Laboratoire de Chimie et Biologie des Métaux, Université Grenoble Alpes, CNRS UMR 5249, CEA, 17 rue des Martyrs, F Grenoble, Cedex, France

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1 Electronic upplementary Material (EI) for Chemical cience. This journal is The Royal ociety of Chemistry 2018 Electronic upporting Information for Insights into Mechanism and Aging of a noble-metal free 2 -evolving Dye-ensitized hotocathode icolas Kaeffer, 1 Christopher D. Windle, 1 Romain isse, 2 Corinne Gablin, 3 Didier Leonard, 3 uno Jousselme, 2 Murielle Chavarot-Kerlidou 1 and Vincent Artero* 1 1 Laboratoire de Chimie et Biologie des Métaux, Université Grenoble Alpes, CR UMR 5249, CEA, 17 rue des Martyrs, F Grenoble, Cedex, France 2 Laboratory of Innovation in urface Chemistry and anosciences (LICE), IMBE, CEA, CR, Université aris-aclay, CEA aclay, Gif-sur-Yvette, Cedex, France. 3 Univ Lyon, CR, Université Claude Bernard Lyon 1, E de Lyon, Institut des ciences Analytiques, UMR 5280, 5, rue de la Doua, F Villeurbanne, France. *to whom correspondence should be addressed. address: vincent.artero@cea.fr, These authors contributed equally

2 q s a b c d e f g h i j l k m n o p Co r t Co C11Et Figure 1. Atoms numbering in Co C11 Et a b c d e f g h i j k l n m p o Co r q s Co C11 Figure 2. Atoms numbering in Co C11 Figure 3. X analysis of a Dyenamo i electrode sintered at 450 C. The core levels of i and of represent main features displayed on the spectrum. The C 1s peak was used as a reference (at ev) for the energy calibration. The presence of carbon is either adventitious (from an external contaminant) and/or residual from the preparation of i.

3 Figure 4. X analysis of a iǀco C11 electrode in the survey mode. Figure 5. igh resolution X analyses of the a) iǀco C11, and iǀrbg-174ǀco C11 electrodes at the baseline-corrected Co 2p core levels.

4 Figure 6. igh resolution X analyses of the a) iǀco C11, iǀrbg-174 and c) iǀrbg-174ǀco C11 electrodes at the baseline-corrected 1s, 2p and 2p core levels. i-co C11 0 i II Co II C C Co II Co II 2C C Co II Figure 7. roposed fragments (with corresponding exact masses) for the attribution of the main peaks detected in the ToF-IM positive mode spectrum at a iǀco C11 electrode. The secondary ions are monocharged cations; their charges are not shown for the sake of clarity.

5 a) [i 4 ] m/z = 154 [i 5 2 ] m/z = 171 Figure 8. egative mode ToF-IM spectra in the m/z range for a) i blank and iǀrbg-174ǀco C11 electrodes. Figure 9. ToF-IM analysis at the surface of the iǀco C11 electrode recorded in the positive mode in the m/z range

6 i II Co II Co II C Co II Figure 10. roposed fragments (with corresponding exact masses) for the attribution of the main peaks detected in the ToF-IM positive spectrum of the iǀrbg-174ǀco C11 electrode. The secondary ions are monocharged cations; their charges are not shown for the sake of clarity. a) Figure 11. a) CVs recorded at a pristine i electrode (black line) and at a iǀco C11 electrode (blue line); successive scans in the cathodic region at a iǀco C11 electrode with a scan rate of 100 mv s 1 in a acl 0.1 M aqueous electrolyte. The broad wave at ~ 0.3 V vs E in the CV measured at a pristine i electrode is attributed to a surface-confined i III/II redox event likely coupled with the exchange of a proton. 1 This feature is also present at the decorated electrode but with a shape slightly modified possibly upon immobilization of the catalyst at the surface.

7 Figure 12. UV-visible spectra of a iǀco C11 electrode (blue lines) and of a pristine i electrode (gray lines) poised at 0.24 V vs E (dotted lines) then at 0.84 V vs E (plain lines) in a acl 0.1 M aqueous electrolyte Absorbance (a.u.) Wavelength (nm) Figure 13. UV-visible spectra of a solution of [Co(D)(D)pn 2 ] (1.05 mm in a 0.1M nbu 4 F 6 solution in MeC) recorded at a t grid electrode poised at 1 V vs Ag/AgCl after 30, 180, 300, 420, 600, 950, 1200, 1300, 1500, 1700, 1800 s (from red to purple) in a 2 / 2 - free glovebox, with a light path of 1.0 mm.

8 a) Figure 14. Current densities vs time at a) iǀrbg-174ǀco C11 and iǀrbg-174ǀc 10 electrodes poised at 0.14 (red line), 0.34 (blue line) and 0.54 (black line) V vs RE under chopped light irradiation in ME 0.1M / acl 0.1 M aqueous electrolyte at p 5.5. Figure 15. LVs at a iǀrbg-174ǀc 10 electrode with (red line), without (black line) or with chopped (blue line) light irradiation recorded at a scan rate of 10 mv s 1 in ME 0.1M / acl 0.1 M aqueous electrolyte at p 5.5.

9 Figure 16. Chronoamperometric measurements performed on three distinct iǀrbg- 174ǀCo C11 electrodes under light irradiation recorded at 0.14 V vs RE in ME 0.1M / acl 0.1 M aqueous electrolyte at p 5.5.

10 a) c) Figure 17. ositive mode ToF-IM spectra in the m/z ranges a) , and c) for the iǀrbg-174ǀco C11 electrode after two hours of light irradiation poised at E = 0.14 V vs RE in a ME 0.1 M/aCl 0.1 M aqueous buffer at p 5.5.

11 a) c) Cl Cl C C Figure 18. roposed fragments (with corresponding exact masses) for the attribution of peaks for Co C11 in a) the positive mode and the negative mode and c) for RBG-174 in the positive mode, in ToF-IM spectra at a iǀrbg-174ǀco C11 electrode after two hours of light irradiation poised at E = 0.14 V vs RE in a ME 0.1 M/aCl 0.1 M aqueous buffer at p 5.5.

12 a) Figure 19. egative mode ToF-IM spectra in the m/z range for the iǀrbg- 174ǀCo C11 electrode a) before and after two hours of light irradiation poised at E = 0.14 V vs RE in a ME 0.1 M/aCl 0.1 M aqueous buffer at p 5.5. a) Figure 20. ositive mode ToF-IM spectra in the m/z range for the iǀrbg- 174ǀCo C11 electrode a) before and after two hours of light irradiation poised at E = 0.14 V vs RE in a ME 0.1 M/aCl 0.1 M aqueous buffer at p 5.5.

13 a) Figure 21. egative mode ToF-IM spectra in the m/z range for the iǀrbg- 174ǀCo C11 electrode a) before and after two hours of light irradiation poised at E = 0.14 V vs RE in a ME 0.1 M/aCl 0.1 M aqueous buffer at p 5.5. a) Figure 22. ositive mode ToF-IM spectra in the m/z range for the iǀrbg- 174ǀCo C11 electrode a) before and after two hours of light irradiation poised at E = 0.14 V vs RE in a ME 0.1 M/aCl 0.1 M aqueous buffer at p 5.5.

14 a) Figure 23. ositive mode ToF-IM spectra in the m/z range for the iǀrbg- 174ǀCo C11 electrode a) before and after two hours of light irradiation poised at E = 0.14 V vs RE in a ME 0.1 M/aCl 0.1 M aqueous buffer at p 5.5. References 1. (a) Dini, D.; alpin, Y.; Vos, J. G.; Gibson, E. A., The influence of the preparation method of ix photocathodes on the efficiency of p-type dye-sensitized solar cells. Coord. Chem. Rev. 2015, , ; ( Boschloo, G.; agfeldt, A., pectroelectrochemistry of nanostructured i. J. hys. Chem. B 2001, 105 (15),