(514h) Solar Fuel Production Via Germanium Oxide-Based Thermochemical Conversion of CO2

Solar fuels such as solar H₂ or syngas are considered to have the potential to fulfill the energy demand of the future. Thermochemical conversion of H₂O and/or CO₂ for producing solar fuels is one of the available possible technologies. Several metal oxides, which include zinc oxide, tin oxide, ceria, doped ceria materials, iron oxide, doped iron oxide materials (ferrites), and perovskites, have been investigated. One of the major issues with utilizing all these mentioned oxides is the requirement for a higher reduction temperature. We are currently working on a two-step germanium oxide redox cycle to overcome this issue. The germanium oxide-based redox cycle is thermodynamically investigated in this investigation to estimate the maximum possible theoretical solar-to-fuel energy conversion efficiency. After understanding the equilibrium compositions associated with the cycle, a detailed process flow configuration is developed. The process flow configuration includes reduction and oxidation reactors, heat exchangers, auxiliary heaters and coolers, an ideal fuel cell, gas separation units, recycle streams, etc. A thermodynamic model is developed, and its computations are carried out using the data obtained from the commercially available HSC Chemistry software. The computational thermodynamic modeling is carried out by varying the thermal reduction temperatures and inert gas flow rates, neglecting the solid-to-solid heat recovery and varying the gas-to-gas heat recovery effectiveness, and including separation units and surface losses from the reduction reactor. Overall, the influence of all the above variables on the solar energy input required to drive the cycle and solar-to-fuel energy conversion efficiency is studied in detail, and the obtained results will be presented.