Most non-PGM catalysts developed in the last decade is a so-called Fe/N/C catalysts, which utilize graphitic carbon materials originated from carbonized polymers,5 carbonized metal organic frameworks6 or both.7,8 All these carbons are conductive as they contained graphitic layers with edges terminated by pyriginic nitrogen atoms. Another non-PGM catalyst type is oxide/oxynitride containing group IV or V metals. As these catalysts are not conductive, they have mostly been supported on carbon materials.9–11 Therefore, both these non-PGM catalyst types should be protected from corrosion of carbon supports accelerated during the startup/shutdown of the cell. Develompment of carbon-support-free non-PGM catalysts is a challenging, attractive option to replace conventional carbon-supported platinum-based catalysts. We therefore recently reported titanium oxynitride (TiOxNy) catalyst free from carbon-supports.12 The activity in acidic media was the highest among the ever reported carbon-support-free oxide based catalysts, whereas the minimum catalyst loading to uniformly coat the grassy carbon disk electrode was also the highest, 2 mg cm–2 due to the high density.
In this study, various attempts have been made to lower the density and thus decrease the catalyst loading. The minimum catalyst loading was successfully reduced to 0.6 mg cm–2, same as the standard of Fe/N/C catalysts. Effect of the loading on activity and visual reaction mechanism will be discussed at the meeting.
The authors gratefully acknowledge Mr. Yusei Tsushima for his help with acquisition of transmission/scanning electron microscopy images. This work was partially supported by a Grant-in-Aid for Scientific Research (C) (17K06180) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan; a research grant from Nippon Sheet Glass Foundation for Materials Science and Engineering in Japan; a research grant, KJ-2539, from the Kato Foundation for Promotion of Science in Japan, a research grant from Nippon Life Insurance Foundation in Japan and a research grant from Yashima Environment Technology Foundation. The X-ray photoelectron spectra were acquired with the support by Nanotechnology Platform of the MEXT of Japan.
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