1. Methodology Electrodeposited Pt and Pt/Ni electrodes for dye sensitized solar cells with improved stability G. Syrrokostas, G. Leftheriotis* and P. Yianoulis Renewable Energy and Environment Laboratory, Dept. of Physics, University of Patras, 26500, Greece email: glefther@physics.upatras.gr, gesirrokos@upatras.gr References [1] Syrrokostas G., Siokou A., Leftheriotis G. and Yianoulis P. Sol. Energy Mater. Sol. Cells 103, 119 (2012) [2] Syrrokostas G., Leftheriotis G. and Yianoulis P. Renewable Energy 72, 164 (2014) [3] Tsekouras G., Mozer A.J. and Wallace G. Journal of the Electrochemical Society, 155 (7) K124-K128 (2008) Introduction One of the main components of a dye sensitized solar cell (DSSC) is the platinized counter electrode [1,2]. The role of the counter electrode is to catalyze the reduction of triiodide ions: Triiodide ions are produced when the dye oxidized by electron donation to the conduction band of TiO 2 is reduced by iodide ions according to the reaction: Although it is thought that these electrodes are stable, it has been shown that degradation takes place after storage of the electrodes in an electrolyte, having the same synthesis as the electrolyte used for dye sensitized solar cells [1]. In order to improve the stability of Pt electrodes, we have used previously electrodeposited nickel (Ni) films as substrates, creating composite dual layered coatings with the form Pt/Ni/FTO/glass. Pt and Ni films were grown using the experimental conditions shown in Table 1 and a three electrode setup. The films were stored in the same electrolyte solution as that used in photovoltaic devices (0.5 M KI, 0.05 M I 2 in 90%/10% propylene carbonate/ethylene glycol). The variation in current density that corresponds to Peak I΄ during the first 100 days of storage in the electrolyte is shown below. Storage in the electrolyte Reference electrode: Ag/AgCl Counter electrode: Pt wire Table 1: Experimental conditions for the deposition of the films Sample Deposition method Nickel Ni charge density (mC/cm 2 ) Deposition method Pt Pt charge density (mC/cm 2 ) Pt/FTO-- Constant voltage -400mV 300s 111.3 Pt/Ni/FTO (A) Constant voltage -1500mV/8s 135.379.4 Pt/Ni/FTO (B) Constant voltage -1500mV/5s 83.388.4 Pt/FTO/ thermal Thermal decomposition Pt films prepared with thermal decomposition have higher catalytic activity towards I 3 - reduction No peak is observed for Ni/FTO/Glass Conclusions  Film morphology is affected by the deposition method and varies from distinct nanoparticles (Pt/FTO) to uniform films (Pt/Ni/FTO).  Films prepared by thermal decomposition of H 2 PtCl 6 are more catalytically active towards triiodide reduction than films prepared by electrodeposition. However the former are more prone to degradation than the latter.  The current density for triiodide reduction of films prepared by electrodeposition with constant current is almost linear with the deposited Pt charge density.  The current density for films prepared by electrodeposition with constant voltage has a plateau and the EAS is almost the same above 60 mC/cm 2 of deposited charge density.  Use of Ni/FTO/glass as a substrate has no effect in the catalytic activity of the electrodes, as observed by cyclic voltammogramm and Tafel plots.  Use of Ni/FTO/glass as a substrate results in less degradation of the electrodes than use of FTO/glass substrate.  The degradation of Pt/Ni/FTO/glass electrodes depends on the amount of deposited Ni. SEM images Electrodeposition Constant voltage Degradation mechanism The main reason for the reduction in the current density after electrolyte storage was Pt dissolution, as verified by XPS measurements. No change in Pt valence was observed [1]. a) Atomic iodine absorbed on Pt b) Degradation. Pt-I pairs depart together [1] Peak I΄ 10 th European Symposium on Electrochemical Engineering 28 Sept. – 02 Oct. 2014 Sardinia, Italy Experimental 1) Properties of Pt films deposited with different techniques 2) Properties of Pt films prepared by electrodeposition with either constant voltage or constant current density The peak current density for I 3 - reduction and the electrochemical active area (EAS) are stabilized, when the deposited Pt charge density exceeds 60 mC/cm 2 for deposition with constant voltage 3) Properties of Pt films deposited on Ni/FTO/glass Nickel is not catalytically active towards triodide reduction No significant changes are observed No significant changes in R CT are observed Sample Deposition method Pt Deposition method Ni 1 J = constant -0.5mA/cm 2 180s 2 V = constant -400mV/300s 3 V = constant -400mV/300s V = constant -1500mV/8s 1) 2) 3) Distinct nanoparticles with sizes less than 100 nm covering only a part of the substrate, as observed also by others [3]. Uniform films result from electrodeposition of Pt on Ni/FTO/glass substrate Acknowledgments Financial support by the “ARISTEIA-I” Action of the “Operational Programme Education and Lifelong Learning” co-funded by the European Social Fund (ESF-EU) and National Resources (Greece), through the project ΄΄COOL-NANO΄΄ Νο 733, is gratefully acknowledged.