Highly Pseudocapacitive NiO Nanoflakes through Surfactant-Free Facile Microwave-Assisted Route

Abstract

A facile and rapid surfactant-free microwave-assisted route is developed to synthesize 10 nm sized NiO nanoflakes with high pseudocapacitive performance for supercapacitor cells. The NiO nanoflakes exhibit mesoporous channels and a surface area as high as 206 m 2 g −1 as revealed under BET study, while the structural identity verified by XRD and IR confirm the phase purity of NiO. NiO nanoflakes maintain ∼85% of their thermal stability at temperature 900 °C which can be related to strong intermolecular forces between the NiO nanoparticles held in the molecular matrix. Electrochemical performance investigated in 6 M KOH solution suggests maximum specific capacitance of 307 F g −1 for the NiO∥NiO cell at 0.5 A g −1 sustaining about 96% capacitance after being successfully cycled up to 3000 cycles. The NiO nanoflakes reveal high conductivity of 33.87 S cm −1 at room temperature. Precisely, nanosized NiO bearing "flake" morphology is of particular interest due to the high surface to volume aspect and porosity featuresthe determining factors for swift ion diffusion into an electrode and improved redox reaction. The illustrated microwave-assisted route unfolds as a direct synthesis method to obtain nanosized NiO flakes with high surface area facilitating excellent device performance characteristics without involving any surface-capping agents.

Fabrication of a Mo‐Doped Strontium Cobaltite Perovskite Hybrid Supercapacitor Cell with High Energy Density and Excellent Cycling Life

“…The pore diameter and pore volume of SCM are found to be 4.67 nm and 0.041 cm 3 g À1 ,r espectively,w hich is likely to provide good electrode/electrolyte contact, high electrolyte accessibility,and excellent chargetransfer. [35] Av ery high value of diffusion coefficient (2.1 10 À9 cm 2 s À1 )i si ndicative of the effective accessibility of OH À ions into the SCM electrode. SCM voltammograms exhibit very high capacitance in KOH (690.4 Fg À1 )c ompared with KNO 3 (67.35 Fg À1 )a t5mV s À1 indicating that OH À ions are highly favorable for intercalationtype energy storage.T he cyclic voltammograms at different scan rates (Figure 4a)d isplay two redoxp eaks, confirming the pseudocapacitive behavior of SCM.T he charging and discharging characteristics shown in Figure 4b are noticeably deviated from isosceles triangular form andt hus exhibit pseudocapacitance.…”

“…The diffusion coefficient of OH À ions was also estimated through the Randle'sp lot ( Figure S10) by using previously reported procedures. [35] Av ery high value of diffusion coefficient (2.1 10 À9 cm 2 s À1 )i si ndicative of the effective accessibility of OH À ions into the SCM electrode. As shown in Figure 4c,t he specific capacitance (and specific capacity) calculated fromg alvanostaticc harge-discharge( GCD) curveso f SCM are 1223.34 Fg À1 (168.88 mAh g À1 )a t1Ag À1 ,9 09.09 Fg À1 (122.7 mAh g À1 )a t5Ag À1 ,a nd 665.12 Fg À1 (87.5 mAh g À1 )a t 10 Ag À1 .E vidently,S CM shows very good capacitance retention (> 50 %) at high current density.T he SCM electrode also www.chemsuschem.org exhibitede xcellent cycling stability and columbic efficiency (93.52 %c apacitance retention after 5000 charge-discharge cycles at 10 Ag À1 ;F igure 4d).…”

“…SCM voltammograms exhibit very high capacitance in KOH (690.4 Fg À1 )c ompared with KNO 3 (67. 35 Fg À1 )a t5mV s À1 indicating that OH À ions are highly favorable for intercalationtype energy storage.T he cyclic voltammograms at different scan rates (Figure 4a)d isplay two redoxp eaks, confirming the pseudocapacitive behavior of SCM.T he charging and discharging characteristics shown in Figure 4b are noticeably deviated from isosceles triangular form andt hus exhibit pseudocapacitance. The phase transformation of SCM does not occur during O 2À intercalation/deintercalation processes unlike in Li-ion batteries ( Figure S7), this supports that SCM is an excellent supercapacitive material.…”

Electrode Materials for Supercapacitors: A Review of Recent Advances

“…The NiO material can exhibit pseudocapacitive behavior. For instance, the NiO nanoflakes synthesized through the microwave-assisted method displayed a high pseudocapacitive performance as electrode material for supercapacitor, as well as a high conductivity of 33.87 Scm −1 at room temperature, and surface area as high as 206 m 2 g −1 [238]. In another study, a Co-Ni/Co 3 O 4 -NiO nano-heterostructures demonstrated a remarkable pseudocapacitance [44].…”

Effect of Electrolyte Concentration on Electrochemical Performance of Bush Like α‐Fe2O3 Nanostructures

“…Among them, transition metal oxide based materials have been employed as electrode materials because they exhibit excellent pseudocapacitive behavior owing to their redox behavior arising from their surface functional groups, grain boundaries and crystal defects. Recently, various transition metal oxides such as V 2 O 5 , [34] MnO 2 , [35] NiO, [36] Co 3 O 4 , [37] Fe 2 O 3 , [38][39] Fe 3 O 4 , [40] and TiO 2 [41] and their composites have been studied for supercapacitor applications. Among them, Iron oxide is a promising candidate owing to its multiple oxidation states, high theoretical specific capacitance (3625 F g À 1 ), suitable potential window, abundance in nature, low cost and non-toxicity.…”