Identification of a new pseudo-binary hydroxide during calendar corrosion of (La, Mg)2Ni7-type hydrogen storage alloys for Nickel–Metal Hydride batteries

•The calendar corrosion of Ni–MH battery alloy system (La, Mg)2Ni7 is investigated.•Combination of μRaman and TEM allows full characterisation of corrosion products.•Influence of Mg substitution in the binary La2Ni7 on corrosion is demonstrated.•La corrodes as La(OH)3 needles with inner hollow nanochannels.•The formation of a pseudo-binary hydroxide Mg1−xNix(OH)2 is evidenced.

To improve the performances of Nickel–Metal Hydride batteries, an important step is the understanding of the corrosion processes that take place in the electrode material. In particular, the present study focuses for the first time on the model (La, Mg)2Ni7 system. The calendar corrosion in 8.7 M KOH medium was investigated from 6 h to 16 weeks immersion. By a unique combination of structural and elemental characterisations, the corrosion products are evidenced in those systems. In particular, we demonstrate that Ni and Mg combine in a pseudo-binary hydroxide Mg1−xNix(OH)2 whereas La corrodes into nanoporous La(OH)3 needles with inner hollow nanochannels.

Graphical abstractEDX-STEM mapping on La1.5Mg0.5Ni7 sample corroded 8 weeks: correlation of Mg and Ni distribution. Figure optionsDownload full-size imageDownload as PowerPoint slide