Dai Dang

A core–shell Pd1Ru1Ni2@Pt/C catalyst with a ternary alloy core and Pt monolayer: enhanced activity and stability towards the oxygen reduction reaction by the addition of Ni

A core–shell structured catalyst, Pd1Ru1Ni2@Pt/C, with a ternary alloy as its core and a Pt monolayer shell was prepared using a two-stage strategy, in which Pd1Ru1Ni2 alloy nanoparticles were prepared by a chemical reduction method, and then the Pt monolayer shell was generated via an underpotential deposition method. It was found that the addition of Ni to the core played an important role in enhancing the catalysts oxygen reduction activity and stability. The optimal molar ratio of Pd : Ru : Ni was about 1 : 1 : 2; the catalyst with this optimal ratio had a half-wave potential approximately 65 mV higher than that of a PdRu@Pt/C catalyst, and its mass activity was up to 1.06 A mg−1 Pt, which was more than five times that of a commercial Pt/C catalyst. The catalysts structure and composition were characterized using X-ray powder diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectrometry. The core–shell structure of the catalyst was demonstrated by the EDS mapping results and supported by the XPS results. We also performed a stability test that confirmed the catalysts superior stability in comparison to that of commercial JM Pt/C (20 wt% Pt).

An ultra high performance multi-element doped mesoporous carbon catalyst derived from poly(4-vinylpyridine)

A high performance doped carbon catalyst with ordered mesoporous structures and a high surface area (1217 m2 g−1) was prepared through a nanocasting-pyrolysis procedure by using poly(4-vinylpyridine) and iron chloride as the precursors and SBA-15 as the template. The catalyst exhibited excellent oxygen reduction reaction (ORR) performance, and was far more active than a commercial Pt/C catalyst in alkaline media, with its half-wave potential (−0.083 V, vs. Ag/AgCl) 64 mV more positive and current density at −0.1 V (vs. Ag/AgCl, −3.651 mA cm−2) almost three times higher than those of a commercial Pt/C catalyst (−0.147 V, vs. Ag/AgCl, and −0.967 mA cm−2), respectively. To our knowledge, it is one of the best carbon-based ORR catalysts to date in an alkaline medium. In addition to the outstanding ORR performance, our catalyst also illustrated excellent stability, methanol tolerance, and high catalytic efficiency. It is found that the total N contents and the compositions of each N species in the catalysts strongly depend on the pyrolysis temperatures. Furthermore, we found that the SBA-15 templates not only give catalysts well-defined mesoporous structures, but also seem to help increase the total N content whilst the proportion of each N species in the catalysts is not changed obviously.

Tuning the Catalytic Activity of Ir@Pt Nanoparticles Through Controlling Ir Core Size on Cathode Performance for PEM Fuel Cell Application

Pulse electrochemically synthesis of a series of core-shell structured Ir@Pt/C catalysts in cathode catalysts layer are achieved to fabricate membrane electrode assemblies (MEA) with cathode ultra-low Pt loading. The single cell performance of the MEAs in a H2/air PEMFC greatly rely on the sizes of the Ir core nanoparticle, and the optimum activity occurs with Ir core size of 4.1 nm. The cathode MEA with core-shell structured catalysts with optimal Ir core size exhibited excellent performance in a H2/air single fuel cell, comparable to that of a commercial Pt/C MEA (Johnson Matthey 40% Pt), even though the Pt loading in Ir@Pt was only 40% that of the commercial Pt cathode (0.04 vs. 0.1 mg cm−2). The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy. Based on the characterization results, especially from XPS, we suggest that the effect of Ir core particle size on MEA performance may arise from the interactions between the Pt shell and the Ir core. The XPS results showed that the Ir@Pt/C-300 catalyst has the highest Pt0 fraction among the four tested samples. This work demonstrates the alternative to enhance the cathode performance in single cell of Pt-based core-shell structured catalysts by varying size of the core metal under the Pt shell.