X-ray photoelectron spectroscopy study of the interaction of lithium with graphene

Graphene-like nanostructures, solely or in combination with redox active compounds, are an important component of battery electrodes. Design of effective electrode materials requires a deep understanding of electrochemical reactions occurring at graphene surfaces. The methods of X-ray photoelectron spectroscopy (XPS) are very helpful in such research, providing the composition of studied samples and electronic state of individual elements. In this chapter, we demonstrate advantages of XPS for monitoring of chemical vapor deposition graphene growth and lithium penetration under graphene layers, disclosing of interactions with metals and interface states.Peer reviewe

Notable reactivity of acetonitrile towards Li2O2/LiO2 probed by NAP XPS during Li–O2 battery discharge

One of the key factors responsible for the poor cycleability of Li–O2 batteries is a formation of byproducts from irreversible reactions between electrolyte and discharge product Li2O2 and/or intermediate LiO2. Among many solvents that are used as electrolyte component for Li–O2 batteries, acetonitrile (MeCN) is believed to be relatively stable towards oxidation. Using near ambient pressure X-ray photoemission spectroscopy (NAP XPS), we characterized the reactivity of MeCN in the Li–O2 battery. For this purpose, we designed the model electrochemical cell assembled with solid electrolyte. We discharged it first in O2 and then exposed to MeCN vapor. Further, the discharge was carried out in O2 + MeCN mixture. We have demonstrated that being in contact with Li–O2 discharge products, MeCN oxidizes. This yields species that are weakly bonded to the surface and can be easily desorbed. That’s why they cannot be detected by the conventional XPS. Our results suggest that the respective chemical process most probably does not give rise to electrode passivation but can decrease considerably the Coulombic efficiency of the battery.This work of A.K-G., J.J.V-V. and D.M.I. was supported by the Russian Ministry of Science and Education (RFMEFI61614×0007) and Bundesministerium für Bildung and Forschung (Project No. 05K2014) in the framework of the joint Russian-German research project “SYnchrotron and NEutron STudies for Energy Storage (SYNESTESia)”. T.K.Z acknowledges Center for Electrochemical Energy of Skolkovo Institute of Science and Technology for financial support. The work of O.O.K., A.I.B and L.V.Y. is performed within the joint project of the Russian Science Foundation (16-42-01093) and DFG (LA655-17/1). We are grateful to HZB for beamtime granted at ISISS and RGBL beamlines. T.K.Z. and A.S.F. thank to the Russian German laboratory at HZB for support provided. Authors are appreciated to Victor Vizgalov for solid electrolyte membrane preparation. Travelling of T.K.Z. was supported by German-Russian Interdisciplinary Science Center (G-RISC).Peer reviewe

Revealing the Active Phase of Copper during the Electroreduction of CO2 in Aqueous Electrolyte by Correlating In Situ X-ray Spectroscopy and In Situ Electron Microscopy.

The variation in the morphology and electronic structure of copper during the electroreduction of CO2 into valuable hydrocarbons and alcohols was revealed by combining in situ surface- and bulk-sensitive X-ray spectroscopies with electrochemical scanning electron microscopy. These experiments proved that the electrified interface surface and near-surface are dominated by reduced copper. The selectivity to the formation of the key C-C bond is enhanced at higher cathodic potentials as a consequence of increased copper metallicity. In addition, the reduction of the copper oxide electrode and oxygen loss in the lattice reconstructs the electrode to yield a rougher surface with more uncoordinated sites, which controls the dissociation barrier of water and CO2. Thus, according to these results, copper oxide species can only be stabilized kinetically under CO2 reduction reaction conditions