Development of Novel Nano-structured Materials with Low-Cost and High Stability for PEM Fuel Cell

Polymer electrolyte membrane fuel cells (PEMFCs) are non-polluting and efficient energy conversion devices that are expected to play a dominant role in energy solutions of the future. However, due to high cost and known degradation issue of Pt electrocatalyst, more durable, efficient, and inexpensive electrocatalysts are required before fuel cells can become commercially viable. This research is revolving around the development of electrocatalysts such as non-noble metal oxygen reduction reaction (ORR) catalyst, new alternative supports, and novel Pt nanostructures to address the above-mentioned challenges in PEMFCs. Firstly, we report the synthesis of nitrogen doped carbon nanotubes (CNx) and nitrogen doped graphene (N-graphene) with the various nitrogen contents. The relationship between structures and ORR activity is investigated in detail. We identified the real active site by the study. Most importantly, CNx and N-graphene have the comparable ORR activity even the improved durability compared with a platinum-based catalyst, showing the potential to replace costly Pt/C catalyst in alkaline fuel cells. Secondly, due to the advantages of N-graphene as not only a support of Pt but the non-noble metal ORR catalyst, we developed three different methods to prepare it: (i) post-treatment of graphene with ammonia (ii) from CNx to N-graphene directly (iii) one-step solvothermal process. Especially, by the solvothermal method, for the first time, nanoflower-like N-graphene was obtained with pure sp2 hybridized carbon and the controllable nitrogen types. Importantly, the synthesized materials exhibit much higher durability as Pt support for fuel cells than commercial carbon powder. Thirdly, previous results have shown that star-like Pt nanowires have both good catalytic activity and durability for ORR. However, there is a limitation in scale up and the controlling length and shape of Pt nanowire for previous method. Here we report a universal method to address the challenge. It is a very simple, green and efficient wet chemical route without any surfactant and template to produce urchin-shaped Pt nanostructures in high yield. In summary, the discoveries in this thesis contribute to development of fuel cell cathode electrocatalysts and make the improvement in electrocatalyst cost and stability

Activity and Durability of Ternary PtRuIr/C for Methanol Electro-oxidation

Carbon supported Pt(1)Ru(1)Ir(x) (0 <= x <= 2) nanoparticles were prepared by it compare nation reductive pyrolysis method and their electrocatalytic activity toward methanol electro-oxidation at 25, 40, and 60 degrees C was investigated. The mass activity (current normalized by the mass of Pt) for methanol electro-oxidation increased as it function of Ir coefficient and cell temperature. Despite the increase in methanol electro-oxidation activity, the addition of Ir does not affect the CO tolerance of the ternary electrocatalyst. The addition of Ir also enhances the durability of the catalyst. The enhancement in activity and durability is discussion based on CO stripping measurements and X-ray photoelectron spectroscopy analysis of the catalysts. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3060111] All rights reserved.ArticleJOURNAL OF THE ELECTROCHEMICAL SOCIETY. 156(3):B397-B402 (2009)journal articl

NH2+ implantations induced superior hemocompatibility of carbon nanotubes

NH(2)(+) implantation was performed on multiwalled carbon nanotubes (MWCNTs) prepared by chemical vapor deposition. The hemocompatibility of MWCNTs and NH(2)(+)-implanted MWCNTs was evaluated based on in vitro hemolysis, platelet adhesion, and kinetic-clotting tests. Compared with MWCNTs, NH(2)(+)-implanted MWCNTs displayed more perfect platelets and red blood cells in morphology, lower platelet adhesion rate, lower hemolytic rate, and longer kinetic blood-clotting time. NH(2)(+)-implanted MWCNTs with higher fluency of 1 × 10(16) ions/cm(2) led to the best thromboresistance, hence desired hemocompatibility. Fourier transfer infrared and X-ray photoelectron spectroscopy analyses showed that NH(2)(+) implantation caused the cleavage of some pendants and the formation of some new N-containing functional groups. These results were responsible for the enhanced hemocompatibility of NH(2)(+)-implanted MWCNTs

The meson BcB_c annihilation to leptons and inclusive light hadrons

The annihilation of the $B_c$ meson to leptons and inclusive light hadrons is analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find that the decay mode, which escapes from the helicity suppression, contributes a sizable fraction width. According to the analysis, the branching ratio due to the contribution from the color-singlet component of the meson $B_c$ can be of order (10^{-2}). We also estimate the contributions from the color-octet components. With the velocity scaling rule of NRQCD, we find that the color-octet contributions are sizable too, especially, in certain phase space of the annihilation they are greater than (or comparative to) the color-singlet component. A few observables relevant to the spectrum of charged lepton are suggested, that may be used as measurements on the color-octet and color-singlet components in the future $B_c$ experiments. A typical long distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.

Three-dimensional full loop simulation of solids circulation in an interconnected fluidized bed

-D full loop CFD simulation of solids circulation is conducted in a complicated circulating-fluidized bed, which consists of a riser, a bubbling bed, a cyclone and a loop-seal. The effects of operating gas velocity, particle size and total solids inventory on the solids circulation rate are investigated based on the system pressure balance of an interconnected fluidized bed. CFD results indicate that the gas velocity in the riser plays a dominant role in controlling the solids circulation rate, whilst the gas velocity in the pot-seal influences in a narrow operating range. The solids circulation rate is strongly influenced by particle size and total solids inventory, but becomes insensitive to the operating conditions in the bubbling bed when the gas velocity is higher than the minimum fluidization velocity

Ultrafast Metal Oxide Reduction at Pd/PdO2 Interface Enables One-Second Hydrogen Gas Detection Under Ambient Conditions

Here, we report a Pd/PdOx sensing material that achieves 1-s detection of 4% H2 gas (i.e., the lower explosive limit concentration for H2) at room temperature in air. The Pd/PdOx material is a network of interconnected nanoscopic domains of Pd, PdO, and PdO2. Upon exposure to 4% H2, PdO and PdO2 in the Pd/PdOx can be immediately reduced to metallic Pd, generating over a >90% drop in electrical resistance. The mechanistic study reveals that the Pd/PdO2 interface in Pd/PdOx is responsible for the ultrafast PdOx reduction. Metallic Pd at the Pd/PdO2 interface enables fast H2 dissociation to adsorbed H atoms, which is otherwise the rate-determining step on PdO2, significantly lowering the PdO2 reduction barrier. In addition, the interconnectivity of Pd, PdO, and PdO2 in Pd/PdOx facilitates the reduction of PdO. The 1-s response time of Pd/PdOx under ambient conditions makes it an excellent alarm for the timely detection of hydrogen gas leaks

Atomic layer deposition for nanomaterial synthesis and functionalization in energy technology

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