Development of Na-Containing Ce–Mn Composite Redox Materials for Integrated Thermochemical Energy Storage and Air Separation Process

Abstract This study proposes an integrated thermochemical energy storage and air separation process and investigates Na-containing Ce–Mn composite oxides as candidate redox materials. The materials were prepared by coprecipitation, and the effects of coprecipitation temperature and Ce mixing ratio on their redox characteristics were evaluated under temperature-swing conditions involving reduction at 550 °C and oxidation at 350 °C. The largest redox swing of 2.5 wt % was obtained at a coprecipitation temperature of 5 °C and a Ce mixing ratio of 7.5 mol %. XRD analysis confirmed the formation of Na0.7MnO2, whose presence was correlated with higher redox performance. The heat of reaction per unit oxygen exchange remained largely constant regardless of Ce loading, suggesting that Ce incorporation did not predominantly contribute as a direct oxygen storage mechanism under the investigated conditions and that Mn-based redox reactions constituted the dominant contribution to oxygen exchange. Repeated redox cycling showed a gradual decrease in redox swing, although reversible oxygen exchange was maintained throughout the investigated cycles.