High-energy resolution X-ray absorption and emission spectroscopy reveals insight into unique selectivity of La-based nanoparticles for CO

The lanthanum-based materials, due to their layered structure andf-electron configuration, are relevant for electrochemical application. Particularly, La₂O₂CO₃ shows a prominent chemoresistive response to CO₂. However, surprisingly less is known about its atomic and electronic structure and electrochemically significant sites and therefore, its structure–functions relationships have yet to be established. Here we determine the position of the different constituents within the unit cell of monoclinic La₂O₂CO₃ and use this information to interpret in situ high-energy resolution fluorescence-detected (HERFD) X-ray absorption near-edge structure (XANES) and valence-to-core X-ray emission spectroscopy (vtc XES). Compared with La(OH)₃ or previously known hexagonal La₂O₂CO₃ structures, La in the monoclinic unit cell has a much lower number of neighboring oxygen atoms, which is manifested in the whiteline broadening in XANES spectra. Such a superior sensitivity to subtle changes is given by HERFD method, which is essential for in situ studying of the interaction with CO₂. Here, we study La₂O₂CO₃-based sensors in realoperandoconditions at 250 °C in the presence of oxygen and water vapors. We identify that the distribution of unoccupied Lad-states and occupied Op- and Lad-states changes during CO₂ chemoresistive sensing of La₂O₂CO₃. The correlation between these spectroscopic findings with electrical resistance measurements leads to a more comprehensive understanding of the selective adsorption at La site and may enable the design of new materials for CO₂ electrochemical applications.