Experimental and DFT study of undoped and A/B-site doped Nd_1-xA_xMn_1-yAl_yO₃ (A = Ca, Sr, Ba) perovskites for thermochemical CO₂ conversion

The development of efficient nonstoichiometric redox materials for solar-driven H₂O/CO₂ splitting via two-step thermochemical cycles requires optimization of redox thermodynamics, kinetics, and material stability. This study investigates neodymium manganite perovskites (Nd_1-xA_xMn_1-yAl_yO₃) as oxygen carriers doped in the A-site (Ca, Sr, Ba) and B-site (Al), and synthesized via a modified Pechini method to achieve a porous and reactive microstructure. Thermogravimetric analysis revealed a critical trade-off between the extent of reduction and reoxidation efficiency, with Nd_0.8Sr_0.2Mn_0.8Al_0.2O₃ emerging as a top-performing formulation. It demonstrated strong CO₂-splitting activity, near-complete reoxidation, and competitive performance compared to benchmark ceria. Kinetic studies showed that Nd_0.6Ca_0.4MnO₃ and Nd_0.8Sr_0.2Mn_0.8Al_0.2O₃ follow phase-boundary-controlled kinetics, while other compositions suffered from diffusion limitations. DFT calculations further validated these findings, showing that 40% Ca or Sr doping yields optimal oxygen vacancy formation energies for thermochemical application. Structural analysis further linked enhanced fuel production to non-ideal intrinsic strain, as revealed by Williamson-Hall plots and elastic mechanical calculations via DFT. These results suggest that defect-induced lattice distortions promote redox activity. This work provides critical insights into the design of high-performance perovskites through balanced dopant selection, redox kinetics, and strain engineering for enhanced solar fuel production.