Surface-oxidation-mediated construction of Ppy@VNO/NG core-shell host targeting highly capacitive and durable negative electrode for supercapacitors

Vanadium nitride (VN)-based materials have been investigated as negative electrode materials for supercapacitors (SCs) owing to their high theoretical capacitances and suitable negative potential windows. However, viable VN-based negative electrode materials suffer from irreversible electrochemical oxidation of the soluble vanadium species, leading to rapid capacitance fading when operated in aqueous electrolytes. Developing a versatile approach to enhance the stability of VN in aqueous electrolytes is still a challenge. Here, an interface engineering strategy is developed to intentionally introduce surface nanolayers of vanadium oxides (VOX) as a reactive template on the VN surface to formulate well-designed polypyrrole@VNO (Ppy@VNO) core-shell nanowires (NWs) incorporated into a 3D porous N-doped graphene (NG) hybrid aerogel as a durable negative electrode for SCs. Experimental and theoretical investigations reveal that the in-situ constructed Ppy@VNO core-shell host can offer more efficient pathways for rapid electron/ion transport and accessible electroactive sites. Most importantly, a reversible surface redox reaction is realized through the transformation of the valence state of V, and a long cyclic stability is achieved. The Ppy@VNO/NG hybrid aerogel can deliver a high specific capacitance of 650 F g−1 at 1 A g−1 with approximately 70.7% capacitance retention (up to the twenty fold current density), and an excellent cycling stability without any capacitance de cay after 10,000 cycles at both low and high current densities (1 and 10 A g−1, respectively). This work paves the way for the development of advanced electrode materials for SCs.