SnO2‑Stabilized SrCO3/SrO Chemical Looping Material for High‑Temperature Thermochemical Energy Storage

Abstract

This work evaluates the potential of strontium carbonate (SrCO3) as a high-temperature thermochemical energy storage (TCES) material and explores the role of tin(IV) oxide (SnO2) as a stabilizing additive under a dynamic additive framework. Composites of SrCO3 with 10–20 wt % SnO2 were evaluated under repeated calcination/carbonation cycles in both atmospheric and pressure-swing conditions. While pure SrCO3 exhibits high initial conversion, it undergoes rapid deactivation, decreasing to 0.11 within nine cycles. In contrast, SrSnO15 (15 wt % SnO2) shows significantly improved multicycle performance, maintaining an effective conversion of 0.47 after 20 cycles and an energy density of 1.06 MJ·kg−1 under demanding conditions (carbonation temperature of 850 °C). X-ray diffraction and SEM analyses reveal that the system evolves through the formation of Sr–Sn oxide phases, including SrSnO3 and Sr2SnO4, which govern both structural stability and reactivity. These results demonstrate that the additive does not behave as an inert spacer but rather as a dynamically evolving component that modifies the reaction pathway through a coupled stabilization–reactivity mechanism. Pressure swing experiments show that lowering the CO2 pressure reduces the calcination temperature and enhances initial conversion; however, this advantage is progressively lost due to the delayed but eventual formation of stable phases. This indicates that pressure swing conditions modify but do not eliminate deactivation. Overall, the findings highlight that phase evolution is an intrinsic feature of Sr-based TCES systems and a key factor in controlling their performance. These insights provide a basis for designing advanced materials through controlled phase evolution, enabling more efficient and durable energy storage technologies.