Perovskite-Based Oxide Catalysts to Improve the Oxygen Evolution and Reduction Activity

Abstract

Unitized regenerative fuel cells (URFCs), which include water electrolysis and fuel cells, have received many attentions due to the production of hydrogen gas and electricity in one electrochemical device. Water electrolysis is one of the most pollution-free and renewable ways to produce hydrogen. However, the slow kinetics of oxygen evolution reactions (OERs) in the URFC anode are limited by high polarization resistance for oxidation of water. Likewise, oxygen reduction reactions (ORRs) for the fuel cell cathode also show slow rates due to the multi-step electrochemical reactions demands of 4-electrons in reactions, limiting the overall reaction rate of the fuel cells. Up to date, the noble metal-based catalysts, such as carbon-supported iridium, ruthenium, platinum and alloys, have still used as OER and ORR catalysts. The use of precious metal-based materials is not suitable for the commercialization of the electrochemical cells. In order to replace these noble metal catalysts, studies of perovskite-based oxide catalysts for URFCs have carried out intensively these days. In particular, various dopants in the perovskite materials may help to improve the electrochemical properties significantly. Herein, the perovskite-based catalysts are synthesized by the glycine-nitrate combustion method with various A site material (Nd, Sm and Gd) in ABO3 structure. Then, the ashes are calcined at 900 oC for 4h in electric furnace at a heating rate of 5 oC min-1. The physicochemical properties of the final products are characterized by several analytic tools such as X-ray diffraction, scanning electron microscope, transmission electron microscope and BET. For electrochemical analysis, a rotating disk electrode system is used with an Hg/HgO and a Pt wire and a 0.1 M KOH solution for reference, counter and electrolyte, respectively. The pre-conditioning of catalysts is carried out by cyclic voltammetry (CV) at a scan rate of 100 mV s-1 for 50 cycles with nitrogen-purged electrolyte. The OER (1.2 V ~ 1.7 V) and ORR (0.05 V ~ 1.2 V) activities are measured by linear sweep voltammetry (LSV) at a scan rate of 5 mV s-1 and for the performance and long-term stability. A. Grimaud, K.J. May, C.E. Carlton, Y.-L. Lee, M. Risch, W.T. Hong, J. Zhou and Y. Shao-Horn, Nat. Comm., 4, 2439 (2013).Y. Liang, Y. Li, H. Wang, J. Zhou, J. Wang, T. Regier, H. Dai, Nature Materials, 10, 780 (2011).J. Kim, X. Yin, K.-C. Tsao, S. Fang and H. Yang, J. Am. Chem. Soc., 136, 14646 (2014).J.-I. Jung, H.Y. Jeong, M.G. Kim, G. Nam, J. Park and J. Cho, Adv. Mater., 27, 266 (2015).J. Suntivich, K.J. May, H.A. Gasteiger, J.B. Goodenough, Y. Shao-Horn, Science, 334, 1383 (2011).J. Suntivich, H. A. Gasteiger, N. Yabuuchi, Y. Shao-Horn, Nature Chemistry , 3, 546 (2011).T. Reier, M. Oezaslan, P.Strasser, ACS Catal., 2, 1765 (2012).I. C. Man, H. Y. Su, F. C. Vallejo, H. A. Hansen, J. I. Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. K. Nørskov, J. Rossmeisl, ChemCatChem, 3, 1159 (2011)