Co-Precipitation Synthesized Ag-Doped Ceria Redox Material (ACRM) for the Thermochemical Conversion of CO\({}_{2}\) into Solar Fuels  
[PERSON]  
1 Department of Chemical Engineering, College of Engineering, Qatar University, Doha P.O. Box 2713, Qatar 1  
[PERSON]  
1 Department of Chemical Engineering, College of Engineering, Qatar University, Doha P.O. Box 2713, Qatar 1  
[PERSON]  
2 Department of Chemical Engineering, University of Tennessee, 615 Mecallie Ave, Chattanooga, TN 37403, USA 2  
ceria (CeO\({}_{2}\)) has emerged as a promising redox material thanks to its enduring stability, rapid reaction kinetics, high vacancy concentration at elevated temperatures, and ease of accessibility [18; 19]. The thermal reduction (TR) of ceria is achieved by releasing O\({}_{2}\) at high temperatures during the first step, followed by re-oxidation with H\({}_{2}\)O or CO\({}_{2}\) into H\({}_{2}\) and CO in the second step. The resulting syngas (a mixture of CO and H\({}_{2}\)) can be converted into storable and transportable liquid hydrocarbons via the Fischer-Tropsch (FT) process [20]. Ultimately, the two-step thermochemical cycle using ceria offers a renewable, environmentally friendly, and long-term solution to meet future energy demand while mitigating CO\({}_{2}\) emissions. In 2006, [PERSON] et al. [21] explored ceria for WS in H\({}_{2}\) via thermochemical cycles. They found that CeO\({}_{2}\) can be thermally reduced to Ce\({}_{2}\)O\({}_{3}\) at 2223 K under reduced pressure due to its favorable redox properties. [PERSON] et al. [19] conducted a thorough examination of the degree of the redox reaction by using ceria in conjunction with CO generation via CDS for over 2000 thermochemical cycles. The results of their investigation revealed a significant elongation in thermal stability with an average non-stoichiometry of 0.0197 and retention of reactivity of 86.4%. [PERSON] et al. [22] demonstrated that non-stoichiometric ceria and a solar cavity receiver reactor can be used for thermochemical WS splitting for up to 500 redox cycles, achieving a solar-to-fuel efficiency of 0.7 to 0.8%. A study used an isothermal pressure swing reactor bed with ceria and CO\({}_{2}\) as feedstock. The study demonstrated a total of 102 CDS cycles throughout 7.5 h, with an average CO production yield of 0.079 \(\upmu\)mol/g\(\cdot\)s [23]. [PERSON] and [PERSON] [24] analyzed the impact of dopants such as Y\({}_{2}\)O\({}_{3}\), Sm\({}_{2}\)O\({}_{3}\), Gd\({}_{2}\)O\({}_{3}\), CaO, and SrO on oxygen nonstoichiometry in ceria for splitting CO\({}_{2}\) and H\({}_{2}\)O at different temperatures and oxygen partial pressures. Their research reveals that higher dopant concentration increases oxygen vacancies in ceria at lower temperatures. [PERSON] et al. [25] have used a combustion synthesis method to produce ceria doped with transition metal ions such as Mn, Fe, Ni, and Cu. They studied the process of TR and re-oxidation for WS to generate H\({}_{2}\). Their research showed that the doping of transition metal cations resulted in higher production of H\({}_{2}\) compared with pure CeO\({}_{2}\). [PERSON] et al. [26] conducted a study on incorporating Hf\({}^{+4}\) and Zr\({}^{+4}\) dopants into CeO\({}_{2}\) for redox thermochemical cycling. The study findings revealed that a 5% dopant concentration of both cations (individually) resulted in high CO generation, with thermal stability lasting over 20 multiple cycles as determined by thermogravimetry setup. [PERSON] et al. [27] studied the effect of metal cation doping on CeO\({}_{2}\) for solar thermochemical WS cycles. Ce\({}_{0.9}\)Hf\({}_{0.1}\)O\({}_{2}\) produced the highest amount of H\({}_{2}\) at 500 \({}^{\circ}\)C and exhibited the least deactivation during the TR step at 1500 \({}^{\circ}\)C. It outperformed CeO\({}_{2}\)-MOx (M = Mn, Fe, Ni, and Pr). A recent study conducted by [PERSON] et al. [28] investigated the impact of eight transition metal cations (M = Fe, Co, Ni, Cu, Zn, Mn, Cr, Zr) as dopants into a CeO\({}_{2}\) for multiple cycles towards CO generation by CO\({}_{2}\).