F868 Journal of The Electrochemical Society, 161 (9) F868-F875 (2014) 0013-4651/2014/161(9)/F868/8/$31.00 © The Electrochemical Society Nanostructured (Ir,Sn)O 2 :F – Oxygen Evolution Reaction Anode Electro-Catalyst Powders for PEM Based Water Electrolysis Karan Sandeep Kadakia, a, * Prashanth Jampani, a, * Oleg I. Velikokhatnyi, b,c Moni Kanchan Datta, b,c Sung Jae Chung, d James A. Poston, e Ayyakkannu Manivannan, e, ** and Prashant N. Kumta a,b,c,d,f, **, z a Chemical and Petroleum Engineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA b Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA c Center for Complex Engineered MultifunctionalMaterials, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA d Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA e US Department of Energy, National Energy Technology Laboratory, Morgantown, West Virginia 26507, USA f Department of Oral Biology, School of Dental Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15217, USA Nanostructured powder catalysts comprising solid solutions of F doped SnO 2 and IrO 2 of different compositions were synthesized by a simple two step approach. High surface area SnO 2 :F was prepared initially using CTAB as a surfactant. (Ir,Sn)O 2 :F was then synthesized by forming a solid state solution with IrCl 4 and SnO 2 :F followed by heat-treatment in air at 400 ◦ C. The catalyst was then coated onto a porous Ti foil and has been studied as a promising anode electro-catalyst for oxygen evolution reaction (OER) in PEM based water electrolysis. The optimal composition of (Ir 0.3 Sn 0.7 )O 2 :10 wt% F displayed electrochemical activity comparable to the commercially available pure IrO 2 demonstrating ∼70 mol% reduction in noble metal content. The electrochemical stability tests also showed that (Ir,Sn)O 2 :F solid solution exhibits much better durability compared to commercial IrO 2 , the standard (OER) catalyst. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0381409jes] All rights reserved. Manuscript submitted February 28, 2014; revised manuscript received May 20, 2014. Published June 6, 2014. This was Paper 1133 presented at the Boston, Massachusetts, Meeting of the Society, October 9–14, 2011. Hydrogen has been considered as a major alternative to fossil fu- els and holds the potential to be the most lightweight fuel to provide reliable and affordable energy to meet the growing global energy demand. 1 A hydrogen based energy system will be benevolent for delivering high quality energy services in an efficient, clean and safe manner thus, trying to fulfill the sustainability goals of the United States. However, it has been a major challenging task in order to eco- nomically generate clean and pure hydrogen combined with storage and distribution. One of the promising approaches for the production of hydrogen is based on splitting water using electricity. 1–6 Water elec- trolysis offers virtually no green house gas emission or toxic byprod- ucts if the electric current is generated using renewable or nuclear energy, thus making it a very plausible option if the efficiency could be increased. 1,2,4,5,7,8 The current technologies for water splitting or water electrolysis are very cost intensive. This impedes the attainment of the targeted hydrogen production costs. Proton Exchange Mem- brane (PEM) based water electrolysis is very cost intensive due to the high capital cost associated with the use of noble metals and noble metal oxides such as platinum, iridium oxide, etc. as electro-catalysts. The current PEM based systems are also relatively small possessing less efficiency and involving labor intensive fabrication. 2,3,6–12 Rutile type noble metal oxides viz., IrO 2 and RuO 2 are well known and are accepted as the standard anode catalysts for the oxygen evolution re- action (OER) in PEM water electrolysis. However, despite the use of these functional noble metal systems, the anodic over-potential and the ohmic resistance in electrolysis cause poor performance account- ing for the sluggish catalytic performance. Also, the noble metal oxide (IrO 2 and/or RuO 2 ) electro-catalysts degrade over time in acidic PEM electrolysis environment, thereby not only diminishing the electro- chemical activity but also reducing the service life of the electrode. 13–24 Researchers have widely explored mixed IrO 2 -RuO 2 and Pt-IrO 2 sys- tems to be used as OER catalysts in the past, which help in improving the electro-catalytic activity and stability. 17,18,20,25–34 ∗ Electrochemical Society Student Member. ∗∗ Electrochemical Society Active Member. z E-mail: pkumta@pitt.edu Identification of new catalysts and especially with significantly less noble metal content exhibiting catalytic activity similar to the noble metal oxides and no compromise in overall performance of the PEM electrolyzer cell would constitute a desirable and major needed break- through. In line with these goals, less expensive and more corrosion resistant metal oxides viz., tin oxide (SnO 2 ), niobium oxide (Nb 2 O 5 ), tantalum oxide (Ta 2 O 5 ) or titanium oxide (TiO 2 ) are excellent candi- dates for use as an OER catalyst instead of the currently used noble metal oxides such as IrO 2 /RuO 2 for PEM based water electrolysis. However, these non-noble metal oxides by themselves show no cat- alytic activity as an anode electro-catalyst in PEM electrolysis. It has been reported 13,15,26,35–44 that mixed oxides obtained by the addition of cheaper metal oxides with the noble metal oxide IrO 2 and/or RuO 2 would help greatly in reducing the cost while maintaining the catalytic activity similar to pure noble metal oxide as well as improving the stability of the mixed metal oxide catalyst. However, the active surface area and electronic conductivity of these mixed oxide decreases with increase in the amount of the cheaper metal oxides, 11,21,35–43,45–48 and as a result, no beneficial effect on the catalytic activity is observed after the addition of the inexpensive metal oxides above a threshold limit. The present work has been carried out to identify an anode electro- catalyst for PEM water electrolysis based on the highly corrosion re- sistant SnO 2 . Tin oxides and F-doped SnO 2 (SnO 2 :F) are well known for their applications in solar cells, heat mirrors etc. 49–51 They are also considered as an attractive alternative to other non-noble metal ox- ides for PEM based water electrolysis due to the improved electronic conductivity of F-doped SnO 2 . SnO 2 :F has been shown to be a good catalyst support for OER in water electrolysis by ab-initio studies and in various electro-catalyst systems explored by us and reported previously. 52–55 However, SnO 2 and SnO 2 :F are both electrochemi- cally inactive for oxygen evolution under PEM electrolysis condi- tions. Thus, IrO 2 electro-catalyst has been added in small amounts to SnO 2 and SnO 2 :F to form a homogeneous solid solution of SnO 2 :F and IrO 2 which acts as an excellent electro-catalyst for OER in PEM based water electrolysis. The solid solution of (Ir,Sn)O 2 :F is expected to have a more favorable microstructure as reported before 15,52,55 since ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 98.111.199.146 Downloaded on 2014-06-07 to IP