Effects of Al content on the electrochemical properties of La0.78Ce0.22Ni3.95-xCo0.65Mn0.3Si0.1Alx alloys at 20-80 °C

The various properties of La0.78Ce0.22Ni3.95-xCo0.65Mn0.3Si0.1Alx (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys at 20-80 °C have been investigated systematically. The equilibrium pressure and hydrogen storage capacity decrease with the increment of Al content, especially at higher temperature. Thus the high stability of the counterpart hydride means the high-Al alloy is more suitable for working at higher temperature. With the increase of Al content, both the discharge capacity and high-rate dischargeability deteriorate at room temperature, but increase gradually at higher temperature (40-80 °C). Electrochemical kinetics and scanning electron microscope analyses were conducted to investigate the mechanism of Al effect on high-temperature properties. The results demonstrate that the dissolution of Al leads to the outcrop of high electro-catalytic Ni atoms on the alloy surface, thus charge-transfer resistance decreases and exchange current density increases, making the high-temperature dischargeability and high-rate dischargeability better for high-Al alloys at 60 °C. Furthermore, the existence of Al improves the stability of the oxide film, enhancing the anti-corrosion property of high-Al alloy at elevated temperature, and consequently results in excellent high-temperature recoverability.