Low-temperature and instantaneous high-rate output performance of AB5-type hydrogen storage alloy with duplex surface hot-alkali treatment.

The excellent low-temperature and instantaneous high-rate output performance of MmNi 3.7 Co 0.7 Mn 0.3 Al 0.3 alloy are obtained via hot-alkali treatment (K alloy) and duplex hot-alkali treatments with reducing agents, including N 2 H 4 (KN alloy), NaH 2 PO 2 (KP alloy) and NaBH 4 (KB alloy). The charge transfer process on the alloy surface is the primary control step that influences the electrochemical properties at −40 °C. Scanning electron microscopy and energy dispersive X-ray analyses demonstrate that a high electrocatalytic Ni-and Co-rich layer is formed via the preferential dissolution of Al and Mn and that the alloy surface oxide is effectively removed via the duplex surface hot-alkali treatments. Thus, the charge-transfer resistance decreases and the exchange current density increases obviously in the treated alloys, making the K, KN, KP and KB alloys exhibit better activation property, high-rate dischargeability and instantaneous high-rate output performance at 20 °C, as well as higher discharge capacity, low-temperature dischargeability and high-power delivery at −40 °C. Based on the overall electrochemical properties of the alloys at various temperatures, a duplex surface modification of the hot-alkali treatment with NaH 2 PO 2 is determined to be the best. [ABSTRACT FROM AUTHOR]