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 H 2 fuel through a two-step thermochemical water splitting cycle, three-dimensionally ordered macroporous (3DOM) Ce 1– x Zr x O 2 ( 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 m 2 /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 Ce 1– x Zr x O 2 synthesized with methanolic precursors had distinct CeO 2 - and ZrO 2 -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 H 2 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 Ce 1– x Zr x O 2 materials exhibited significantly faster kinetics during water splitting compared to sintered, micrometer-sized CeO 2 granules. Pechini-derived 3DOM Ce 0.8 Zr 0.2 O 2 maximized both H 2 production and peak production rates, offering better catalytic performance over 3DOM CeO 2 .