Huiyu Song

High Performance Fe- and N- Doped Carbon Catalyst with Graphene Structure for Oxygen Reduction

Proton exchange membrane fuel cells are promising candidates for a clean and efficient energy conversion in the future, the development of carbon based inexpensive non-precious metal ORR catalyst has becoming one of the most attractive topics in fuel cell field. Herein we report a Fe- and N- doped carbon catalyst Fe-PANI/C-Mela with graphene structure and the surface area up to 702 m2 g−1. In 0.1 M HClO4 electrolyte, the ORR onset potential for the catalyst is high up to 0.98 V, and the half-wave potential is only 60 mV less than that of the Pt/C catalyst (Loadings: 51 μg Pt cm−2). The catalyst shows high stability after 10,000 cyclic voltammetry cycles. A membrane electrode assembly made with the catalyst as a cathode is tested in a H2-air single cell, the maximum power density reached ~0.33 W cm2 at 0.47 V.

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.

Conversion of polystyrene foam to a high-performance doped carbon catalyst with ultrahigh surface area and hierarchical porous structures for oxygen reduction

A high-performance doped carbon catalyst with ultrahigh surface area (1123 m2 g−1) and hierarchical porous structures was prepared through an economical, non-template pyrolyzing approach using cross-linked polystyrene, melamine and iron chloride as precursors. The catalyst exhibits excellent oxygen reduction reaction (ORR) performance, outstanding methanol tolerance, remarkable stability, and high catalytic efficiency (nearly 100% selectivity for the four-electron ORR process). Remarkably, its ORR activity can even surpass that of the commercial Pt/C catalyst in alkaline media, with a half-wave potential 20 mV more positive. To the best of our knowledge, it is also one of the most active ORR catalysts in alkaline media to date. By investigating the effects of N dopants and Fe residue on the catalysts ORR performance, we find that residual Fe is as important as doped nitrogen in enhancing the ORR performance. The catalysts high ORR performance, outstanding stability and excellent methanol tolerance, combined with its hierarchical porous morphology, make it promising for the application in novel, environmentally friendly electrochemical energy systems. This research also provides a potential way to turn waste into wealth.

Pd nanoparticles decorating flower-like Co3O4 nanowire clusters to form an efficient, carbon/binder-free cathode for Li–O2 batteries

A novel high-performance air cathode was prepared by synthesizing Co3O4 nanowire clusters on a nickel foam (NF) substrate and then decorating these clusters with Pd nanoparticles using a pulse electrodeposition method. This carbon-free and binder-free cathode had a well-defined, flower-like morphology, presenting clusters composed of nanowires with a diameter of ∼60 nm and a length of ∼5 μm on which were located Pd particles as small as 10 nm. The new cathode exhibited excellent low polarization and superior cycling performance. We found that its enhanced electrochemical properties could be attributed to the homogeneous distribution of Pd nanoparticles on the Co3O4 nanowires, which ensured uniform growth of Li2O2 on the Pd/Co3O4/NF electrodes. This, in turn, significantly improved the cathodes OER/ORR activity and aided the formation of discharge products with uniform morphologies, as well as the decomposition of these discharge products during recharging.

High performance LiFePO4 microsphere composed of nanofibers with an alcohol-thermal approach

A novel hierarchical nano/microstructure of LiFePO4 microspheres consisting of nanofibers has been synthesized by a solvothermal approach with a mixture of water and 1,2-propanediol as solvent. The influences of temperature and solvent composition on the morphology and electrochemical performance of the products are investigated. The optimum temperature is 140 °C, and the optimum solvent composition is 1 : 5 for the volume ratio of water to 1,2-propanediol. The initial discharge capacity of the LiFePO4/C microsphere electrode is high and up to 163.9 mA h g−1 and the capacity increased gradually to 164.9 mA h g−1 after 10 cycles, indicating the excellent stability of the materials.

A high-performance composite ORR catalyst based on the synergy between binary transition metal nitride and nitrogen-doped reduced graphene oxide

We report a composite catalyst in which binary transition metal nitride nanoparticles (NPs) were mounted on nitrogen-doped reduced graphene oxide (TiCoNx/N-rGO). The catalyst exhibited outstanding oxygen reduction activity in an alkaline medium. In its optimal form, our catalyst yielded a half-wave potential of 0.902 V (vs. RHE), ∼30 mV more positive than that of the commercial Pt/C catalyst, and its current density at 0.9 V (vs. RHE) reached 2.51 mA cm−2. The ORR activity of our transition metal nitride-mounted N-rGO was much higher than the activities of transition metal nitride alone or N-rGO alone, revealing a strong synergistic effect between the two materials. Further, the catalyst mounted with Ti and Co binary NPs exhibited higher ORR activity than the catalyst mounted solely with Ti nitride NPs, indicating the significant improvement gained by the addition of cobalt. XPS analysis results showed that the mounting of transition metal nitride clearly changed the amount and distribution of N species in the catalyst, causing the percentage of active pyridinic-N species to increase significantly. Moreover, changes in the binding energies of C and Ti atoms proved the synergy between TiCoNx NPs and N-rGO. We therefore ascribe the superior electrochemical activity of our TiCoNx/N-rGO catalyst to this synergy and to the improvement resulting from the addition of Co. In addition to its outstanding ORR activity, this catalyst also showed excellent stability and methanol tolerance, making it a promising Pt-free ORR catalyst for alkaline H2/O2 fuel cells and direct methanol fuel cells.

Three dimensional palladium nanoflowers with enhanced electrocatalytic activity towards the anodic oxidation of formic acid

Three-dimensional palladium nanoflowers (Pd-NF) composed of ultrathin Pd nanosheets were synthesized by a solvothermal approach. The Pd-NF catalyst shows 6.6- and 5.5-fold enhancements in mass activity and surface activity compared to normal palladium nanoparticles (Pd-NP) in the electro-oxidation of formic acid.

Ultra-high-performance core–shell structured Ru@Pt/C catalyst prepared by a facile pulse electrochemical deposition method

Core–shell structured catalysts, made by placing either a monolayer or a thin layer of a noble metal on relatively cheap core-metal nanoparticles, are fascinating and promising fuel cell catalysts due to their high utilization of noble metals. Here, we report our development of a core–shell structured catalyst, Ru@Pt/C, generated by a novel and facile pulse electrochemical deposition (PED) approach. We demonstrate that compared with a commercial Pt/C catalyst, this novel catalyst achieves over four times higher mass activity towards the anodic oxidation of methanol, and 3.6 times higher mass activity towards the cathodic reduction of oxygen. Importantly, we find that the intrinsic activity of Pt in this Ru@Pt/C catalyst is doubled due to the formation of the core–shell structure. The catalyst also shows superior stability: even after 2000 scans, it still retains up to 90% of the peak current. Our findings demonstrate that this novel PED approach is a promising method for preparing high-performance core–shell catalysts for fuel cell applications.

A Co-doped porous niobium nitride nanogrid as an effective oxygen reduction catalyst

Transition metal nitrides have recently attracted significant interest as electrocatalysts for the oxygen reduction reaction (ORR) owing to their low electrical resistance and good corrosion resistance. In this paper, we describe the preparation of a Nb-based binary nitride material with a porous nanogrid morphology/structure. The catalyst exhibited good catalytic activity and high stability towards oxygen reduction. We also intensively investigated the effect that doping with a second transition metal had on the performance of the catalyst. We found that the ORR activity of NbN could be enhanced significantly by enriching the d electrons of Nb through doping with a second transition metal, and that doping with cobalt resulted in the best improvement. Our optimal catalyst, Nb0.95Co0.05N, had an ORR activity ∼4.6 times that of NbN (current density @ 0.6 V vs. the RHE). XPS results revealed that Co doping increased the proportion of Nb in a low-valence state, which may be one of the most important reasons for the enhanced performance. Another important reason is the high surface area resulting from the porous nanogrid morphology. As transition metal doping is an attractive way to enhance the activity of nitride catalysts, our work may provide an effective pathway to achieve this.

Effects of tailoring and dehydrated cross-linking on morphology evolution of ordered mesoporous carbons

In this study, using a template (Pluronic P123) as an in situ carbon source, ordered mesoporous carbons (OMC) were successfully synthesized through directing carbonization of templates. Two key factors in the morphology evolution of mesoporous carbon materials were introduced, one is the tailoring role of micelles by ethanediol, and the other is the dehydrated cross-linking effect by sulfuric acid. Through the two factors, the morphology of as-synthesized ordered mesoporous carbons can be altered from bulks to rods and even to sheets. Transmission electron microscopy (TEM) showed ordered mesoporous carbon rods (OMCR) and ordered mesoporous carbons sheets (OMCS) possessed regular morphology and good mesopore structure. Nitrogen adsorption–desorption analysis confirmed that both OMCR and OMCS had high surface area and uniform mesopore distribution, OMCR had the highest surface area (919 m2 g−1) and OMCS had the biggest pore size (9.11 nm). This study also showed that OMCR and OMCS were good carbon carriers; the size of Pt loading nanoparticles can be decreased to 3 nm and Pt/OMCS especially presents very high Pt dispersion and uniformly smallest Pt nanoparticles (2.49 nm).