A direct evidence of enhanced water molecule splitting by increasing defect concentration in Al.sub.2-xMg.sub.xO.sub.3 hydroelectric cells (HECs) has been elaborated for green electricity generation. Existence of F, F.sup.+ and Mg.sup.0 defect centers in nanoporous Al.sub.2-xMg.sub.xO.sub.3 (x = 0-0.5) cell pellets has been confirmed by optical spectroscopy. Increased defect density from ~ 1.45 x 10.sup.15 cm.sup.-3 to 5.4 x 10.sup.16 cm.sup.-3 induced by increasing Mg doping concentration is found to be a key factor to control water molecule dissociation/splitting at alumina surface. Small polaron hopping-assisted ionic conduction for enhanced current density is analyzed by impedance spectroscopy. The maximum, 15 mA, current is obtained in Al.sub.2-xMg.sub.xO.sub.3 HEC for x = 0.5 concentration resulting in 13.5 mW off-load peak output power as compared to 4.95 mW peak output power in pure alumina HEC. A theoretical modeling of Nyquist spectra analyzes ion-solid interaction for real charge transfer process in HEC. Deliberate defect creation in alumina devised for water molecule dissociation at room temperature paves the way to fabricate a facile green electricity generation source in the form of HEC. Al.sub.2-xMg.sub.xO.sub.3-based hydroelectric cell is a very low-cost device to generate green electricity besides providing eco-friendly by-products without use of photocatalytic activity, acid/alkali or electrolyte. Moreover, presented innovative alumina-based HEC would be a big step for mitigating industrial waste consisting of alumina. Graphic abstract Polaron assisted hopping of OH.sup.- ions in the lattice of Al.sub.2-xMg.sub.xO.sub.3 HEC and green electricity generation in the form of V-I plot.