Control of Heterogeneity in Nanostructured Ce_1–<i>x</i>Zr_<i>x</i>O₂ Binary Oxides for Enhanced Thermal Stability and Water Splitting Activity

Abstract

To enhance the kinetics and overall production of renewable H2 fuel through a two-step thermochemical water splitting cycle, three-dimensionally ordered macroporous (3DOM) Ce1–xZrxO2 (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) materials were synthesized via colloidal crystal templating. The interconnected macropore system in these materials facilitates ready access to a relatively large active surface area (tens of m2/g), which benefits the heterogeneous reaction. Two different synthetic routes were employed, a methanolic solution of metal chloride salts, and a Pechini-type gel. These routes produced significant differences in the compositional homogeneity of the resulting mixed oxide. 3DOM Ce1–xZrxO2 synthesized with methanolic precursors had distinct CeO2- and ZrO2-rich domains, whereas the Pechini samples contained only a single phase. At higher Zr content, heterogeneities present in the samples from the methanolic synthesis increased both the productivity and peak production rates of H2 compared to the single-phase Pechini samples. Increasing the content of Zr in the mixed oxides also stabilized the 3DOM structure at 825 °C. All 3DOM Ce1–xZrxO2 materials exhibited significantly faster kinetics during water splitting compared to sintered, micrometer-sized CeO2 granules. Pechini-derived 3DOM Ce0.8Zr0.2O2 maximized both H2 production and peak production rates, offering better catalytic performance over 3DOM CeO2.