Enhancement of the capacitance of rich-mixed-valence Co-Ni bimetal phosphide by oxygen doping for advanced hybrid supercapacitors

Tailoring of the electrode microstructure and its active components for the development of high-performance supercapacitors was rather indispensable to advance current technologies. Therefore, we fabricated a novel O-doped Co-Ni nanophosphide (O-CoxNiyP) with a porous structure. Our approach included the synthesis of 3D Co-Ni precursors with tunable Co/Ni ratio utilizing a phosphorization treatment. Our characterization results indicated that incorporating the optimized O content into CoxNiyP could tune its electronic structure and yield mixed valences of metals and P, which was beneficial to enhance electrochemical reactivity. The O-Co1Ni4P-based electrode with the 1:4 Co:Ni molar ratio manifested the best performance as demonstrated by its specific capacity, which was equivalent to 717.1 C/g (at 1 A/g). This value was significantly higher than those of other O-CoxNiyP family electrodes. The cycling stability of the electrode containing O-Co1Ni4P as an active material was found to be excellent: it demonstrated a 95.1% capacity retention after 5000 10 A/g cycles. We also assembled an asymmetric supercapacitor containing O-Co1Ni4P as a positive electrode material and commercial activated carbon as a negative electrode material. The device demonstrated very high energy density (47.5 Wh/kg) and 90.3% capacity retention after 10,000 cycles. These results established that our anion-doping method represented a novel strategy for improving the electrochemical performance of transition metal-based material. These discoveries were useful for energy storage applications. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study focused on optimizing the microstructure and active components of electrodes for high-performance supercapacitors. The novel O-doped Co-Ni nanophosphide with a porous structure demonstrated improved electrochemical reactivity and specific capacity. The O-Co1Ni4P electrode showed excellent performance and cycling stability, leading to a high energy density supercapacitor with good capacity retention after numerous cycles. This anion-doping approach represents a novel strategy for enhancing the electrochemical performance of transition metal-based materials.