Photocatalytic nitrogen fixation driven by solar energy is recognized as an environmental-friendly candidate for sustainable ammonia production. In spite of the recent advances, development of efficient photocatalysts with high N₂ fixation efficiency is still challenging but highly desirable. 

Researchers from the Shenzhen Institutes of Advanced Technology (SIAT) of the Chinese Academy of Sciences have developed a new black phosphorous (BP) based nano material which has incredible activity on photocatalytic nitrogen fixation.  

Previous studies from SIAT and other institutes indicated the good photocatalytic activites of BP based materials on hydrogen evolution, molecular oxygen activation and organic synthesis. However, the application of BP based materials on photocatalytic nitrogen fixation was rarely reported.  

In the present study, the scientists found that a new BP nanostructure with a flake-like shape and edge-rich rugged surface (eBP NFs) could be easily synthesized by a chemical etching exfoliation method.  

The characterizations revealed that eBP NFs was constructed by many individual tiny crystal grains of BP. The random stacking of the BP crystal grains generated the uneven thickness of eBP NFs as well as its rugged surface and explained the many grain boundaries at the edges and corners on the surface of eBP NFs. 

In this unique "polycrystalline"-like structure, the eBP NFs were fully covered by these edges of the crystal domains. This new BP nanostructure with edge-rich morphology was quite different from those of other common exfoliated BP nanoflakes that exhibited monocrystalline-like structure with a smooth surface and even thinness. 

The eBP NFs could catalyzed N₂ fixation at a rate as high as 2.37 mmol·h^-1·g^-1 under visible-light irradiation, which was comparable to the most efficient photocatalytic systems.  

Moreover, after irradiation for 8h, the ammine production rate did not decrease, confirmed the excellent catalytic stability of eBP NFs. 

The researchers also investigated the corresponding charge transfer dynamic process. The photocurrent of eBP NFs in N₂ was much larger than that in Argon (Ar). In the ultrafast transient absorption test, the average lifetime of eBP NFs in Ar was 6.62 ps, which was much longer than eBP NFs in N₂.  

These results clearly revealed the electron transfer from eBP NFs to adsorbed N₂ and the process was crucial to photocatalytic ammonium production. 

This study was published in the Journal of Physical Chemistry Letters.

Image of eBP NFs by Transmission Electron Microscope. (Image by SIAT)

Media Contact: 
ZHANG Xiaomin 
Email: xm.zhang@siat.ac.cn