Room Temperature Ion Beam Synthesis of Ultra‐Fine Molybdenum Carbide Nanoparticles: Toward a Scalable Fabrication Route for Earth‐Abundant Electrodes

Abstract

Molybdenum carbides are promising low‐cost electrocatalysts for electrolyzers, fuel cells, and batteries. However, synthesis of ultrafine, phase‐pure carbide nanoparticles (diameter < 5 nm) with large surface areas remains challenging due to uncontrollable agglomeration that occurs during traditional high temperature syntheses. This work presents a scalable, physical approach to synthesize molybdenum carbide nanoparticles at room temperature by ion implantation. By tuning the implantation conditions, various molybdenum carbide phases, stoichiometries, and nanoparticle sizes can be accessed. For instance, molybdenum ion implantation into glassy carbon at 30 keV energy and to a fluence of 9 × 1016 at cm−2 yields a surface η‐Mo3C2 with a particle diameter of (10 ± 1) nm. Molybdenum implantation into glassy carbon at 60 keV to a fluence of 6 × 1016 at cm−2 yields a buried layer of ultrafine γ’‐MoC/η‐MoC nanoparticles. Carbon ion implantation at 20 keV into a molybdenum thin film produces a 40 nm thick layer primarily composed of β‐Mo2C. The formation of nanoparticles in each molybdenum carbide phase is explained based on the Mo‐C phase diagram and Monte‐Carlo simulations of ion‐solid interactions invoking the thermal spike model. The approaches presented are widely applicable for synthesis of other transition metal carbide nanoparticles as well.

Grain Boundary-Rich Tungsten Carbide Nanoparticle Films Exhibit High Intrinsic Activity Toward Hydrogen Evolution

“…The measurement of the composition and phase of the implanted samples by RBS, XPS, GIXRD, and STEM provides important mechanistic insights into tungsten carbide formation by ion implantation. In our previous work, we showed that molybdenum carbide nanoparticles of different phases and sizes can be accessed by ion implantation . We elucidated the role played by collision cascades and thermal spikes in determining the nanoparticle phase and size.…”

“…Traditional TMC syntheses require a transition metal, carbon-based gaseous precursors, and high temperatures (>900 K) to achieve carburization. , High temperatures and long synthesis times cause agglomeration of initially formed nanoparticles and coking, ultimately lowering the surface area and catalytic performance of the synthesized carbide materials . Other pyrolysis-based syntheses use expensive or toxic metal complexes such as W­(CO) 6 and Cp 2 W 2 (CO) 4 (DMAD) with long carburization periods (>12h). , Alternative methods using a microwave furnace and ion implantation have been shown to avoid particle agglomeration while maintaining phase control and industrial scalability, ultimately leading to highly active nanostructured transition metal carbides. , The ultrafast cooling periods (>10 4 K s –1 ) also allow metastable phase formation.…”

High Turnover Frequency for the Hydrogen Evolution Reaction on Molybdenum Carbide Thin Films Synthesized by Ion Implantation

“…The ensuing orbital hybridization between the 1s orbital of the H atom and the 4d z 2 orbital of the Mo atom forms a weaker σ bond, thus aligning Δ G H* with the Sabatier principle . This highly active carbide surface is facilitated by the unique synthesis conditions that are realized through ion implantation …”

“…30 This highly active carbide surface is facilitated by the unique synthesis conditions that are realized through ion implantation. 19 To understand the underlying mechanism of HER on the MC catalysts, Tafel plots were created from the polarization curves.…”

“…Ion implantation offers a promising and scalable pathway for synthesizing transition metal (TM) carbide surfaces and ultrafine nanoparticles at ambient temperature. − In this work, thin films containing polycrystalline β-Mo 2 C (dominant) and γ′-MoC nanoparticles were successfully synthesized by carbon implantation into a molybdenum thin film (20 kV, 2 × 10 17 atoms cm –2 ). The implantation depth and carbon surface concentration were systematically varied by controlling the energy and implantation fluence .…”