XPS. The powders were deposited on carbon tape and X-ray photoelectron spectroscopy (XPS) performed using an ESCA2SR spectrometer (ScientaOmicron GmbH) using monochromated Al Kα radiation (1486.6 eV, 20 mA emission at 300 W, 1 mm spot size) with a base vacuum pressure of ~1×10 -9 mbar. Charge neutralisation was achieved using a low energy electron flood source (FS40A, PreVac). Binding energy scale calibration was performed using C-C in the C1s photoelectron peak at 284.4 eV. Three points were measured for each powder. XPS survey scans were used to establish the relative atomic contribution, the areas under the following peaks: C1s, O1s, F1s and N1s at 285, 530, 690, 400 eV binding energy respectively, were calculated and corrected using relative sensitivity factors from the Scofield library in CasaXPS , and a standard deviation provided from the three repeats.