Understanding the mechanism of H2 promoted SrCO3 decomposition in SrCO3/SrO thermochemical energy storage

SrCO₃/SrO thermochemical energy storage is a promising technology. The sintering of strontium-based materials caused by the high temperature during SrCO₃ decomposition is the major challenge for this technology. Herein, a novel method that integrates CO₂ conversion and SrCO₃/SrO thermochemical energy storage by using H₂ to promote SrCO₃ decomposition was proposed. Experimental results show that at 900 °C, the maximum decomposition rate of SrCO₃ in the H₂ atmosphere is 10 times higher than that in the N₂ atmosphere. Within 600 s, the conversion of SrCO₃ in the H₂ atmosphere is 23 times higher than that in the N₂ atmosphere. Additionally, the selectivity of CO exceeds 93 %. Density functional theory calculations reveal that the optimal reaction pathway for H₂ promoted SrCO₃ decomposition is the one-step decomposition of HCO₃^–. Electronic density difference analysis shows that H atom adsorption on CO₃^2– weakens the C–O bonds, effectively decreasing the reaction energy barrier. During the H₂ dissociation process, active sites of the strontium-based material could not catalyze the reaction effectively because of the physical adsorption of H₂. This results in a high energy barrier of 4.65 eV for this elementary reaction, which thus becomes the rate-determining elementary reaction in the H₂ promoted SrCO₃ decomposition process. Compared with direct decomposition, H₂ promoted SrCO₃ decomposition reduces the rate-determining energy barrier by 16.1 %. Besides, SrO exhibits a self-catalytic effect on the H₂ promoted SrCO₃ decomposition reaction. This study provides a novel strategy for optimizing SrCO₃/SrO thermochemical energy storage systems and offers a theoretical basis for further development.