Electrocatalytic performance of different Mo-phases obtained during the preparation of innovative Pt-MoC catalysts for DMFC anode

Electrochemical studies of new binary Pt-MoC electrocatalysts prepared by carbothermal-reduction method have been developed. The XRD and XPS characterization allows to determine the structure of core–shell Mocarb-particles, with a reduced-Mo core (Mo2C, MoO2 and/or Mo0) and a MoO3-shell (2–3 nm). Upon adding Pt, Pt interacts with MoO3-shell. The oxidation of: (i), CO by cyclic voltamperometry (CV) followed by in situ differential electrochemical mass spectrometry (DEMS); and, (ii), methanol by CV and chronoamperometric techniques were carried out at room temperature. The results show an improvement in the Pt-tolerance to CO-presence with the presence of reduced Mocarb phases (decreasing the potential in 65 mV RHE), without significant difference between the binary catalysts. An additional Mo-redox pre-peak is observed at 0.4RHE V. This process is related to Mo4+-to-Mo6+ oxidation developed on the MoO3-shell of Mocarb-particles, which is catalysed by Pt. This Mo-oxidation/reduction couple is affected (shifts towards more negative potentials) by the CO adsorption on Pt-centres. DEMS results show that CO-oxidation occurs in the potential region of this Mo-oxidation. The binary Pt-Mocarb catalysts show similar behaviour for methanol oxidation as those for CO-stripping ones. Nevertheless, the chronoamperometric curves display a catalytic performance improvement (highest activity and stability) using Pt-MoC/CBv catalyst regarding the other binary catalysts. This best behaviour with Mo2C-phase enhances to increases the temperature up to 60 °C (typical value for low-temperature FCs in-operation). MeOH electrooxidation results of the three binary Pt-Mocarb/C catalysts and the Pt-reference material at room temperature (20 °C). (a) Cyclic voltamperometric curves. (b) Chronoamperometric profiles at 650 mV. [Display omitted] ► Binary Pt-Mocarburized catalysts improve Pt tolerance to CO: shift of 65 mVRHE to negative potential. ► The Mo-oxidation pre-peak involves Mo4+ to Mo6+ and the CO2-production observed by DEMS. ► DEMS results show Mo-oxidation pre-peak (related to Mo4+-to-Mo6+), which involves both Mo oxidation and CO2 production. ► Best performance (activity and stability) for MeOH oxidation was observed with binary Pt-Mo2C phase. ► Performance of Pt-MoC catalyst enhances during the MeOH oxidation at 60 °C.