PD Research Report for the 2016 year
Name（Research group） Wang Heng
（Yoshikawa Research Group, Graduate School of Science and Technology）
Research Theme

Development of nanohybrid system between metal carbides and nanoporous
carbons for high performance rechargeable batteries

Research PeriodApril 1, 2016 ~ August 12, 2016

Research Results（about 2,500 characters in Japanese, about 65 lines times 90 characters in English）
At present, various carbon materials, such as active carbon, graphite, carbon nanotubes, and graphene,
have been reported so far and extensively studied in energy storage fields. Nanoporous carbon materials
with high surface areas are attractive, because they can enhance the performance of carbons inapplications such as batteries, supercapacitors, and catalysis applications. Great efforts have been
devoted towards the preparation of nanoporous carbons. For instance, highly-ordered nanoporous
carbons have been prepared by using inorganic hard-templates including zeolites and mesoporous silicas.
As another approach, inorganic–organic mesostructured hybrids have been recently demonstrated to beexcellent precursors for making nanoporous carbons.
Currently, nanoporous carbon particles are mainly being prepared by carbonization of organic spheres.
For instance, by using several polymer spheres, nanoporous carbon spheres with tunable nanopore sizes
can be obtained. The generation of nanopores inside the polymer spheres is spontaneous during thecarbonization. Nevertheless, formation of uniform pore sizes is not easy, the present method by using
mesoporous silica nanoparticles as hard-templates
includes several steps, which is somewhat complicated(a)in the case of large-scale production. In order toovercome the above drawbacks, alternative ways forfacile preparation of nanoporous carbons with
controlled particle sizes are in much demand. Recently,
porous metal–organic frameworks (MOFs), as typicalinorganic–organic hybrids,

have been

used

as(b)

precursors to prepare nanoporous carbons throughthermal conversion. The obtained nanoporous carbons
showedattractivefeatures,

includingultra-highspecific surface areas, ultra-large pore volumes, andcontrolled pore structure. Here, I used a facile route(c)

for the preparation of monodispersed ZIF-8 crystals
with controlled particle sizes ranging from thenanometer scale to the micrometer scale under various
conditions. Then, the obtained starting precursors
ZIF-8 crystals were converted into nanoporous
carbons, retaining their original shapes.

Figure 1. SEM images of ZIF-8 of (a)～50mm,Three sets of ZIF-8 samples with different particle (b)～700 nm, (c)～1.5 μm.

sizes within a wide range was synthesizedaccording to the method described in theliterature.1 Figure 1 shows scanning electron
microscopy (SEM) images of ZIF-8 crystals
prepared under different conditions. The SEM
imagesshowthatthewelldispersednanocrystals in polyhedral shape with sizes
from 50 nm to 1.5 μm. In general, the particle
size of ZIF-8 is determined by the speed of
crystal nucleation and growth via coordinationand deprotonation equilibria of ligands. A fast

Figure 2. Powder XRD patterns of ZIF-8 with

nucleation speed with a short reaction timedifferent particle size.

leads to small nanoparticles, while a slow nucleation speed with a long reaction time tends to yield large
crystals. SEM observations demonstrate the success of the size-controlled syntheses (for the uniform
particle size distributions).
To examine the crystal structure of the three ZIF-8 samples with different particle sizes, powder XRD
measurement was performed. All the samples exhibited pure crystals with cubic I43m group, whichmatched with the well-known ZIF-8 crystal structure (Figure 2.). The obtained ZIF-8 crystals withdifferent particle sizes as templates/precursors underwent pyrolysis at 900 °C under Ar gas to afford
porous carbons. In this process, the generated ZnO was reduced by carbon to give evaporative Zn at suchhigh temperature. Pure carbons with graphitic structure were obtained according to XRD patterns. TheSEM observations illustrate that the obtained carbons are well dispersed and have retained sizes andmorphology from their precursors, ZIF-8 crystals.
In conclusion, ZIF-8 crystals with controlled particle sizes ranging from the nanometer scale tomicrometer scale have been successfully synthesized as templates/precursors. Then, the obtained ZIF-8
crystals were successfully converted into nanoporous carbons, retaining their original shapes. Compared
to traditional approaches, this one-pot approach without any complicated steps is really simple. We will
prepare hybrid materials between layered metal carbides and the nanoporous carbon for lithium ionbatteries and supercapacitors.
References:
1, Nagy L. Torad, Ming Hu, Yuichiro Kamachi, Kimiko Takai, Masataka Imura, Masanobu Naito andYusuke Yamauchi. Chem. Commun., 2013, 49, 2521-2523.
Articles, presentations:Preparation of gamma-LiV 2 O 5 from polyoxovanadate cluster Li 7 V 15 O 40 and its battery performance as
cathode active materials, H. Wang, J. Isobe, Takeshi Shimizu, D. Matsumura, T. Ina, H. Yoshikawa,
paper in preparation.
Reaction mechanism and electrochemical performance of amorphous Vanadium polyoxovanadatecathode for Li-ion batteries, H. Wang, J. Isobe, Takeshi Shimizu, D. Matsumura, H. Yoshikawa, paper in
preparation.