| 학회 | 한국재료학회 |
| 학술대회 | 2018년 가을 (11/07 ~ 11/09, 여수 디오션리조트) |
| 권호 | 24권 2호 |
| 발표분야 | 9. 한-일 재료공학 심포지엄(KMST 2018)-오거나이저: 권도균 교수(한국항공대) |
| 제목 | OER mechanism of Cobalt-based layered compounds |
| 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 precisely determine the OER active site for finding the decisive factor of OER catalysts. Among them, we especially attempt to improve the OER performance of Co-based oxides by choosing a mixed valence compound for our interest of study. To directly determine the OER active site of Co-based oxides, we used in-situ electrochemical impedance spectroscopy measurements and synchrotron X-ray absorption spectroscopy measurements. We systematically studied the OER performances of Ca3Co4O9-δ, a series of misfit layered compounds. 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). By using Pechini method for the synthesis of Ca3Co4O9-δ, significant improvement in the OER activity was observed. The OER activity enhancement cannot be simply explained by normalizing the current density with the electrochemically active surface area (Figure 1). Therefore, this OER activity enhancement was further explored by in-situ electrochemical impedance spectroscopy measurements at 1.2-1.7 V vs. RHE and synchrotron X-ray absorption spectroscopy measurements after 100 OER cycles. We clearly observed that the Co2+ does not serve as the cation for synergistic effect, instead it is the main cation that contributes to the OER performance of Ca3Co4O9-δ. We therefore conclude that the OER active site for Ca3Co4O9-δ is Co2+ instead of Co3+. 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. ACKNOWLEDGEMENT This work was partly supported by a Grant-in-Aid for Scientific Research (B 15H04169) from the Japan Society for the Promotion of Science. |
| 저자 | Shigeto HIRAI1, Masaya FURUNAKA2, Shunsuke YAGI3, Tomoya OHNO4, Takeshi MATSUDA1 |
| 소속 | 1School of Earth, 2Energy and Environmental Engineering, 3Kitami Institute of Technology, 4Japan |
| 키워드 | The oxygen evolution reaction; Active site; Layered compounds; Cobalates |
