Significance of interface barrier at electrode of hematite hydroelectric cell for generating ecopower by water splitting

Abstract

Recent increase in energy demand and associated environmental degradation concern has triggered more research towards alternative green energy sources. Eco-friendly energy in facile way has been generated from abundantly available iron oxides using only few microliters of water without any external energy source. Hydroelectric cell (HEC) compatible to environment benign, low cost oxygen-deficient mesoporous hematite nanoparticles has been used for splitting water molecules spontaneously to generate green electricity. Hematite nanoparticles have been synthesized by coprecipitation method. Chemidissociated hydroxyl group presence on hematite surface has been confirmed by infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). Surface oxygen vacancies in nanostructured hematite have been identified by transmission electron microscopy (TEM), XPS, and photoluminescence (PL) measurement. Hematite-based HEC delivers 30 mA current with 0.92 V emf using approximately 500 μL water. Maximum off-load output power 27.6 mW delivered by 4.84 cm2 area hematite-based HEC is 3.52 times higher than reported 7.84 mW power generated by Li-magnesium ferrite HEC. Electrochemistry of HEC in different irreversible polarization loss regions has been estimated by applying empirical modeling on V-I polarization curve revealing the reaction and charge transport mechanism of cell. Tafel slope 22.7 mV has been calculated by modeling of activation polarization overvoltage region of 0.11 V. Low activation polarization indicated easy charge/ion diffusion and faster reaction kinetics of Ag/Zn electrode owing to lesser energy barrier at interface. Dissociated H3O+ ions diffuse through surface via proton hopping, while OH− ions migrate through interconnected defective crystallite boundaries resulting into high output cell current.