Studies on structural and optical behavior of nanoporous potassium-substituted magnesium ferrite nanomaterials, and their application as a hydroelectric cell

In recent years, alkali metal substituted spinel magnesium ferrites have been considered as potential materials for the fabrication of hydroelectric cells for the generation of green electricity without using any electrolyte. The purpose of potassium substitution was to observe the crystallite size variation, stretching molecular bonds, micro strain, porosity, defect centres, the surface morphology and HEC behavior of the prepared ferrites as monovalent potassium leads to occupying the octahedral site of Fe and Mg, which acts as reactive site for absorption and dissociation of the water molecule. The crystallite size and porosity of entire samples Mg_1−xK_xFe₂O₄ (x = 0.0–0.4) were found using Scherer’s equation between 11.15 and 36.20 nm and 22–53%, respectively, in XRD analysis, which decreased with the increase in alkali metal content. This decrease in lattice constant and unit cell volume may have been due to the compressive stress developed within the crystal structure, resulting in the negative strain as evident from W–H plot. Rietveld refinement was executed for pure and highest doped samples from the available XRD data to achieve the refined diffraction parameters. The FTIR analysis revealed the shift of molecular bands towards lower wavenumbers with the increase in K⁺ content. The SEM micrographs show agglomeration in the materials and porosity in the synthesized samples, and further, a decrease in grain size from 1.264 to 0.79 μm. The porous structure enhances the chemidissociation of water molecules followed by physisorption to generate the electric current. The PL spectra showed the emission wavelength between 275 and 400 nm, which indicates the presence of oxygen vacancies, leading to the chemidissociation of water molecules. Nanoparticles of the compositions have been investigated for hydroelectric cell application. The voltage–current characteristics performance of all the compositions fabricated as hydroelectric cells reveals the offload current and open circuit voltage between 1.4 and 7.8 mA and 0.74 and 0.86 V, respectively.