A research team led by Kazuhiko Maeda at the Tokyo Institute of Technology has developed a new photocatalyst. They 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.

In line with the depletion of fossil fuels and the suggested problems 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.

Dye-sensitized H2 evolution using a wide-gap metal oxide. Image Credit: Tokyo Institute of Technology. Click image for the largest view.

The new photocatalyst consists 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 fuel.

The new material, reported in a paper published in the 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 optimize 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 said.

“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,” explained 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.

Its great to see a press release that points out that the research is yielding dihydrogen gas (H2) and not hydrogen gas (H). There is getting to be quite a number of processes and catalysts not rich in super expensive platinum. If the storage issue was worked out hydrogen should have quite a future. That storage matter needs the best, the brightest, most innovative and intuitive minds working at it. Or find the best way lock the hydrogen to some carbon and simply call it good.


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