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Gold Nanoparticle Modified Carbon Fiber Microelectrodes for Enhanced Neurochemical Detection

For over 30 years, carbon-fiber microelectrodes (CFMEs) have been the standard for neurotransmitter detection. Generally, carbon fibers are aspirated into ...

American University

Palladium nanocrystals enclosed by {100} and {110} crystal facets, were successfully synthesized through an aqueous one-pot synthesis method. A new thermal annealing approach was developed for fabricating these palladium nanocrystals as a working electrode on a gas permeable membrane to study the facet effects of the oxygen reduction process in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpy][NTf2]). Results were compared with the same processes at a conventional platinum electrode. Our study shows that the structural difference between the two facets of Pd nanocrystals has little effect on the oxygen reduction process but significantly affects the oxidation process of the superoxide. It is found that the Pd{110}/IL interface can better stabilize superoxide radicals revealed by a more positive oxidation potential compared to that of Pd{100}. In addition, the analytical characteristic of utilizing both palladium nanocrystals as electrodes for oxygen sensing is comparable with a polycrystal platinum oxygen sensor, in which Pd{110} presents the best sensitivity and lowest detection limit. Our results demonstrate the facet-dependence of oxygen reduction in an ionic liquid medium and provide the fundamental information needed to guide the applications of palladium nanocrystals in electrochemical gas sensor and fuel cell research. 

Facet effects of palladium nanocrystals for oxygen reduction in ionic liquids and for sensing applications.

Doping with foreign atoms is an effective approach to significantly enhance the catalytic performance of carbon materials for oxygen reduction reaction (ORR). In this paper, a colloidal silica template method was employed to synthesize nitrogen and iron codoped ordered mesoporous carbon for ORR electrocatalysis. The carbon materials were thoroughly characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy measurements. The porosity was quantified by nitrogen adsorption/desorption measurements that showed the formation of ordered mesoporous structures with a BET specific surface area up to 953.8 m g and the mesopores mostly centered at ca. 25 nm, close to the size of the colloidal silica. The resulting mesoporous carbon exhibited apparent ORR activity in alkaline media, which was highly comparable to that of commercial Pt/C (20 wt%), with the onset potential at +0.99 V vs. RHE. This was ascribed largely to nitrogen dopants, with additional contributions from the trace amounts of iron dopants, and the reactions appeared to be facilitated by the formation of a mesoporous structure. Moreover, the mesoporous carbon showed better stability, resistance against fuel crossover, and selective activity than Pt/C. This work demonstrates a new paradigm for the preparation of heteroatom-doped carbon materials that are promising alternatives to Pt-based catalysts for fuel cells.

Ordered mesoporous carbons codoped with nitrogen and iron as effective catalysts for oxygen reduction reaction.

Chemically controlling crystal structures in nanoscale is challenging, yet provides an effective way to improve catalytic performances. Pt-based nanoframes are a new class of nanomaterials that have great potential as high-performance catalysts. To date, these nanoframes are formed through acid etching in aqueous solutions, which demands long reaction time and often yields ill-defined surface structures. Herein we demonstrate a robust and unprecedented protocol for facile development of high-performance nanoframe catalysts using size and crystallographic facet-controlled PtNi tetrahexahedral nanocrystals prepared through a colloidal synthesis approach as precursors. This new protocol employs the Mond process to preferentially dealloy nickel component in the ⟨100⟩ direction through carbon monoxide etching of carbon-supported PtNi tetrahexahedral nanocrystals at an elevated temperature. The resultant PtNi alloy tetrahexahedral nanoframes possess an open, stable, and high-indexed microstructure, containing a segregated Pt thin layer strained to the Pt-Ni alloy surfaces and featuring a down-shift d-band center as revealed by the density functional theory calculations. These nanoframes exhibit much improved catalytic performance, such as high stability under prolonged electrochemical potential cycles, promoting direct electro-oxidation of formic acid to carbon dioxide and enhancing oxygen reduction reaction activities. Because carbon monoxide can be generated from the carbon support through thermal annealing in air, a common process for pretreating supported catalysts, the developed approach can be easily adopted for preparing industrial scale catalysts that are made of Pt-Ni and other alloy nanoframes.

Shouzhong Zou

Department of Chemistry

American University

Gold Nanoparticle Modified Carbon Fiber Microelectrodes for Enhanced Neurochemical Detection