Water splitting on the mesoporous surface and oxygen vacancies of iron oxide generates electricity by hydroelectric cell

Abstract

The impact of water splitting by specially processed maghemite/iron oxide for generating ecologically sustainable, low-cost green electricity is a vital step. In the present work, a facile and a low-cost chemical synthesis technique has been adopted to produce versatile, oxygen deficient, mesoporous maghemite (iron oxide) nanostructure. The maghemite nanoparticles have been synthesized by the oxidation of magnetite nanoparticles, using a coprecipitation technique followed by heat treatment at elevated temperature 350 °C for 2 h. In the modified process, oxygen (VO) and iron vacancies (VFe) in maghemite have been systematically created. The VFe sites generated at octahedral sites due to Fe2+ ion oxidation has been estimated by Raman and X-ray photoelectron spectroscopy (XPS). Water splitting is prominently occurring at VO sites. Splitting of polar water molecules on the surface oxygen vacancies of nanoporous ferrite and metal oxide pellets has been translated into a primary hydroelectric cell by attaching two dissimilar electrodes to the pellets to generate an electric current. However, preferable associative water adsorption on VFe sites have been confirmed by unique XPS bands with multilayered physisorbed water adsorption modes. The role of VFe, VO sites in water molecule dissociation, and further dissociated ions diffusion kinetics through respective maghemite and magnetite pellets has been thoroughly explored by dielectric measurements. Maghemite based hydroelectric cell (HEC) has delivered a maximum current of 19 mA and emf 0.85 V by using only 200 μL water. The maximum electrical power 16.15 mW delivered by maghemite HEC is 0.58, 0.42 times lower than the respective magnetite, hematite HECs. The magnitude of dielectric relaxation is reduced in maghemite due to preferable associative water adsorption on VFes compared to other iron oxides. Hence, lesser VO concentration, larger average pore size along with the presence of hydrophobic VFe sites are responsible for the lower performance of maghemite based HEC. Variation in spinel magnetite, maghemite HEC performance has been analysed by simulating its V–I characteristic curve. The electricity generation by maghemite HEC is reduced due to lower VO concentration along with the presence of hydrophobic VFe sites reducing the overall number of dissociated ions. Hydroelectric cell from earth- abundant iron oxide is an eco-friendly, bio-compatible, and cost-effective green energy source by water splitting at room temperature.