Compendium of Hydrogen Energy

Hydrogen Energy Conversion

Frano Barbir, Angelo Basile, T. Nejat Veziroglu

• Publisher: Woodhead Publishing
• Year: 2015
• Print ISBN: 9781782423638
• eBook ISBN: 9781782423850
• Topic: Technology & Engineering
• Subtopic: Renewable Power Resources
• Index: Technology & Engineering

Compendium of Hydrogen Energy: Hydrogen Energy Conversion, Volume Three is the third part of a four volume series and focuses on the methods of converting stored hydrogen into useful energy. The other three volumes focus on hydrogen production and purification; hydrogen storage and transmission; and hydrogen use, safety, and the hydrogen economy, respectively.Many experts believe that, in time, the hydrogen economy will replace the fossil fuel economy as the primary source of energy. Once hydrogen has been produced and stored, it can then be converted via fuel cells or internal combustion engines into useful energy.This volume highlights how different fuel cells and hydrogen-fueled combustion engines and turbines work. The first part of the volume investigates various types of hydrogen fuel cells, including solid oxide, molten carbonate, and proton exchange membrane. The second part looks at hydrogen combustion energy, and the final section explores the use of metal hydrides in hydrogen energy conversion.- Highlights how different fuel cells and hydrogen-fueled combustion engines and turbines work- Features input written by leading academics in the field of sustainable energy and experts from the world of industry- Examines various types of hydrogen fuel cells, including solid oxide, molten carbonate, and proton exchange membrane- Presents part of a very comprehensive compendium which, across four volumes, looks at the entirety of the hydrogen energy economy

Part One

Fuel cells

1

Proton exchange membrane fuel cells

B.G. Pollet*; A.A. Franco^†,‡,§; H. Su*; H. Liang*; S. Pasupathi* ^* Eau2Energy, Nottingham, UK
^† Université de Picardie Jules Verne, Amiens Cedex, France
^‡ Réseau sur le Stockage Electrochimique de l’Energie (RS2E), Amiens, France
^§ ALISTORE European Research Institute, Amiens Cedex, France

Abstract

When oil, one of the most important energy sources in the history of mankind, was first discovered in Pennsylvania almost 150 years ago, the fuel cell had already been known for 20 years, invented by Sir William Grove, “father of the fuel cell,” in 1839. Back then it was an idea that was far ahead of its time. Today, however, it is the most important development in the history of decentralized energy supply. Today, fuel cells are widely considered to be efficient and nonpolluting power sources offering much higher energy densities and energy efficiencies than any other current energy storage devices. Fuel cells are, therefore, considered to be promising energy devices for the transport, mobile, and stationary sectors. A fuel cell is an “electrochemical” device operating at various temperatures (up to 1000 °C) that transforms the chemical energy of a fuel (hydrogen, methanol, natural gas, etc.) and an oxidant (air or pure oxygen) in the presence of a catalyst into water, heat, and electricity. Furthermore, the power generated by a fuel cell depends largely upon the catalytic electrodes and materials used. There are currently six main groupings of fuel cell available: (i) proton exchange membrane fuel cell (PEMFC) including direct methanol fuel cell; (ii) alkaline fuel cell (AFC); (iii) phosphoric acid fuel cell (PAFC); (iv) molten carbonate fuel cell (MCFC); (v) solid oxide fuel cell (SOFC); and (vi) microbial fuel cell (MFC). PEMFC, AFC, PAFC, and MFC operate at low temperatures in the range of 50–200 °C and MCFC and SOFC at high temperatures in the range of 650–1000 °C. This chapter focuses on the proton exchange membrane fuel cell (PEMFC).

Keywords

Hydrogen

PEMFC

Materials

Modelling

Degradation

1.1 Fabrication and manufacturing of fuel cells

1.1.1 Introduction

Fuel cells have emerged as a vital alternative energy solution to reduce societal dependence on internal combustion engines and lead acid batteries. Fuel cells promise significantly improved energy efficiency with zero or low greenhouse gas emissions, and they are expected to play a key role in the hydrogen economy. Fuel cell technology is based upon the simple CHEMICAL reaction given in the following equation:

$2{\mathrm{H}}_2+{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}$

(1.1)

The proton exchange membrane fuel cell (PEMFC) is one of the most elegant types of fuel cells, which is fed hydrogen, which is oxidized at the anode, and oxygen that is reduced at the cathode. The protons released during the oxidation of hydrogen are conducted through the proton exchange membrane to the cathode. As the membrane is not electrically conductive, the electrons released from the hydrogen travel along the electrical detour provided, and an electrical current is generated. These reactions and pathways are shown schematically in Figure 1.1.

Figure 1.1 Schematic of a single typical PEMFC. Copyright Bruno G. Pollet.

1.1.2 Principles of membrane electrode assembly

The membrane electrode assembly (MEA) is the heart of PEMFCs, where the electrochemical reactions take place to generate electrical power. The MEA is pictured in the schematic of a single PEMFC shown in Figure 1.2. The MEA is typically sandwiched by two flow field plates that are often mirrored to make a bipolar plate when cells are stacked in series for greater voltages.

Figure 1.2 Single PEMFC schematic.

The MEA consists of a proton exchange membrane, catalyst layers (CLs), and gas diffusion layers (GDLs). Typically, these components are fabricated individually and then pressed to together at high temperatures and pressures. An ideal MEA would allow all active catalyst sites in the CL to be accessible to the reactant (H₂ or O₂), protons, and electrons and would facilitate the effective removal of produced water from the CL and GDL.

Analogous cathode and anode reactions in the MEA for a H₂/O₂ fuel cell are

$\mathrm{Cathode}:\frac{1}{2}{\mathrm{O}}_2+2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2\mathrm{O}$

(1.2)

$\mathrm{Anode}:{\mathrm{H}}_2\to 2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}$

(1.3)

The flow of ionic charge through the electrolyte must be balanced by the flow of electronic charge through an outside circuit, and it is this balance that produces electrical power.

Several review articles in the literature cover specific aspects of PEMFC. The MEA fabrication technologies is a key element for creating a fuel cell that will perform at a high level. Over the past several decades, great efforts have been made to optimize the CL, MEA structures, and fabrication methods have been developed. In this chapter, we attempt to cover some MEA fabrication methods commonly practiced in a low-temperature fuel cell laboratory, with emphasis on applied aspects. Some mention of techniques that are useful in the investigation of various aspects of fuel cells, such as the alkaline fuel cell (AFC) and the phosphoric acid fuel cell (PAFC).

1.1.3 Overview of MEA components

1.1.3.1 Catalyst layer

The CL is a key component in the gas diffusion electrodes (GDEs), as the location where electrochemical reactions take place. The CLs need to be designed to generate high rates of the desired reactions and minimize the amount of catalyst necessary for reaching the required levels of power output. An ideal CL should maximize the active surface area per unit mass of the electrocatalyst and minimize the obstacles for reactant transport to the catalyst, for proton transport to exact positions, and for product removal from the cell; these requirements entail an extension of the three-phase boundary.

1.1.3.2 Gas diffusion layer

The porous GDL in PEMFCs ensures that reactants effectively diffuse to the CL. In addition, the GDL is the electrical conductor that transports electrons to and from the CL. Typically, GDLs are constructed from porous carbon paper, or carbon cloth, with a thickness in the range of 100–300 μm. The GDL also assists in water management by allowing ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of contributors
• Woodhead Publishing Series in Energy
• Part One: Fuel cells
• Part Two: Hydrogen combustion and metal hydride batteries
• Index
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