Exploring Battery‐Type ZnO/ZnFe₂O₄ Spheres‐3D Graphene Electrodes for Supercapacitor Applications: Advantage of Yolk−Shell over Solid Structures

Abstract

Recently, a ZnO/ZnFe2O4 composite has been reported to be a promising material for energy storage, owing to its large specific capacity and good redox activity. However, due to the inability to accommodate its strong volumetric variations during operation, it fails to retain its capacitance, which remains as a significant hitch. Herein, we present our attempt towards solving this through a binder‐free electrode design comprising a porous yolk−shell ZnO/ZnFe2O4 composite matrixed inside a 3D network of graphene, which, in turn, is grown on Ni foam. The design exhibits a four‐fold increase in its specific capacitance, yielding 1334 F g−1 (specific capacity of 370.5 mAh g−1) at a current density of 0.5 A g−1 in comparison to that of the ZnO/ZnFe2O4 electrodes (309 F g−1 (85.8 mAh g−1) at 0.5 A g−1) comprising solid metal oxide spheres. The major advantage of the design is the well‐defined yolk−shell architecture that provides free space for volume expansion during long cycling processes and channels for ionic transportation; whereas, the conductive 3D graphene network and porous Ni foam facilitate electronic conduction. The availability of free space in yolk−shell sphere electrodes facilitates the capacitance retention of up to 80 % beyond 5000 cycles at a current density of 1 A g−1, which is in contrast to the capacitance retained by the solid spheres of only approximately 60 %. These results directly demonstrate the significant consequence of the yolk−shell architecture‐based binder‐free design and its promising potential in high‐performing supercapacitors and batteries.

Multi-functional O2–H2 electrochemistry by an abundant mineral: a novel and sustainable alternative for noble metals in electrolyzers and metal–air batteries

“…The reason for the more intense D band in both the samples is that GO has oxygen functional groups and in rGO, although oxygen functionalities are reduced, it forms defects during the reduction process. 38 Further, in the Raman spectrum of HAG, the symmetrical valence vibration line (PO 4 ) 3À is the most intense peak. The characteristic Raman peak of HA at 960 cm À1 along with the D and G bands of rGO further confirm the formation of the HAG composite (Fig.…”

Surface alteration driven bi-functional catalytic activity of alkali niobate-N doped graphene composite for exalted oxygen electrochemistry

“…Among all the NN-X samples, NN-800 showed the best bi-catalytic activity and was selected for further characterization as a composite with N-doped graphene. For this purpose, graphene oxide (GO) was synthesized by the modified Hummer's method [37,38]. To form the composite, GO (0.2 g) was dispersed in N, N-Dimethylformamide (50 mL) using ultrasonication for 2 h. After adding 0.1 g of NN-800 platelets and 50 mL of NH 3 ⋅H 2 O to the GO dispersion, the resulting solution was refluxed at 80 • C for 12 h. The final product was alternatively washed with ethanol and water, followed by drying in the vacuum oven at 60 • C. The electrocatalytic activity was also compared with N-doped graphene which was synthesized as the above mentioned method without the addition of NN platelets and denoted as N-G.…”

Rational Construction of V2O5@rGO with Enhanced Pseudocapacitive Storage for High‐Performance Flexible Energy Storage Device

“…Currently, lithium‐ion batteries (LIBs) and supercapacitors (SCs) represent the predominant electrochemical power sources and energy storage devices . Compared to the restrictions of LIBs including relatively low power, flammable organic electrolyte and long charging time, SCs stands as a forerunner and market leader with many advantages as an alternative source of energy storage mechanism . The main motivation and reason is the fact that the rapid reaction kinetics occurs on or near the surface of the electrode, and thus facilitates very high power density, and long cycling lifespan .…”