課題番号 ：S-15-KU-0045
利用形態 ：機器利用
利用課題名（日本語） ：新規ナノ合金触媒の開発
Program Title (English) ：Development of novel nanoalloy catalysts
利用者名（日本語） ：山内　美穂
Username (English) ：M. Yamauchi
所属名（日本語） ：九州大学カーボンニュートラル・エネルギー国際研究所
Affiliation (English) ：International Institute for Carbon-Neutral Energy Research, Kyushu University

１．概要（Summary ）
In recent years, transition metal oxide spinels have been intensively studied as promising bifunctional electrocatalysts for oxygen reduction-oxidation reactions. In this work, we successfully in-situ synthesized MCo2O4 (M=Ni, Mn, and Co) nanoparticles (3~6 nm) on polymer-wrapped pristine multi-wall carbon nanotubes (MWNT/polymer) based on a solvothermal method. The effect of the temperature of solvothermal treatment, the concentration of precursors, and the addition of ammonia water on the morphology and electrocatalytic performance of the resultant catalysts was investigated. Furthermore, a homemade zinc-air battery using MWNT/polymer/NiCo2O4 cathode and zinc anode was fabricated and a promising power density of 47 mW cm-2 was obtained at 25°C.
２．実験（Experimental）
The MWNTs (15 mg) were mixed with PyPBI (5 mg) in DMAc (20 mL) and sonicated for 6 h to form PyPBI-wrapped MWNTs (MWNT-PyPBI). Nickel acetylacetonate (8.8 mg), cobalt acetylacetonate (17.5 mg), and MWNT-PyPBI (10 mg) were then sonicated in ethanol (30 mL), water (1.9 mL), and ammonia water (0.6 mL) for 15 min. The obtained suspension was then refluxed at 80 °C for 20 h, and subsequently transferred to a Teflon autoclave (60 mL) for a solvothermal treatment at 150 °C for 3 h. The obtained composite catalyst was denoted MWNT-PyPBI-NixCo3-xO4. For comparison, nickel acetylacetonate (22.6 mg) or cobalt acetylacetonate (26.3 mg) was separately used following the same preparation procedure, and the products were denoted as MWNT-PyPBI-Ni(OH)2 and MWNT-PyPBI-Co3O4, respectively. In order to clarify the role of PyPBI, bare MWNTs were also used as the support for the Ni/Co oxide and Ni(OH)2. The crystal structure was characterized by X-ray diffraction analysis (XRD, SmartLab, Rigaku Corp.). The microstructures of the catalysts were observed using an SU9000 (Hitachi High-Technologies) op-erated at 30 kV. The electron conditions were determined by X-ray photoelectron spectroscopy (XPS, AXIS-ULTRA, Shimazu Corp.). The crystallinity of the MWNTs was evaluated by Raman spectroscopy (533nm, Raman-touch, Nanophoton Corp.).
３．結果と考察（Results and Discussion）
Pristine multi-walled carbon nanotubes (MWNTs) were wrapped by pyridine-based polybenzimidazole (PyPBI) to which uniform NixCo3-xO4 nanocrystals were homogeneously deposited by the solvothermal method without damaging the MWNTs, in which PyPBI acted as efficient anchoring sites for the deposition of spinel oxide nanocrystals with ~5 nm size. The obtained catalyst (MWNT-PyPBI-NixCo3-xO4) outperformed most state-of-the-art non-precious metal-based bifunctional catalysts; namely, for OER, the potential at 10 mA cm-2 and Tafel slope in 1 M KOH solution were 1.54 V vs. RHE and 42 mV dec-1, respectively. For ORR, the onset and half-wave potentials are 0.918 V and 0.811 V vs. RHE, respectively. Moreover, the MWNT-PyPBI-NixCo3-xO4 demonstrates an excellent durability for both ORR and OER.

４．その他・特記事項（Others）
None

５．論文・学会発表（Publication/Presentation）
(1)Jun Yang, 藤ヶ谷剛彦,中嶋直敏, 電気化学会第83回大会, 平成２８年３月

６．関連特許（Patent）
None