Research on electrochemical characteristics and microstructure of Mm(NiMnAl)4.9Co0.2 rapidly quenched alloy

The cycling stability of low-Co hydrogen storage alloy was improved by rapid quenching. A low-Co hydrogen storage alloy with outstanding properties was obtained with a content of Co as low as 2.7 wt.%. It was first found that the quenching rate could affect the discharge capacity of the alloy: when the quenching rate was lower than 10 m/s, rapid quenching increased the discharge capacity and when the quenching rate was higher than 15 m/s, it significantly decreased the discharge capacity. In addition, the cycle life of the Mm(NiMnAl)4.9Co0.2 alloy could not be increased when the quenching rate was lower than 10 m/s, but instead, its cycle life was lowered to less than that of the as-cast alloy. The microstructures of the alloy were investigated by XRD and TEM in order to understand and explain these special properties. [Copyright &y& Elsevier]