for the differences of the Co-S electrodes were investigated. It is found that the reversible reaction between Co and Co(OH)(2) is dominant for all the Co-S electrodes. The various existence forms of sulfur result in distinct utilization of Co in the samples, leading to quite different electrochemical properties. (C) 2011 Elsevier Ltd. All rights reserved.