Utilization of MnFe2O4 Redox Ferrite for Solar Fuel Production via CO2 Splitting: A Thermodynamic Study

A thermodynamic efficiency analysis of MnFe2O4-based CO2 splitting (CDS) cycle is reported. HSC Chemistry software is used for performing the calculations allied with the model developed. By maintaining the reduction nonstoichiometry equal to 0.1, variations in the thermal energy required to drive the cycle and solar-to-fuel energy conversion efficiency as a function of the ratio of the molar flow rate of inert sweep gas to the molar flow rate of Mn-ferrite, reduction temperature, and gas-to-gas heat recovery effectiveness are studied. This study confirms that the thermal reduction temperature needed to achieve reduction nonstoichiometry equal to 0.1 is reduced when the inert gas flow rate is increased. Conversely, due to the requirement of the additional energy to heat the inert gas, the thermal energy required to drive the cycle is upsurged considerably. As the solar-to-fuel energy conversion efficiency depends significantly on the thermal energy required to drive the cycle, a reduction in it is recorded. As the ratio of the molar flow rate of inert sweep gas to the molar flow rate of Mn-ferrite is increased from 10 to 100, the solar-to-fuel energy conversion efficiency is decreased from 14.9% to 9.9%. By incorporating gas-to-gas heat recovery, a drastic drop in the thermal energy required to drive the cycle is attained which further resulted in a rise in the solar-to-fuel energy conversion efficiency. The maximum solar-to-fuel energy conversion efficiency (17.5%) is achieved at the ratio of the molar flow rate of inert sweep gas to the molar flow rate of Mn-ferrite equal to 10 as well as 20 when 90% of gas-to-gas heat recovery is applied.