Sivakumar Pasupathi

FeN stabilized FeN@Pt core–shell nanostructures for oxygen reduction reaction

The high cost and poor stability of catalysts are the main obstacles for the commercialization of proton exchange membrane (PEM) fuel cells, particularly, the catalysts for the oxygen reduction reaction (ORR). Here, PtFe nanocatalysts with different Pt to Fe atomic ratios are prepared by the impregnation-reduction method and subsequently thermal annealing in NH3 at ambient pressure. XRD, STEM, XPS and ICP are employed to investigate the corresponding physico-chemical properties of the as-prepared catalysts, which demonstrate that the samples are Pt-rich core–shell nanostructures. The cyclic voltammetry method is used to investigate their electrochemical performance, and the results show that these catalysts display high ORR activity in O2-saturated 0.1 mol L−1 HClO4 aqueous solutions, with PtFe3N/C displaying the highest mass activity of 369.32 mA mg−1 Pt in 0.90 V vs. RHE, which is about 3 times higher than that of a commercial Pt/C catalyst (129.15 mA mg−1 Pt) at the same potential. Moreover, it is also found that the as-prepared catalysts are almost 2 times more stable than the commercial Pt/C. The ORR activity is slightly affected after 30k cycles in O2-saturated HClO4 aqueous solutions. This low cost ORR catalyst, which exhibits a high performance, opens up possibilities for designing core–shell nanostructures for energy conversion.

Electrophoresis and stability of nano-colloids: History, theory and experimental examples

The paper contains an extended historical overview of research activities focused on determining interfacial potential and charge of dispersed particles from electrophoretic and coagulation dynamic measurements. Particular attention is paid to nano-suspensions for which application of Standard Electrokinetic Model (SEM) to analysis of experimental data encounters difficulties, especially, when the solutions contain more than two ions, the particle charge depends on the solution composition and zeta-potentials are high. Detailed statements of Standard Electrokinetic and DLVO Models are given in the forms that are capable of addressing electrophoresis and interaction of particles for arbitrary ratios of the particle to Debye radius, interfacial potentials and electrolyte compositions. The experimental part of the study consists of two groups of measurements conducted for Pt/C nano-suspensions, namely, the electrophoretic and coagulation dynamic studies, with various electrolyte compositions. The obtained experimental data are processed by using numerical algorithms based on the formulated models for obtaining interfacial potential and charge. While analyzing the dependencies of interfacial potential and charge on the electrolyte compositions, conclusions are made regarding the mechanisms of charge formation. It is established that the behavior of system stability is in a qualitative agreement with the results computed from the electrophoretic data. The verification of quantitative applicability of the employed models is conducted by calculating the Hamaker constant from experimental data. It is proposed how to explain the observed variations of predicted Hamaker constant and its unusually high value.

Components for PEM Fuel Cells: An Overview

Fuel cells, as devices for direct conversion of the chemical energy of a fuel into electricity by electrochemical reactions, are among the key enabling technologies for the transition to a hydrogen-based economy. Among the various types of fuel cells, polymer electrolyte membrane fuel cells (PEMFCs) are considered to be at the forefront for commercialization for portable and transportation applications because of their high energy conversion efficiency and low pollutant emission. Cost and durability of PEMFCs are the two major challenges that need to be addressed to facilitate their commercialization. The properties of the membrane electrode assembly (MEA) have a direct impact on both cost and durability of a PEMFC. An overview is presented on the key components of the PEMFC MEA. The success of the MEA and thereby PEMFC technology is believed to depend largely on two key materials: the membrane and the electro-catalyst. These two key materials are directly linked to the major challenges faced in PEMFC, namely, the performance, and cost. Concerted efforts are conducted globally for the past couple of decades to address these challenges. This chapter aims to provide the reader an overview of the major research findings to date on the key components of a PEMFC MEA.

Overview of Membrane Electrode Assembly Preparation Methods for Solid Polymer Electrolyte Electrolyzer

© 2012 Bladergroen et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Overview of Membrane Electrode Assembly Preparation Methods for Solid Polymer Electrolyte Electrolyzer

Synthesis and optimisation of IrO2 electrocatalysts by Adams fusion method for solid polymer electrolyte electrolysers

IrO 2 as an anodic electrocatalyst for the oxygen evolution reaction (OER) in solid polymer electrolyte (SPE) electrolysers was synthesised by adapting the Adams fusion method. Optimisation of the IrO 2 electrocatalyst was achieved by varying the synthesis duration (0.5 - 4 hours) and temperature (250 - 500°C). The physical properties of the electrocatalysts were characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD). Electrochemical characterisation of the electrocatalysts toward the OER was evaluated by chronoamperometry (CA). CA analysis revealed the best electrocatalytic activity towards the OER for IrO 2 synthesised for 2 hours at 350 o C which displayed a better electrocatalytic activity than the commercial IrO 2 electrocatalyst used in this study. XRD and TEM analyses revealed an increase in crystallinity and average particle size with increasing synthesis duration and temperature which accounted for the decreasing electrocatalytic activity. At 250°C the formation of an active IrO 2 electrocatalyst was not favoured.

High-Performance and Durable Membrane Electrode Assemblies for High-Temperature Polymer Electrolyte Membrane Fuel Cells

Membrane electrode assemblies (MEAs) with gas diffusion electrodes (GDEs) fabricated by various catalyst layer (CL) deposit technologies were investigated for the application of high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC). The physical properties of the GDEs were characterized by scanning electron microscopy (SEM) and pore size distribution. The electrochemical properties were evaluated and analyzed by polarization curve, Tafel equation, electrochemistry impedance spectroscopy (EIS), and cyclic voltammetry (CV). The results showed that the electrodes prepared by ultrasonic spraying and automatic catalyst spraying under irradiation (ACSUI) methods have superior CL structure and high electrochemistry activity, resulting in high fuel cell performances. Durability tests revealed the feasibility of the electrodes for long-term HT-PEMFC operation.

PEMFC for aeronautic applications: A review on the durability aspects

Abstract Proton exchange membrane fuel cells (PEMFC) not only offer more efficient electrical energy conversion, relative to on-ground/backup turbines but generate by-products useful in aircraft such as heat for ice prevention, deoxygenated air for fire retardation and drinkable water for use on-board. Consequently, several projects (e.g. DLR-H2 Antares and RAPID2000) have successfully tested PEMFC-powered auxiliary unit (APU) for manned/unmanned aircraft. Despite the progress from flying PEMFC-powered small aircraft with 20 kW power output as high as 1 000 m at 100 km/h to 33 kW at 2 558 m, 176 km/h [1, 2, 3], durability and reliability remain key challenges. This review reports on the inadequate understanding of behaviour of PEMFC under aeronautic conditions and the lack of predictive methods conducive for aircraft that provide real-time information on the State of Health of PEMFCs. Highlights: The main research findings are – To minimize performance loss due to high altitude and inclination by adjusting cathode stoichiometric ratio. – To improve quality of oxygen-depleted air by controlling operating temperature and stoichiometric ratio. – Need to devise real time prediction methods conducive for determining PEMFC SoH in aircraft.

Advances in HT-PEMFC MEAs

PEM (polymer electrolyte membrane) technology has been used in low-temperature fuel cells and high-temperature fuel cells, as well as water electrolyzers, for many years. Such electrochemical devices are of great interest and importance in the establishment of the so-called Hydrogen Economy . Advancement in polybenzimidazole (PBI)-based high-temperature proton exchange membrane fuel cells (HT-PEMFCs), specifically for stationary applications, has been achieved through systematic optimization of its components. Membrane electrode assembly (MEA) is the heart of an HT-PEMFC, and the fabrication of MEA is a key step for “real” HT-PEMFC applications. A series of studies on developing high-performance MEAs for PBI or ABPBI-based high-temperature fuel cells (120–180°C) are presented in this chapter. Some critical points and perspectives on developing high-performance MEAs are also summarized.

HT-PEMFC Modeling and Design

Modeling and simulation studies of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are important in order to better understand the operational behavior of the fuel cell and its performance and lifetime. These models play important roles in the understanding and prediction of HT-PEMFC performance and durability by analyzing various crucial parameters such as species concentrations, local current densities, temperature gradients, and pressure distributions within the fuel cell. These fuel cell modeling studies are often performed at the single cell level or stack level based on specific requirements and it may be either steady-state or dynamic using isothermal or nonisothermal models. The details of the modeling and simulation studies of HT-PEMFC at fuel cell level and stack level models including thermal management and electrochemical models are discussed in this chapter.

Catalysts for High-Temperature Polymer Electrolyte Membrane Fuel Cells

Increasing the temperature of polymer electrolyte membrane fuel cells (PEMFCs) implies advantages and disadvantages in terms of material cost, performance, and degradation. Platinum (Pt) is the best catalytic material for high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) electrodes, owing to the possibility it affords of minimizing CO poisoning with temperature enhancement. Nevertheless, it involves an increase in overall cost, mainly due to the larger platinum loadings used (when compared to Pt loadings for low-temperature polymer electrolyte membrane fuel cells). On the other hand, cathodic electrocatalysts still require that the kinetics of the sluggish oxygen reduction reaction be improved. Another disadvantage associated with the use of anodic and cathodic electrocatalysts is the corrosion of both carbon supports and catalytic nanoparticles, which is promoted by the increase in temperature. In this section, the most important factors affecting the performance of these materials are described and a brief description of the state of the art in the design and use of new materials in HT-PEMFCs is presented.