Surface Characterization and Platinum-like Electrocatalytic Activity of Nano-Scale Platinum Deposited on Transition Metal Carbide Nanotubes via Atomic Layer Deposition

Due to the similar electronic and geometric structures between transition metal carbides (TMC) and Platinum (Pt), Pt supported on TMC surfaces (a.k.a., Pt/TMC) has been the focus of significant research interest. This presentation focuses on a new class of electrocatalyst fabrication in which high purity β-molybdenum carbide (referred to as Mo₂C hereafter) was synthesized into hollow nanotubes and subsequently modified with nanoscale platinum particles (1-5 nm) deposited via rotary Atomic Layer Deposition (ALD) (referred to as Pt/Mo₂C).  X-Ray diffraction (XRD) measurements of Mo₂C and Pt/Mo₂C showed no molybdenum peaks and a very small amount of unreacted multi-wall carbon nanotubes (MWCNT) in the Mo₂C samples, indicating that Pt was primarily supported on Mo₂C nanotubes. Strong interaction between Pt nanoparticles and the Mo₂C nanotube support was observed in lattice spacing changes from high resolution transmission electron microscopy (HRTEM) images, in addition to Pt binding energies from x-ray photoelectron spectroscopy (XPS) results of Pt/Mo₂C.  Atomic adsorption spectroscopy (AAS) measurements of Pt mass in Pt/Mo₂C samples showed an average of 2.4% Pt loading in Pt/Mo₂C nanoparticles. The electochemically active surface area (ECSA) of the 2.4% Pt/Mo₂C was found to be 70% higher than commercial 20% Pt/C, indicating an increased number of electrochemically active sites, possibly resulting from the interaction between ALD-deposited Pt nanoparticles and Mo₂C nanotube support. 

Cyclic voltammograms of the 2.4% Pt/Mo₂C catalyst showed higher hydrogen oxidation reaction (HOR)  activity than commercial 20% Pt/C, while bare Mo₂C did not demonstrate any significant HOR activity. For the hydrogen evolution reaction (HER), the 2.4% Pt/Mo₂C showed similar activity to the 20% Pt/C, while bare Mo₂C nanotube showing noticeable, but not significant HER activity.  Another focus of this talk is to present the 2.4% Pt/Mo₂C catalyst performance in a PEMFC anode (HOR), which outperformed the commercial 20% Pt/C with up to a 403% increase in peak power density and 448% increase in current density. Consequently, the reported Pt/Mo₂C validates a new fabrication approach for practical nanoscale electrocatalysts where the supported catalyst is deposited via atomic layer deposition onto high purity transition metal carbide nanotubes. Ongoing work in our group focuses upon long-term stability, the corrosion mechanism, and ORR activity of the Pt/Mo₂C catalyst.  Furthermore, we are conducting systematic investigations on how the number of ALD cycles affects the size and distribution of Pt on Mo₂C nanotube and subsequent HER, ORR activity and PEMFC performance of resultant catalysts.