A DFT-based kinetic equation for Co3O4 decomposition reaction in high-temperature thermochemical energy storage

Thermal energy storage supports stable grid integration of variable renewable energy sources by reducing power curtailment and generation costs. Thermochemical energy storage (TCES) offers high energy density and long-duration, long-distance storage advantages, making it a focus in large-scale applications such as concentrated solar power plants. Metal oxide systems like Co3O4/CoO are widely used due to their operational flexibility, yet limited understanding of their decomposition kinetics hinders optimization of TCES materials and reactor design. In this study, we developed a rate equation based on density functional theory and transition state theory to identify the reaction mechanisms and rate constants at the gas-solid interface, prior to predict Co3O4 decomposition kinetics. A microkinetic model was then constructed to couple surface reactions with oxygen ion diffusion across the bulk, which was integrated into a reactor model accounting for mass transfer steps. The model's accuracy was validated against the data from the micro-fluidized bed thermogravimetric analyzer experiments. For particles smaller than 150 mu m, the formation step of adsorbed O-2 (energy barrier of 0.8 eV) controls the reaction rate, while gas diffusion dominates the reaction rate for particles larger than 500 mu m. To conclude, the optimal conditions for maximizing charge-discharge kinetics in TCES applications were identified as: 850-900 degrees C, 0-10 vol% O-2, and 150-500 mu m. This model provides theoretical guidance for optimizing TCES materials and reactor design, reducing experimental costs while maintaining accuracy.