Magnetic field assisted synthesis of Co2P hollow nanoparticles with controllable shell thickness for hydrogen evolution reaction

A novel method to prepare hollow Co2P nanoparticles (NPs) with controllable shell thicknesses is proposed. In this method, high magnetic field was employed to tune the shell thickness. The mechanism of shell-tuning by magnetic field was discussed. The formation of Co2P hollow NPs involves two main processes: the dissolution of CoO on the surface of Co NPs, and the Kirkendall effect process. Magnetic field can reduce the particle size and tune the shell thickness by accelerating the dissolution process and slowing down the Kirkendall effect process. The effects of shell thickness on the stability of the hollow NPs were investigated. During the hydrogen evolution reaction (HER) process in alkaline medium, the Co2P hollow NPs with shell thicker than 3.90 nm have good structure stability and perform a good catalytic performance. Nevertheless, when shell thickness is reduced to 3.32 nm, there is a great change in the hollow structure. It will fracture into small NPs and lead to significant degradation of activity. This work develops a reasonable method to synthesize small-sized transition metal phosphides hollow particles with adjustable shell thickness, and provides a reference for balancing the activity and stability of hollow particles, which is significant to prepare hollow nanoparticles with good catalytic performance. (C) 2019 Elsevier Ltd. All rights reserved.