Methane assisted low temperature isothermal thermochemical water splitting over Pt/CeO2 nanorods

Abstract

Thermochemical water splitting (TCWS) is a promising route to produce hydrogen using heat, but conventional redox cycles typically require large temperature swings at 800–1400 °C, which limits materials stability and process efficiency. Herein we demonstrate isothermal, methane assisted TCWS at 300 °C using Pt/CeO2 nanorods as a redox active platform. Catalysts with 1 and 5 wt% Pt were characterised by XRD, HRTEM, H2-TPR, Raman spectroscopy, XPS and XAS to relate structure and reducibility to oxygen vacancy formation and redox performance. Under isothermal cycling, methane is used as a sacrificial chemical reductant to generate oxygen vacancies at Pt-ceria perimeter sites, while subsequent exposure to H2O produces H2 exclusively from water in the oxidation step. At 300 °C, 1 wt% Pt/CeO2 nanorods reach cumulative H2 yields of 20 mLg−1 over four redox cycles and 5 wt% Pt/CeO2 reaches 27.5 mLg−1, with limited loss of nanorod morphology. D2O labelling experiments at 300 °C confirm that D2 and HD form only in the oxidation window, whereas H2 formed in the CH4 reduction window originates from methane reforming. At 400 °C, the isotopic response shows additional D2 formation during the CH4 step and coincides with nanorod sintering and Pt agglomeration, indicating a change in the redox pathway. XPS and Raman analysis indicate that moderate Pt loading increases the accessible Ce3+ fraction and defect level in the CeO2 lattice while preserving a well-defined Pt-ceria perimeter. Although the absolute H2 productivity is modest and methane is consumed sacrificially, the results establish a low temperature, isothermal TCWS process that exploits Pt-ceria perimeter chemistry at 300 °C and provide a mechanistic basis for designing chemically assisted looping redox cycles hydrogen production.