Mon‐Che Tsai

The sluggish kinetics of the oxygen reduction reaction (ORR), the instability of platinum on the carbon support, and carbon corrosion are still critical issues affecting the activity and long-term durability of polymer electrolyte membrane fuel cells. An ideal solution would be to modify the catalytic supports to enhance the durability and performance of supported catalysts. Here we have synthesized multiwalled carbon nanotube (MWCNT) supported ultrathin TiO2 films (MWCNT@UT-TiO2) using a simple modified sol–gel method. Our approach takes advantage of the strong metal support interactions (SMSIs) between the MWCNT@UT-TiO2 support and platinum nanoparticles, which results in a decrease of the d-band vacancy of platinum due to electron transfer from the support, thereby enhancing the performance of the supported catalysts. Our results revealed that Pt–MWCNT@UT-TiO2 has better catalytic activity and durability compared to Pt–MWCNT and Pt–C with equivalent Pt loadings.

Although bimetallic core@shell structured nanoparticles (NPs) are achieving prominence due to their multifunctionalities and exceptional catalytic, magnetic, thermal, and optical properties, the rationale underlying their design remains unclear. Here we report a kinetically controlled autocatalytic chemical process, adaptable for use as a general protocol for the fabrication of bimetallic core@shell structured NPs, in which a sacrificial Cu ultrathin layer is autocatalytically deposited on a dimensionally stable noble-metal core under kinetically controlled conditions, which is then displaced to form an active ultrathin metal-layered shell by redox-transmetalation. Unlike thermodynamically controlled under-potential deposition processes, this general strategy allows for the scaling-up of production of high-quality core-shell structured NPs, without the need for any additional reducing agents and/or electrochemical treatments, some examples being Pd@Pt, Pt@Pd, Ir@Pt, and Ir@Pd. Having immediate and obvious commercial potential, Pd@Pt NPs have been systematically characterized by in situ X-ray absorption, electrochemical-FTIR, transmission electron microscopy, and electrochemical techniques, both during synthesis and subsequently during testing in one particularly important catalytic reaction, namely, the oxygen reduction reaction, which is pivotal in fuel cell operation. It was found that the bimetallic Pd@Pt NPs exhibited a significantly enhanced electrocatalytic activity, with respect to this reaction, in comparison with their monometallic counterparts.

The nanosized effects of Pt catalysts in terms of surface coverage, electrochemical response, and reaction kinetics during the electro-catalytic methanol oxidation reaction (MOR) have been extensively investigated by the systematic electrochemical measurements, in situ electrochemical FTIR spectroscopy (EC-FTIRS) technique and Density Functional Theory (DFT) computational approaches. In contrast to bulk Pt, a relatively higher COads coverage on the nanosized Pt catalyst was observed at the end of forward sweep (+1.0 V/RHE) from the in situ EC-FTIR investigations. From the DFT calculations, it was demonstrated that the reaction barrier of COads + OHads → COOHads is higher on the edge site of a Pt55 cluster (55 Pt atoms) than that on the facet site of a slab Pt model. The IR observations resulted from the fact that the electro-catalytic MOR appears to be diffusion-controlled on the bulk Pt catalyst, whereas on the nanosized Pt catalyst, it was kinetic-controlled due to both the higher kinetic barrier of COads + OHads reaction and lower diffusion resistance. The surface coverage models of the electro-catalytic MOR on the bulk and the nanosized Pt catalysts have been reasonably proposed via the combined understanding of the in situ EC-FTIR and DFT computational results. The proposed models can reasonably be further elaborated and explained by the systematic electrochemical measurements.