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Visiting Associate Professor

Keiko Waki

Associate Professor of Tokyo Institute of Technology

Research Interests

Fuel Cells Application

Keiko Waki and her research group have studied in making defects by using acid treatments and the chemical drilling process with CoOx nano-catalysts for functionalizing multi-walled carbon nanotubes (MWCNTs) in Tokyo institute of Technology. They found that the pure carbon catalysts prepared by the sequences of chemical drilling and Ar annealing to create defects and then removing the oxygen functional groups can reach an onset potential as high as 0.77V (vs. RHE). It is proposed that the defective edges with topological defects could be the active sites for oxygen reduction reaction which is the cathodic reaction for fuel cells. Further interesting point is that such active edges could be recovered by repeat of Ar annealing after the degradation induced by an electrochemical durability test. Meanwhile, her team has also investigated the effect of defects and functional groups for nitrogen doping by using rapid thermal annealing for carbon nanotube/carbon black to open the way of 30 sec’s NH3 annealing to efficiently obtain a highly active non-noble metal catalyst.



Fig 1. TEM image of the defects formed on CNT by the chemical drilling method1)

Solar Cells Application

Recently, attention has been paid to perovskite solar cells, which are low-cost, easy to produce and reach high efficiency. However, perovskite solar cells are still suffering from the reproducibility and durability problems. Keiko Waki’s team has investigated the perovskite solar cells by using different types of MWCNTs as the electrodes instead of traditional HTM/gold electrodes. They found that the oxygen-functional-groups decorated MWCNTs have potential to strengthen the interaction between the electrode and perovskite. It has been discovered that with the strengthened interface, solar cells prepared with a diverse I-V characteristics can converge to a typical cell performance through the self-recrystallization of perovskite at room temperature. The most interesting result was the ability of functionalized CNTs to make use of the self-recrystallization nature to form a stronger junction between the perovskite and CNTs. An extreme example is a cell that had an initial efficiency of 3% turning out to be 11% after the storage.

Fig 2 I-V curves of the perovskite cells with the carbon electrodes (The diverse initial characteristics converged after storage 3))

Current interest: In April, 2022, Keiko Waki has been joining with Prof. Dauskardt’s group to develop the devices by using the Rapid Spray Plasma Processing (RSPP) for sustainable energy technology.




  • Keiko Waki, Raymond A Wong, Haryo S Oktaviano, Takuya Fujio, Takuro Nagai, Koji Kimoto, Koichi Yamada, “Non-nitrogen doped and non-metal oxygen reduction electrocatalysts based on carbon nanotubes: mechanism and origin of ORR activity “, Energy & Environmental Science 7 (6), 1950-1958 (2014)
  • Ti Chen, Jiuting Chen and Keiko Waki,An activity recoverable carbon nanotube based electrocatalysts: rapid annealing effects and importance of defects”, Carbon 129, 119-127 (2018)
  • Jie Chen, Ti Chen, Tangliang Xu, Jia-Yaw Chang, Keiko Waki, “MAPbI3 Self-Recrystallization Induced Performance Improvement for Oxygen-Containing Functional Groups Decorated Carbon Nanotube-Based Perovskite Solar Cells”, Solar RRL 3 (12), 1900302(2019)
  • Lijie Zhang, Keiko Waki,” The influence of carboxyl group on nitrogen doping for defective carbon nanotubes toward oxygen reduction reaction”, Carbon 189, 369-376 (2022)



Durand Building., Rm. 111