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Our collaborative work with Prof. Takashi Kato (Tokyo University) on confinement-derived highly aniosometric Co₃O₄ structures has been published in Crystal Growth & Design. Congrats to first author Viktoria Grün, who performed most of the experimental work during her research stay in Japan.

Nanostructured spinel-type cobalt(II,III) oxide (Co₃O₄) finds applications in a wide range of technological fields including clean energy conversion systems and electrochemicical devices. Low-dimensional morphologies have been identified as particularly promising for the optimization of transport characteristics and the design of anisometric building blocks for the controlled assembly into higher order superstructures. We here introduce a facile bio-inspired room-temperature approach to direct precipitation of one-dimensional basic cobalt carbonate as a precursor to Co₃O₄ by combining confined submicrometer reaction environments with a carboxylated structure-directing polyelectrolyte. Variation of the polymer concentration and molecular weight then affords control over the mode of infiltration into cylindrical track-etch membrane pores. While a high concentration of the polyelectrolyte additive induces the formation of high aspect ratio smooth fibers with a length resembling the entire pore volume, shorter porous rods with a needle-like substructure are deposited at low polymer concentrations or higher molecular weights. The generality of the infiltration mechanism is demonstrated by gradual substitution of Co²⁺ ions by Mn²⁺. Calcination pseudomorphically transforms the resulting intramembrane basic cobalt and manganese carbonate rods and fibers into hierarchical one-dimensional oxides with a porous nanoparticle-based mesostructure.

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