Supporting Information for. Electrochemical Water Oxidation Using a Copper Complex

Transcription

1 Electronic Supplementary Material (ESI) for Dalton Transactions. This journal is The Royal Society of Chemistry 28 Supporting Information for Electrochemical Water Oxidation Using a Copper Complex Sebastian Nestke, a Emanuel Ronge, b Inke Siewert a * a Universität Göttingen, Institut für Anorganische Chemie, Tammannstr. 4, 3777 Göttingen, Germany b Universität Göttingen, Institut für Materialphysik, Friedrich-Hund-Platz, 3777 Göttingen, Germany inke.siewert@chemie.uni-goettingen.de Table of content Instrumentation... 2 Molecular Copper Oxygen Evolution Catalysts... 2 Electrochemical Measurements... 3 GC-TCD Traces... Vis Spectroscopy... Surface Analysis... References... 4

2 Instrumentation A combined glass electrode (Metrohm ) filled with 3 M KCl in water was used for ph determination (daily calibration). For the electrochemical investigations a Gamry Instruments Reference 6 or Reference 6+. All electrochemical measurements were performed with ir compensation using the positive feedback method which is implemented in the PH2 software of Gamry. The UV/vis spectra were recorded with an Agilent Cary 5 UV-VIS-NIR spectrometer or Analytic Jena SPECORD 5 PLUS spectrometer. GC experiments of the headspace were carried out with a Shimadzu GC-24 equipped with a TCD detector and a molecular sieve column (5 Å, 8/, 2 m length, 2 mm ID). Methane was used as internal standard and injected into the headspace before each CPE. To calculate no2, a calibration curve by measuring known quantities of no2/nch4 mixtures was done. The SEM and EDX analysis was carried out with a Nova NanoSem 65 in-situ SEM from FEI. A through the lens (TL) and an Everhart-Thornley (ET) detector was used to take images at an acceleration voltage of kv. For the energy-dispersive X-ray spectroscopy (EDX) an Oxford Instrument X-max detector was deployed. The EDX measurements were carried out at an acceleration voltage of 2 kv and a live time of 9 s for every measuring point. Molecular Copper Oxygen Evolution Catalysts Figure S. Overview of selected mononuclear copper oxygen evolution catalysts, ref. see main text. 2

3 Electrochemical Measurements 2 ph 8. 2 ph ph ,2,4,6,8,,2,4,6,8-2,2,4,6,8,,2,4,6,8-2,2,4,6,8,,2,4,6,8 2 ph ph. 2 ph ,2,4,6,8,,2,4,6,8-2,2,4,6,8,,2,4,6,8-2,2,4,6,8,,2,4,6,8 2 ph. 2 ph.5 2 ph ,2,4,6,8,,2,4,6,8-2,2,4,6,8,,2,4,6,8-2,2,4,6,8,,2,4,6,8 Figure S 2. ph dependent CV data of in Millipore water ([] mm, I=. M PO4 3, without Chelex, ν =. Vs - ). 3

4 5 Fc/Fc + % H 2 O % H 2 O I /µa ,5,,5,,5 E vs. Fc/Fc + /V Figure S 3. CV data of in acetonitrile with % (red) and % (black) water ([] mm, I =. M n Bu4NPF6, ph = 8, ν =. Vs ) Phosphate,,5,,5 2, Carbonate Borate -25 -,5 -, -,5,,5,,5 2, 2 5 Acetate 5 5,,5,,5 2,,,5,,5 2, Figure S 4. CV data of in Millipore water employing a BDD electrode and various buffer salts ([] mm, I =. M buffer, ph = 2). Borate, carbonate and acetate buffer solutions were adjusted to ph 2 with NaOH and used without Chelex. 4

5 Q /C Q /C,,8,6,4, t /s, t /s Figure S 5. Bulk electrolysis experiments in Millipore water with and a 7 mm GC rod in a two-compartment cell. The GC rod was polished and conditioned by 3 CV cycles between.6 V and. V in electrolyte solution prior CPE. Left: E appl =.494 V, right: E appl =.944 V; ([] mm, I =. M PO4 3, ph = 2) ,2,4,6,8,,2,4,6,8 Figure S 6. CV data of using the GC plates ([] mm, I=. M PO4 3, ν =. Vs -, ph = 2) after conditioning and before CPE. The red curve represents the CV of in electrolyte solution and the black curve pure electrolyte solution ,2,4,6,8,,2,4,6,8 Figure S 7. CV data of 3 M CuSO4 in. M Na2CO3 using the GC plates (I=. M, ν =. Vs, ph.8) after conditioning and before CPE, (without Chelex ). 5

6 Q /C CuSO t /s Figure S 8. Charge vs. time plot during CPE using GC plates. Blue: 3 mm CuSO4 in. M Na2CO3 solution, E appl =.3 V; red:, E appl =.494 V ([] mm, I=. M PO4 3, ph 2); black: pure electrolyte solution, E appl =.494 V (I=. M PO4 3, ph = 2). i /ma after CPE of solution after CPE of electrolyte solution,5,,5 Figure S 9. CV data of the reused electrode in new electrolyte solution after 3 min CPE at E appl =.494 V ([] mm, I =. M PO4 3, ν =. Vs, ph = 2). The GC-electrode was rinsed off but not polished between the experiments. 8 (3 C) ( C) reused electrode (2 C) 6 Q /C t /s Figure S. Plot of the electric charge vs. time during CPE with the reused electrode in new electrolyte solution (red), polished and conditioned electrode in electrolyte solution (black), polished and conditioned electrode in solution (blue). 6

7 st Cycle th Cycle 2th Cycle,2,4,6,8,,2,4, st Cycle th Cycle 2th Cycle,2,4,6,8,,2,4,6 Figure S. Left: 2 successive scans of ([] mm) in Millipore water; right: 2 successive scans of free solution. (I =. M PO4 3, =. Vs -, ph = 2) mvs - -,5,,5,,5 2, Figure S 2. Scan rate dependent CV data of in Millipore water ([] mm, I =. M PO4 3, ph = 2), background subtracted. i 2 p /na data points linear fit y = 2.279E-9 x i c /i p /Vs - -/2 /V -/2 s /2 5, 4,5 4, 3,5 3, 2,5 2,,5, data points linear fit y =.5 x +.24 Figure S 3. Left: Plot of the square of the peak current for the Cu(II) reduction in dependence of the scan rate. Right: Plot of the ratio of the catalytic current (E =.494 V) over the current of the Cu(II) reduction vs. the square root of the scan rate. i p =.4463 n p F A ( n p F υ D R T D = R T m F 3 A 2 c ) =.24 5 cm2 s (S) (S2) 7

8 ,2,4,6,8,,2,4,6, Zn-,2,4,6,8,,2,4,6,8 Figure S 4. CV data of (left)) and the equivalent zinc (right) in Millipore water ([] mm, I =. M PO4 3, =. Vs -, ph = 2).,6,5,4,3,2,,,9,8,7 y = -.53x +.42 y = -.25x +.74 st inflection point, data point 2nd inflection point, data point linear fit ph Figure S 5. Plot of the potential of the inflection points of the CV data at different ph, black: st inflection point, red: 2 nd inflection point. 6 4 H 2 O, ph 2 D 2 O, pd 2 2,2,4,6,8,,2,4,6,8 Figure S 6. CV data of in Millipore water ([] mm, I =. M PO4 3, =. Vs -, ). Red: H2O (ph = 2), black: D2O (pd = 2). K2HPO4 was used for the D2O solution and the pd was adjusted with NaOD. The ph* was measured with a glass electrode and converted to pd by adding.45. [] 8

9 ,5,,5,,5 2, ,5,,5,,5 2, Figure S 7. CV data of and eq. (left) and eq. (right) of H2O2 ([] mm, I =. M PO4 3, ph = 2) Phosphate,,5,,5 2, Carbonate Borate -, -,5,,5,,5 2, Acetate ,,5,,5 2,,,5,,5 2, Figure S 8. CV data of in Millipore water with various buffer salts ([] mm, I =. M buffer, ph = 2). Borate, carbonate and acetate buffer solutions were adjusted to ph 2 with NaOH and used without Chelex. 9

10 GC-TCD Traces 8 N 2 6 Complex solution Electrolyte solution U /µv 4 2 O 2 CH t /s Figure S 9. GC-TCD traces of the headspace after 3 min CPE (E appl =.494 V, I =. M PO4 3, ph = 2). Red: trace after CPE of electrolyte solution; black: trace after CPE of solution ([] mm). Vis Spectroscopy Absorbance,5,,5 + eq. H 2 O 2 + eq. H 2 O 2, /nm Figure S 2. Vis spectra of the solution in the presence of various amounts of H2O2 ([] mm, I =. M, ph 2). Absorbance,5,,5 after after /nm Figure S 2. Vis spectra of the solution before CPE (black), after CPE at.494 V (green), and after CPE at.944 V (red), ([] mm, I =. M PO4 3, ph = 2).

11 , [] [] after CPE [] + H 2 O 2 Absorbance, /nm Figure S 22. Vis spectra of the solution before CPE (red), after CPE at.494 V (black), and with ex. H2O2 (blue), ([] mm, I =. m PO4 3, ph = 2).

12 Surface Analysis Figure S 23. SEM pictures of the GC electrode after CPE employing mm solution of at ph = 2, applied potential of.49 V. Intensity (counts) C 3 Cu Spectrum O 2 Cu P Si Ca Cu Energy (kev) Intensity (counts) C O Spectrum Energy (kev) Figure S 24. EDX spectra of the GC electrode after CPE employing mm solution of at ph = 2, applied potential of.49 V; left picture: EDX spectrum, position see Figure S 22; Right: EDX spectrum 2, position see Figure S 22. 2

13 Figure S 25. SEM pictures of the GC electrode after CPE without the at ph = 2, applied potential of.49 V. Intensity (counts) C O Energy (kev) Figure S 26. EXD spectra of the GC electrode after CPE without the at ph = 2, applied potential of.49 V. 3

14 CPE with Cu(II)SO4 was used as reference system for copper deposition, which was reported by Meyer and co-worker. [2] A 3 mm Cu(II)SO4 solution (in. M Na2CO3) was electrolysed 3 minutes at.3 V (Figure S 8). Figure S 27. SEM pictures of the GC electrode after CPE employing 3 mm solution of CuSO4 at ph.8, applied potential of.3 V. 6 C Cu Intensity (counts) 4 2 O Cu Cu Energy (kev) Figure S 28. EDX spectra of the GC electrode after CPE employing 3 mm solution of CuSO4 at ph.8, applied potential of.3 V. Figure S 29. SEM pictures of a bare GC electrode. References [] A. Krężel, W. Bal, J. Inorg. Biochem. 24, 98, [2] Z. Chen, T. J. Meyer, Angew. Chem. Int. Ed. 23, 52, 7 73; Angew. Chem. 23, 25,