Abstract
With global warming and the depletion of fossil resources, our fossil-fuel-dependent society is expected to shift to one that instead uses hydrogen (H2) as clean and renewable energy. Water-splitting photocatalysts can produce H2 from water using sunlight, which are almost infinite on the earth. However, further improvements are indispensable to enable their practical application. To improve the efficiency of the photocatalytic water-splitting reaction, in addition to improving the semiconductor photocatalyst, it is extremely effective to improve the cocatalysts (loaded metal nanoclusters, NCs) that enable the reaction to proceed on the photocatalysts. We have thus attempted to strictly control metal NCs on photocatalysts by introducing the precise-control techniques of metal NCs established in the metal NC field into research on water-splitting photocatalysts. Specifically, the cocatalysts on the photocatalysts were controlled by adsorbing atomically precise metal NCs on the photocatalysts and then removing the protective ligands by calcination. This work has led to several findings on the electronic/geometrical structures of the loaded metal NCs, the correlation between the types of loaded metal NCs and the water-splitting activity, and the methods for producing high water-splitting activity. We expect that the obtained knowledge will lead to clear design guidelines for the creation of practical water-splitting photocatalysts and thereby contribute to the construction of a hydrogen-energy society.
Highlights
For Au24Pd/BaLa4Ti4O15, the EXAFS results indicate that Pd is located on the surface of the loaded metal NCs and is bound to S (Fig. 16B).[233]
We studied the effect of heteroatom substitutions on the water-splitting activity using Au25/BaLa4Ti4O15, Au24Pd/BaLa4Ti4O15, and Au24Pt/BaLa4Ti4O15.233 In this experiment, the measurements were performed under the condition that only Ar was flowed
Loading of atomically precise metal NCs (i) When Aun(SG)m NCs are used as precursors, it is possible to load Aun NCs with a controlled number of constituent atoms on BaLa4Ti4O15 and SrTiO3. (ii) To load Aun NCs while maintaining the number of constituent atoms of the precursor NCs, it is indispensable to use Aun(SG)m NCs with high stability in solution as the precursor. (iii) If hydrophobic metal NCs are used as precursors, replacing some of the ligands of the NCs with hydrophilic ligands via ligand exchange is an effective means of loading atomically precise metal NCs on the photocatalyst. (iv) An increase in the amount of loaded NCs induces an increase in the particle size of the loaded NCs
Summary
When this system is used, the energy medium (H2) can be circulated, preventing the problem of energy depletion. Modern chemistry is expected to improve the functionality of the photocatalysts, electrolysis cells, and fuel cells
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