Electron energy loss spectra (EELS) were measured with a CEFID (Ceos GmbH, Heidelberg, Germany) spectrometer on a double aberration-corrected Themis-Z microscope (Thermo Fisher Scientific Electron Microscopy Solutions, Hillsboro, USA, (TFS)) at an accelerating voltage of 200 kV. The EELS data was recorded in STEM mode at a beam current of 60 pA, a semi-convergence angle of 21 mrad, and a semi-collection angle of 60 mrad, using an ELA direct detection camera (Dectris AG, Baden, Switzerland). Radiation damage to the tungsten oxide was minimized by repeated rapid frame scanning in a focus frame while accumulating the energy-loss spectra. The fine calibration of the spectrometer's energy scale was performed against standards (Si, a-Al2O3, NiO, BN, C) and respective XANES reference data reported in the NIMS data base.