A binder-free cobalt phosphate hydrate (Co(PO)·8HO) multilayer nano/microflake structure is synthesized on nickel foam (NF) via a facile hydrothermal process. Four different concentrations (2.5, 5, 10, and 20 mM) of Co and PO were used to obtain different mass loading of cobalt phosphate on the nickel foam. The Co(PO)·8HO modified NF electrode (2.5 mM) shows a maximum specific capacity of 868.3 C g (capacitance of 1578.7 F g) at a current density of 5 mA cm and remains as high as 566.3 C g (1029.5 F g) at 50 mA cm in 1 M NaOH. A supercapattery assembled using Co(PO)·8HO/NF as the positive electrode and activated carbon/NF as the negative electrode delivers a gravimetric capacitance of 111.2 F g (volumetric capacitance of 4.44 F cm). Furthermore, the device offers a high specific energy of 29.29 Wh kg (energy density of 1.17 mWh cm) and a specific power of 4687 W kg (power density of 187.5 mW cm).

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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 Ni(PO)·8HO 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 (1552 F g) at an applied current of 5 mA cm and can retain 84% of its initial capacity after 10 000 cycles. Furthermore, the supercapattery composed of Ni(PO)·8HO/NF as positive electrode and activated carbon as negative electrode can offer a high specific energy of 33.4 Wh kg with the power of 165.5 W kg. As an electrocatalyst for nonenzymatic glucose sensor, Ni(PO)·8HO/NF shows an exceptional sensitivity (24.39 mA mMcm) 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 Ni(PO)·8HO/NF electrode, due to its excellent electrochemical performance, can be successfully applied in electrochemical energy-storage and biosensor applications.

Simultaneous heterogeneous growth of one-dimensional nanorod supported three-dimensional microflower structures on nickel foam enhanced the non-capacitive faradaic energy storage performance due to the synergistic contribution from the hierarchical hybrid nanostructure.

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The supercapattery is an ideal energy storage device that combines excellent power density and rate capability of supercapacitors and the greater energy density of batteries. With superior storage capacity and long life, this device can be employed in next-generation artificial cardiac pacemakers as a rechargeable energy source for the lifetime of the pacemaker (at least 15−20 years). However, current hybrid energy storage devices are often limited by less than ideal performance of either the supercapacitor or battery. Here, we develop a low cost and scalable prototype supercapattery with cobalt phosphate as positive and activated carbon as negative electrodes. This positive electrode exhibits a maximum specific capacity of 215.6 mAh g −1 (≈1990 F g −1 ), ever reported in a metal phosphate based electrode. The supercapattery delivers a high energy density of 3.53 mWh cm −3 (43.2 Wh kg −1 ) and a power density of 425 mW cm −3 (5.8 kW kg −1 ). Furthermore, the device can retain 79% voltage even after 4 min self-discharge, enough to provide power during cardiac emergencies. This hybrid device provides excellent performance and stability under physiological temperature range (35−41 °C), retaining 68% of specific capacity after 100 000 cycles at room temperature (25 °C) and up to 81.5% after 20 000 cycles at 38 °C, demonstrating its effectiveness as a potential power source for the next-generation implanted medical devices.

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