Control of heterogeneity in nanostructured Ce_1-xZr _xO₂ Binary oxides for enhanced thermal stability and water splitting activity

To enhance the kinetics and overall production of renewable H₂ fuel through a two-step thermochemical water splitting cycle, three-dimensionally ordered macroporous (3DOM) Ce_1-xZr _xO₂ (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 Ce_1-xZr_xO₂ 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 Ce _1-xZr_xO₂ materials exhibited significantly faster kinetics during water splitting compared to sintered, micrometer-sized CeO₂ granules. Pechini-derived 3DOM Ce_0.8Zr _0.2O₂ maximized both H₂ production and peak production rates, offering better catalytic performance over 3DOM CeO ₂.