Karine Servat

Shape-dependent electrocatalytic activity of free gold nanoparticles toward glucose oxidation

The synthesis of shape and size-controlled free gold nanoparticles (AuNPs) was achieved by wet chemical methods. The UV–vis spectroscopy measurements and transmission electron microscopy characterizations confirmed the fine distribution in size and shape of the AuNPs. The zeta potential measurements permitted the evaluation of the stability of the AuNPs suspension. For the first time, the shape dependence on the electrocatalytic activity of these NPs is thoroughly investigated. The underpotential deposition (UPD) of lead reveals that their crystallographic facets are affected by their shape and growth process. Moreover, the glucose oxidation reaction strongly depends on the shape of AuNPs. Indeed, the gold nanocuboids (GNCs) and the spherical gold nanoparticles (GNSs) are significantly more active than the gold nanorods (GNRs) followed by the polyhedrons (GNPs). The oxidation process occurs at low potential for GNCs whereas the current densities are slightly higher for GNSs electrodes. Most importantly, the control of the shape and structure of nanomaterials is of high technological interest because of the strong correlation between these parameters and their optical, electrical and electrocatalytic properties.

Selective TEMPO‐Catalyzed Chemicals vs. Electrochemical Oxidation of Carbohydrate Derivatives

TEMPO‐catalyzed electrochemical oxidation of carbohydrate derivatives was performed and compared with chemical oxidation, which requires the use of co‐oxidants. Allyl‐protected derivatives could be readily oxidized by both methods. Electrochemical selective oxidation of primary positions has been adapted to unprotected mono‐ and oligosaccharides.

Facile synthesis of highly active and durable PdM/C (M = Fe, Mn) nanocatalysts for the oxygen reduction reaction in an alkaline medium

The efficient design of highly active and durable materials towards the ultimate goal of improving kinetics of the oxygen reduction reaction (ORR), which allow enhanced performance in solid alkaline membrane fuel cells (SAMFCs), remains elusive. Seminal studies have shown that by alloying a noble metal such as palladium to a transition metal, it is possible to tune the electronic and/or bifunctional properties enabling substantial ORR performance to be achieved, thereby designing a costly catalyst. Herein, we address and discuss new findings from deeper ORR investigations at palladium-based nanostructures in an alkaline medium. We exploited and manipulated the straightforward and fast synthesis method, the so-called “Bromide Anion Exchange”, to prepare surfactant-free PdM/C (M = Fe, Mn) nanocatalysts exhibiting unprecedented activity and stability towards ORR. PdFe/C from bromide anion exchange (BAE) enables 40- and 4-fold enhancement in terms of exchange current density and kinetic current density and ca. 100 mV gains compared to the polyol microwave-assisted method. After 20 000 cycles of accelerated potential cycling test (APCT), our findings indicate that the present PdM/C bimetallics outperform, to the best of our knowledge, most of the data reported for ORR in alkaline media for Pd-based transition metals. The improved catalytic performances are assigned to the absence of any organic contaminants or protective ligands on their surface and their relatively heterogeneous character comprising nanoalloys and nanowire oxides.

Highly Selective Oxidation of Carbohydrates in an Efficient Electrochemical Energy Converter: Cogenerating Organic Electrosynthesis

The selective electrochemical conversion of highly functionalized organic molecules into electricity, heat, and added-value chemicals for fine chemistry requires the development of highly selective, durable, and low-cost catalysts. Here, we propose an approach to make catalysts that can convert carbohydrates into chemicals selectively and produce electrical power and recoverable heat. A 100% Faradaic yield was achieved for the selective oxidation of the anomeric carbon of glucose and its related carbohydrates (C1-position) without any function protection. Furthermore, the direct glucose fuel cell (DGFC) enables an open-circuit voltage of 1.1 V in 0.5 m NaOH to be reached, a record. The optimized DGFC delivers an outstanding output power Pmax =2 mW cm(-2) with the selective conversion of 0.3 m glucose, which is of great interest for cogeneration. The purified reaction product will serve as a raw material in various industries, which thereby reduces the cost of the whole sustainable process.

High impact of the reducing agent on palladium nanomaterials: new insights from X-ray photoelectron spectroscopy and oxygen reduction reaction

Palladium has exceptional affinity with hydrogen and the evolution of the surface of its nanomaterials prepared from chemical methods over time is still unclear. Here, the reducing agent effect on Pd nanomaterials and their long-term chemical stability were scrutinized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The subsequent impact on the catalytic properties was examined using the electrochemical oxygen reduction reaction (ORR). We have discovered that the nature of the reducing agent has noteworthy effects on the final composition of Pd nanomaterials prepared from chemical methods. The surface state of the nanomaterials prepared by using sodium borohydride as reducing agent (Pd/C–NaBH4) is radically different from those obtained from L-ascorbic acid (Pd/C–AA). In addition to pure metal, two oxides were identified: PdO and PdOx (x > 1). XRD analysis has upheld the presence of PdO only in Pd/C–NaBH4, thus underpinning the conclusion that NaBH4 has drastically changed the Pd structure. Furthermore, the reducing agent substantially affects the electrocatalytic properties. The ORR starts with enhanced kinetics (E > 1 V vs. RHE) by a 4-electron process, producing p(H2O2) < 0.5% associated with excellent durability over 5000 cycles. Both catalysts outperform all reported data for Pd electrocatalysts. The novelty of this work is combining ex/in situ XPS and XRD analyses together with ORR as a catalytic model. Overall, this work represents a clear development in our understanding of Pd affinity towards hydrogen and paves new ways for the successful synthesis of Pd-based nanomaterials free from hydrides and oxides, and having impressive catalytic activities.

Identification of chemicals resulted in selective glycerol conversion as sustainable fuel on Pd-based anode nanocatalysts

Palladium-based nanoparticles were prepared using mild microwave-assisted heating. The activity of carbon supported PdM (M = Mn and Fe) toward glycerol oxidation in alkaline medium was studied by coupling electrochemical, analytical and in situ spectroscopic techniques. The complementary findings showed that glycerol was converted into oxalate, tartronate, glycerate, glycolate and formate. The ex situ analytical methods (liquid chromatography and mass spectrometry) were helpful to reveal glycerate as the major reaction product on PdM/C anodes, while from in situ infrared spectroscopy measurements no irreversible adsorbed poisoning species was detected in glycerol or intermediate oxidation to carbonate at the prepared electrodes. The correlation of the analytical and physicochemical (XRD, EDX and TEM) results concerned the shift of the onset potential toward lower values and the high Faradaic currents due to electronic structures provided by the Mn and Fe contents to the Pd based materials. Accordingly, glycerol is a sustainable raw material, which can be used in cogeneration processes for renewable energy sources and selective production of added-value molecules.

Kinetic Investigations of Glycerol Oxidation Reaction on Ni/C

This study evaluates the electrochemical oxidation of glycerol using a nickel-supported catalyst under several well-defined experimental conditions. The influence of scan rate, temperature, glycerol, and NaOH concentrations were systematically investigated. The slope of the log-log relationship of the anodic peak current for glycerol oxidation as a function of the scan rate indicates that the electrochemical glycerol oxidation is a complex mechanism partially limited by diffusion-controlled process. This is in agreement with the temperature effect on glycerol oxidation, since the slope value associated with the relationship between the logarithm of the current density of the anodic peak and the inverse of temperature also indicates a diffusion process. When the glycerol concentration increases, the peak associated to its oxidation also increases, but it seems to reach a limit. This behavior was associated with two main effects, i.e., the saturation of the active catalytic sites on the electrode surface and the change in the glycerol oxidation mechanism as demonstrated by FTIR spectroscopic measurements.

Advances in Electrocatalysis for Energy Conversion and Synthesis of Organic Molecules

Ubiquitous electrochemistry is expected to play a major role for reliable energy supply as well as for production of sustainable fuels and chemicals. The fundamental understanding of organics-based electrocatalysis in alkaline media at the solid-liquid interface involves complex mechanisms and performance descriptors (from the electrolyte and reaction intermediates), which undermine the roads towards advance and breakthroughs. Here, we review and diagnose recently designed strategies for the electrochemical conversion of organics into electricity and/or higher-value chemicals. To tune the mysterious workings of nanocatalysts in electrochemical devices, we examine the guiding principles by which the performance of a particular electrode material is governed, thus highlighting various tactics for the development of synthesis methods for nanomaterials with specific properties. We end by examining the production of chemicals by using electrochemical methods, from selective oxidation to reduction reactions. The intricate relationship between electrode and selectivity encourages both of the communities of electrocatalysis and organic synthesis to move forward together toward the renaissance of electrosynthesis methods.

Decorated nanotube buckypaper as electrocatalyst for glucose fuel cells

We present novel metallic/bimetallic (Pt, Au-Pt) nanoparticle-decorated carbon nanotubes and bilirubin oxidase-decorated carbon nanotubes deposited on nano-tube buckypaper as promising supported electro-catalytic systems and as electrode material respectively for mixed-reactant biofuel cell applications at neutral pH. We found that the novel enzyme-decorated carbon nanotubes on nanotube buckypaper material is a promising cathode for glucose biofuel cells. It exhibited a high tolerance and catalytic activity resulting in higher current densities compared to carbon black based electrodes.

Electrochemical Reactivity at Free and Supported Gold Nanocatalysts Surface

This chapter presents an overview on size, structure, morphology, composition as well as the effect of the support on the electrocatalytic properties of gold nanoparticles (AuNPs). It was found that the electrocatalytic properties of unsupported AuNPs strongly depend on their size and shape. Consequently, the electrocatalytic properties of AuNPs can be tuned. Furthermore, to design high-performance electrocatalysts with minimal precious metal content and cost, the direct immobilization of metal NPs onto carbon-based substrates during their synthesis constitutes another elegant alternative and has been thoroughly examined. These “easy-to-use” supports as scaffolds for AuNPs, namely carbon black, carbon paper, etc., offer beneficial contributions. Indeed, thanks to their high available surface area, good electronic conductivity and synergis‐ tic effect between the chemical species present on their surface and the loaded NPs, carbon-based supports enable maximizing the efficient utilization of the catalysts toward drastic enhancement in both activity and durability. We also examined different judicious combinations of (electro)analytical techniques for the unambiguous determi‐ nation of the reaction product(s) over the Au-based nanocatalysts, using glucose as model molecule given its importance in electrocatalysis. The performances of carbonsupported AuNPs as anode materials in direct glucose fuel cell in alkaline medium were