Size-Dependent Catalytic Activity of Cobalt Phosphides

for Hydrogen Evolution Reaction

Xiaoke Li^1,2, Luhua Jiang^1,*, Jing Liu¹, Qingfeng Hua¹, Erdong Wang², Guangwen Xie¹

¹ College of Materials Science & Engineering, Qingdao University of Science and Technology, 53 Zhengzhou Road, Qingdao, Shandong 266042, China

² Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, Liaoning 116023, China

Abstract

Transition metal phosphides are a class of promising electrocatalysts for hydrogen evolution reaction (HER) to replace noble metals. In this work, we for the first time synthesize carbon supported CoP nanoparticles with the average particle sizes from 3.3 to 9.2 nm, via a solvothermal process followed by low-temperature topological phosphorization, and the size-dependent HER activity of the CoP is investigated by virtue of TEM, XRD, XPS and the electrochemical techniques. It is discovered that the 9.2nm-CoP particles possess high intrinsic HER catalytic activity as compared to the 3.3nm-CoP, although the smaller one displays a high overall catalytic activity due to the large surface area. Detailed studies manifest that the small CoP particles suffer from serious oxidation once exposing to air. In contrast, the relatively large CoP particles could remain most cobalt in the metallic state, which is beneficial for the desorption of H_ads, the rate determining step of the HER process over CoP surface. In addition, the low charge transfer resistance across the liquid/solid interfaces also contributes to the excellent HER activity of the relatively large CoP particles.

Keywords: Cobalt Phosphide; Particle Size Effect; Hydrogen Evolution; Electrocatalyst; Water Electrolysis.

Corresponding author: luhuajiang@qust.edu.cn