In this study, we prepared hexagonal and monoclinic phases of La
2O
2CO
3 nanoparticles by different wet preparation methods and investigated their phase-related CO
2 behavior through field-emission scanning microscopy, high-resolution transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, CO
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In this study, we prepared hexagonal and monoclinic phases of La
2O
2CO
3 nanoparticles by different wet preparation methods and investigated their phase-related CO
2 behavior through field-emission scanning microscopy, high-resolution transmission electron microscopy, Fourier transform infrared, thermogravimetric analysis, CO
2-temperature programmed desorption, and linear sweeping voltammetry of CO
2 electrochemical reduction. The monoclinic La
2O
2CO
3 phase was synthesized by a conventional precipitation method via La(OH)CO
3 when the precipitation time was longer than 12 h. In contrast, the hydrothermal method produced only the hexagonal La
2O
2CO
3 phase, irrespective of the hydrothermal reaction time. The La(OH)
3 phase was determined to be the initial phase in both preparation methods. During the precipitation, the La(OH)
3 phase was transformed into La(OH)CO
3 owing to the continuous supply of CO
2 from air whereas the hydrothermal method of a closed system crystallized only the La(OH)
3 phase. Based on the CO
2-temperature programmed desorption and thermogravimetric analysis, the hexagonal La
2O
2CO
3 nanoparticles (HL-12h) showed a higher surface CO
2 adsorption and thermal stability than those of the monoclinic La
2O
2CO
3 (PL-12h). The crystalline structures of both La
2O
2CO
3 phases predicted by the density functional theory calculation explained the difference in the CO
2 behavior on each phase. Consequently, HL-12h showed a higher current density and a more positive onset potential than PL-12h in CO
2 electrochemical reduction.
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