成果報告書詳細
管理番号20160000000157
タイトル*平成27年度中間年報 固体高分子形燃料電池利用高度化技術開発事業 普及拡大化基盤技術開発 酸化物系触媒の革新的高機能化のためのメカニズム解析
公開日2016/5/28
報告書年度2015 - 2015
委託先名国立大学法人横浜国立大学 国立大学法人東京大学 昭和電工株式会社
プロジェクト番号P15001
部署名新エネルギー部
和文要約
英文要約Title: Development of Advanced PEFC Utilization Technologies/Development of Fundamental Technologies for PEFC Promotion/Advanced analysis of metal oxide cathode for innovative performance (FY2015-FY2017) FY2015 Annual Report

In order to develop oxide-based cathodes for polymer electrolyte fuel cells, we performed mechanism analysis for innovative high-functionalization in oxide-based oxygen-reduction electrocatalysts. In order to develop noble-metal- and carbon-free cathodes, titanium-niobium oxides were prepared as active materials for oxide-based cathodes and the factors affecting the oxygen reduction reaction (ORR) activity were evaluated. The high concentration sol-gel method was employed to prepare the precursor. Heat treatment in Ar containing 4% hydrogen at 700?900 oC was effective for conferring ORR activity to the oxide. Notably, the onset potential for the ORR of the catalyst prepared at 700 oC was approximately 1.0 V vs. RHE, resulting in high quality active sites for the ORR. X-ray (diffraction and photoelectron spectroscopic) analyses and ionization potential measurements suggested that localized electronic energy levels were produced via heat treatment under reductive atmosphere. Adsorption of oxygen molecules on the oxide may be governed by the localized electronic energy levels produced by the valence changes induced by substitutional metal ions and/or oxygen vacancies. In addition, we newly added Cs-STEM-EDX and Cs-STEM-EELS those enable us to observe atom-level structures and electronic states of outermost catalyst surfaces even if they have amorphous structures. These analyses showed that the reduction of Ti4+ ions and increase of Ti3+ ion density play a main role in the improvement of ORR-activity.
Zirconium oxide-based model catalysts using carbon materials were prepared by to analyze the effect of nitrogen on the ORR activity. Nano-sized zirconium oxide particles were highly dispersed on the carbon black support (ZrOx/CB). The ORR activity of the ZrOx/CB was same as the previous our zirconium oxide-based catalysts. XPS suggested that the oxygen vacancies acted as active sites for the ORR.
We performed theoretical analysis about zirconium oxide to investigate the generation of the ORR activity of the oxide-based cathodes. Zirconium oxides with tetragonal crystalline structure having oxygen vacancies had definite ORR activity according to experimental results. (1 0 1) plane which was most stable among other plane of the tetragonal zirconia was chosen as model structure to investigate the reaction coordinate for the ORR. Associative reaction mechanism was assumed to estimate the energy level of the reaction intermediates. The free energy of the reaction intermediates calculated through the reaction coordinate revealed that when oxygen vacancies existed on the surface the reduction reaction spontaneously proceeded. However, the final intermediate, OH, adsorbed strongly on the oxygen vacancies to stabilize the oxide surface without oxygen vacancies. The energy barrier of the formation of the oxygen vacancies was estimated to be ca. 6 eV. Therefore, the theoretical analysis revealed that the stabilization of the oxygen vacancies was most important point to proceed the ORR.
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