Bottom-up synthesis of semiconductive carbonaceous nanosheets on hematite photoanode for photoelectrochemical water splitting

Coupling two-dimention carbon materials like graphene on photodelectrode can achieve high-efficiency photoelectrochemical cells. Bottom-up synthesis of carbon-based two-dimensional materials in green media from simple molecules is very attractive but remains a challenge. Carbohydrate is an ideal precursor for the synthesis but previous report requires pyrolysis at high temperature (> 700 ℃). Herein, starting with glucose, we develop a low temperature (210 ℃) synthesis of carbonaceous nanosheets in aqueous solution of glucose. With the aid of ethylenediamine and Fe³⁺/Fe²⁺/Co²⁺/Ni²⁺ ions, the nanosheets can grow on hematite nanorod array with very close contact. Importantly, a metallic region is formed at the interface due to atom distribution distortion, which can promote the charge transfer. The activity can be greatly enhanced by about 500% due to fast charge transfer. This is much better than that prepared by physically or chemically mixing graphene and hematite (< 200%). The enhancement is mainly due to the deformation area between the nanosheets and the hematite. The effective hole diffusion length increases from 2 to 8 nm and lifetime of charge carrier also increases, as confirmed by ultrafast transient absorption spectra. This method provides more opportunity for simple, mild and cost-effective fabrication of carbon-based two-dimensional by bottom-up method.