Supporting Information. Neutral water splitting catalysis with a high FF triple junction. polymer cell

Transcription

1 Supporting Information Neutral water splitting catalysis with a high FF triple junction polymer cell Xavier Elias,,1 Quan Liu,,1 Carolina Gimbert-Suriñach, *,, 2 Roc Matheu, 2 Paola Mantilla- Perez, 1 Alberto Martinez-Otero, 1 Xavier Sala, 4 Jordi Martorell *,1,3 and Antoni Llobet *,2,4 1 ICFO-Institut de Ciències Fotòniques, The Barcelona Institute of Science and Technology, Castelldefels (Barcelona), Spain 2 Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, Avinguda Països Catalans 16, Tarragona, Spain 3 Departament de Física, Universitat Politècnica de Catalunya, Terrassa, Spain 4 Departament de Química, Universitat Auto noma de Barcelona (UAB), Cerdanyola del Valle s, Barcelona, Spain * Corresponding authors cgimbert@iciq.es, jordi.martorell@icfo.es, allobet@iciq.cat S1

2 Outline Materials and methods S3 GC-RuO 2 anodes SST-NiMoZn cathodes ITO-CoPi anodes Electrochemical methods Instrumentation Supporting electrolytes Electrochemical cell Three electrode configuration experiments Two electrode configuration experiments (water splitting with TJSC) S5 Figure S1. Chronopotentiometry experiments comparing ITO-CoPi and GC-RuO 2 anodes. S7 Figure S2. J-V curves of triple-junction solar cell and three series-connected solar cell. S7 Figure S3. Current vs time profile of a WS reaction with triple junction solar cell, GC-RuO 2 anode and SST-NiMoZn with and without UV light. S8 Figure S4. Long time water splitting experiments S8 S2

3 GC-RuO 2 anodes Carbon substrates and geometric surface: Glassy carbon rods (HTW ) of two different diameters (5 and 10 mm) were used as graphite support for the anodes. The geometrical surface of the anodes was estimated to be 4.1 cm 2 and 10 cm 2 respectively under our working conditions unless indicated differently. The former was used for 1.5h experiments in a 20 ml total volume electrochemical cell, and the latter was used for longer experiments (>1.5 h) in a 50 ml total volume electrochemical cell. Procedure for pre-catalyst immobilization: GC-RuO 2 were prepared according to the literature. 1 A glassy carbon rod was immersed in a 0.5 mm solution of the ruthenium molecular precursor Ru-MP in acetone containing tetrabutylammoniumhexafluorophosphate (0.1 M) as supporting electrolyte. The glassy carbon rod was used as working electrode, a Pt wire as a counter electrode and SSCE as reference electrode in a three electrode configuration cell with a single compartment. The GC-Ru-PC modified electrode was used as a working electrode in a three electrode configuration in a two compartment cell at ph 7. A current of 280 μa was applied to convert the grafted ruthenium pre-catalyst (GC-Ru-PC) to RuO 2 based electrode (GC-RuO 2 ) (30 minutes for the rod d=5 mm and 45 minutes for the rod d=10 mm). The GC-RuO 2 electrode was then washed with water and air-dried. Catalyst loading, superficial concentration (Γ ) and TON The amount of ruthenium catalyst was estimated by integrating the charge under the Ru(III)/Ru(II) redox wave of GC-Ru-PC in a cyclic voltammogram at ph=7 (Q Ru ). 1 Q Ru was used to calculate the superficial concentration and TON by applying the formulas Γ ( mol cm 2) = S3

4 QRu A F and TON = Q O2 4 Q Ru. Where A is the geometrical area, F is the Faradaic constant and Q O2 is the charge of the produced oxygen assuming a 100% Faradaic efficiency. The catalyst (ruthenium) superficial concentration of our GC-RuO 2 electrodes was 0.15 nmol Ru/cm 2. SST-NiMoZn cathodes NiMoZn was electrodeposited adapting the same method reported by Nocera. 2 Stainless steel substrates were covered with tape to expose 1cm 2 and then pre-treated at -2V vs Ag/AgCl in 0.5M H 2 SO 4 for 3 min. The NiMoZn was then deposited from a solution containing NiCl 2 6H 2 O (0.04M), Na 2 MoO 4 (0.17M), Na 4 P 2 O 7 10 H 2 O (0.077M), NaHCO 3 (0.89M) and ZnCl 2 (3x10-4 M), with hydrazine (0.018M) being added immediately before plating. The current density was 50 ma cm -2 for 1 h. Afterwards the deposit was immersed in 10% KOH for 1 night, washed thoroughly with water and dried under air. ITO-CoPi anodes CoPi was deposited on ITO, covering the substrate with Teflon tape to expose 1cm 2. A two compartment electrochemical cell with a glass frit junction was used. The working compartment contained a 0.5 mm solution of Co(NO 3 ) 2 6H 2 O and 0.1M potassium phosphate (KPi) at ph 7, whereas the auxiliary side contained only KPi. The reference electrode was Ag/AgCl and Pt mesh was used as auxiliary electrode.the catalyst (cobalt) loading of the resulting electrodes was 0.30 μmol/cm 2. S4

5 Electrochemical methods Instrumentation All electrochemical experiments were performed using a PAR 263A EG&G potentiostat, IJ- Cambria HI-660D or IJ-Cambria HI-600D potentiostat. Supporting Electrolytes Phosphate buffered solution (47 mm) was used as electrolyte for all electrochemical experiments at ph 7. Only phosphate anions (H 2 PO4 - /HPO 2-4 ) and K + contributed to the ionic strength (I = 0.1 M). Electrochemical cell A two-compartments cell of 10 ml per compartment with a separation frit was used for both two electrode and three electrodeconfiguration electrochemical experiments unless otherwise indicated. The electrodes were placed inside and connected to the potentiostat. The solution was purged with N 2 for minutes prior to the performance of any experiment. A bigger cell (25 ml per compartment) with the same set up was used for experiments that were longer than 1.5h to collect larger amounts of hydrogen and oxygen gas. Three electrode configuration experiments All experiments were done in a two compartment cell, the reference and the working electrode were placed in the same and first compartment and the counter electrode was placed in the second compartment. The scan rate in Cyclic Voltammetries (CV) was 100 mv/s and ir compensation was applied. Chronopotentiometry was used to simulate a water splitting experiment with a solar cell, using analogous currents ( ma for the anode and ma for the cathode). The counter electrode (CE) was a Pt mesh and the Reference Electrode S5

6 (RE) was Ag/AgCl (KCl sat.). All the potentials are given against the Ag/AgCl (KCl sat.) unless indicated differently. Two electrode configuration experiments (water splitting experiments using a triple junction OPV cell) All experiments were done in a stirred two compartment electrochemical cell using 6mL of 0.1M potassium phosphate buffer (KPi) at ph7 in each compartment. The solution was purged with N 2 for minutes prior to the performance of any experiment. The amount of charge (Q) passing through the cell during the course of the experiments was measured by performing bulk electrolysis with a potentiostat at 0V bias, connecting the working lead to the ITO side of the solar cell and the reference and auxiliary leads directly to the electrode working as a cathode. In this configuration, the potentiostat works as an ammeter. Although the resistance between the two electrodes was measured before and after the gas production (R ), no ir compensation was applied. The amount of hydrogen and oxygen generated by the reactions was measured in the headspaces of each compartment of the electrochemical cell with Clark electrodes (Unisense), waiting at the end of the illuminating period until the signal was no longer increasing. In several cases hydrogen gas was also measured by Gas Chromatography coupled to thermal conductivity detectors, with results being consistent with those obtained with the Clark electrode. S6

7 Figure S1. Chronopotentiometry experiments using a two-compartment electrochemical cell, 0.1M phosphate buffer, ph = 7, Ag/AgCl reference electrode, Pt mesh as counter electrode and GC-RuO 2 (d=5mm, red) or ITO-CoPi (black) as working electrode. The anodic current was set at 0.28 ma in both experiments. The potential is given versus the Ag/AgCl electrode. Figure S2. J-V curves of triple-junction solar cell and three series-connected solar cell. S7

8 Figure S3. Current vs time profile of water splitting experiments using triple junction solar cell, GC-RuO 2 anode and NiMoZn cathode in a two compartment cell containing 0.1M phosphate buffer, ph = 7, under AM 1.5G illumination with a GG400 filter (black trace, TJSC = 8.5%), and without CG400 filter (blue trace, TJSC = 8.7%). Figure S4. Stability tests of a water splitting experiment using a triple junction solar cell ( TJSC = 8.5 %), GC-RuO 2 anode and SST-NiMoZn cathode in a two compartment cell containing 0.1M phosphate buffer, ph = 7, under AM 1.5G illumination with a GG400 filter. The current fluctuations are most likely due to the connection of the circuit with the top thin silver contact layer that slowly damages over time. S8

9 1. Matheu, R.; Francàs, L.; Chernev, P.; Ertem, M. Z.; Batista, V.; Haumann, M.; Sala, X.; Llobet, A. ACS Catalysis. 2015, 5, Reece, S. Y.; Hamel, J. A.; Sung, K.; Jarvi, T. D.; Esswein, A. J.; Pijpers, J. J. H.; Nocera, D. G. Science 2011, 334, 645. S9