Modulation of Schottky Barrier Height and Electronic Structure in Transition-Metal@Nitrogen-Doped-Carbon Core–Shell Cocatalysts Loaded with MnxCd1–xS Nanorods for Enhanced Photocatalytic Hydrogen Evolution

Abstract

Transition-metal (TM)/carbon nanocomposites have emerged as a type of low-cost high-efficiency photocatalysis cocatalyst for their high photoactivity comparable to typical noble metals such as Pt. However, the underlying cocatalytic mechanism in this combined nanoscaled system has not been understood sufficiently. In this work, a core–shell nanoparticle (NP) cocatalyst has been designed and synthesized by using three kinds of large-work-function TMs (Co, Ni, and Cu) and nitrogen-doped carbon (NC) to construct a core–shell structure (TM@NC), and its photocatalytic hydrogen evolution performance has been studied with Mn_xCd_1–xS nanorods (NRs). It has been found that the TMs endow the TM@NC NPs with large work functions, which act as efficient electron traps. Significantly, the Schottky barrier height at the interface of TM@NC and Mn_xCd_1–xS can be modulated by the embedded TMs, and therefore the transfer efficiency of the photoelectrons can be adjusted. Thus, the relationships between photoactivity and the Schottky barrier height can be obtained. The NC layer in the TM@NC structure not only protects the embedded TMs from overoxidation but also provides abundant catalytic sites for hydrogen evolution reaction. Meanwhile, the electronic structure of the NC layer can be refined by the embedded TMs as well, favoring the release of hydrogen from its surface. As a result, all the TM@NC NP cocatalysts exhibit comparable cocatalytic activity to optimized Pt NPs, and the Ni@NC sample obviously outperforms Pt. This work highlights the effect of the Schottky barrier in adjusting the photocatalytic activity and provides deep insight into the photoactivity engineering of photocatalysts by incorporating TMs with semiconductor materials.