Structural, optical and electrical behaviour of sodium-substituted magnesium nanoferrite for hydroelectric cell applications

The incredible hydroelectric cell (HEC) has made a significant and effective turnaround for the generation of green and eco-friendly electricity alternative in recent years. In this research, magnetic nanoparticles of Mg 1− x Na x Fe 2 O 4 ( x = 0.0–0.3) have been prepared by sol–gel technique to fabricate hydroelectric cells to generate green electricity. The thermal analysis of magnesium ferrite was studied by TG–DTA analyzer. The major weight loss was seen in the temperature between 300 and 500 °C. The crystallite size of the prepared materials decreased from 33 to 16 nm by increasing Na + content in magnesium ferrite, which was confirmed by XRD and TEM analyses. The porosity of ferrite increased and was found highest for x = 0.2, Na substitution. EDX analysis confirmed the presence of Fe, Mg, O and Na elements in the substituted nanoferrite. The photoluminescence emission wavelengths ranging from 455 to 581 nm, corresponding to the defect states and oxygen voids, confirmed that sodium increased the defects in magnesium ferrite. The systematic increase in energy band gap from 2.06 to 2.16 eV of Mg 1− x Na x Fe 2 O 4 was observed with the increase in sodium content x, which satisfies the Brus effective mass model. The impedance spectroscopy of the Na-substituted ferrite exhibits a significant drop in impedance values compared with the pristine ferrite. The defects and nanopores created by sodium-substituted magnesium ferrite enhanced the water dissociation and generated electricity by redox reaction at electrodes (Zn and Ag) in the fabricated hydroelectric cell. The V−I polarization plot of Mg 1− x Na x Fe 2 O 4 -based HEC demonstrated offload current ranging from 7 to 15 mA. HEC of x = 0.2 sodium-substituted magnesium ferrite exhibited the highest offload current (mA) of 15 mA, maximum power of 14.19 mW and current density of 2.4 mA/cm 2 due to low charge transfer resistance, highest porosity and high defects observed by PL.