| 학회 | 한국재료학회 |
| 학술대회 | 2016년 가을 (11/16 ~ 11/18, 경주 현대호텔) |
| 권호 | 22권 2호 |
| 발표분야 | H. 한-일 재료공학 워크샵 |
| 제목 | The New Finding of the OER Activity Descriptor |
| 초록 | As demonstrated by Suntivich et al. (2011)[1], when the number of electrons in the eg orbital is close to unity for transition metals, perovskite oxides exhibit maximum catalytic activity toward the oxygen evolution reaction (OER). In other words, Mn3+, Ni3+, Co3+ and Fe4+ become OER active sites for electrocatalysts based on these cations. However, LaMnO3 and Mn3O4 are based on Mn3+ and exhibits a significantly lower specific OER activity[2] compared with LaCoO3 and LaNiO3. It is therefore important to explore what causes degradation of the OER activity of Mn3+-based (t2g3 eg1) compounds to improve their catalytic activity. We attempt to improve the performance of Mn3+-based oxides by controlling the degradation factors of their OER activities. To directly compare the OER activities of Mn3+-based oxides containing more than two cation sites, Mn3+ concentrations at the octahedral site and their initial crystal structures were maintained. Mn3-xCoxO4 (0≤x＜1), a series of tetragonally distorted spinel compounds, satisfies this condition, as their octahedral sites remain occupied by only Mn3+ ions. We systematically studied the OER performances of Mn3+-based oxides by Co3+-substitution. Electrochemical measurements were conducted in 0.10 M KOH using a rotating ring disk electrode rotator at 1600 rpm, in combination with a bipotentiostat. In addition, a Pt wire counter electrode, and an Hg/HgO reference electrode filled with 0.10 M KOH were used. Electrochemical measurements were conducted with O2 saturation, where the equilibrium potential of the O2/H2O redox couple was fixed at 0.304 V vs. Hg/HgO (or 1.23 V vs. RHE). With an increase in Co content, significant improvements in the OER activities were observed for Mn3+-based oxides (Figure 1)[3]. The OER activities of Mn3+-based oxides increased linearly with the suppression of the Jahn-Teller distortion. When the Jahn-Teller distortion of Mn3+O6 octahedra is suppressed due to the increase in Co content, the overlap of the antibonding Mn3+ eg orbitals with the O 2p orbitals of the oxygen adsorbate becomes stronger (Figure 1). The OER activity of Mn3+-based oxides should therefore be enhanced due to the stronger binding of OER intermediates to the catalytic surface. We therefore conclude that the suppression of Jahn-Teller distortion enhances the OER activity of Mn3+-based oxides. REFERENCES [1] J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough and Y. Shao-Horn, Science, 2011, 334, 1383. [2] B. Han, M. Risch, Y. L. Lee, C. Ling, H. Lia and Y. Shao-Horn, Phys. Chem. Chem. Phys., 2015, 17, 22576. [3] S.Hirai, S.Yagi, A.Seno, M. Fujioka, T.Ohno and T. Matsuda, RSC Adv., 2016, 6, 2019. |
| 저자 | Shigeto HIRAI1, Shunsuke YAGI2, Tomoya OHNO3, Takeshi MATSUDA2 |
| 소속 | 1Kitami Institute of Technology, 2Japan, 3The Univ. of Tokyo |
| 키워드 | The oxygen evolution reaction; Activity descriptor; Jahn-Teller distortion |
