Oxygen Evolution and Reduction Activity of Perovskite-Based Oxide Catalysts

Abstract

Unitized regenerative fuel cells (URFCs), which include fuel cells and water electrolyzers, have received many interests because the hydrogen fuel and electricity can be produced by only an electrochemical device. However, the oxygen electrode in the URFCs exhibit slow kinetics for both oxygen evolution reactions (OERs) and oxygen reduction reactions (ORRs). As a results, efficiency of the hydrogen production using URFCs is limited due to the high polarization resistance of the electrode for water splitting. Likewise, the productions of electricity are also restricted by the tardiness of ORRs because of the 4-electrons multi-step electrochemical reactions, then decreasing the overall reaction rate of the fuel cells. Up to now, the noble metal-based catalysts, such as carbon-supported platinum, iridium, ruthenium and their alloys, have still used as bifunctional OER and ORR catalysts to overcome the slow reaction kinetics. However, the utilization of precious metal-based catalysts is inappropriate for making the commercialization of the electrochemical cells. In order to replace these expensive catalysts, researches of perovskite-based oxide catalysts for URFCs have performed significantly. In particular, double-perovskite structured materials show the great potential as the bifunctional electrocatalyst with various dopants such as lanthanides (A-site) and transition metals (B-site). In this study, the double perovskite-based catalyst are selected and several transition metals (Mn, Fe, Ni and Cu) are doped to enhance their electrocatalytic activity and durability. The catalysts are synthesized by the combustion method and calcined at 900 oC for 4h in the electric furnace at a heating rate of 5 oC min-1. The physicochemical properties of the final samples are characterized by various tools such as X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope and transmission electron microscope. For the electrochemical analysis, a rotating disk electrode (RDE) system is used with a 0.1 M KOH solution, an Hg/HgO and a Pt wire for electrolyte, reference electrode and counter electrode, respectively. The electrochemical activities are measured by linear sweep voltammetry (LSV) at a scan rate of 5 mV s-1 for OER (1.2~1.7 V) and ORR (0.05~1.2 V). The long-term stability of the catalysts for OER are also analyzed by potential cycling between 1.25 and 1.65 V at a scan rate of 200 mV s-1 for 1,500 cycles. 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) * Corresponding authors: jyoung@sejong.ac.kr (J.-Y. Park)