Self-organization of alternating acetate- and carbonate-based interlayer spaces in bimetallic CoZn layered hydroxide salts

Layered hydroxide salts (LHS) are versatile functional materials whose properties can be tailored by the composition of metal hydroxide layers and interlayer anions. Here, a novel cobalt–zinc layered hydroxide salt (Co–Zn–LHS) containing distinct intercalated layers of acetate and carbonate anions was reported. A comprehensive combination of indirect experimental data, compiled using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Raman scattering, ultraviolet–visible (UV–Vis) spectroscopy, and thermal analysis, strongly indicated the formation of a single ordered phase with alternating mixed Co Zn hydroxide layers separated by acetate and carbonate interlayer spaces. The structure exhibited a basal periodicity of about 19.9 Å, close to the sum of typical carbonate- and acetate-LHS spacings, and showed up to twelve basal reflections with a coherent scattering domain size of approximately 500 Å, evidencing long-range ordering along the stacking direction. Anion-exchange experiments demonstrated the selective replacement of acetate FTIR bands, while carbonate bands remained essentially unchanged, which was consistent with the spatial separation of the two anionic interlayer spaces. The highest degree of ordering was achieved at near-equimolar Co/Zn ratios, where Zn preferentially stabilized tetrahedral sites and Co occupied octahedral positions. Thermal analysis revealed a sharp collapse of the layered structure at 240–300 °C, followed by transformation into a mixed Zn–Co–O oxide phase. Electrodes prepared from the optimized Co–Zn–LHS showed a specific capacity of 40 mAh g −1 (equivalent to a specific capacitance of 314 F g −1 ), with 61% capacity retention at 10 A g −1 . These results demonstrated a new route toward mixed-anion LHS materials with long-range ordered interlayer architectures.