High-energy resolution X-ray absorption and emission spectroscopy reveals insight into unique selectivity of La-based nanoparticles for CO2

CO 2 has become a challenge for our society and we have to develop new materials for its photo-/electrocatalysis, chemoresistive sensing, and storage. Particularly, for the variety of electrochemical applications the selective interaction of CO 2 and charge transfer with solids is in the foreground, but their origins are poorly understood. Our story will undoubtedly showcase how to access the key information, which is relevant for electrochemical application from in situ X-ray absorption spectroscopy/X-ray emission spectroscopy studies. The lanthanum-based materials, due to their layered structure and f -electron configuration, are relevant for electrochemical application. Particularly, La 2 O 2 CO 3 shows a prominent chemoresistive response to CO 2 . 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 La 2 O 2 CO 3 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 La 2 O 2 CO 3 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 CO 2 . Here, we study La 2 O 2 CO 3 -based sensors in real operando conditions at 250 °C in the presence of oxygen and water vapors. We identify that the distribution of unoccupied La d -states and occupied O p - and La d -states changes during CO 2 chemoresistive sensing of La 2 O 2 CO 3 . 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 CO 2 electrochemical applications.