Cationic and anionic redox contributions to the charge storage mechanism of vanadium oxynitride

초록

The fundamental charge storage mechanism of vanadium oxynitride (VOxNy), a promising pseudocapacitive material, remains elusive in acidic media, impeding its rational design. Herein, we systematically unravel this mechanism in H2SO4 and HClO4 electrolytes using a combined electrochemical, in situ Raman, and X-ray photoelectron spectroscopy investigation. Our findings reveal a paradigm-shifting mechanism where, in addition to conventional multivalent vanadium redox (V4+/V3+/V2+) at negative potentials, reversible anionic redox of lattice nitrogen and oxygen (N3- /N2- and O2-/O-) dominates charge storage in the positive potential window. Crucially, this synergistic interplay between cationic and anionic redox is dictated by the electrolyte. The strongly coordinating sulfate anion enables both pathways, delivering a high specific capacitance and robust cycling stability. Conversely, the weakly coordinating perchlorate anion suppresses the cationic redox, leading to inferior performance. This definitive identification of active anionic redox and its dependence on electrolyte chemistry provides a powerful new strategy for engineering next-generation supercapacitors.

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