Using XPS to compare the changes in electronic state of tungsten with electrochemical reduction, we identified some key differences between the films reduced in different electrolytes. The W 4f photoemission spectra for a pristine film and films reduced in electrolytes containing Na + or K + are shown in Figure with the fitting parameters reported in Table . The W 4f photoemission spectra for films reduced in TBA + and Li + are shown in Figures and.