(IP34-24) 12nd International Conference on LEEM/PEEM (2020 online version)

Ti oxidation state drives higher performance in Ti3C2Tx MXenes probed by XAS

Ameer Al-Temimy1,2, Babak Anasori3, Michael Naguib4, Katherine A. Mazzio1, Florian Kronast1, Mohamad-Assaad Mawass1, Kaitlyn Prenger3, Narendra Kurra3, Mykola Seredych3, Simone Raoux1,5, Yury Gogotsi4, Tristan Petit1

1 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany 2 Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany 3 Department of Physics and Engineering Physics, Tulane University, New Orleans, LA 70118, USA 4 Department of and Engineering, and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, PA 19104, USA 5 Institute of Physics, Humboldt University Berlin, Newtonstr. 15, 12489 Berlin, Germany

Email: [email protected]

Titanium carbide MXenes, a representative member of the large MXene family, is usually terminated by a mixture of –OH, –O–, and –F terminations, denoted by Tx. The oxygen surface terminations of MXene are redox active sites of highly hydrophilic nature, together with the confined water between MXene nanosheets, ensures a fast ion diffusion. The redox pseudocapacitance has been mostly studied so far with pristine MXene but the energy density of MXene-based electrodes, after intercalation, may be increased, owing to that MXene interlayer spacing becomes larger [1]. Intercalation of Ti3C2Tx MXene with molecules or cations is essential for electrochemical [2]. Using sulfuric acid as an electrolyte, MXenes demonstrates significant enhancement in the capacitance due to the pseudocapacitive charging mechanism. Nevertheless, the impact of intercalation on the MXene chemical and electronic structure is poorly investigated yet.

Herein, we used X-ray photoemission electron microscopy (X-PEEM) which enables acquiring XA spectra with approximately 30 nm spatial resolution. The XA spectra at the Ti L-edge allows us to characterize the Ti electronic structure, extremely impacts the electrochemical performance, of pristine, -, and cations-intercalated Ti3C2Tx MXenes [3,4]. Furthermore, the XA spectra at the O K-edge reveal the lateral oxygen concentration over individual MXene particles which helps us to visualize the oxygen-containing species accordingly. For example, urea intercalation is strongly impact the Ti oxidation state, leading to that the electrochemical performance is increased by 56% relative to pristine Ti3C2Tx MXene. Interestingly, the increase in the Ti oxidation state in Ti3C2Tx MXenes was found to play a significant role. This study demonstrates the importance of intercalation as alters the surface chemistry of MXene.

References [1] M. R. Lukatskaya, et al., Science 341, 1502 (2013). [2] B. Anasori, M. R. Lukatskaya, Y. Gogotsi, 2D metal carbides and nitrides (MXenes) for energy storage. Nat. Rev. Mater. 2, 16098 (2017). [3] A. Al-Temimy,et al. Enhancement of Ti3C2 MXene Pseudocapacitance after Urea Intercalation Studied by Soft X-ray Absorption Spectroscopy. J. Phys. Chem. C 124, 5079–5086 (2020) [4] A. Al-Temimy,et al. Spatially resolved X-ray absorption spectrospy investigation of individuial cation-intercalated Ti3C2Tx MXene particles. Applied Surface Science, Accepted, 147157 (2020). https://doi.org/10.1016/j.apsusc.2020.147157