José J. Linares

Study of the acclimation stage and of the effect of the biodegradability on the performance of a microbial fuel cell

In this work, it has been studied the production of electricity and the oxidation of the pollutants contained in a synthetic wastewater fed with glucose and peptone of soybean as carbon sources, using a mediator-less microbial fuel cell (MFC). Special attention has been paid to the acclimation stage, in which it was found that with high hydraulic and solid retention times it is possible to obtain a very efficient process with a 90% COD removal and practically total conversion of COD into electricity (considering the typical stoichiometric yield of heterotrophic biomass). The influence of concentration sludge was studied working with three different amounts of suspended solids, from 120 to 14000 mg. The maximum power density increased exponentially with the concentration sludge from 2.1 mW m(-2) to 11 mW m(-2) at the highest concentration sludge. More over, the percentage of the influent COD used to produce electricity was higher than 100% when the highest sludge concentration was used. This was explained taking into account the endogenous metabolism of micro-organisms presented in the system. Moreover, wastewater with two different compositions, but with the same COD concentration, were studied. One with 50% of glucose and 50% of peptone of soybean and the other, with 80% of peptone and 20% of glucose. Spite of the wastewater with 50% of glucose is more biodegradable than the other composition used, the microbial fuel cell performance obtained was lower than with the other (2.1 mW m(-2) with respect to 6.8 mW m(-2) when 80% of peptone was used). This means that the degradation of peptone occurs through the production of intermediates that favour electricity.

NiMnOx/C: A Non-noble Ethanol-Tolerant Catalyst for Oxygen Reduction in Alkaline Exchange Membrane DEFC

A non-noble oxygen reduction catalyst based on nickel−manganese oxide supported on high-surface area carbon has been synthesized by a mild hydrothermal treatment, resulting in nanocrystalline needles. Cyclic voltammetry showed the electrochemical redox characteristics of this material, evidencing the appearance of peaks associated to consecutive reversible transitions involving Mn(IV)/Mn(III) and Mn(III)/Mn(II). The catalyst displayed a high activity for the oxygen reduction, despite that the complete reduction was not achieved, consuming less than three electrons of the four available in the oxygen molecule. More importantly, this activity did not decay under the presence of ethanol, revealing the high ethanol tolerance of this material. Finally, single-cell results have demonstrated the suitability of this material as cathode catalysts for alkaline DEFC: The open circuit voltage and the maximum power densities are close to those obtained by a standard Pt/C catalyst.

Performance of a direct glycerol fuel cell using KOH doped polybenzimidazole as electrolyte

This paper studies the influence of the operating variables (glycerol concentration, temperature and feed rate) for a direct glycerol fuel cell fed with glycerol using polybenzimidazole (PBI) impregnated with KOH as electrolyte and Pt/C as catalyst. Temperature displays a beneficial effect up to 75 oC due to the enhanced conductivity and kinetics of the electrochemical reactions. The optimum cell feed corresponds to 1 mol L-1 glycerol and 4 mol L-1 KOH, supplying sufficient quantities of fuel and electrolyte without massive crossover nor mass transfer limitations. The feed rate increases the performance up to a limit of 2 mL min-1, high enough to guarantee the access of the glycerol and the exit of the products. Finally, the use of binary catalysts (PtRu/C and Pt3Sn/C) is beneficial for increasing the cell performance.

PBI-Based Composite Membranes

This chapter focuses on the review of PBI-based composite membranes. These are composite materials with inorganic nanoparticles, such as, hygroscopic oxides, heteropolyacids and their derivates, and pyrophosphate, ionic liquids, and even carbon-based materials. Information about the membrane preparation, physicochemical characterization, proton conductivity, and fuel cell results has been provided. In most of the cases, good results have been presented in the literature, improving key properties such as the mechanical and thermal properties, and more importantly, the proton conductivity, which has impacted positively on the fuel cell performance. However, continuous investigations must be done to improve the fuel cell performance for practical applications.

Influence of the current density on the electrochemical treatment of concentrated 1-butyl-3-methylimidazolium chloride solutions on diamond electrodes.

This paper focuses on the influence of the current density treatment of a concentrated 1-butyl-3-methylimidazolium chloride (BMImCl) solution on an electrochemical reactor with a boron-doped diamond (BDD) anode. The decrease in the total organic carbon (TOC) and the BMImCl concentration demonstrate the capability of BDD in oxidizing ionic liquids (ILs) and further mineralizing (to CO2 and NO3−) more rapidly at higher current densities in spite of the reduced current efficiency of the process. Moreover, the presence of Cl− led to the formation of oxychlorinated anions (mostly ClO3− and ClO4−) and, in combination with the ammonia generated in the cathode from the nitrate reduction, chloramines, more intensely at higher current density. Finally, the analysis of the intermediates formed revealed no apparent influence of the current density on the BMImCl degradation mechanism. The current density presents therefore a complex influence on the IL treatment process that is discussed throughout this paper.

The Gas Diffusion Layer in High Temperature Polymer Electrolyte Membrane Fuel Cells

1.1 Polymer electrolyte membrane fuel cells. Operation at high temperature (120-200oC) 1.1.1 General overview Polymer Electrolyte Membrane Fuel Cells (PEMFC) can be considered as one of the most attractive type of fuel cells. They are able to produce efficiently high power densities. In addition, the use of a polymer electrolyte implies several advantages (Fuel Cell Handbook, 2004), such as low problems of sealing, assembling and handling. No corrosive acids, compared to Phosphoric Acid Fuel Cells (PAFC) are used, and the low temperature of the cell allows faster responses to changes in load demands. The characteristics of these cells make them especially suitable for automotive applications, even though they are also used for stationary generation, and currently, there is a great research effort for its application on portable devices (laptops, mobile phones, cameras, etc.). PEMFC are composed of the following basic elements:  Ionic exchange membrane (PEM).  Gas diffusion layer (GDL).  Catalytic layer (CL).  Monopolar/bipolar (in case of a stack) plates. The combination of the GDL+CL+PEM forms the membrane-electrode-assembly (MEA), which is the real heart of a PEMFC. This MEA can be formed by applying pressure and temperature to the (GDL+CL) in the anode side/PEM/(GDL+CL) in the cathode side (hot pressing procedure), or by directly depositing the CL onto the PEM, and subsequent hot pressing with the GDL. Ionic exchange membrane fulfils the role of allowing the transient of ionic charges from the anode to the cathode, closing the electrical circuit. It also possesses a low permeability to the gases, in order to avoid the depolarization of the electrode (Savadogo, 2004). A high mechanical and chemical stability is also required for these materials, due to the harsh operational conditions (oxidant and reducing gases in an acid medium). The most extended PEM material is Nafion®, a perflurosulphonated material, whose structure consists of a perfluorocarbon skeleton (Teflon-like), onto which, branch chains with pendant sulphonic acid groups are located, allowing the transient of ionic charges (see Figure 1).