Jun 08, 2020 | |
Integrating nanomaterial with light-absorbing molecule powers hydrogen production from water and sunlight(Nanowerk News) Scientists at Tokyo Institute of Technology (Tokyo Tech) 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. |
|
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 (Figure 1). The new photocatalyst is capable of generating H2 from water with a turnover frequency of 1,960 per hour and an external quantum yield of 2.4 %. | |
Figure 1. Dye-sensitized H2 evolution using a wide-gap metal oxide. (Image: Tokyo Tech) | |
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 ("An Artificial Z-scheme Constructed from Dye-Sensitized Metal Oxide Nanosheets for Visible Light-Driven Overall Water Splitting"), 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 (Figure 2). | |
Figure. 2 An illustration of visible-light-driven H2 evolution on ruthenium-dye/HCa2Nb3O10 nanosheet. (©American Chemical Society) | |
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 — 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. |
Source: Tokyo Institute of Technology | |
Subscribe to a free copy of one of our daily Nanowerk Newsletter Email Digests with a compilation of all of the day's news. |