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

摘要

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 Mo_(carb)-particles, with a reduced-Mo core (Mo_2C, MoO_2 and/or Mo°) and a MoO_3-shell (2-3 nm). Upon adding Pt, Pt interacts with MoO_3-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 chro-noamperometric techniques were carried out at room temperature. The results show an improvement in the Pt-tolerance to CO-presence with the presence of reduced Mo_(carb) phases (decreasing the potential in 65 mV _(RHE)), without significant difference between the binary catalysts. An additional Mo-redox pre-peak is observed at 0.4_(rhe) V. This process is related to Mo~(4+)-to-Mo~(6+) oxidation developed on the MoO_3-shell of Mo_(carb),-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-Mo_(carb) 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 Mo_2C-phase enhances to increases the temperature up to 60℃ (typical value for low-temperature FCs in-operation).