Ting Shu

Transition Metal Nitride Coated with Atomic Layers of Pt as a Low-Cost, Highly Stable Electrocatalyst for the Oxygen Reduction Reaction

The main challenges to the commercial viability of polymer electrolyte membrane fuel cells are (i) the high cost associated with using large amounts of Pt in fuel cell cathodes to compensate for the sluggish kinetics of the oxygen reduction reaction, (ii) catalyst degradation, and (iii) carbon-support corrosion. To address these obstacles, our group has focused on robust, carbon-free transition metal nitride materials with low Pt content that exhibit tunable physical and catalytic properties. Here, we report on the high performance of a novel catalyst with low Pt content, prepared by placing several layers of Pt atoms on nanoparticles of titanium nickel binary nitride. For the ORR, the catalyst exhibited a more than 400% and 200% increase in mass activity and specific activity, respectively, compared with the commercial Pt/C catalyst. It also showed excellent stability/durability, experiencing only a slight performance loss after 10,000 potential cycles, while TEM results showed its structure had remained intact. The catalysts outstanding performance may have resulted from the ultrahigh dispersion of Pt (several atomic layers coated on the nitride nanoparticles), and the excellent stability/durability may have been due to the good stability of nitride and synergetic effects between ultrathin Pt layer and the robust TiNiN support.

A hollow spherical doped carbon catalyst derived from zeolitic imidazolate framework nanocrystals impregnated/covered with iron phthalocyanines

A hollow spherical doped carbon catalyst with a large surface area and hierarchical porous structure is prepared by pyrolyzing zeolitic imidazolate framework nanocrystals (Z8Ncs) impregnated/covered with iron phthalocyanines (FePcs). It is found that the doping of FePcs into the Z8Nc precursor plays a crucial role in the structural evolution of the resulting hollow-core porous carbon as well as its high catalytic performance. Doped carbon catalysts derived from either Z8Ncs or FePcs exhibit poor activity towards oxygen reduction, whereas the catalyst derived from Z8Ncs impregnated/covered with FePcs exhibits extremely high performance in both acidic and alkaline media. In 0.1 M HClO4, its onset potential reaches up to 0.910 V, and its half-potential (0.790 V) is only 60 mV lower than that of the 20 wt% Pt/C catalyst (0.850 V). In 0.1 M KOH, its ORR activity even surpasses that of Pt/C. We suggest that the high performance of the catalyst is attributable to the following factors: (i) the high active site density caused by doping FePcs into/onto the highly porous, N-rich Z8Ncs, (ii) the high surface area and adequate active site exposure caused by its hollow spherical morphology, and (iii) the hierarchical porous structure which further facilitates the diffusion and adsorption of oxygen molecules.

Enhanced electro-oxidation of formic acid by a PdPt bimetallic catalyst on a CeO2-modified carbon support

PdPt bimetallic catalysts that employ CeO2-modified carbon black as a support have been prepared using an organic colloidal method. PdPt/CeO2-C shows excellent performance toward the anodic oxidation of formic acid. The effects of varying both Pd to Pt ratio and CeO2 content have been investigated. The optimal Pd to Pt atomic ratio is 15, indicating that addition of small amounts of Pt can significantly enhance the activity of the catalyst. When the CeO2 content in the catalyst reaches as high as ∼15 wt.%, the catalyst shows the maximum activity. Adding CeO2 not only enhances the catalytic activity of the material, but may also change the mechanism of its catalysis of the anodic oxidation of formic acid. Pd15Pt1/15CeO2-C exhibited 60% higher activity than Pd/C, and had a negative shift in onset potential of more than 0.1 V. Based on characterization by X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis and transmission electron microscopy, the interactions between the components are revealed and discussed in detail.

A platinum monolayer core-shell catalyst with a ternary alloy nanoparticle core and enhanced stability for the oxygen reduction reaction

We synthesize a platinum monolayer core-shell catalyst with a ternary alloy nanoparticle core of Pd, Ir, and Ni. A Pt monolayer is deposited on carbon-supported PdIrNi nanoparticles using an underpotential deposition method, in which a copper monolayer is applied to the ternary nanoparticles; this is followed by the galvanic displacement of Cu with Pt to generate a Pt monolayer on the surface of the core. The core-shell Pd1Ir1Ni2@Pt/C catalyst exhibits excellent oxygen reduction reaction activity, yielding a mass activity significantly higher than that of Pt monolayer catalysts containing PdIr or PdNi nanoparticles as cores and four times higher than that of a commercial Pt/C electrocatalyst. In 0.1 M HClO4, the half-wave potential reaches 0.91 V, about 30 mV higher than that of Pt/C. We verify the structure and composition of the carbon-supported PdIrNi nanoparticles using X-ray powder diffraction, X-ray photoelectron spectroscopy, thermogravimetry, transmission electron microscopy, and energy dispersive X-ray spectrometry, and we perform a stability test that confirms the excellent stability of our core-shell catalyst. We suggest that the porous structure resulting from the dissolution of Ni in the alloy nanoparticles may be the main reason for the catalysts enhanced performance.