ENERGY MATERIALS Defect-mediated ionic hopping and green electricity generation in Al 22x Mg x O 3 -based hydroelectric cell Rekha Gupta 1 , Jyoti Shah 1 , Rojaleena Das 2 , Sandeep Saini 3 , and R. K. Kotnala 1, * 1 CSIR-National Physical Laboratory, New Delhi 110012, India 2 Amity University, Gurugram, India 3 Indian Institute of Technology Roorkee, Roorkee, India Received: 17 June 2020 Accepted: 20 August 2020 Published online: 14 September 2020 Ó Springer Science+Business Media, LLC, part of Springer Nature 2020 ABSTRACT A direct evidence of enhanced water molecule splitting by increasing defect concentration in Al 2-x Mg x O 3 hydroelectric cells (HECs) has been elaborated for green electricity generation. Existence of F, F ? and [Mg] 0 defect centers in nanoporous Al 2-x Mg x O 3 (x = 0–0.5) cell pellets has been confirmed by optical spectroscopy. Increased defect density from * 1.45 9 10 15 cm -3 to 5.4 9 10 16 cm -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 2-x Mg x O 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 2-x Mg x O 3 -based hydroelectric cell is a very low-cost device to generate green electricity besides providing eco-friendly by-products without use of photo- catalytic activity, acid/alkali or electrolyte. Moreover, presented innovative alumina-based HEC would be a big step for mitigating industrial waste con- sisting of alumina. Handling Editor: Joshua Tong. Address correspondence to E-mail: rkkotnala@gmail.com https://doi.org/10.1007/s10853-020-05280-4 J Mater Sci (2021) 56:1600–1611 Energy materials