Novel CoZnNi oxyphosphide-based electrode with high hydroxyl ion adsorption capacity for ultra-high volumetric energy density asymmetric supercapacitor

Achieving a high volumetric energy density supercapacitor is of great significance for portable energy storage devices while still a major challenge. Herein, we design and fabricate self-supporting electrodes using CoZnNi oxyphosphide nanoarrays sandwiched graphene/carbon nanotube (CZNP/GC) film with highly exposed active sites. Benefitting from the modified electronic structures, high accessible surface areas, and the integrated structure, the well-designed CZNP/GC electrode exhibits an ultra-high volumetric capacitance of 2096.4 F cm(-3) at a current density of 1 A g(-1). Moreover, a high-performance negative electrode of carbon/rGO/CNTs (C/GC) is also fabricated using the same CoZn-metal-organic frameworks precursor. The assembled asymmetric supercapacitor CZNP/GC//C/GC displays an ultra-high volumetric energy density of 71.8 W h L-1 at 960 W L-1. After 6000 charge-discharge cycles, the device still maintains 85.6% of the original capacitance. The density functional theory calculation is studied and the negative adsorption energy proves that the OH- adsoption process onto the surface of as-prepared electrode is thermodynamically favorable, facilitating the electrochemical reaction. This work provides a new option in constructing tailorable electrodes with a well-defined hierarchical structure for supercapacitor and beyond. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

Achieving a high volumetric energy density supercapacitor remains a major challenge. In this study, self-supporting electrodes using CoZnNi oxyphosphide nanoarrays sandwiched graphene/carbon nanotube film were designed and fabricated, leading to an ultra-high volumetric capacitance. Moreover, a high-performance negative electrode was also successfully prepared, and an assembled asymmetric supercapacitor exhibited an ultra-high volumetric energy density and good cyclic stability.