New insights into the pulverization of LaNi5-based alloys with different Co contents from electrochemical acoustic emission measurements

• LaNi5-based electrodes were studied by electrochemical acoustic emission.
• The acoustic events related to the particle cracking were identified.
• The particle cracking occurs mostly during the first charge.
• The influence of the Co content on the alloy pulverization was quantified.

The pulverization (particle cracking) of LaNi5-based electrodes with different Co contents (ca.5, 8 and 10 wt%) is studied by means of electrochemical acoustic emission measurements. Through an appropriate analysis of the acoustic signals detected during electrode cycling, the acoustic events related to particle cracking can be identified and quantified. It is shown that the particle cracking occurs mostly during the first charge. For the 5 and 8 wt% Co alloys, the particle cracking is mainly detected in the early stage of the hydriding reaction, i.e.when the α-to-β phase transition is initiated. In contrast, for the 10 wt% Co alloy, the particle cracking is more progressive during the first charge with the presence of two successive increases of the acoustic activity, which is attributed to the formation of an intermediate γ-phase hydride. On the basis of the number of acoustic events detected during the first charge, the influence of the Co content on the alloy pulverization is quantified with mean values of 13700, 5600 and 1300 events for a Co content in the alloy of 5, 8 and 10 wt%, respectively.