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The crystal structure of anodically electrodeposited MnO₂ nanocrystals can be manipulated by introducing complexing agents in the electrodeposition solutions. MnO₂ nanocrystals with three types of crystal structures were observed: hexagonal ε-MnO₂ (complex-free), defective rock salt MnO₂ (ethylenediaminetetraacetic acid), and defective antifluorite MnO₂ (citrate). The capacitive performance of the MnO₂ nanocrystals depends strongly on their crystal structures. MnO₂ with defective rock salt and antifluorite structures exhibit better capacitive properties than ε-MnO₂. The electrochemical capacitance differences can be explained in terms of the crystal chemistry. In both the defective rock salt and antifluorite MnO₂, an anomalous trend was observed. The specific capacitance does not decrease with increasing scanning rate. A possible reason is that certain physicochemical changes, such as phase transformations …