Enhancing the photoelectrocatalytic performance of metal-free graphdiyne-based catalyst

Abstract

As a new member of the carbon family, graphdiyne is an intrinsic semiconductor featuring a natural bandgap, which endues it potential for direct application in photoelectric devices. However, without cooperating with other active materials, conventional hexacetylene-benzene graphdiyne (HEB-GDY) shows poor performances in photocatalysis and photoelectric devices due to its non-ideal visible light absorption, low separation efficiency of the photogenerated carriers and insufficient sites for hydrogen production. Herein, we report a molecular engineering strategy for the regulation of GDY-based carbon materials, by incorporating a strong pyrene absorption group into the matrix of graphdiyne, to obtain pyrenyl graphdiyne (Pyr-GDY) nanofibers through a modified Glaser-Hay coupling reaction of 1,3,6,8-tetraethynylpyrene (TEP) monomers. For comparison, phenyl graphdiyne (Phe-GDY) nanosheets were also constructed using 1,3,4,6-tetraethynylbenzene (TEB) as a monomer. Compared with Phe-GDY, Pyr-GDY exhibits a wider visible light absorption band, promoted efficiency of the charge separation/transport and more sufficient active sites for water reduction. As a result, Pyr-GDY alone displays superior photoelectrocatalytic performance for water splitting, giving a cathode photocurrent density of ~138 μA cm−2 at a potential of −0.1 Vversus normal hydrogen electrode (NHE) in neutral aqueous solution, which is almost ten and twelve times as high as those of Phe-GDY (14 μA cm−2) and HEB-GDY (12 μA cm−2), respectively. Such a performance is also superior to those of most reported carbon-based metal-free photocathode. The results of theoretical calculations reveal that the carbon atoms in the acetylene bonds are the active sites for proton reduction. This work offers a new strategy for the construction of graphdiyne-based metal-free photo-electrocatalysts with enhanced photoelectrocatalytic performance.