Nickel-Doped Sodium Cobaltite 2D Nanomaterials: Synthesis
and Electrocatalytic Properties
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Abstract
In
this work we report a synthetic pathway to two-dimensional nanostructures
of high oxidation state lamellar cobalt oxides with thicknesses of
only few atom layers, through the combined use of precipitation in
basic water at room temperature and gentle solid state topotactic
transformation at 120 °C. The 2D nanomaterials are characterized
by X-ray diffraction, nitrogen porosimetry, scanning electron microscopy,
transmission electron microscopy and especially scanning transmission
electron microscopy coupled to energy dispersive X-ray analysis and
electron energy loss spectroscopy to assess the composition of the
nanosheets and the oxidation state of the transition metal species.
We show that the nanosheets preserve high oxidation states Co<sup>3+</sup> and Co<sup>4+</sup> of high interest for electrocatalysis
of the oxygen evolution reaction (OER). By combining high Co oxidation
state, surface-to-volume ratio and optimized nickel substitution,
the 2D nanomaterials produced in a simple way exhibit high OER electrocatalytic
activity and stability in alkaline aqueous electrolyte comparable
to standard materials obtained in harsh thermal conditions