Electroplating of Ni-PTFE composite film on AB(5) type hydrogen storage alloy powder

Ni-PTFE (PolyTetraFluoroEthylene) composite film was formed on hydrogen sto rage alloy (MH alloy) powder particles by means of electroplating method. M H alloy powder (mean diameter, 50 mum) with the composition of MmNi(3.65)Co (0.75)Al(0.25)Mn(0.35) (Mm denotes Misch metal) was used. The electroplatin g apparatus equipped with rotating bath was designed to electroplate the Ni -PTFE composite film on the MH alloy powder particles. The bath was rotated at high speed (350 rpm) to make electrical contact between the particles a nd the belt-ring cathode made of titanium placed on the inside wall of the bath. The electrolyte solution added MH alloy powder and PTFE powder was ag itated by intermittent rotation. PTFE powder particle (mean diameter, 5 mum ) was suspended in the electrolyte solution with a cationic surfactant. The electroplating efficiency on the MH alloy powder was calculated to be 6 0%. The Ni-PTFE composite film was uniformly deposited on the individual pa rticle, and was observed to be a little bit porous. The surface area after plating was 3.5 times larger than that of the original alloy powder. As the results of PCT (Pressure Composition Temperature) measurement, characteris tics of hydrogen gas absorption-desorption such as the equilibrium pressure , the absorption amount and the hysteresis were found to be maintained. The corrosion resistivity in a strong alkaline solution was extremely enhanced . Even after immersing in 6 mol dm(-3) KOH at 70 degreesC for 72 h, no form ation of Mm (OH)(3) on the surface of Ni-PTFE plated MH alloy was detected, and especially, the dissolving Mn decreased to less than one twentieth amo unt of original MH alloy.