Electrocatalytic Properties of Mixed-Oxide-Containing Composite-Supported Platinum for Polymer Electrolyte Membrane (PEM) Fuel Cells

Abstract

TiO2-based mixed oxide–carbon composite supports have been suggested to provide enhanced stability for platinum (Pt) electrocatalysts in polymer electrolyte membrane (PEM) fuel cells. The addition of molybdenum (Mo) to the mixed oxide is known to increase the CO tolerance of the electrocatalyst. In this work Pt catalysts, supported on Ti1−xMoxO2–C composites with a 25/75 oxide/carbon mass ratio and prepared from different carbon materials (C: Vulcan XC-72, unmodified and functionalized Black Pearls 2000), were compared in the hydrogen oxidation reaction (HOR) and in the oxygen reduction reaction (ORR) with a commercial Pt/C reference catalyst in order to assess the influence of the support on the electrocatalytic behavior. Our aim was to perform electrochemical studies in preparation for fuel cell tests. The ORR kinetic parameters from the Koutecky–Levich plot suggested a four-electron transfer per oxygen molecule, resulting in H2O. The similarity between the Tafel slopes suggested the same reaction mechanism for electrocatalysts supported by these composites. The HOR activity of the composite-supported electrocatalysts was independent of the type of carbonaceous material. A noticeable difference in the stability of the catalysts appeared only after 5000 polarization cycles; the Black Pearl-containing sample showed the highest stability.

Composites of Titanium–Molybdenum Mixed Oxides and Non-Traditional Carbon Materials: Innovative Supports for Platinum Electrocatalysts for Polymer Electrolyte Membrane Fuel Cells

“…As demonstrated in Figure 10 , ORR current density ( j ) in the mixed kinetic–diffusion controlled region was greater on the reference Pt/C compared to the Pt/Ti (1−x) Mo x O 2 –C electrocatalysts. A similar behavior for composite-supported catalysts was observed in our recent study [ 46 ]. As shown in Figure 10 , for all fresh catalysts, comparable onset potentials for the ORR (~955 ± 10 mV) can be seen; this value indicates high activity in this reaction.…”

“…It may be noted that the reduced Mo content of this composite was also relatively high, pointing towards a possible correlation between the isovalent nature of the Mo incorporation and the crystallite size of the oxide. However, the elemental maps of Ti, Mo, and O obtained on TiMoGNP (Figure 4) were completely congruent, indicating that Mo was incorporated into the crystal lattice of the TiO 2 or at least tightly bound to the mixed oxide surface, as we found in the case of the other carbonaceous starting materials [46].…”

“…However, the elemental maps of Ti, Mo, and O obtained on TiMoGNP ( Figure 4 ) were completely congruent, indicating that Mo was incorporated into the crystal lattice of the TiO 2 or at least tightly bound to the mixed oxide surface, as we found in the case of the other carbonaceous starting materials [ 46 ].…”

Nitrogen doped carbonaceous materials as platinum free cathode electrocatalysts for oxygen reduction reaction (ORR)

“…The onset potential in acidic media (E on-ac ) for all Pt-free carbon-based catalysts was ≤ 0.5 V (see Table 4; Fig. 6A), which was much lower than that of the commercial Pt/C catalyst (0.96 V [80]). This fact indicates that N-doped carbon-derived materials have limited ORR activity in acidic environments.…”

“…S7 demonstrate the anticipated rise in current densities at higher rotational speeds, which corresponds to a quicker diffusion of oxygen onto the catalyst surface. The current density at low potentials clearly depends on the rotation speed, proving that the oxygen reduction is diffusion-limited [80]. For each catalyst, the onset potential-the potential at which the reduction begins-was calculated.…”