(422a) Conversion of CO2 into Solar Fuels Via the Thermochemical Redox Reactions Involving Ni-Ferrite

The conversion of carbon dioxide (CO2) and water (H2O) into solar fuels, particularly syngas, plays a crucial role in establishing sustainable transportation fuels for the future. This process leverages a two-step thermochemical cycle that utilizes metal oxides (MOs). Within this framework, CO2 is transformed into carbon monoxide (CO) through a technique known as CO2 splitting (CDS). The resultant CO can subsequently be combined with hydrogen (H2), produced from the water splitting (WS) process, to generate syngas—an important precursor in fuel synthesis.

In this research endeavor, we conducted a thorough evaluation of the solar-to-fuel energy conversion efficiency of the nickel ferrite (Ni-ferrite) redox splitting cycle by performing a detailed thermodynamic analysis. A key objective of this study was to investigate the impact of varying the molar flow rate of an inert sweep gas, which was systematically altered between 10 to 100 mol/s, on several process parameters associated with the Ni-ferrite redox cycle.

The findings revealed that the molar flow rate of the inert sweep gas had a significant effect on the thermal reduction temperature. Notably, as the flow rate increased from 10 to 50 mol/s, a marked decrease in the thermal reduction temperature was observed. However, the effect became less pronounced as the flow rate progressed from 50 to 100 mol/s. Despite the slight upward trend in the energy required to reduce the Ni-ferrite as the flow rate increased, it was found that the energy penalty incurred was considerably lower when the reduced Ni-ferrite was subjected to heating from the re-oxidation temperature back to the thermal reduction temperature.

Furthermore, the implementation of gas-to-gas heat exchangers played a pivotal role in reducing the overall energy expenditure needed for heating the inert sweep gas. Thus, while increasing the molar flow rate of the inert sweep gas contributed to a decrease in the thermal reduction temperature, there was a counterbalancing effect on the total solar energy required to sustain the cycle. Ultimately, this research highlighted that the solar-to-fuel energy conversion efficiency peaked at a molar flow rate of 10 mol/s for the inert sweep gas, after which it diminished as the flow rate escalated to 100 mol/s.