Ž . Journal of Molecular Catalysis A: Chemical 160 2000 277–285 www.elsevier.comrlocatermolcata ž / 2q Nafion–RuO –Ru bpy composite electrodes for efficient 2 3 electrocatalytic water oxidation K. Chandrasekara Pillai a, ) , A. Senthil Kumar a , Jyh-Myng Zen b a Department of Physical Chemistry, UniÕersity of Madras, Guindy Campus, Madras, 600 025, India b Department of Chemistry, National Chung-Hsing UniÕersity, Taichung 402, Taiwan Received 5 January 2000; accepted 1 May 2000 Abstract Ž . 2q Electrocatalytic water oxidation to evolve O was studied on a Nafion–RuO –Ru bpy composite electrode. The O 2 2 3 2 evolution current efficiency was largely improved for the multi-component electrode over the Nafion–RuO and Nafion– 2 Ž . 2q Ž . 2q Ru bpy individuals. The redox mediation through the Ru bpy was found to dominate over the RuO catalytic effect 3 3 2 in the water oxidation mechanism. The specific surface area of the RuO , which was prepared at different temperatures 2 Ž . 300–7008C , used in fabricating the composite electrode also played an important role in the overall water oxidation mechanism. Both the reaction and electrode parameters were optimized to get effective electrocatalytic current values in this study. q 2000 Elsevier Science B.V. All rights reserved. Ž . 2q Keywords: Electrocatalysis; Water oxidation; Nafion; RuO ; Ru bpy 2 3 1. Introduction Water oxidation has been the focus of inten- sive study due to its importance in photosynthe- sis, and in designing artificial photosynthetic system for solar energy conversion to obtain a w x renewable energy resource 1–8 . Unfortu- nately, the high overpotential for the 4e y oxida- tion of H O to O makes the process less 2 2 feasible. One way to improve this is to use Ž . suitable oxygen evolution catalysts Cat , OER like RuO , IrO , PtO , etc., together with pho- 2 2 2 Ž . Ž . 2q tosensitizers PSn , such as Ru bpy , 3 ) Corresponding author. Fax: q 91-44-2352870. Ž . E-mail address: kchandra@unimad.ernet.in K.C. Pillai . Ž . 2q Ž . 2q Fe bpy , Fe phen , etc. On the other hand, 3 3 various molecular-based catalysts, such as oxo- Žw Ž . bridged ruthenium dimers L H O Ru–O– 2 2 Ž . x 4q X Ru H O L , where L s 2,2 -bipyridine and 2 2 X X X w 4,4 -dichloro or 5,5 -dichloro-2,2 -bipyridine 5, x. 9–12 , in combination with suitable oxi- dants, like Ce 4q , MnO y , IO y , PbO , BrO y , 4 4 2 3 Ž . 3q Ž . 3q Ru bpy , Fe bpy were also reported for 3 3 w x this purpose 13 . The chief advantage in using the integrated Cat rPSn system, however, is OER that the Cat contains specific higher oxida- OER Ž Ž . Ž . tion redox groups e.g., Ru VII rRu VI and Ž . Ž . . Ru VI rRu IV for RuO and surface area, 2 which cannot be expected in the simple molecu- wx lar-based catalyst systems 8 . Majority of work shows that the catalyst RuO and the photosen- 2 1381-1169r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S1381-1169 00 00262-4