Highly Selective Pt/TiO_x Catalysts for the Hydrogen Oxidation Reaction

Abstract

Reducing the cathode degradation in proton exchange membrane fuel cells during start-up and shut-down events (where the anode is filled with H 2 and air) is crucial for its widespread automotive implementation. The use of selective catalysts for the hydrogen oxidation reaction (HOR) that sparingly reduce oxygen on the anode could significantly reduce the carbon corrosion on the cathode. Herein, we report a novel system of carbon supported Pt/TiO x catalysts that combines the unique properties of a strong metal−support interaction (SMSI) with the known advantages of a carbon support. Highresolution transmission electron microscopy of the selective catalyst shows the encapsulation of the Pt nanoparticles (NPs) by a TiO x layer resulting from the SMSI. Rotating disk electrode experiments confirmed that Pt oxidation and oxygen reduction are hindered due to the TiO x layer. Furthermore, a high HOR activity that is retained even at high potentials proved the superior HOR selectivity of the catalyst.

Stable, Active, and Methanol-Tolerant PGM-Free Surfaces in an Acidic Medium: Electron Tunneling at Play in Pt/FeNC Hybrid Catalysts for Direct Methanol Fuel Cell Cathodes

“…We note that the overall structural and electrochemical characterization results of the present study bear a strong analogy with a recent report from Gasteiger's group on a powder catalyst consisting of Pt nanoparticles deposited on TiO x , themselves supported on carbon black and finally subjected to a thermal treatment at 400°C in 5% H 2 /Ar (labelled Pt/TiO x /C 400°C, H2 in Ref. 68 ). The ORR activity normalized by the Pt mass was 50 times lower for Pt/TiO x /C 400°C, H2 compared to a reference Pt/C material with same Pt particle size.…”

“…While the authors reported much lower ORR activity for Pt/TiO x /C than for Pt/C, comparable activities were observed for the hydrogen oxidation reaction (HOR) in acidic and alkaline medium. 68 This behavior is, again, strongly analogous to that of Pt@FeO x core-shell particles, with high HOR activity in acidic medium (Figure 4 in Ref. 69 46 for all RDE measurements, consisting of 20 CVs between 0.05 and 1.1 V vs. RHE.…”

“…Fe 1.0 d and Pt 2.0 Fe 1.0 d, respectively). The authors in Ref 68. proposed that the strongly suppressed ORR activity but retained HOR activity for their Pt@TiO x particles relative to Pt particles may be explained by the fact that only the Pt core is electrochemically active and O 2 (or H 2 ) must diffuse through the TiO x overlayer in order to react.…”

Correlation between the TiO2 encapsulation layer on Pt and its electrochemical behavior

“…Although the existence of thin encapsulation layers on metal catalysts was recently proved by electron microscopy, [10][11][12][13][14] structure-property relationships were rarely investigated, especially in the case of electrochemical properties. [15][16][17] The lack of systematic studies is related to both, challenges in the synthesis and characterization of comparable model materials with and without encapsulation layer. Moreover, the high temperature and reducing atmosphere employed to obtain SMSI materials often cause sintering and perfect encapsulation of the catalyst instead of thin and/or inhomogeneous encapsulation layers.…”

“…[22,23] Furthermore, a very recent study reported that encapsulated Pt on TiO 2 can act as a selective catalyst for hydrogen oxidation reaction. [16] On the one hand, the selective H + permeability through the TiO 2 encapsulation layer prevents the oxygen reduction reaction on Pt. On the other hand, selectivity can also be driven by exploiting the conductivity dependence of the material.…”