Transition-metal-incorporated molybdenum phosphide nanocatalysts synthesized through post-synthetic transformation for the hydrogen evolution reaction

Abstract

Post-synthetic chemical transformation is a recently emerging nanomaterial manufacturing method for obtaining materials with precisely modulated properties. Through post-synthetic transformation methods, foreign elements are exchanged or incorporated into presynthesized nanoparticles (NPs). However, metal phosphides have not been primarily used as starting materials because of their strong bonding characteristics. In this study, we synthesized bimetallic transition metal phosphide (TMP) NPs through a cation addition reaction using amorphous molybdenum phosphide (MoP) as the starting material, which is a promising catalyst for the hydrogen evolution reaction (HER). The additional metal elements, namely Co and Ni, were successfully incorporated into the parent MoP NPs, which led to only marginal changes in size or shape, even after 12 hours of reaction. Because morphological factors strongly influence catalytic activity, nanocatalysts with identical morphologies provide a direct comparison among NPs with various chemical properties. The Co- and Ni-incorporated MoP NPs exhibited significantly enhanced catalytic activities for the HER, with similar electrochemically active surface areas. In particular, Co-1.5 h-MoP showed the highest HER activity (167 mV at −10 mA cm−2) and durability among the samples in 0.5 M H2SO4. Such an improvement in catalytic activity through the cation addition reaction may be ascribed to the difference in the electronegativities of the original and newly added metal cations, as confirmed by X-ray photoelectron spectroscopy (XPS), resulting in abundant metal-P bonding and oxidation resistivity. This study provides a new advanced platform for directly analyzing the inherent characteristics of nanomaterials for diverse applications, especially electrocatalysis.