Surface processes of H_2 on rare earth based hydrogen storage alloys with various surface modifications

摘要

This paper reviews typical nad significant results of the studeis for the surface processes in H_2 absorption by rate earth based hydrogen storage alloys (RE-HSA). The kinematics of the hydrogen uptake by RE-HSA in the H_2 gas and electrochemical reactions can driastically be influenced by spontaneous and intentioanl modifications of the surface of RE-HSA. This paper deals with the following prototypical cases: The formation of the ocide layer on the surface of the alloys shifts the rate controlling step of the H_2 absorption from H_2 dissociation on the surface with thin oxide layers to the H permeation through the layer as the layer grows. Partial substitution of Ni with Al, Co or Mn for LaNi_(5-x)(Al, Mn, Co)_x results in the change in the surface H_2 processes, depending upon each substituent element. The penetration of alkaline atoms (Li, Na, K) into surface of the alloys markedly enhances eh initial activation in the H_2 gas and electrochemical reactions. The fluorination treatmetn of the alloy surfaces effectively protects in the H_2 gas and electrochemical reactions. The fluorination treatment of the alloy surfaces effectively protects the surface from the attack of contaminations in the H_2 gas.