Enhanced Oxygen Evolution Activity of 3D Nanostructured Cobalt Oxides through Doping with Various Transition Metal Oxides

Abstract

Photoelectrochemical water-splitting is one of the most renewable and clean ways to produce hydrogen by water electrolysis [1]. However, the oxygen evolution reaction (OER) in anode side of photoelectrochemical water-splitting system shows sluggish kinetics with the high polarization loss due to the 4-electron pathway likewise oxygen reduction reaction (ORR) in fuel cell operating conditions [2-5].Up to now, noble metals, such as iridium, ruthenium and platinum, have still used as OER catalysts [6]. In comparison with these noble metal catalysts, studies of transition metal oxide catalysts (TMOCs) for photoelectrochemical water-splitting systems have not carried out intensively, although they have similar (or more active) properties about OER [7, 8]. In addition, various state-of-art nanotechnologies for fabricating TMOCs may contribute to improve OER properties significantly for water-splitting [9, 10].In this work, a variety of nanostructured cobalt oxides (NCOs) are synthesized by the hydrothermal method using urea, hydrogen peroxide and polyvinylpyrrolidone. Then, various transition metal oxides are doped to NCO matrix during hydrothermal reaction. Their physicochemical properties were confirmed by using various analytic techniques such as SEM, TEM, BET, and XRD.For electrochemical characterizations, a rotating disk electrode system is adopted with an Ag/AgCl reference electrode and a Pt counter electrode in 0.1 M KOH electrolyte. A pretreatment where cyclic voltammetry (CV) post-purging nitrogen gas in the potential range of 0.05 – 1.2 V versus reversible hydrogen electrode (RHE) conducted at a scan rate of 100 mV s-1 for 50 cycles is used for activation of catalyst surface. The OER activity is measured by linear sweep voltammetry (LSV) from 1.2 to 1.7 V at a scan rate of 5 mV s-1 and is compared the oxygen evolution activity at specific current density. J. Jhang, K. Sasaki, E. Sutter, R. R. Adzic, Science, 315, 220 (2007).Y. Liang, Y. Li, H. Wang, J. Zhou, J. Wang, T. Regier, H. Dai, Nature Materials, 10, 780 (2011).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).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)T. Reier, M. Oezaslan, P.Strasser, ACS Catal., 2, 1765 (2012).Y. J. Sa, K. Kwon, J. Y. Cheon, F. Kleitz, S. H. Joo, J. Mater. Chem. A, 1, 9992 (2013).J. Y. Cheon, C. Ahn, D. J. You, C. Pak, S. H. Hur, J. Kim, S. H. Joo, J. Mater. Chem. A, 1, 1270 (2013).C. A. Wang, S. Li, L. An, Chem. Comm., 49, 7427 (2013).X. Rui, H. Tan, D. Sim, W. Liu, C. Xu, H. H. Hng, R. Yazami, T. M. Lim, Q. Yan, J. Power Sources, 222, 97 (2013). * Corresponding authors: jyoung@sejong.ac.kr (J.-Y. Park)