Nov 14, 2019
Prof. LI Can's team and Prof. LI Rengui's team from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), together with Prof. YAN Jianchang’s team from the Institute of Semiconductors of CAS, achieved new advances in spatial charge separation for artificial photosynthesis.
They revealed that surface polarity-induced surface electric field can effectively promote spatial separation of photogenerated charges and greatly enhance the activity of photocatalytic overall water splitting (OWS).
The core issue of artificial photosynthesis for solar fuel is the photogenerated charge separation. It remains challenging to develop effective strategies to promote the separation and transportation of photogenerated charges.
Although the crystal morphology and crystal facets can be used to modulate photogenerated charge seperation, how to rationally design and tune the intrinsic polarity of semiconductor materials and how the surface polarity influence the charge separation remain unclear.
In this study, the scientists chose a typical semiconductor gallium nitride (GaN) as a mode. GaN nanorod arrays with definite surface polarity were fabricated and exposed with top polar surface and side nonpolar surface, obvious spatial charge separation could take place between the two surfaces.
The photogenerated electrons were accumulated on the nonpolar surface, while the holes on the polar surface. It was supposed to originate from different surface band bending induced by the different surface dipole moment between the polar and nonpolar surfaces, which drives the photogenerated electrons and holes to migrate selectively, promoting the charge separation effectively.
Furthermore, the photoelectrochemical tests and photocatalytic reactions revealed that the efficiency of charge separation between the polar and nonpolar surface could exceed 80%, about ten times higher than the film counterpart and the highest value in this kind of material.
Based on this unique charge separation, reduction cocatalyst and oxidation cocatalyst can be deposited on the nonpolar and polar surface respectively. These can enhance the quantum efficiency of photocatalytic overall water splitting from 0.9% to 6.9%.
This work proposes a novel strategy to promote charge separation and lays a theoretical foundation of the construction of highly efficient artificial photosynthesis systems. It also provides new insights to understand the intrinsic driving force for photogenerated charge separation.
The study was published in Angew. Chem. Int. Ed. It was supported by the "Transformational Technologies for Clean Energy and Demonstration", Strategic Priority Research Program of the Chinese Academy of Sciences, Key Research Program of Frontier Sciences of Chinese Academy of Sciences and National Science Foundation of China.
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