Multifunctional Nickel Phosphate Nano/Microflakes 3D Electrode for Electrochemical Energy Storage, Nonenzymatic Glucose, and Sweat pH Sensors

Abstract

Multifunctional, low-cost electrodes and catalysts are desirable for next-generation electrochemical energy-storage and sensor applications. In this study, we demonstrate the fabrication of Ni₃(PO₄)₂·8H₂O nano/microflakes layer on nickel foam (NF) by a facile one-pot hydrothermal approach and investigate this electrode for multiple applications, including sweat-based glucose and pH sensor as well as hybrid energy-storage device, e.g., supercapattery. The electrode displays a specific capacity of 301.8 mAh g^-1 (1552 F g^-1) at an applied current of 5 mA cm^-2 and can retain 84% of its initial capacity after 10 000 cycles. Furthermore, the supercapattery composed of Ni₃(PO₄)₂·8H₂O/NF as positive electrode and activated carbon as negative electrode can offer a high specific energy of 33.4 Wh kg^-1 with the power of 165.5 W kg^-1. As an electrocatalyst for nonenzymatic glucose sensor, Ni₃(PO₄)₂·8H₂O/NF shows an exceptional sensitivity (24.39 mA mM^-1cm^-2) with a low detection limit of 97 nM (S/N = 3). Moreover, as a sweat-based pH sensor, the electrode is capable of detecting human sweat pH values ranging from 4 to 7. Therefore, this three-dimensional nanoporous Ni₃(PO₄)₂·8H₂O/NF electrode, due to its excellent electrochemical performance, can be successfully applied in electrochemical energy-storage and biosensor applications.