One-pot green synthesis of hierarchically porous ZnCr2O4 spinel for enhanced charge storage.

The increasing worldwide energy crisis and the pressing necessity to have sustainable energy management systems have heightened studies in the development of advanced energy storage systems. The novelty of this work is the development of a one-pot green hydrothermal route to prepare hierarchically porous ZnCr2O4 using renewable phytochemical constituents to assist and control the formation of the material for sustainable energy-storage applications. The enhanced electrochemical performance originates from the synergistic effect of nanoscale crystallinity, porous morphology, and fast ion/electron transport kinetics. Structural analysis through XRD validates the creation of pure cubic spinel ZnCr2O4 with an average crystallite size of about 20 nm indicating a well-defined crystallinity. Raman spectroscopy also confirms the integrity of the structure by characteristic vibrational modes of the spinel lattice. The analysis of the SEM indicates that it has a hierarchically porous and agglomerated nanostructure, which is advantageous to the electrochemical activity, and the distribution of Zn, Cr, and O is homogenized without any impurities, as EDX and elemental mapping show. Electrochemical analysis shows that there is high pseudocapacitive behavior with mixed charge storage behavior through analysis of CV. GCD results show that the specific capacitance of GCD is high, 233.8 F g-1 at 0.8 A g-1, and that it has reasonable rate capability at elevated current densities. EIS data show that there is a low charge transfer resistance (R ct = 2.53 Ω) and increased ion diffusion coefficient (∼9.11 × 10-9 cm2 s-1) which demonstrates good electrochemical kinetics. The synergistic effect of nanoscale crystallinity, porous morphology, and green synthesis approach is credited to the improved performance. The present paper has identified the promise of ZnCr2O4 as an efficient and sustainable electrode material with great potential in future applications in next-generation energy storage systems and hybrid device architectures.