Integrating nanomaterial with light-absorbing molecule powers hydrogen production from water and sun

Date:
June 8, 2020
Source:
Tokyo Institute of Technology
Summary:
Scientists have developed a hybrid material constructed from a metal
oxide nanosheet and a light-absorbing molecule for splitting water
molecules (H2O) to obtain dihydrogen (H2) under sunlight. Since
H2 can be used as carbon-free fuel, this study provides relevant
insight towards clean energy generation.



FULL STORY ==========================================================================
In line with the depletion of fossil fuels and the environmental problems
our planet faces due to their combustion, developing technology for
clean energy generation is a topic of global interest. Among the various methods proposed to generate clean energy, photocatalytic water splitting
is showing much promise.

This method utilizes solar energy to split water (H2O) molecules and
obtain dihydrogen (H2). The H2 can then be used as a carbon-free fuel
or as raw material in the production of many important chemicals.


==========================================================================
Now, a research team led by Kazuhiko Maeda at Tokyo Tech has developed
a new photocatalyst consisting of nanoscale metal oxide sheets and a
ruthenium dye molecule, which works according to a mechanism similar to dye-sensitized solar cells. While metal oxides that are photocatalytically active for overall water splitting into H2 and O2 have wide band gaps, dye-sensitized oxides can utilize visible light, the main component of sunlight. The new photocatalyst is capable of generating H2 from water
with a turnover frequency of 1960 per hour and an external quantum yield
of 2.4%.

These results are the highest recorded for dye-sensitized photocatalysts
under visible light, bringing Maeda's team a step closer to the goal of artificial photosynthesis -- replicating the natural process of using
water and sunlight to sustainably produce energy.

The new material, reported in Journal of the American Chemical Society,
is constructed from high-surface-area calcium niobate nanosheets
(HCa2Nb3O10) intercalated with platinum (Pt) nanoclusters as H2-evolving
sites. However, the platinum-modified nanosheets do not work alone, as
they do not absorb sunlight efficiently. So a visible light-absorbing
ruthenium dye molecule is combined with the nanosheet, enabling
solar-driven H2 evolution.

What makes the material efficient is the use of nanosheets, which
can be obtained by chemical exfoliation of lamellar HCa2Nb3O10. The high-surface-area and structural flexibility of the nanosheets maximize dye-loadings and density of H2 evolution sites, which in turn improve
H2 evolution efficiency. Also, to optimise performance, Maeda's team
modified the nanosheets with amorphous alumina, which plays an important
role in improving electron transfer efficiency. "Unprecedentedly, the
alumina modification for nanosheets promotes dye-regeneration during the reaction, without hindering electron injection from the excited-state dye
to the nanosheet NOT -- the primary step of dye- sensitized H2 evolution," Maeda says.

"Until just recently, it was considered very difficult to achieve
H2 evolution via overall water splitting under visible light using a dye-sensitized photocatalyst with high efficiency," explains Maeda. "Our
new result clearly demonstrates that this is indeed possible, using
a carefully designed molecule- nanomaterial hybrid." More research
still needs to be done, as it will be necessary to further optimize
the design of the hybrid photocatalyst to improve the efficiency and
long-term durability. Photocatalytic water splitting may be a crucial
means of meeting society's energy demands without further harming the environment, and studies like this one are essential stepping stones to reaching our goal of a greener future.


========================================================================== Story Source: Materials provided by Tokyo_Institute_of_Technology. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Takayoshi Oshima, Shunta Nishioka, Yuka Kikuchi, Shota Hirai,
Kei-ichi
Yanagisawa, Miharu Eguchi, Yugo Miseki, Toshiyuki Yokoi, Tatsuto
Yui, Koji Kimoto, Kazuhiro Sayama, Osamu Ishitani, Thomas
E. Mallouk, Kazuhiko Maeda. An Artificial Z-Scheme Constructed
from Dye-Sensitized Metal Oxide Nanosheets for Visible Light-Driven
Overall Water Splitting. Journal of the American Chemical Society,
2020; 142 (18): 8412 DOI: 10.1021/ jacs.0c02053 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200608132540.htm

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