Facile Hydrothermal Synthesis of Feather-like Nickel Phosphite As Cathode Materials for Supercapacitors

Recently, supercapacitors have attracted plenty of attentions, due to its high power density, long cycling lifespan and excellent stability. According to the charge storage mechanism, supercapacitors can be divided into double layer capacitors and pseudocapacitors. Moreover, the pseudocapacitors depend on faradic reaction and can result in much higher specific capacitance than double layer capacitors. For instance, nickel-based compounds exhibit outstanding performance reported in many literatures.

In this work, we successfully synthesize the feather-like nickel phosphite via a facile hydrothermal route at 200 ℃ for 24 h, employing Ni(NO₃)₂ as nickel source, sodium pyrophosphate as phosphorus source and the mixture of deionized water and glycol as solvent. The diffraction peaks of the product are well matched with the standard diffraction patterns of the orthorhombic Ni(HPO₃) (H₂O) (JCPDS NO. 01-082-0075) as shown in Figure 1a. The SEM image in Figure 1b reveals the morphology of the sample is feather-like structure.

Figure 2a exhibits cyclic voltammetry curves of the nickel phosphite in 6 M KOH electrolyte at different scan rate from 1 to 50 mV s^-1, which indicates the electrode is highly reversible with excellent electrochemical capability and redox processes. The galvanostatic charge-discharge curves measured at different current densities are shown in Figure 2b. The corresponding specific capacitance values of the nickel phosphite are calculated from the discharge curves as shown in Figure 2c. Figure 2d shows the Nyquist plots of the nickel phosphite. Therefore, the nickel phosphite were good candidates for high performance energy storage.