posted on 2024-01-20, 00:29authored byRobin
N. Dürr, Pierfrancesco Maltoni, Shihui Feng, Sagar Ghorai, Petter Ström, Cheuk-Wai Tai, Rafael B. Araujo, Tomas Edvinsson
When electrocatalysts are prepared, modification of the
morphology
is a common strategy to enhance their electrocatalytic performance.
In this work, we have examined and characterized nanorods (3D) and
nanosheets (2D) of nickel molybdate hydrates, which previously have
been treated as the same material with just a variation in morphology.
We thoroughly investigated the materials and report that they contain
fundamentally different compounds with different crystal structures,
chemical compositions, and chemical stabilities. The 3D nanorod structure
exhibits the chemical formula NiMoO4·0.6H2O and crystallizes in a triclinic system, whereas the 2D nanosheet
structures can be rationalized with Ni3MoO5–0.5x(OH)x·(2.3 –
0.5x)H2O, with a mixed valence of both
Ni and Mo, which enables a layered crystal structure. The difference
in structure and composition is supported by X-ray photoelectron spectroscopy,
ion beam analysis, thermogravimetric analysis, X-ray diffraction,
electron diffraction, infrared spectroscopy, Raman spectroscopy, and
magnetic measurements. The previously proposed crystal structure for
the nickel molybdate hydrate nanorods from the literature needs to
be reconsidered and is here refined by ab initio molecular dynamics
on a quantum mechanical level using density functional theory calculations
to reproduce the experimental findings. Because the material is frequently
studied as an electrocatalyst or catalyst precursor and both structures
can appear in the same synthesis, a clear distinction between the
two compounds is necessary to assess the underlying structure-to-function
relationship and targeted electrocatalytic properties.