Research Areas

Outline

We are conducting basic research on A. Recycling of waste siliconB. Fabrication of metal oxides by electrochemical approaches, C. Micro/nano-structuring by electrochemical approaches, D. Development of next-generation capacitors, E. Development of electrocatalysis and sensors, from the viewpoints of methodology, structure, and performance. The common point among these research themes is observation and control of chemical reactions in heterogeneous systems. We aim to extract and solve specific subjects using various procedures. The subjects should be solved by an environmentally-friendly, energetically favorable, and recyclable process, while the product is hopefully required to contribute to the supply and storage of clean energy. 
I hope that these activities can make students to be capable researchers who understand a phenomenon as it is, find out an essence of a subject, and express it accurately. At the same time, they will have a bird’s eye view for the whole research plan.

Prof. Masaharu Nakayama

※If you have any questions on our research, please don’t hesitate to contact us anytime. Please e-mail to Nakayama.

Research themes

A. Recycling of waste silicon

Recycling of waste silicon

Solar cell is an energy source that can realize a low-carbon society. Manufacturing of silicon wafers, the raw material of most solar cells, is accompanied by simultaneous generation of a large amount of silicon waste.
On the other hand, the rapid market growth of solar cells in recent years has caused a shortage of raw silicon materials. In this research, we aim to develop a chemical process for recycling kerf loss silicon to “solar grade” silicon. The process mainly consists of (i) hydrobromination of the waste silicon to synthesize bromosilanes with high purity and (ii) reduction of the obtained bromosilanes to deposit solar grade silicon.

References

B. Fabrication of metal oxides by electrochemical approaches

 Fabrication of metal oxides by electrochemical approaches

We found that oxidative electrolysis of Mn(II) ions in the presence of other cations (guest) creates layered manganese oxides (host), called birnessite, as a thin film on the surface of electrode. This method can intercalate a variety of cationic molecules between MnO2 layers because the host can adjust itself to accommodate guest cations during electrodeposition. The above figure depicts the birnessite intercalated with cationic surfactants. Because of its extra-large interlayer distance (~3nm), the interlayer space can be regarded as a “nanoreactor” filled with organic solvent, where electrons can be delivered through the MnO2 walls to/from the underlying electrode. Thus, electrocatalytic reactions have been achieved on the surfactant/MnO2 film.    We expect to create and establish a new host-gest system that has not been accomplished by conventional insulating porous materials (clays, zeolites, etc.)

References

C. Micro/nano-structuring by electrochemical approaches

Micro/nano-structuring by electrochemical approaches

The right upper figure shows porous MnO2 film that was electrodeposited on orderly arranged polystyrene beads on an electrode substrate, from manganese sulfate solution. This structure provides high electrolyte accessibility and high surface area, improving the electroactivity. 
The right lower figure shows Cu2O directly electrodeposited by applying potential pulses from the bottom of a porous alumina template. This structure can be recognized as a result of crystalline growth starting from Cu2O nuclei deposited from the nano-sized pores. In addition, we are conducting the micro/nano-fabrication using highly an ordered porous alumina template, taking into account application for metamaterials.

References

D. Development of next-generation capacitors

Development of next-generation capacitors

As shown in the right figure, layered manganese oxide consists of bicontinuous networks of solid and pore which enables both electrons and cations to move fast and reversibly. We have prepared various layered MnO2 and examined their pseudocapacitive properties with the aim of application to next-generation capacitors. We recently reported the orientation control of MnO2 layers to improve the capacitance.

References

E. Development of electrocatalysis and sensors

Development of electrocatalysis and sensors

Cathodically-grown layered MnO2 was found to be highly electroactive and function as a good catalyst toward several species in water. Particularly, birnessite with small crystalline size can effectively oxidize formaldehyde (FA). Based on the anodic current, a high-performance sensor for FA has been proposed (right figure).

References