Synthesis and characterization of biogenic iron oxides of different nanomorphologies from pomegranate peels for efficient solar hydrogen production

An eco-friendly green synthesis of mesoporous iron oxide (hematite) using pomegranate peels through a low-cost and massive product method was investigated. The mass of pomegranate peels was varied to control the morphology of the produced hematite (Fe2O3). The structures, textures and optical properties of the products were investigated by FTIR, XRD, FE-SEM, and UV–Vis spectroscopy. Three different Fe2O3 morphologies were obtained; Fe2O3(I) nanorod like shape, Fe2O3(II) nanoparticles, and Fe2O3(III) nanoporous structured layer. The bandgap values for Fe2O3 (I), (II) and (III) were 2.71, 2.95, and 2.29 eV, respectively. The newly hematite samples were used as promising photoelectrodes supported on graphite substrate for the photoelectrochemical (PEC) water splitting toward the efficient production of solar hydrogen. The number of generated hydrogen moles was calculated per active area to be 50 μmol h−1 cm−2 for electrode III, which decreased to 15.3 μmol h−1 cm−2 for electrode II. The effects of temperature (30–70 °C) on the PEC behavior of the three electrodes were addressed. Different thermodynamic parameters were calculated for the three electrodes, which showed activation energies of 13.4, 16.8, and 15.2 kJ mol−1, respectively. The electrode stability was addressed as a function of the number of runs and exposure time in addition to electrochemical impedance study. Finally, the conversion efficiency of the incident photon-to-current (IPCE) was estimated under the monochromatic illumination. The optimum value was ∼11% @ 390 nm for Fe2O3(III) electrode.