Strategically Tuned Ultrathin Nickel Phosphate Nanosheet Thin-Film Electrode as Cathode for High-Power Hybrid Supercapacitor Device

Abstract

Improved capacitive performance of the electrochemical energy storage devices can be achieved by manipulating the morphology of electroactive electrode material. Therefore, in the present work, the size and shape of microsheets of nickel phosphate electrode material are manipulated by varying hydrolyzing agent (urea) concentration in the chemical bath deposition method. Formation of hydrous nickel phosphate (Ni 3 (PO 4 ) 2 • 8H 2 O) in thin-film form over stainless steel substrate is confirmed by structural analysis, and change in microstructure from microsheets to nanosheets with hydrolyzing agent variation is observed in field emission scanning electron microscopy (FE-SEM) analysis. Strategically tuned ultrathin nanosheets of nickel phosphate deliver a high specific capacity of 471 C g −1 (specific capacitance, 1177 F g −1 ) at a 0.5 mA cm −2 current density. Moreover, a hybrid asymmetric supercapacitor device made up of nickel phosphate and reduced graphene oxide as cathode and anode, respectively, exhibits a specific capacitance of ∼108 F g −1 at a 4 A g −1 current density. Also, the hybrid supercapacitor device exhibits a maximum energy density of 38.2 Wh kg −1 at a high power density of 3.2 kW kg −1 with excellent cyclic stability (99%) over 5000 cycles. The excellent cyclic stability and actual practical demonstration [lightning 12 white light-emitting diode (LEDs)] suggest that a morphologically tuned nickel phosphate thin film is the best cathode for hybrid energy storage devices.

Urea-Assisted Nickel-Manganese Phosphate Composite Microarchitectures with Ultralong Lifecycle for Flexible Asymmetric Solid-State Supercapacitors: A Binder-Free Approach

“…Generally, varying the concentration of hydrolyzing agent alters the morphological architectures . Field emission scanning electron microscopy (FE-SEM) investigations were carried out to evaluate the effect of urea concentration on the morphologies of NMP series thin films obtained after hydrothermal process, as shown in Figure a–e.…”

“…Generally, varying the concentration of hydrolyzing agent alters the morphological architectures. 57 Field emission scanning electron microscopy (FE-SEM) investigations were carried out to evaluate the effect of urea concentration on the morphologies of NMP series thin films obtained after hydrothermal process, as shown in Figure 3a−e. The lowmagnification (300×) and high-magnification (2000×, 800×) FE-SEM images clearly demonstrate the Ni−Mn phosphate composite microstructures formed on the surface of NF substrates.…”

“…Similarly, our previous work on cobalt phosphate with varied urea concentrations by the hydrothermal process showed the alteration of microplates to microflakes. 14 Moreover, Marje et al 57 prepared nickel phosphate by a chemical bath deposition route and observed the alteration of microsheet to nanosheetlike structures using varied concentrations of urea. Also, Ibupoto et al 26 reported the architectural variation (nanoflowers to nanowires) of hydrothermally synthesized Co 3 O 4 with varying urea contents.…”

Ni3Se4 Nanostructure as a Battery‐type Positive Electrode for Hybrid Capacitors

“…At a scan rate 5 mV s −1 , the calculated specific capacities of NS‐15E(1), NS‐10E(1), NS‐20(1), and NS‐15E(0.75) are 417 C g −1 , 380 C g −1 , 314 C g −1 , and 323 C g −1 , respectively. The C s values of all the materials tend to decrease at higher scan rates as there is no sufficient time available for the electrolyte ions for the complete charge accumulation [48] …”

“…The C s values of all the materials tend to decrease at higher scan rates as there is no sufficient time available for the electrolyte ions for the complete charge accumulation. [48] Thereafter, to investigate the charge storage mechanism, a graph between log (peak currents) vs log (scan rates) was plotted according to the power law relation (Eq. 1 and Eq.…”