Solar thermochemical hydrogen production based on chemical-looping oxygen removal: a hydrogen-centric multi-energy system with cascaded heat recovery

Solar thermochemical cycle for water decomposition offers a sustainable pathway for hydrogen generation, yet conventional systems face challenges such as high reduction temperatures, high deoxygenation energy consumption, and low energy efficiency. This study proposes an innovative hydrogen-centric multi-energy system integrating chemical-looping oxygen removal to address these limitations, which employs a cascaded heat recovery mechanism that converts residual thermal energy from the thermochemical cycle into electricity, cold energy and thermal energy through a combined cooling-heating-power (CCHP) unit. The system utilizes chemical-looping reactions to absorb oxygen byproducts and lower partial oxygen pressure in the reduction step, while introducing inert gases to enhance heat utilization during oxidation reactions, coupled with thermodynamic optimization strategies to dynamically balance energy allocation between hydrogen production and cogeneration processes. Thermodynamic analysis reveals that at a reduction temperature of 1500 °C and pressure ratio of 2.5, the system achieves solar utilization and exergy efficiencies of 23.7% and 22.6%, respectively. Elevating the temperature to 1600 °C further improves efficiencies to 26.4% and 25.6%, with a corresponding solar collector area requirement of 35.3 m² to meet annual per capita energy demands. This work provides a viable strategy to reduce oxygen partial pressure with low energy consumption and valorize waste heat in thermochemical cycles, thereby advancing scalable solar hydrogen production.