Enhanced CO2 adsorption and anti-sintering potential of Ni- and Mn-doped CaO(001) for calcium-looping thermochemical energy storage: A first-principles study

Abstract

Calcium-looping thermochemical energy storage based on the reversible CaCO3/CaO reaction is attractive for concentrating solar power and industrial waste heat recovery, but CaO suffers from sintering and deactivation during repeated high temperature cycling. In this work, density functional theory was used to compare pristine CaO(001) with substitutionally Ni- and Mn-doped CaO(001) surfaces. Local structural distortion, charge redistribution, projected density of states, CO2 adsorption, and Ca4O4 cluster anchoring were analyzed. Both dopants reduce the local ionicity of the surface and create more polarizable adsorption sites. CO2 adsorption is strengthened from −1.814 eV on pristine CaO to −2.107 eV on Ni-doped CaO and −1.952 eV on Mn-doped CaO, accompanied by enhanced charge transfer and molecular bending. Electronic structure analysis shows that the improvement arises from stronger interfacial orbital hybridization, particularly involving transition-metal 3d states. The Ca4O4 cluster model indicates stronger anchoring on doped surfaces, with Mn-doped CaO showing the largest adsorption energy. These results suggest that Ni doping is more favorable for CO2 adsorption, whereas Mn doping offers greater anti- sintering potential for CaO-based thermochemical energy storage materials.