Investigation of carbon-supported Pt nanocatalyst preparation by the polyol process for fuel cell applications

Decrease in the Surface Tension of Nanobubble Dispersion in Water: Results of Surface Excess of Bulk Nanobubbles at Interfaces

The effect of nanobubbles (NBs) on the surface tension of liquid was investigated by three methods of different measuring principles, pendant drop (PD), Wilhelmy, and du Noüy methods, over a wide range of number concentration of bulk NBs (BNBs). In all of the three methods, the surface tension decreased in proportion to the number concentration of BNBs and the proportional constant was different among the three methods. Such behavior was inferred to be caused by the surface excess of BNBs at the gas-liquid or solid-liquid interface. In the PD method, the hydrophobic interaction between BNBs and air around a drop seems to cause the surface excess of BNBs along the surface of water drops. It brings about a subtle change in its profile, resulting in the decrease in surface tension, which takes a time of hundreds of seconds. Meanwhile, in the Wilhelmy and du Noüy methods, electrostatic attractive force between BNBs and a plate or ring is a likely cause of surface excess at the solid-liquid interface, resulting in the instantaneous decrease in surface tension. This study also provides a practical methodology of comparison for surface tension of NB dispersion: surface tension shall be compared among different samples with the same measurement method. Especially in the PD method, retention time of droplets before measurement shall be the same among samples.

Stochastic Kinetics of Nanocatalytic Systems

Catalytic reaction events occurring on the surface of a nanoparticle constitute a complex stochastic process. Although advances in modern single-molecule experiments enable direct measurements of individual catalytic turnover events occurring on a segment of a single nanoparticle, we do not yet know how to measure the number of catalytic sites in each segment or how the catalytic turnover counting statistics and the catalytic turnover time distribution are related to the microscopic dynamics of catalytic reactions. Here, we address these issues by presenting a stochastic kinetics for nanoparticle catalytic systems. We propose a new experimental measure of the number of catalytic sites in terms of the mean and variance of the catalytic event count. By considering three types of nanocatalytic systems, we investigate how the mean, the variance, and the distribution of the catalytic turnover time depend on the catalytic reaction dynamics, the heterogeneity of catalytic activity, and communication among catalytic sites. This work enables accurate quantitative analyses of single-molecule experiments for nanocatalytic systems and enzymes with multiple catalytic sites.

Kinetic Isotope Effect as a Tool To Investigate the Oxygen Reduction Reaction on Pt-based Electrocatalysts - Part II: Effect of Platinum Dispersion

We investigated the oxygen reduction reaction (ORR) mechanism on Pt nanoparticles (NPs) dispersed on several carbon blacks with various physicochemical properties (i. e. specific surface ranging from 80 to 900 m²  g^-1 , different graphitization degree, etc.). Using the kinetic isotope effect (KIE) along with various electrochemical characterizations, we determined that the rate determining step (RDS) of the ORR is a proton-independent step when the density of Pt NPs on the surface of the carbon support is high. Upon decrease of the density of Pt NPs on the surface, the RDS of the ORR starts involving a proton, as denoted by an increase of the KIE >1. This underlined the critical role played by the carbon support in the oxygen reduction reaction electrocatalysis by Pt supported on high surface area carbon.

Nanocatalytic chemohydrodynamic instability: Deposition effects

Due to the high surface area to volume ratio of nanoparticles, nanocatalytic reactive flows are widely utilized in various applications, such as water purification, fuel cell, energy storage, and biodiesel production. The implementation of nanocatalysts in porous media flow, such as oil recovery and contaminant transport in soil, can trigger or modify the interfacial instabilities called viscous fingering. These instabilities grow at the interface of the fluids when a less viscous fluid displaces a high viscous one in porous media. Here the flow dynamics and the total amount of chemical product are investigated when two reactive miscible fluids meet in a porous medium while undergoing A+B+n → C+n reaction. Nanocatalysts (n) are dispersed in the displacing fluid and deposited gradually with time. Four generic regimes are observed over time as a result of the particle deposition: (1) the initial diffusive regime, where the flow is stable with decreasing production rate, (2) the mixing-dominant fingering regime, where the flow is unstable and the production rate generally increases, (3) the transition regime, where the production rate generally decreases regardless of whether the system is stable or unstable, and (4) the final zero-production regime, where the product diffuses and fades away in the channel. Although the general trend shows a decreasing reaction rate with nanocatalysts deposition, there is a period in which the production rate increases due to the moderate deposition rates. Such an increase of production, however, is not observed in two groups: first, those systems in which the nanocatalysts do not change the viscosity of the base fluid and, second, a subgroup of the systems that are stable before and after the reaction in the absence of deposition.

Synergistic Effect of Nitrogen Doping and MWCNT Intercalation for the Graphene Hybrid Support for Pt Nanoparticles with Exemplary Oxygen Reduction Reaction Performance

The potential of graphene–multi-walled-carbon nanotube (G-M) hybrids prepared by the one-pot modified Hummers method followed by thermal annealing has been demonstrated by employing one as an electrocatalyst support for oxygen reduction reaction (ORR). N doping effectively modified the electronic structure of the G-M hybrid support, which was beneficial for the uniform distribution of Pt nanoparticles, and ORR activities were further improved. The newly prepared Pt/N-G-M catalyst demonstrated higher electrochemical activity than Pt/G-M and Pt/G catalysts. Even compared with commercial 20 wt % Pt/C (JM20), Pt/N-G-M delivered a better half-wave potential and mass activity. In terms of the durability test, Pt/N-G-M maintained 72.7% of its initial electrochemical active surface area (ECSA) after 2000 repeated potential cycles between 0 and 1.2 V in acidic media in relation to the 44.4% retention for JM20. Moreover, the half-wave potential for Pt/N-G-M showed only a minimal change, significantly superior to the 139 mV of loss for JM20. It is expected that Pt/N-G-M can be the potential candidate as a highly efficient and durable catalyst if utilized in proton exchange membrane fuel cells (PEMFCs).

Effect of different solvent ratio (ethylene glycol/water) on the preparation of Pt/C catalyst and its activity toward oxygen reduction reaction

Particle size and distribution of 50 wt% Pt/C can be determined by the volume ratio of EG/H₂O in the synthesis.

Promotional effect of copper(ii) on an activated carbon supported low content bimetallic gold–cesium(i) catalyst in acetylene hydrochlorination

Cu-added low content AuCs/AC worked as highly active, stable and cost-effective catalyst for acetylene hydrochlorination. Our findings suggest that the AuCuCs/AC catalyst can be envisioned as a viable alternative to commercial toxic HgCl₂for acetylene hydrochlorination.

Sonochemical synthesis of carbon supported Sn nanoparticles and its electrochemical application

A sonochemical approach was employed to prepare Vulcan carbon XC-72R supported by Sn nanoparticles at room temperature in the presence of ethylene glycol. The reduction of metallic Sn ion and ethylene glycol takes place and in turn the glycolate ion as formed acts as a stabilizing agent. Transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy have illustrated that the metallic Sn nanoparticles are successfully embedded on the carbon. The significantly observed reduction over potential for oxygen reduction reaction displays a higher catalytic activity of carbon supported by Sn nanoparticles due to the large surface area of the modified electrode.

Influences of pH value in deposition-precipitation synthesis process on Pt-doped TiO2 catalysts for photocatalytic oxidation of NO

This work has been undertaken to study the influences of pH value on the characteristics and activity of photocatalyst by deposition-precipitation method during its preparation process. A series of Pt-modified TiO2 were prepared by deposition-precipitation method at different pH values as well as wet impregnation method, and characterized by XRD, XPS, TEM, UV-Vis and photoluminescence (PL). It was found that the catalysts had the highest photocatalytic activity for NO conversion when pH value was kept at around 7. And the sample prepared by deposition-precipitation method showed higher activity than that by impregnation method. This was mainly due to their high value in highly-dispersed platinum oxides (PtOx) content on the surface of the catalysts. The results from UV-Vis absorption showed that highest absorbance was obtained for Pt/TiO2 prepared at pH values of around 7. And PL spectra results indicated that the recombination rate of photogenerated electrons and holes of the samples prepared by deposition-precipitation method was lower than that prepared by impregnation method. And in the zeta potential study, the pH values for the isoelectric point of the preparing slurry of 0.05 wt.%Pt/TiO2 and 0.5 wt.%Pt/TiO2 were determined to be 6.5-8.5, which further confirmed the enrichment of PtOx dopants for the catalysts repapered when pH value was around 7.