Acquisition parameters: The XPS measurements were performed using a Kratos Amicus/ESCA 3400 instrument. The sample was irradiated with 240 W unmonochromated Mg Kα x-rays, and photoelectrons emitted at 0° from the surface normal were energy analyzed using a DuPont type analyzer. The pass energy was set at 150 eV and either a Shirley or linear baseline was removed from all reported spectra. CasaXPS was used to process raw data files. Data file organization: Report.xlsx: Summarized quantitative analysis result. Notes.pptx: This file. Folder vms: Sample-name-survey.vms: Raw data, survey scan. No processing Sample-name-narrows.vms: Raw data, high resolution scans. No processing All-analyzed.vms: Processed data which contains all spectra from all samples. “vms” files can be opened using CasaXPS software package. The software can be downloaded from http://www.casaxps.com/casaxps2315.htm Folder PDF: PDF version of overlaid spectra. Spectra shown in PDF files are energy calibrated. Folder TXT: TXT version of the processed data. Each spectrum is a separate txt file (e.g. La 3d scan from sample LaFe.4Co.6O3-Red is named Fe4Co6-Red-La3d.txt) Data interpretation: All spectra were energy calibrated with measured adventitious hydrocarbon C 1s peak position at 284.5 eV. See C 1s peak fitting example from sample LaFe.4Co.6O3-Ox. Hydrocarbon C-C C=C C-H C-O C=O

Let’s first focus on the LaFe.4Co.6O3 samples. Co 2p region has two spin orbit peaks: Co 2p 1/2 and Co 2p 3/2. Additionally, there are satellite features at the left side of the main peaks. One can use satellite features of Co 2p spectra to distinguish Co oxidation states. Co (II) has observable satellite at ~786 eV whereas Co (III) state does not show distinct satellite feature. Comparing the Co 2p spectra from Fe4Co6-Red (black) and Fe4Co6-Ox (red), it’s obvious that the Co is reduced from Co(III) to Co(II). Co 2p 3/2 Co 2p 1/2 Co 2p 3/2 satellite Co 2p 1/2 satellite

The Fe 2p region also has two spin-orbit peaks: Fe 2p 1/2 and Fe 2p 3/2. The binding energy of Fe 2p 3/2 at ~710 eV is consistent with fully oxidized Fe. No significant oxidation state change between Fe4Co6-Red and Fe4O6-Ox. Fe 2p 1/2 Fe 2p 3/2

La 3d region has two spin-orbit peaks: La 3d 3/2 and La 3d 5/2 La 3d region has two spin-orbit peaks: La 3d 3/2 and La 3d 5/2. Each peak is further split by two multiplet splitting peaks. Therefore, we see four visible components, even though there is only one chemical state. The binding energy of La 3d 5/2 (the position of the rightmost component) is ~833.1 eV for LaFe.4Co.6O3-Ox and ~834.3 for LaFe.4Co.6O3-Red. These values are consistent with La3+ state. However, the fact that the binding energy is different by more than 1 eV suggest the La could be in different phases for these two samples. The magnitude of the multiplet spitting of La 3d 5/2 are chemically diagnostic. For example, La2O3 has a ΔE of 4.6 eV; La(OH)3 has ΔE of 3.9 eV and La2(CO3)3 has a ΔE of 3.5 eV. The measure ΔE for LaFe.4Co.6O3-Ox is 3.94 eV and for LaFe.4Co.6O3-Red is 3.3 eV. This is also suggesting that La could be in different phases in these two samples. XRD result may reveal more supportive data to do phase identification on these two samples. La 3d 3/2 La 3d 5/2 ΔE

The LaFe. 3Co. 7O3 samples are significantly different than the other The LaFe.3Co.7O3 samples are significantly different than the other .4.6 samples. XPS shows the samples lost most of the Co and Fe. (See below the Co 2p region and Fe 2p region). On the other hand, La concentration is higher than the .4.6 samples. (See the Excel spreadsheet for atomic concentrations)

The La 3d region of the. 3. 7 samples are similar to the. 4. 6 samples The La 3d region of the .3.7 samples are similar to the .4.6 samples. The binding energy of the La 3d 5/2 for the Ox sample is 835.3 eV and 835.2 eV for the Red sample. The ΔE for the Ox sample is 3.12 eV and 3.25 eV for the Red sample. La 3d 3/2 La 3d 5/2 ΔE

The. 3. 7 samples also have Sr identified by XPS The .3.7 samples also have Sr identified by XPS. Below shows the Sr 3d region. The measured binding energy is ~133.1 eV. This is consistent with Sr2+ state.