Yoshikazu Ito lab, University of Tsukuba

Three-dimensional nanoporous graphene

Three-dimensional (3D) nanoporous graphene with preserved 2D Dirac electronic characters was successfully synthesized. The nanoporous graphene is constructed by a single layer graphene sheet that is continuously inter-connected to form a complex 3D network structure. This free-standing nanoporous graphene with an excellent crystallinity possesses high electron mobility, holding great promise for the applications in electronic, optic and energy related devices. The nanoporous graphene were grown by a nanoporous metal based chemical vapor deposition (CVD) method in Figure (a). The overall morphology of the nanoporous graphene in Figure (b) shows a 20 um thick free-standing bulk sheet. Although the 3D nanoporous graphene has a complex structure, it is demonstrated to be ~5000 cm2/Vs in electron mobility and a mass-less Dirac cone system. As the conventional transistor requires electron mobility of 200 cm2/Vs, it is greatly expected that this nanoporous graphene will bring new 3D graphene devices.

3D graphene transistor

SEM images and capacitance of 3D graphene with different pore size

Steam generation by a thin porous graphene sheet.

Three-dimensional nanoporous graphene for hydrogen evolution

Three-dimentional (3D) nitrogen(N) and sulfur(S) co-doped nanoporous graphene with preserved high conductivity was successfully synthesized. The 3D NS-doped nanoporous graphene is constructed by a few layer graphene sheets that are continuously inter-connected to form a complex 3D network structure. Due to the nitrogen and sulfur co-doping and abundant nanoporous structures, the catalysis towards hydrogen evolution reaction has been successfully activated inside and outside the nanoporous graphene at absence of any metal catalysts. This hydrogen harvesting technology with 3D metal-free graphene catalyst shows a great promise for achieving economic hydrogen energy at high efficiency for green energy innovation.

Figure Metal-free chemically doped three dimensional graphene electrode for hydrogen evolution. References:

Acceleration of electrochemical CO₂ reduction by catalyst supports

Accelerating the CO₂-recycling process is crucial for preventing global warming. Electrochemical reduction allows the efficient conversion of CO₂ into useful chemical compounds with catalysts. During the electrolytic synthesis of CO₂, an increase in voltage accelerates the synthesis of the target product and enhances byproduct formation. Thus, we are looking for new mechanisms that allow us to accelerate the production rate (high speed) and prevent byproduct formation (high selectivity) simultaneously.

New CO₂ supply route 2 accelerates electrochemical CO₂ reduction

Corrosion resistant non-noble metal catalyst

The dream of hydrogen-powered cars has excited many people as a solution for the huge amount of carbon dioxide fossil-fuel burning vehicles emit into the atmosphere daily. However, the production of hydrogen gas has been slowed by the lack of cheap catalysts required to split water efficiently. In this process, hydrogen nuclei, called protons, need to combine to form hydrogen gas, H2. Nickel and Ni-based alloy are seen as promising cheap alternatives to platinum, but these metals corrode easily when exposed to the acidic conditions of the reaction. One solution is to use graphene, a single sheet of carbon atoms arranged in a honeycomb lattice, to protect the catalyst. Thus, we are challenging to employ the graphene covering non-noble electrodes or other new catalysts in PEM-type water electrolyzers for practical applications.

Metal-air batteries

High capacity metal-air (Li, Zn, K etc) battery is a new type of secondary battery which has attracted great attention in recent years because of the high theoretical capacity and energy density. However, the practical implementation of the new battery is limited by the low cycling stability and poor energy efficiency. To solve these challenging issues, developing new cathode materials with high electrochemical stability and low charge/discharge overpotentials is a crucial topic to realize carbon neutral society.

Li-O2 battery and mechanism of the electrode reactions

Demonstration of Li-O2 battery (green LED)

The mathematics of repulsion for new graphene catalysts

Changing the geometry of three-dimensional (3D) graphene, which is made of networks of carbon atoms, by adding chemicals or introducing topological defects, can improve its catalytic properties. The new mathematical model, called standard realization with repulsive interaction (SRRI), reveals the relationship between these changes and the properties that arise from them. The mathematical model can be used as an effective pre-screening tool for exploring new 2D and 3D carbon materials for unique properties. We are looking for a new carbon network for physics and chemistry.

Simplification of carbon network and mathematical determination of geometry. Mathematical abstraction from carbon network to mathematical modeling for the standard realization and the standard realization with repulsive interaction.