Structural and Electronic Features of β‑Ni(OH)2 and β‑NiOOH from First Principles

• Published in: Journal of physical chemistry. C Vol. 119; no. 43; pp. 24315 - 24322
• Main Authors: Tkalych, Alexander J, Yu, Kuang, Carter, Emily A
• Format: Journal Article
• Language: English
• Published: American Chemical Society 29.10.2015
• Subjects: batteries; catalysts; chemical bonding; crystal structure; geometry; oxygen production; protons; thermodynamics
• ISSN: 1932-7447; 1932-7455; 1932-7455
• DOI: 10.1021/acs.jpcc.5b08481

NiO x , long studied for its use in nickel-based secondary batteries, has been the subject of much recent interest due to its efficacy as an oxygen evolution catalyst. Despite extensive study over more than a century, however, many outstanding questions remain surrounding both the structure and the activity of NiO x . Further compounding this ambiguity is the recent finding that much of the previous experimental work on NiO x may have been influenced by incidental doping. Here, we report a computational study of the two simplest members of the NiO x family: β-Ni­(OH)2 and β-NiOOH. Using DFT+U calculations, we first identify a β-NiOOH structure with a staggered arrangement of intercalated protons that is more consistent with experimental crystal structures of β-NiOOH than previously proposed geometries. Next, by conducting a thorough study of various initial spin configurations of this β-NiOOH structure, we found that a low-spin d7 Ni3+ configuration is always favored, which suggests a Jahn–Teller distortion, rather than disproportionation, explains the different Ni–O bond distances found in experiment. G 0 W 0 calculations performed on β-Ni­(OH)2 and β-NiOOH reveal electronic structures consistent with previous experimental results. Lastly, calculations of various low-index surface energies of both β-Ni­(OH)2 and β-NiOOH demonstrate that the (001) surface is the most thermodynamically stable surface, in keeping with numerous experimental results but in contrast to recent computational models.