Platinum/Cerium oxide-based catalysts for methanol electro oxidation were prepared by the occlusion deposition technique. Composite glassy carbon (GC) electrodes were modified and then tested towards the methanol electro oxidation half reaction in acid and alkaline medium. Cyclic voltammetry and chronoamperometry techniques were used to test the catalytic response of the composite electrodes. AFM studies were carried out in order to have a measurement of the particle size and distribution of the platinum/ceria catalyst on HOPG.

Highly efficient Pt-TiO2 composite photoelectrodes were synthesized by combining two novel deposition methods: ACVD and a room temperature RF (radio frequency) magnetron sputtering method. A room temperature RF magnetron sputtering method allowed uniform deposition of Pt nanoparticles (NPs) onto the as-synthesized nanostructured columnar TiO2 films by ACVD. Pt NP sizes from 0.5 to 3 nm demonstrating a high particle density (>1012 cm−2) could be achieved by varying deposition time with constant pressure and power intensity. As-synthesized Pt-TiO2 films were used as photoanodes for water photolysis. Pt nanoparticles deposited onto the TiO2 film for 20s produced the highest photocurrent (7.92 mA/cm2 to 9.49 mA/cm2) and maximized the energy conversion efficiency (16.2 % to 21.2 %) under UV illumination. However, as the size of Pt particles increased, more trapping sites for photogenerated electron-hole pairs decreased photoreaction.

The Transition metal oxides such as TiO2 and CeO2 as catalyst and co-catalyst materials were studied for methanol oxidation. The metal oxide nanoparticles were impregnated into carbon aerogel and Pt-Ru/C (Tanaka) by modified sol-gel Pechini method and heat-treated at different temperatures. Crystal structure, particle size and composition of the catalyst particles were studied using XRD, TEM and EDS techniques. The electrochemical activity and stability of these catalyst materials were studied in acidic medium and the results were compared to their corresponding specific and active surface areas. The aerogel supported metal oxides were stable and proved for better methanol oxidation, while a significant synergetic effect in electro-oxidation is observed when the metal oxides were impregnated into the structure of Pt-Ru/C catalyst. The methanol-oxidation was further improved after heat treatment due to its improved structural and surface properties.

To demonstrate the effects of particle size and alloying on hydrogen adsorption on metals, we explore stable configurations of Pd-Pt alloy using a 55-atom cubo-octahedron. Via first-principles based cluster expansion method, we obtained groundstate configurations and show how their hydrogen adsorption energies change with Pd-Pt composition. Comparison with surface adsorption energies further shows the effect of particle size.

Nanorod arrays of chromium (Cr) were grown on glassy carbon (GC) electrodes by a dc magnetron sputtering glancing angle deposition (GLAD) technique. The Cr nanorods were used as low-cost, high surface area, metallic supports for a conformal layer of Pt thin film catalyst, as a potential low-loading electrocatalyst for the oxygen reduction reaction (ORR) in polymer electrolyte membrane (PEM) fuel cells. A dc magnetron sputtering small angle deposition (SAD) technique was utilized for a conformal coating of Pt on Cr nanorods. The ORR activity of SAD-Pt/GLAD-Cr electrodes was investigated using cyclic voltammetry (CV) and rotating-disk electrode (RDE) techniques in a 0.1 M HClO4 solution at room temperature. A reference sample consisting of GLAD Cr nanorods coated with a Pt thin film deposited at normal incidence (θ = 0o) was prepared and compared with the SAD-Pt/GLAD-Cr nanorods. Compared to GLAD Cr nanorods coated with Pt thin film at θ = 0o, the SAD-Pt/GLAD-Cr nanorod electrode exhibited higher ECSA and area-specific and mass-specific ORR activity. These results indicate that the growth of catalyst layer on the base-metal nanorods by the SAD technique provides a more conformal and possibly a nanostructured coating, significantly enhancing the catalyst utilization.

The use of three-way catalysts is an accepted method to minimize NOx and CO emissions generated by internal combustion engines. These catalysts are generally formed by the support, stabilizers, promoters metal and transition metals, the most used metals of the platinum group. The use of cerium as a promoter is usually related to its ability to store oxygen and structural aspects such as the property of increasing the dispersion of metals and slow change of phase of the stabilizing support. On the other hand, the metal copper was explored as a possible replacement for palladium and platinum in the reduction of NO by CO. In this work, fibers of cerium oxide doped with copper were obtained from an acetate solution of cerium and coppers nitrates and polyvinyl butyral (PVB). This solution went through the process of electrospinning to produce nanostructured fibers. After heat treatment, cerium oxide fibers were obtained. These fibers were characterized structurally by scanning electron microscopy (SEM), had their specific surface area determined by BET method, were subjected to thermogravimetric test to determine their thermal decomposition and were analyzed by X-ray diffraction. The catalytic activity was assessed by the amount of O2 consumed and CO and CO2 formed for the combustion of methane and air. SEM images show fibers oriented randomly in the substrate. TEM images show that the diameter of the fibers is approximately 100 nm and the size of its crystallites are around 20 nm. In the presence of the catalyst, the combustion reaction started around 500°C, with the consumption of methane and oxygen and the formation of CO and/or CO2. There was no emission of NO and NOx gases during the tests with catalysts.

Lanthana-supported Ni and Co catalysts were investigated by “operando” techniques (XAS and APPES) for methane reforming reactions. The samples were prepared by the “solid phase crystallization” method (spc), where the precursors La(Ni1-xCox)O3 contains homogeneously distributed metals (Ni, Co) in the crystal structure (perovskite), which, on further reduction, result in the formation of catalytic system Ni1-xCox/La2O3. The monometallic samples (NiLaO3, CoLaO3) have been compared with a bimetallic system of an intermediate composition Ni0.5Co0.5LaO3. This “operando” study has allowed us to obtain important conclusions about the bimetallic particles and the metal-support interactions. The data revealed the formation of bimetallic particles (NiCo); on these ones, the Ni avoids the Co oxidation during the reaction. However, this protection does not induce an improvement in the activity, which presents an intermediate behaviour between Ni/La2O3 and Co/La2O3. These bimetallic particles form a pseudo-alloy with the surface enriched in cobalt (under reduced conditions), resulting nearly in a core-shell structure (Ni@Co).

We confirmed that GaN photocatalyst with NiO cocatalyst (GaN-NiO) continuously produced hydrogen from water for 500 hours without any extra bias. The GaN-NiO photocatalyst was hardly etched and 184-mL hydrogen gas was produced from the electric charge of 1612 coulombs, the Faradic efficiency of which was 89.2%. The conversion efficiency from incident light energy to hydrogen chemical energy was 0.98% in average for 500 h. The incident photon-to-current conversion efficiency (IPCE) was 50% at 300 nm and 35% at 350 nm after the experiment, which was much higher than those of other semiconductor-based photocatalysts.

Herein, we investigated the effects of polyaniline (PANI) and polypyrrole (PPY) in their native and co-assembled forms as a thin layer on Pt nanoparticle-decorated multi-walled carbon nanotubes (Pt/MWCNTs) toward the ethanol oxidation reaction (EOR). The co-assembled conducting PANI-PPY deposited Pt/MWCNTs was successfully synthesized and demonstrated significant enhancement of the electro-catalytic activity and stability toward EOR as revealed by electrochemical characterizations. The presented results indicate that in the co-assembled form, PANI and PPY retained their own superior effects on the enhancement of stability and catalytic activity via intermediate species removal and ethanol adsorption, respectively. This preliminary result reveals a new strategy for the use of conducting polymers as potential catalyst supports due to its facile fabrication and functionalization, cost effectiveness and environmental friendliness in comparison to alloys and metal oxides, factors which are necessary for the practical application of direct ethanol fuel cells in the near future.

ABSTRACT

Shape-controlled Ag and Pd nanocrystals were synthesized using seed-mediated techniques using β-cyclodextrin (β-CD) as structuring agent. First, seeds were obtained by reacting Na2PdCl4 or AgNO3 with a strong reducing agent, NaBH4 in the presence of sodium citrate dihydrate acting as stabilizing agent. These seeds were then injected into a growth solution containing the same metallic precursor, ascorbic acid (as a weak reducing agent) and β-CD as structuring agent. TEM results emphasize a strong influence of the relative concentration of β-CD on the final morphology. In the case of silver, well-facetted nanocrystals were obtained with a progressive shift from kinetically to thermodynamically-controlled nanoobjects when increasing the β-CD/Ag molar ratio. On palladium, β-CD leads to the formation of dendrites (urchin-like) or multipods through controlled aggregation of primary particles. The use of β-CD does not interfere negatively with the catalytic properties of the Pd nanocrystals in the hydrogenation of cinnamaldehyde.

Bismuth vanadate (BiVO4) thin films are deposited by a low-cost and scalable spray pyrolysis method. Its performance under AM1.5 illumination is mainly limited by slow water oxidation kinetics. We confirm that cobalt phosphate (Co-Pi) is an efficient water oxidation catalyst for BiVO4. The optimum thickness of BiVO4 is 300 nm, resulting in an AM1.5 photocurrent of 1.9 mA/cm2 at 1.23 V vs. RHE when catalyzed with Co-Pi. Once the water oxidation limitation is removed, the performance is limited by low charge separation efficiency. This causes more than 60% of the electron-hole pairs to recombine before reaching the respective interfaces. The slow electron transport is shown to be the main cause of this low efficiency, and future efforts should therefore be focused on addressing this key limitation.

The solid-gas phase photoassisted reduction of carbon dioxide (artificial photosynthesis) was performed using ferroelectric lithium niobate and titanium dioxide as photocatalysts. Illumination with a high pressure mercury lamp and visible sunlight showed lithium niobate achieved unexpectedly high conversion of CO2 to products despite the low levels of band gap light available and outperformed titanium dioxide under the conditions used. The high reaction efficiency of lithium niobate is explained due to its strong remnant polarization (70 μC/cm2) thought to allow longer lifetime of photo induced carriers as well as an alternative reaction pathway.

We have compared the rates of CO formation on Cu and Cu oxide surfaces during the electrochemical reduction of CO2 in aqueous media. On metallic Cu surfaces, H2 formation is the main reaction at potentials less cathodic than –1.16 V(NHE). At this potential the formation of CO becomes significant, while CH4 appears at potentials more cathodic than –1.36 V(NHE). On electrodeposited Cu oxide surfaces there is a complex transient response. During reduction at constant potential (–1.1 V(NHE)), there is a large, transient cathodic current that corresponds to reduction of the oxide layer. After this initial oxide reduction, the current density stabilizes and the formation rates of H2 and CO show a more slowly varying transient behavior. The H2 formation rate is roughly 3x higher than on freshly cleaned Cu foil, but is largely independent of the thickness of the initial oxide layer. In contrast, the CO formation rate is at least one order of magnitude higher on the (reduced) Cu oxide samples than on Cu foil at the same potential. These results are interpreted as evidence that CO formation is enhanced at low-coordination number Cu sites present on freshly nucleated Cu clusters following oxide reduction.

Porous CoO/Mn2O3 Fischer-Tropsch (F-T) catalysts have been studied in CO hydrogenation. These CoO/Mn2O3 catalysts have been synthesized by incipient wetness impregnation method. These mesoporous catalysts have pore diameters of 2-25 nm and a surface area of 9.0 m2/g. The gas and liquid products have been analyzed by an online gas chromatograph. The solid products were characterized by gas chromatograph-mass spectroscopy. These microsize cobalt catalysts exhibit good activity with 72.1% CO conversion and they are very stable in a 48 h stream test at 280ºC. The selectivity to paraffins is above 95%. Few wax products were synthesized with a yield of less than 2%. The size effects of the cobalt catalysts have been studied by scanning electron microscopy.

We report in this communication on the photoelectrochemical (PEC) performances of copper tungstate (CuWO4) material class. This study was performed on 2-micron thick samples fabricated using a low-cost co-sputtering deposition process, followed by an 8-hour long annealing at 500°C in argon. Microstructural analysis pointed out that the post-deposition treatment was critical to achieve photocatalytic activity. Subsequent characterizations revealed that polycrystalline CuWO4 photoanodes owned promising characteristics for solar-assisted water splitting, i.e (i) an optical band-gap of 2.2 eV, (ii) a flat-band potential of -0.35 V vs. SCE and (iii) conduction and valence band-edges that straddle water splitting redox potentials. CuWO4 photoanodes generated 400 μA.cm-2 at 1.6V vs. SCE under simulated AM1.5G illumination in 0.33M H3PO4 with virtually no dark current up to this potential. Impedance analysis pointed out that large charge transfer resistances (2,500 Ω.cm2) could be the main weakness of this material class. Current research activity is focused on solving this issue to achieve higher PEC performances.

CexGd1-xO2-δ (CGO)-supported Ni nano grains were prepared initially by electrolessly depositing Ni-B alloy nano particles onto an activated carbon (AC). The as-deposited Ni-B particles were then transferred from AC to CGO through the metallo-organic precursor approach. The resultant Ni/CGO catalysts displayed excellent catalytic activity and chemical stability against coking and sulfur poisoning in catalyzing autothermal reforming (ATR) of a surrogate diesel fuel, comprising dodecane, tetralin and a substituted thiophene. For comparison purpose, a Ni/CGO catalyst prepared by the conventional impregnation method was employed in the same ATR system. These two catalytic systems exhibited rather discrepant outcomes. It was found that the Ni(B)/CGO catalyst was capable of repressing selectivity of ethylene during the reforming process. In addition to this, CGO played a critical role in thermal cracking hydrocarbon chains and inhibiting sulfur poisoning.