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Transition‐Metal Oxynitride: A Facile Strategy for Improving Electrochemical Capacitor Storage

The use of transition‐metal oxide (TMO) as an extended‐life electrochemical energy storage material remains challenging because TMO undergoes volume expansion during energy storage. In this work, a transition‐metal oxynitride layer (TMON, M: Fe, Co, Ni, and V) was synthesized on TMO nanowires to address the crucial issue of volume expansion. The unique oxynitride layer possesses numerous active sites, excellent conductivity, and outstanding stability. These characteristics enhance specific capacitance and alleviate volume expansion effectively. Specifically, the specific capacity of the TMON electrode is enhanced by approximately twofold relative to that of its corresponding oxide. Notably, the capacitance of the TMON remains above 94% even after 10 000 cycles. This result indicates that the cycling performance of the TMON electrode is superior to that of its corresponding oxide. First‐principles and quantitative kinetics analyses are performed to investigate the mechanism underlying the improved electrochemical performances of the TMON layers. Results demonstrate that the proposed TMON layer has attractive applications in the fields of energy storage, conversion, and beyond.