Giuseppe A. Camara

Effect of thermal treatment on the performance of CO-tolerant anodes for polymer electrolyte fuel cells

Abstract In this work, carbon-supported Pt:Ru electrocatalysts, mainly for application in polymer electrolyte fuel cells, have been prepared by different methods. The materials were tested in single cells with respect to the hydrogen–oxidation reaction in the presence of CO, and the performances, before and after thermal treatments, compared to that of state-of-the-art, commercial E-TEK catalysts. In most cases, it was found that the performance of the anode improves substantially after the thermal treatment of the material. Of the several methods considered, the preparation of the catalyst via the formation of a sulfite complex, followed by a thermal treatment, gave the best results, comparable to those obtained with the state-of-the-art catalyst.

Agglomeration and Cleaning of Carbon Supported Palladium Nanoparticles in Electrochemical Environment

AbstractHere we investigate the electrochemical behavior of Pd/C synthesized by reduction with ethylene glycol in the presence of polyvinylpyrrolidone (EG-PVP). EG-PVP produces nanoparticles (NPs) with a narrow size distribution, but some of them remain covered by impurities after the synthesis. After successive voltammetric cycles, NPs become cleaner, but some agglomeration and structural modification occur; these effects affect the electrochemical behavior of Pd/C in different ways, so we used CO as a probe to better understand the processes taking place. CO stripping shows that the general features of the multiple oxidation peaks change with the number of cycles. Possibly, CO and OH from different NPs react when the particles agglomerate, contributing to CO stripping changes. Finally, different active areas are found when the charges involved in CO oxidation and PdO reduction are compared. Such differences are rationalized in terms of a balance between the increase of sites which promote the oxidation of CO and the loss of area provoked by the growing of the particles. FigureAfter successive voltammetric cycles, Pd/C NPs become cleaner with slightly agglomeration, which lead to increase of the electrochemically active surface area. The value of area reaches a maximum, after this point the agglomeration is the main effect and contributes to the surface area decay. The agglomeration facilitates the CO electrooxidation reaction among NPs

Mobility and Oxidation of Adsorbed CO on Shape-Controlled Pt Nanoparticles in Acidic Medium

The knowledge about how CO occupies and detaches from specific surface sites on well-structured Pt surfaces provides outstanding information on both dynamics/mobility of COads and oxidation of this molecule under electrochemical conditions. This work reports how the potentiostatic growth of different coverage CO adlayers evolves with time on both cubic and octahedral Pt nanoparticles in acidic medium. Data suggest that during the growth of the CO adlayer, COads molecules slightly shift toward low coordination sites only on octahedral Pt nanoparticles, so that these undercoordinated sites are the first filled on octahedral Pt nanoparticles. Conversely, on cubic Pt nanoparticles, adsorbed CO behaves as an immobile species, and low coordinated sites as well as (100) terraces are apparently filled uniformly and simultaneously. However, once the adlayer is complete, irrespectively of whether the CO is oxidized in a single step or in a sequence of different potential steps, results suggest that COads behaves as an immobile species during its oxidation on both octahedral and cubic Pt nanoparticles.

Electrooxidation of ethanol on Pt and PtRu surfaces investigated by ATR surface-enhanced infrared absorption spectroscopy

Herein, it was investigated for the first time the electro-oxidation of ethanol on Pt and PtRu electrodeposits in acidic media by using in situ surface enhanced infrared absorption spectroscopy with attenuated total reflection (ATR-SEIRAS). The experimental setup circumvents the weak absorbance signals related to adsorbed species, usually observed for rough, electrodeposited surfaces, and allows a full description of the CO coverage with the potential for both catalysts. The dynamics of adsorption-oxidation of CO was accessed by ATR-SEIRAS experiments (involving four ethanol concentrations) and correlated with expressions derived from a simple kinetic model. Kinetic analysis suggests that the growing of the CO adsorbed layer is nor influenced by the presence of Ru neither by the concentration of ethanol. The results suggest that the C-C scission is not related to the presence of Ru and probably happens at Pt sites.

Chapter 2 – Contributions of External Reflection Infrared Spectroscopy to Study the Oxidation of Small Organic Molecules

Publisher Summary This chapter discusses the electro-oxidation of small organic molecules through the application of in-situ Fourier transform infrared spectroscopy (FTIRS). The in-situ FTIRS technique was used for characterizing diverse electrochemical systems involving faradaic and non-faradaic processes. Carbon monoxide (CO) is considered to be a poison for alcohol oxidation. When alcohols having more than one carbon atom are oxidized, the presence of CO indicates that the catalyst is able to produce the scission of a C–C bond. At the same time this is also a desirable property for an electrode material. Carbon monoxide electro-oxidation at platinum electrodes depends on the adsorption potential. The presence of CO helps in H-bonding association and ice formation at Pt surfaces. Under ultrahigh vacuum (UHV) conditions, water is absorbed via the oxygen atom; whereas at the electrochemical interface, the orientation of water depends on the potential. The examples discussed in this chapter show both the potential and limitations of in-situ FTIRS for studying complex electrode processes.

Alternative Uses for Biodiesel Byproduct: Glycerol as Source of Energy and High Valuable Chemicals

Glycerol was firstly faced as a residue, since it is massively produced from the transesterification of vegetable oils and animal fat, corresponding to roughly 10% of the total amount of biodiesel. The recent high availability of glycerol has decreased its price and increased the risks of environmentally inadequate disposal. Now, this small chain alcohol is faced as a powerful alternative for energy conversion and production of chemicals with commercial interest. Its three hydrated carbons make this organic a noticeable substrate to produce other carbonyl compounds and to be used to produce energy in electrochemical devices collectively known as direct alcohol fuel cells. The development in the electrocatalysis field opened up new strategies to convert glycerol into power and chemicals, by using fuel cells and electrolyzer reactors. In both systems, the efficiency of the process depends on several aspects, as the medium, applied potential, and mainly on the surface reaction taking place at the interface between solution and electrode. In this chapter, we discuss the use of glycerol in these electrochemical systems and illustrate some experimental results regarding fundamental and applied science. Namely, we describe some advances in the understanding of the glycerol electro-oxidation reaction interpreted by spectroscopy and chromatographic techniques. Novel nanomaterials currently applied to improve the catalysis of the reaction are also shown. Moreover, we comment some results regarding fuel cells, microfluidic fuel cells, and electrolyzers fed by glycerol and the perspectives and challenges of its use.

Estimating the Time-Dependent Performance of Nanocatalysts in Fuel Cells Based on a Cost-Normalization Approach

Researchers have developed new catalysts for fuel cells (FC), whose performances are compared after applying different normalization procedures. However, there is not a standard procedure. The current produced from CO electrooxidation was compared for Pt4Ru5Sn1/C and homemade Pt/C nanoparticles (NPs) normalized by different methods and the use of different methods renders different interpretations. Since the whole field aims to maximize the cost-effectiveness, a complementary method to normalize currents and power in terms of the total cost of the nanocatalyst, the Catalyst-based Cost method (CbC), was proposed. CbC considers the cost of all metals employed to build the catalyst, not only those ones with available surfaces. By applying a simple smoothing method on the prices in a time series, we were able to forecast the prices and consequently the power density of a FC. CbC provides tools for industrials forecast the designing of nanomaterials with improved efficiency and low cost.

Ethylene Glycol Electro-Oxidation on Platinum-Free Surfaces: How the Composition of PdRuRh Surfaces Influences the Catalysis

-1 ). The electrochemical results show that the ethylene glycol oxidation is sensitive to the composition of the catalysts, being PdRuRh 74:09:17 the composition which presents the best catalytic activity. Also, conversely to Pt, these surfaces do not present a self-inhibitory effect when the EG concentration is increased. FTIR results indicate a complex reaction mechanism under these conditions, where glycolic acid, oxalic acid, formic acid and CO2 are detected as electro-oxidation products. The best catalytic activity observed for PdRuRh 74:09:17 can be understood in terms of a higher selectivity towards the production of CO2, which is the oxidation pathway that involves the release of the major number of electrons.

All at once: how electrochemistry can be used to design and access multiple compositions in a single sample

A library of binary PtRh thin-film electrocatalysts was obtained by potentiostatic co-electrodeposition of Pt4+ and Rh3+ on a gold wire in a capillary cell, the capillary separating on the one hand the Pt4+ compartment and on the other hand the Rh3+ compartment. More specifically, this capillary cell enables to hinder the mobility of the ions from the one compartment to the other, thereby creating a continuous gradient of concentrations of Pt4+ and Rh3+ in the solution along the gold wire; as a result, the surface of the gold wire substrate witnesses crossed gradients of Pt4+ and Rh3+ during the electrodeposition, and countless PtRh compositions can be generated on the surface of a single sample. The feasibility of the protocol was confirmed by electron probe microanalysis and sections of the film (with lengths of 1 mm) were subsequently accessed by cyclic voltammetry. The results demonstrate the potential of this approach to perform compositional studies in a single piece of substrate and open new perspectives of studies in catalysis and electrocatalysis with a relatively low-cost and time-saving approach.

Electrocatalytic oxidation of carbon monoxide

This work discusses some important aspects related to the carbon monoxide electrooxidation reaction on Pt single crystal electrodes in acidic media. The mechanistic aspects are discussed in terms of the formation of compact structures developed when CO is adsorbed. The main ideas presented here are focused on the mechanistic aspects that take into account the existence of such structures. The classical kinetic mechanisms of Lagmuir-Hinshelwood and Eley-Rideal are discussed considering the superficial mobility of CO or nucleation-growing of islands formed by oxygen-containing adsorbates.