Modified Sawhorse Waveform for the Voltammetric Detection of Oxytocin.

Carbon fiber microelectrodes (CFMEs) have been used to detect neurotransmitters and other biomolecules using fast-scan cyclic voltammetry (FSCV) for the past few decades. This technique measures neurotransmitters such as dopamine and, more recently, physiologically relevant neuropeptides. Oxytocin, a pleiotropic peptide hormone, is physiologically important for adaptation, development, reproduction, and social behavior. This neuropeptide functions as a stress-coping molecule, an anti-inflammatory agent, and serves as an antioxidant with protective effects especially during adversity or trauma. Here, we measure tyrosine using the Modified Sawhorse Waveform (MSW), enabling enhanced electrode sensitivity for the amino acid and oxytocin peptide. Applying the MSW, decreased surface fouling and enabled codetection with other monoamines. As oxytocin contains tyrosine, the MSW was also used to detect oxytocin. The sensitivity of oxytocin detection was found to be 3.99 ± 0.49 nA/µM, (n=5). Additionally, we demonstrate that applying the MSW on CFMEs allows for real time measurements of exogenously applied oxytocin on rat brain slices. These studies may serve as novel assays for oxytocin detection in a fast, sub-second timescale with possible implications for in vivo measurements and further understanding of the physiological role of oxytocin.

Spinach-Derived Porous Carbon Nanosheets as High-Performance Catalysts for Oxygen Reduction Reaction.

Biomass-derived porous carbon materials are effective electrocatalysts for oxygen reduction reaction (ORR), with promising applications in low-temperature fuel cells and metal-air batteries. Herein, we developed a synthesis procedure that used spinach as a source of carbon, iron, and nitrogen for preparing porous carbon nanosheets and studied their ORR catalytic performance. These carbon sheets showed a very high ORR activity with a half-wave potential of +0.88 V in 0.1 M KOH, which is 20 mV more positive than that of commercial Pt/C catalysts. In addition, they showed a much better long-term stability than Pt/C and were insensitive to methanol. The remarkable ORR performance was attributed to the accessible high-density active sites that are primarily from Fe-N x moieties. This work paves the way toward the use of metal-enriching plants as a source for preparing porous carbon materials for electrochemical energy conversion and storage applications.

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 glass capillaries, pulled to a fine taper, and then sealed using an epoxy to create electrode materials that are used for fast scan cyclic voltammetry testing. The use of bare CFMEs has several limitations, though. First and foremost, the carbon fiber contains mostly basal plane carbon, which has a relatively low surface area and yields lower sensitivities than other nanomaterials. Furthermore, the graphitic carbon is limited by its temporal resolution, and its relatively low conductivity. Lastly, neurochemicals and macromolecules have been known to foul at the surface of carbon electrodes where they form non-conductive polymers that block further neurotransmitter adsorption. For this study, we modify CFMEs with gold nanoparticles to enhance neurochemical testing with fast scan cyclic voltammetry. Au3+ was electrodeposited or dipcoated from a colloidal solution onto the surface of CFMEs. Since gold is a stable and relatively inert metal, it is an ideal electrode material for analytical measurements of neurochemicals. Gold nanoparticle modified (AuNP-CFMEs) had a stability to dopamine response for over 4 h. Moreover, AuNP-CFMEs exhibit an increased sensitivity (higher peak oxidative current of the cyclic voltammograms) and faster electron transfer kinetics (lower ΔEP or peak separation) than bare unmodified CFMEs. The development of AuNP-CFMEs provides the creation of novel electrochemical sensors for detecting fast changes in dopamine concentration and other neurochemicals at lower limits of detection. This work has vast applications for the enhancement of neurochemical measurements. The generation of gold nanoparticle modified CFMEs will be vitally important for the development of novel electrode sensors to detect neurotransmitters in vivo in rodent and other models to study neurochemical effects of drug abuse, depression, stroke, ischemia, and other behavioral and disease states.

SEIRAS Study of Chloride-Mediated Polyether Adsorption on Cu.

Surface-enhanced infrared absorption spectroscopy is used to examine the co-adsorption of a selection of polyethers with Cl- under conditions relevant to superconformal Cu electrodeposition in CuSO4-H2SO4 electrolytes. In 0.1 mol/L H2SO4, a potential-dependent mixed SO4 2--H3O+/H2O layer forms on weakly textured (111) Cu thin-film surfaces. With the addition of 1 mmol/L NaCl, the SO4 2--H3O+/H2O adlayer is displaced and rapidly replaced by an ordered halide layer that disrupts the adjacent solvent network, leading to an increase in non-hydrogen-bonded water that makes the interface more hydrophobic. The altered wetting behavior facilitates co-adsorption of polyethers, such as poly(ethylene glycols), polyoxamers, or polyoxamines. Interfacial water is displaced by co-adsorption of the hydrophobic polymer segments on the Cl--terminated surface, while the hydrophilic ether oxygens are available for hydrogen bond formation with the solvent. The combined polyether-Cl- layer serves as an effective suppressor of the Cu electrodeposition reaction by limiting access of Cuaq 2+ to the underlying metal surface. This insight differs from previous work which suggested that polymer adsorption is mediated by Cu+-ether binding.

High-Indexed Pt3Ni Alloy Tetrahexahedral Nanoframes Evolved through Preferential CO Etching.

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 PtNi4 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 PtNi4 tetrahexahedral nanocrystals at an elevated temperature. The resultant Pt3Ni 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.

MoS2 Nanosheets Supported on Hollow Carbon Spheres as Efficient Catalysts for Electrochemical Hydrogen Evolution Reaction.

Hybridizing structured carbon materials with MoS2 has been demonstrated to be an effective method to increase the electrochemical hydrogen evolution reaction (HER) activity and durability of MoS2. In this study, we report the growth of MoS2 nanosheets on the surface of uniform hollow carbon spheres (HCS) to form a hydrangea-like nanocomposite. The HCS were formed through carbonization of a phenol formaldehyde template, and the MoS2 nanosheets were grown on the HCS surfaces through a hydrothermal method. The nanocomposites have the advantages of significantly improved electrical conductivity, ease of varying the MoS2 loading, and minimizing stacking of MoS2 nanosheets, which are manifested by their remarkably improved HER performance. The well-tuned carbon-MoS2 composite shows a Tafel slope of 48.9 mV dec-1, an onset potential of -0.079 V (vs reversible hydrogen electrode), and an overpotential of 126 mV at the current density of 10 mA cm-2 after 1000 potential cycles.

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

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 m2 g-1 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.

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

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.

Electrocatalysis of formic acid on palladium and platinum surfaces: from fundamental mechanisms to fuel cell applications.

Formic acid as a natural biomass and a CO2 reduction product has attracted considerable interest in renewable energy exploitation, serving as both a promising candidate for chemical hydrogen storage material and a direct fuel for low temperature liquid fed fuel cells. In addition to its chemical dehydrogenation, formic acid oxidation (FAO) is a model reaction in the study of electrocatalysis of C1 molecules and the anode reaction in direct formic acid fuel cells (DFAFCs). Thanks to a deeper mechanistic understanding of FAO on Pt and Pd surfaces brought about by recent advances in the fundamental investigations, the "synthesis-by-design" concept has become a mainstream idea to attain high-performance Pt- and Pd-based nanocatalysts. As a result, a large number of efficient nanocatalysts have been obtained through different synthesis strategies by tailoring geometric and electronic structures of the two primary catalytic metals. In this paper, we provide a brief overview of recent progress in the mechanistic studies of FAO, the synthesis of novel Pd- and Pt-based nanocatalysts as well as their practical applications in DFAFCs with a focus on discussing studies significantly contributing to these areas in the past five years.

Length tunable penta-twinned palladium nanorods: seedless synthesis and electrooxidation of formic acid.

Palladium nanorods with controlled lengths from 100 to 500 nm and a fixed width of 20 nm were synthesized for the first time by a seedless approach. These rods show higher peak current densities than Pd cubes for formic acid oxidation and the catalytic activity decreases with increasing rod length.

B-doped Pd catalyst: boosting room-temperature hydrogen production from formic acid-formate solutions.

Facile production of hydrogen at room temperature is an important process in many areas including alternative energy. In this Communication, a potent boron-doped Pd nanocatalyst (Pd-B/C) is reported for the first time to boost hydrogen generation at room temperature from aqueous formic acid-formate solutions at a record high rate. Real-time ATR-IR spectroscopy is applied to shed light on the enhanced catalytic activity of B-doping and reveals that the superior activity of Pd-B/C correlates well with an apparently impeded COad accumulation on its surfaces. This work demonstrates that developing new anti-CO poisoning catalysts coupled with sensitive interfacial analysis is an effective way toward rational design of cost-effective catalysts for better hydrogen energy exploitation.

Opp-dibenzoporphyrins as a light-harvester for dye-sensitized solar cells.

New opp-dibenzoporphyrins were prepared in a concise method that was based on a Pd(0)-catalyzed cascade reaction. These porphyrins, which contained carboxylic-acid linker groups on benzene rings that were fused to the porphyrin at their ß,ß'-positions, were examined as sensitizers for dye-sensitized solar cells for the first time. Whereas all of the porphyrins showed solar-energy-to-electricity conversion, an opp-dibenzoporphyrin with conjugated carboxylic-acid linkers displayed the highest conversion efficiency and an exceptionally high J(sc) value. Cyclic voltammetry of these porphyrins suggested that the fusion of two aromatic benzene rings onto the periphery of the porphyrin lowered the HOMO-LUMO energy gap; the incorporation of a conjugated carboxylic-acid linker group decreased the HOMO-LUMO gap even further. These CV data are consistent with DFT calculations for these porphyrins and agree well with the UV/Vis absorption- and fluorescence spectra of these porphyrins.

In situ surface-enhanced Raman spectroscopic studies of nafion adsorption on Au and Pt electrodes.

Understanding interactions between Nafion (perfluorosulfonic acid) and Pt catalysts is important for the development and deployment of proton exchange membrane fuel cells. However, study of such interactions is challenging and Nafion/Pt interfacial structure remains elusive. In this study, adsorption of Nafion ionomer on Au and Pt surfaces was investigated for the first time by in situ surface-enhanced Raman spectroscopy. The study is made possible by the use of uniform SiO(2)@Au core-shell particle arrays which provides very strong enhancement of Raman scattering. The high surface sensitivity offered by this approach yields insightful information on interfacial Nafion structure. Through spectral comparison of several model compounds, vibration assignments of SERS bands were made. The SER spectra suggest the direct interaction of sulfonate group with the metal surfaces, in accord with cyclic voltammetric results. Comparison of present SERS results with previous IR spectra was briefly made.

ortho-Phenylenes: unusual conjugated oligomers with a surprisingly long effective conjugation length.

ortho-Phenylenes represent a fundamental but relatively unexplored class of conjugated molecular architecture. We have developed a robust synthetic approach to monodisperse o-phenylene oligomers which we have demonstrated by synthesizing a homologous series up to the dodecamer. The o-phenylenes exhibit complex conformational behavior but are biased toward a specific 2-fold-symmetric conformation which we believe corresponds to a stacked helix. Surprisingly, the series exhibits long-range delocalization, as measured by bathochromic shifts in UV/vis spectra. Although the overall magnitude of the shifts is modest (but comparable to some other classes of conjugated materials), the effective conjugation length of the series is approximately eight repeat units. The oligomers also exhibit an unusual hypsochromic shift in their fluorescence spectra with increasing length. The origin of these trends is discussed in the context of conformational analysis and DFT calculations of the frontier molecular orbitals for the series.

Synthesis and oxygen reduction activity of shape-controlled Pt(3)Ni nanopolyhedra.

Platinum-based alloys have been extensively shown to be effective catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Most of these catalysts are nanoparticles without shape control. Recently, extended Pt(3)Ni(111) surfaces prepared in ultrahigh vacuum were demonstrated to possess enhanced ORR catalytic activity as compared to the state-of-the-art carbon supported Pt (Pt/C) nanoparticle catalysts. How and whether this promising surface can be transformed into practical nanoscale electrocatalysts used in PEMFCs remain a challenge. We report a new wet-chemical approach of preparing monodisperse Pt(3)Ni nanoctahedra and nanocubes terminated with {111} and {100} facets, respectively. We further show that the ORR activity on the Pt(3)Ni nanoctahedra is approximately 5-fold higher than that of nanocubes with a similar size. Comparison of ORR activity between carbon-supported Pt(3)Ni nanoctahedra and commercial Pt/C reveals that the Pt(3)Ni nanoctahedra are highly active electrocatalysts. This synthetic strategy may be extended to the preparation of other shape-controlled fuel cell electrocatalysts.

Solution-based evolution and enhanced methanol oxidation activity of monodisperse platinum-copper nanocubes.

Shape-controlled catalysis: High-quality Pt-Cu nanocubes with an average size of about 8 nm (see picture, scale bar = 20 nm) were synthesized from a high-temperature organic solution system in the presence of various capping ligands. These cubic Pt-Cu nanocrystals terminated with {100} facets demonstrated a superior catalytic activity towards methanol oxidation compared to similar sized Pt-Cu and Pt nanospheres.

Electrooxidation of CO on uniform arrays of Au nanoparticles: effects of particle size and interparticle spacing.

Uniform arrays of Au nanoparticles with controlled size and interparticle distance were synthesized by using polystyrene-b-poly(2-vinylpyridine) as a template and an Ar plasma treatment. These uniform arrays of nanoparticles are ideal model systems for studying the effects of particle size and interparticle distance on their catalytic activity. Electrooxidation of carbon monoxide (CO) on these particle arrays in CO-saturated 0.1 M NaOH was examined. On particle arrays with a particle size of ca. 4 nm and an interparticle distance varying from 28 to 80 nm, rotating disk electrode (RDE) voltammetric results show that the half-wave potential for CO oxidation shifted to more positive potentials as the interparticle distance increased. This apparent kinetic difference can be explained by the CO diffusion pattern change with the interparticle distance. On particle arrays with a similar interparticle distance but varying size from 2.4 to 9.0 nm, the electrooxidation of CO shows a particle size-dependent activity, with the highest activity obtained on 4.2 nm Au particles, as revealed by the Tafel plot. The Tafel slope also depends on the particle size, with the smallest slope obtained on 4.2 nm particles. The particle size-dependent catalytic activity was tentatively explained in terms of the size-dependent adsorption properties. A brief comparison was made with the results from gas phase CO oxidation on Au nanoparticles.

Electrooxidation of carbon monoxide and methanol on platinum-overlayer-coated gold nanoparticles: effects of film thickness.

The electrooxidation of carbon monoxide and methanol on Pt-coated Au nanoparticles attached to 3-aminopropyl trimethoxysilane-modified indium tin oxide electrodes was examined as a function of Pt film thickness and Au particle coverage. For the electrodes with medium and high Au particle coverages, the CO stripping peak position shifts to more negative values with increasing Pt film thickness, from ca. 0.8 V (vs Ag/AgCl) at 1 ML to 0.45 V at 10 ML. Accompanying this peak potential shift is the sharpening of the peak width from more than 150 to 65 mV. For the electrode with low Au particle coverage, similar peak width narrowing was also observed, but the peak potential shift is much smaller, from 0.85 V at 1 ML of Pt to 0.65 V at 10 ML. These observations are compared with the CO oxidation on bulk Pt electrodes and on Pt films deposited on bulk Au electrodes. The film-thickness-dependent CO oxidation is explained by d band theory in terms of strain and ligand effects, the particle size effect, and the particle aggregation induced by Pt film growth. Corresponding to the increasing CO oxidation activity, the current density of methanol oxidation grows with the Pt film thickness. The peak potential and current density reach the same values as those obtained on a polycrystalline bulk Pt electrode when more than 4 ML of Pt is deposited on the Au particle electrodes with a particle coverage higher than 0.25. These results suggest that it is feasible to reduce Pt loading in methanol fuel cells by using Pt thin films as the anode catalyst.

Surface-enhanced Raman spectroscopic evidence of methanol oxidation on ruthenium electrodes.

Electrooxidation of methanol on Ru surfaces was investigated using in situ surface-enhanced Raman spectroscopy. Although the cyclic voltammogram did not show a significant methanol oxidation current on Ru, a Raman band at approximately 1970-1992 cm(-1) was observed from 0.4 to 0.8 V in 0.1 M HClO(4) + 1 M methanol. By comparing with the C-O stretching band (nu(CO)) of carbon monoxide (CO) adsorbed on RuO(2)(110) in the ultrahigh vacuum and on oxidized Ru electrodes, the observed spectral feature is assigned to nu(CO) of adsorbed CO (CO(ads)) on RuO(2). The formation of CO(ads) suggests that methanol oxidation does occur on Ru at room temperature, which is in contrast to the perception that Ru is not active for the reaction. The lack of significant methanol oxidation current is attributed to the competing rapid surface oxidation, which forms inactive surface oxides and therefore inhibits the methanol oxidation.