The large-scale practical application of fuel cells will be difficult to realize if the expensive platinum-based electrocatalysts for oxygen reduction reactions (ORRs) cannot be replaced by other efficient, low-cost, and stable electrodes. Here, we report that vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells. In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of -80 millivolts and a current density of 4.1 milliamps per square centimeter at -0.22 volts, compared with -85 millivolts and 1.1 milliamps per square centimeter at -0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.

We report on the synthesis, characterization, and electrochemical performance of novel, ultrathin Pt monolayer shell-Pd nanowire core catalysts. Initially, ultrathin Pd nanowires with diameters of 2.0 ± 0.5 nm were generated, and a method has been developed to achieve highly uniform distributions of these catalysts onto the Vulcan XC-72 carbon support. As-prepared wires are activated by the use of two distinctive treatment protocols followed by selective CO adsorption in order to selectively remove undesirable organic residues. Subsequently, the desired nanowire core-Pt monolayer shell motif was reliably achieved by Cu underpotential deposition followed by galvanic displacement of the Cu adatoms. The surface area and mass activity of the acid and ozone-treated nanowires were assessed, and the ozone-treated nanowires were found to maintain outstanding area and mass specific activities of 0.77 mA/cm(2) and 1.83 A/mg(Pt), respectively, which were significantly enhanced as compared with conventional commercial Pt nanoparticles, core-shell nanoparticles, and acid-treated nanowires. The ozone-treated nanowires also maintained excellent electrochemical durability under accelerated half-cell testing, and it was found that the area-specific activity increased by ~1.5 fold after a simulated catalyst lifetime.

This paper describes the adsorption of electroactive methylene blue (MB) dye onto single-walled carbon nanotubes (SWNTs) to form an electrochemically functional nanostructure and its layered nanocomposite. UV-visible and FT-IR spectroscopy and electrochemistry used for characterization of the MB adsorption onto SWNTs reveal that MB essentially interacts with SWNTs through charge-transfer and hydrophobic interactions, leading to the formation of a MB-SWNT adsorptive nanostructure which exhibits distinct electrochemical properties from those of MB adsorbed onto a glassy carbon (GC) electrode. The interactions between MB and the SWNTs are demonstrated to closely associate with the structural properties of the SWNTs by comparing the electrochemical properties of MB adsorbed onto different substrates, i.e., glassy carbon, SWNTs, and SWNTs intentionally sidewall functionalized with hydroxyl groups (SWNT-OHs). The stable adsorption of water-soluble and positively charged MB molecules onto the SWNTs is further demonstrated to be able to solubilize the formed nanostructure in water quite well and to fabricate a functional nanocomposite by layer-by-layer assembling of the formed nanostructure on a solid substrate.

Multilayer films of shortened multiwalled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon electrodes with the layer-by-layer (LBL) method, based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) and negatively charged and shortened MWNTs. The film assembly and electrochemical property as well as the electrocatalytic activity toward O2 reduction of the MWNT multilayer film are studied. Scanning electron microscopy, the quartz crystal microbalance technique, ultraviolet-visible-near-infrared spectroscopy, and cyclic voltammetry are used for characterization of film assembly. Experimental results revealed that film growth is uniform, almost with the same coverage of the MWNTs in each layer, and that the assembled MWNTs are mainly in the form of small bundles or single tubes on the electrodes. Electrochemical studies indicate that the LBL assembled MWNT films possess a remarkable electrocatalytic activity toward O2 reduction in alkaline media. This property, combined with the well-dispersed, porous and conductive features of the MWNT film illustrated with the LBL method, suggests the potential application of the MWNT film for constructing an efficient alkaline air electrode for energy conversions.

Carbon nanotubes (CNTs) have been proved to be a novel type of nanostructure with unique structural, electronic and mechanical properties and have drawn extensive attention since their discovery. [1][2][3] Research over the past decade has revealed that the CNTs constitute a new form of carbon materials that are finding striking applications in many fields, such as energy conversion and storage, 4,5 electromechanical actuators, 6,7 chemical sensing 8 and so forth. Generally, the nanotubes can be divided into two categories: single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). The former can be regarded as a graphene cylinder formed by rolling seamlessly a single graphene sheet along an (m,n) lattice vector in the sheet. The (m,n) indices is a central parameter governing the metallicity and chirality of the tubes. The latter is composed of coaxial multilayer graphene tubes with interlayer space of 0.34 nm. The diameter varies from 0.4 nm to 3 nm for the SWNTs and from 1.4 nm to 100 nm for the MWNTs (typical transmission electron microscopic images of the CNTs are shown in Fig. 1).Due to the unique physical and chemical properties and thus the striking applications in various research and industrial fields, the CNTs have drawn extensive interest over the past decade. To date, we have witnessed great successes in the synthesis of the CNTs and in understanding of their chemical and physical properties. Several excellent reviews concerning these issues have appeared in the literature. 9,10 Currently, increasing interests are being focused on the construction of the CNT-based functional nanodevices with novel properties for practical applications.On the other hand, the CNTs represent a new kind of carbonbased materials and are superior to other kinds of carbon materials commonly used in electrochemistry, such as glassy carbon (GC), graphite and diamond, mainly in the special structural features and unique electronic properties. As a result, besides their striking applications in other fields, study of the CNT electrochemistry thus far has revealed that these unique properties of the CNTs substantially make them useful for electrochemical investigations, e.g., electrocatalysis, direct electrochemistry of proteins and electroanalytical applications such as electrochemical sensors and biosensors. 11,12 The electroanalytical applications of the CNTs for construction of This review addresses recent developments in electrochemistry and electroanalytical chemistry of carbon nanotubes (CNTs). CNTs have been proved to possess unique electronic, chemical and structural features that make them very attractive for electrochemical studies and electrochemical applications. For example, the structural and electronic properties of the CNTs endow them with distinct electrocatalytic activities and capabilities for facilitating direct electrochemistry of proteins and enzymes from other kinds of carbon materials. These striking electrochemical properties of the CNTs pave the way to CNT-based bioelectrochemist...

We describe a simple method for preparing multimetallic nanoparticles by in situ decomposition of the corresponding Prussian blue analogue, which is adsorbed on carbon black. The example involves the AuNi(0.5)Fe core of the Pt(ML)/Au(1)Ni(0.5)Fe core-shell electrocatalyst for the oxygen reduction reaction. The core contains 3-5 surface atomic layers of Au, which play an essential role in determining the activity and stability of the catalyst. The Pt(ML)/AuNi(0.5)Fe electrocatalyst exhibited Pt mass and specific activities of 1.38 A/mg(Pt) and 1.12 × 10(-3) A/cm(2)(Pt), respectively, both of which are several times higher than those of commercial Pt/C catalysts. Its all-noble-metal mass activity (0.18 A/mg(Pt,Au)) is higher than or comparable to those of commercial samples. Stability tests showed an insignificant loss in activity after 15,000 triangular-potential cycles. We ascribe the high activity and stability of the Pt(ML)/AuNi(0.5)Fe electrocatalyst to its hierarchical structural properties, the Pt-core interaction, and the high electrochemical stability of the gold shell that precludes exposure to the electrolyte of the relatively active inner-core materials.

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This study demonstrates a novel electrochemical method for sensitive determination of biological thiols including homocysteine, cysteine, and glutathione based on rational functionalization of single-walled carbon nanotubes (SWNTs) with synthetic triptycene orthoquinone (TOQ). Unlike previous strategies used for the functionalization of the carbon nanotubes to fabricate new kind of electrochemically functional nanostructures, the method demonstrated here is essentially based on understanding of the redox properties inherent in the SWNTs themselves. It is demonstrated that the electrochemical oxidation of the thiols at the SWNT-modified electrode is redox-mediated by the quinone-like functional groups at the tube ends and that the low density of such functional groups leads to a follow-up oxidation of the thiols at a more positive potential at the electrode. To mimic the redox properties of the SWNTs and thus to increase the catalytic sites onto the SWNTs, we rationally choose the synthetic TOQ and attach such a compound onto the SWNTs. As a result, it is found that the rational attachment of TOQ onto the SWNTs substantially results in a sufficient electrocatalysis toward the thiols at a low potential of 0.0 V with enhanced sensitivities (i.e., almost by a factor of 10-fold) for the determination of such kind of species in relative to those at the SWNT-modified electrode. The high sensitivity and the good stability as well as the high reproducibility of the TOQ/SWNT-modified electrodes substantially make them very useful for reliable and durable determination of the biological thiols.