H2 generation from thermochemical water-splitting using yttria stabilized NiFe2O4 core-shell nanoparticles

Abstract

This investigation reports synthesis of core-shell NiFe2O4/Y2O3 nanoparticles by sol-gel technique and their H2 volume generation ability via thermochemical water-splitting reaction at 900 °C–1100 °C. Thermochemical water-splitting process involves a cyclic operation of a low-temperature water-splitting step and relatively high temperature regeneration step using redox materials. Because of the cyclic nature of the process, the redox materials undergo thermal fatigue leading to grain growth or sintering, consequently, steady H2 production is not realized in multiple thermochemical cycles. In this study, attempts were made to achieve steady H2 volume generation in multiple thermochemical cycles using core-shell nanoparticles, which were synthesized using precursors such as NiCl2, FeCl2, and YCl3, and pluronic P123 surfactant template. H2 volume generated by NiFe2O4/Y2O3 core-shell nanoparticles was found to be relatively stable over multiple thermochemical cycles. Contrasting to this, the H2 volume generation was found to decrease continuously over multiple thermochemical cycles using NiFe2O4 nanoparticles as well as NiFe2O4/Y2O3 powdered mixture of nanoparticles. The transient O2 profiles were also compared for both the core-shell nanoparticles and powdered mixture during multiple regeneration steps. Detailed transmission electron microscopy (TEM) analysis clearly provided evidence of core-shell morphology with NiFe2O4 core encapsulated by Y2O3 shell. The grain size and morphological properties of as-prepared nanoparticles were compared with the nanoparticles obtained after thermochemical water-splitting reaction using powdered X-ray diffraction, and scanning electron microscopy.