Investigation of H Sorption and Corrosion Properties of Sm₂Mn_xNi_7−x (0 ≤ x < 0.5) Intermetallic Compounds Forming Reversible Hydrides

• Main Authors: Nicolas Madern, Véronique Charbonnier, Judith Monnier, Junxian Zhang, Valérie Paul-Boncour, Michel Latroche
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: Energies
• Subjects: metallic hydrides; Ni-MH batteries; corrosion; rare earths; magnetic measurements
• Online Access: https://www.mdpi.com/1996-1073/13/13/3470

Intermetallic compounds are key materials for energy transition as they form reversible hydrides that can be used for solid state hydrogen storage or as anodes in batteries. AB_y compounds (<i>A </i>=<i> </i>Rare Earth (RE); <i>B </i>=<i> </i>transition metal; 2 < <i>y </i>< 5) are good candidates to fulfill the required properties for practical applications. They can be described as stacking of [AB₅] and [AB₂] sub-units along the c crystallographic axis. The latter sub-unit brings a larger capacity, while the former one provides a better cycling stability. However, AB_y binaries do not show good enough properties for applications. Upon hydrogenation, they exhibit multiplateau behavior and poor reversibility, attributed to H-induced amorphization. These drawbacks can be overcome by chemical substitutions on the A and/or the B sites leading to stabilized reversible hydrides. The present work focuses on the pseudo-binary Sm₂Mn_xNi_7−x system (0 ≤ x < 0.5). The structural, thermodynamic and corrosion properties are analyzed and interpreted by means of X-ray diffraction, chemical analysis, scanning electron microscopy, thermogravimetric analysis and magnetic measurements. Unexpected cell parameter variations are reported and interpreted regarding possible formation of structural defects and uneven Mn distribution within the Ni sublattice. Reversible capacity is improved for <i>x</i><i> </i><i>></i><i> </i>0.3 leading to larger and flatter isotherm curves, allowing for reversible capacity >1.4 wt %. Regarding corrosion, the binary compound corrodes in alkaline medium to form rare earth hydroxide and nanoporous nickel. As for the Mn-substituted compounds, a new corrosion product is formed in addition to those above mentioned, as manganese initiates a sacrificial anode mechanism taking place at the early corrosion stage.