Atomic-Scale Mechanism on Nucleation and Growth of Mo₂C Nanoparticles Revealed by in Situ Transmission Electron Microscopy

Abstract

With a similar electronic structure as that of platinum, molybdenum carbide (MoC) holds significant potential as a high performance catalyst across many chemical reactions. Empirically, the precise control of particle size, shape, and surface nature during synthesis largely determines the catalytic performance of nanoparticles, giving rise to the need of clarifying the underlying growth characteristics in the nucleation and growth of MoC. However, the high-temperature annealing involved during the growth of carbides makes it difficult to directly observe and understand the nucleation and growth processes. Here, we report on the use of advanced in situ transmission electron microscopy with atomic resolution to reveal a three-stage mechanism during the growth of MoC nanoparticles over a wide temperature range: initial nucleation via a mechanism consistent with spinodal decomposition, subsequent particle coalescence and monomer attachment, and final surface faceting to well-defined particles with minimum surface energy. These microscopic observations made under a heating atmosphere offer new perspectives toward the design of carbide-based catalysts, as well as the tuning of their catalytic performances.

Atomic-Scale in Situ Observations of Crystallization and Restructuring Processes in Two-Dimensional MoS2 Films

“…Previous literature has found both parallel and perpendicular layer growth in thicker MoS 2 films depending on exact synthesis conditions. 37,76 Importantly we note that the observation of our two-segment morphology is in excellent agreement with previous ex situ studies on annealed PVD MoS 2 films, 30,77 that is, films that were deposited and processed under similar deposition condition as ours, in which the same two-segment morphology was reported.…”

Molybdenum Carbide‐Based Electrocatalysts for Hydrogen Evolution Reaction

“…[51,52] According to the latesta tomic-scale observation of nucleation and growth mechanism of Mo 2 C, at hree-stage high temperature is necessary to obtain nanosized Mo 2 Cp articles. [53] For raw materials, ammonium molybdate is an essential feedstock to providea nM os ource while carbon sources vary from carbonaceous gases,a mine, to carbon nanomaterials or even biomass materials. [54,55] The synthesis of Mo x Cm aterials normally involves two steps:t he pre-cursor preparation followed by the consequent formation of the final electrocatalysts.…”

“…Therefore, the appropriate temperature plays a crucial role in forming the designed crystalline structure of Mo x C during the carburization process . According to the latest atomic‐scale observation of nucleation and growth mechanism of Mo 2 C, a three‐stage high temperature is necessary to obtain nanosized Mo 2 C particles . For raw materials, ammonium molybdate is an essential feedstock to provide an Mo source while carbon sources vary from carbonaceous gases, amine, to carbon nanomaterials or even biomass materials .…”

Study on the reduction of commercial MoO3 with carbon black to prepare MoO2 and Mo2C nanoparticles

“…Meanwhile, the materials obtained from sintering nanoparticles at the low temperature had much smaller grain size and more superior mechanical behavior than the materials obtained from micrometer‐sized . Therefore, the unique chemical and physical properties of molybdenum carbide nanoparticles have enhanced its popularity in the fields of materials and chemical science …”