Nanostructured (Co, Ni)-Based Compounds Coated on a Highly Conductive Three Dimensional Hollow Carbon Nanorod Array (HCNA) Scaffold for High Performance Pseudocapacitors

The electrochemical performance of the pseudocapacitive materials is seriously limited by poor electron and ions transport. Herein, an advanced integrated electrode has been designed by growing the pseudocapacitive materials, including Co_xNi_1–x(OH)₂, Co_xNi_1–xO, and (Co_xNi_1–x)₉S₈, on a three-dimensional hollow carbon nanorod arrays (HCNA) scaffold. The HCNA scaffold not only can provide large surface area for increasing the mass loading of the pseudocapacitive materials, but also is with good electrical conductivity and hollow structure for facilitating fast electron and electrolyte ions transport, and thus improve the electrochemical performance. Particularly, in comparison with Co_xNi_1–x(OH)₂ and Co_xNi_1–xO nanosheets, (Co_xNi_1–x)₉S₈ nanosheets on the HCNA scaffold exhibit better electrochemical performance. The discharge areal capacitance of the (Co_xNi_1–x)₉S₈/HCNA electrode can be achieved to 1.32 F cm^–2 at 1 mA cm^–2, ∼1.5 times as that of the Co_xNi_1–x(OH)₂/HCNA electrode. The rate capability performance is also improved. 71.8% of the capacitance is retained with increasing the discharge current density from 1 to 10 mA cm^–2, in contrast to ∼59.9% for the Co_xNi_1–x(OH)₂/HCNA electrode. Remarkably, the cycling stability is significantly enhanced. ∼111.2% of the initial capacitance is gained instead of decaying after the 3000 cycles at 8 mA cm^–2, while there is ∼11.5% loss for the Co_xNi_1–x(OH)₂/HCNA electrode tested under the same condition. Such good electrochemical performance can be ascribed by that (Co_xNi_1–x)₉S₈ exhibits the similar energy storage mechanism as Co_xNi_1–x(OH)₂ and Co_xNi_1–xO, and more importantly, is with better electrical conductivity.