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Microscopic Oxygen Reduction Mechanism of Carbon Electrocatalysts with Addition of Trace Nitrogen

—Step toward Understanding the Microscopic Mechanisms of Oxygen Activation by Non-Platinum Group Electrocatalysts—

2018.08.10


National Institute for Materials Science (NIMS)
Hokkaido University

In a framework of collaboration study, NIMS, Hokkaido University and Ulm University (Germany) discovered that an addition of trace amount of nitrogen (≤1 atomic %) transforms carbon materials into electrocatalysts showing a high oxygen reduction reaction (ORR) activity, a key reaction in fuel cells. This study also succeeded in identifying microscopic ORR mechanisms.

(“Microscopic electrode processes in the four-electron oxygen reduction on highly-active carbon-based electrocatalysts,” Ken Sakaushi, Markus Eckardt, Andrey Lyalin, Tetsuya Taketsugu, R. Jürgen Behm and Kohei Uosaki; ACS Catalysis August 12:00 pm on 9, 2018; doi:10.1021/acscatal.8b01953)

Abstract

  1.  In a framework of collaboration study, NIMS, Hokkaido University and Ulm University (Germany) discovered that an addition of trace amount of nitrogen (≤1 atomic %) transforms carbon materials into electrocatalysts showing a high oxygen reduction reaction (ORR) activity, a key reaction in fuel cells. This study also succeeded in identifying microscopic ORR mechanisms. Platinum group metals—a limited resource—are currently used as the main ORR catalyst. Our results may advance basic and applied researches on metal-free carbon-based electrocatalysts as practical alternatives to platinum group electrocatalysts, facilitating the use of abundant and sustainable materials to produce energy.
  2. ORR determines fuel cell’s energy efficiency but it is known to be difficult to activate this reaction due to sluggish kinetics. Only specific metals, such as platinum, were previously believed to be capable of catalyzing ORR with a high efficiency. However, recent reports have indicated that nitrogen-doped carbon materials are also able to catalyze ORR. Carbon-based electrocatalyst is attracting a wide variety of interests worldwide because of the possibility to replace limited and expensive platinum with affordable carbon and nitrogen materials, leading to the production of environmentally-friendly fuel cells at lower cost. The ORR mechanisms on nitrogen-doped carbon materials, however, had not been well understood.
  3. The NIMS-led collaboration research team recently synthesized several clean metal-free carbon-based model catalysts with different doped nitrogen contents and chemical structures. The team then used these catalysts to investigate the microscopic mechanism of ORR. In the course of study, the team checked the configuration and the distribution of nitrogen on a surface of catalysts in detail, and this data was used to construct theoretical models to analyzed microscopic ORR mechanisms based on density-functional theory calculations. As a result, the team succeeded in demonstrating that metal-free carbon materials with a trace amounts of nitrogen can show capable of a high ORR activity. Indeed, the oxygen activation mechanisms can be explained by an experiment-theory concerted study.
  4. By understanding transformation mechanisms of metal-free carbon materials into active electrocatalysts is expected to facilitate the design of highly active carbon-based electrocatalysts. In the future studies, we will apply this knowledge to the search for carbon-based catalysts with superior activities in a line with our goal to synthesize catalysts enabling efficient electricity production using ubiquitous materials.
  5. This research was led by Dr Ken Sakaushi (Senior Researcher, Center for Green Research on Energy and Environmental Materials, NIMS), Markus Eckardt (Doctoral Student, Ulm University; also a NIMS intern), Prof. Tetsuya Taketsugu (Professor, Faculty of Science, Hokkaido University), Prof. Dr. R. Jürgen Behm (Professor, Institute of Surface Chemistry and Catalysis, Ulm University). This project was supported by the JSPS Grant-in-Aid for Young Scientists (B) (Project No. 17K14546), the JSPS Grant-in-Aid for Scientific Research (A) (Project No. 16KT0047), the MEXT Program for Development of Environmental Technology using Nanotechnology, the MEXT program entitled “High priority post-K computer issue: Development of new fundamental technologies for high-efficiency energy creation, conversion/storage and use” and a research grant from the Japan Prize Foundation.
  6. This study will be published in ACS Catalysis (as a “Just Accepted” manuscript), a journal of the American Chemical Society, on August 9, 2018.

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Contacts

(Regarding this project)
Ken Sakaushi
Senior Researcher
Center for Green Research on Energy and Environmental Materials
National Institute for Materials Science
Tel: +81-29-860-4945
E-Mail: SAKAUSHI.Ken=nims.go.jp
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Tetsuya Taketsugu
Professor
Department of Chemistry, Faculty of Science
Hokkaido University
Tel: +81-11-706-3535
E-Mail: take=sci.hokudai.ac.jp
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