Direct Alcohol Fuel Cells for Portable Applications: Fundamentals, Engineering and Advances

By Alexandra M. F. R. Pinto, Vania Sofia Oliveira and Daniela Sofia Castro Falcao

Direct Alcohol Fuel Cells for Portable Applications: Fundamentals, Engineering and Advances presents the fundamental concepts, technological advances and challenges in developing, modeling and deploying fuel cells and fuel cell systems for portable devices, including micro and mini fuel cells. The authors review the fundamental science of direct alcohol fuel cells, covering, in detail, thermodynamics, electrode kinetics and electrocatalysis of charge-transfer reactions, mass and heat transfer phenomena, and basic modeling aspects. In addition, the book examines other fuels in DAFCs, such as formic acid, ethylene glycol and glycerol, along with technological aspects and applications, including case studies and cost analysis.

Researchers, engineering professionals, fuel cell developers, policymakers and senior graduate students will find this a valuable resource. The book’s comprehensive coverage of fundamentals is especially useful for graduate students, advanced undergraduate students and those new to the field.

• Provides a comprehensive understanding of the fundamentals of DAFCs and their basic components, design and performance
• Presents current and complete information on the state-of-the-art of DAFC technology and its most relevant challenges for commercial deployment
• Includes practical application examples, problems and case studies
• Covers the use of other fuels, such as formic acid, ethylene glycol and glycerol

• Language: English
• Publisher: Academic Press
• Release date: Sep 8, 2018
• ISBN: 9780128118986

Alexandra M. F. R. Pinto

Alexandra M. F. R. Pinto obtained her PhD on Combustion in 1991, after which she focused her activities on the transport phenomena area with particular interest in Mass Transfer and Characterization of two-phase flow patterns using advanced optical techniques. She integrated the know-how acquired with other skills of her core formation in chemical engineering into energy applications, in particular direct methanol and ethanol fuel Cells, microbial fuel cells, PEM fuel cells and hydrogen generators and storage systems. Dr. Pinto develops her research activities in the CEFT–Transport Phenomena Research Centre since its foundation in 1997, where she is presently the leader of the Energy Group. She was principal investigator in nine national projects and participated in other 12 projects, including two with industry partners. She has also been a member of European Network FCTESTNET (Fuel Cell Testing and Standardisation Network). Currently, Dr. Pinto is a professor at Renewable Energies and Chemical Engineering Laboratory of the Chemical Engineering Department of Porto University (DEQ-FEUP), Portugal, where she is director of the Doctoral Program in Chemical and Biological Engineering.

Book preview

Direct Alcohol Fuel Cells for Portable Applications

Fundamentals, Engineering and Advances

First Edition

Alexandra M.F.R. Pinto

Vânia B. Oliveira

Daniela S. Falcão

Table of Contents

Cover image

Title page

Copyright

Preface

Acknowledgments

1: Introduction to direct alcohol fuel cells

Abstract

1.1 What is a direct alcohol fuel cell (DAFC)?

1.2 Working principles

1.3 Advantages and disadvantages

1.4 Target applications and markets

1.5 Main challenges for DAFCs

Chapter summary

2: Direct alcohol fuel cells basic science

Abstract

2.1 Direct alcohol fuel cells thermodynamics

2.2 Electrode kinetics of DAFC reactions

2.3 Catalysis of electrochemical oxygen reduction and alcohol oxidation

2.4 Charge transport in DAFCs

2.5 DAFC mass transfer

2.6 DAFC heat transfer

Chapter summary

3: Direct alcohol fuel cells (DAFCs) basic modeling

Abstract

3.1 Passive DAFCs basic modeling

3.2 A 1D analytical passive DMFC model

3.3 Adaptation of the model to ethanol

3.4 DAFCs mechanistic models

Chapter summary

4: Experimental methods of characterization

Abstract

4.1 Overview of testing techniques

4.2 Fuel cell testing

4.3 Half-cell testing

4.4 Lifetime and durability

Chapter summary

5: Other fuels for direct fuel cells (DFCs)

Abstract

5.1 Direct ethylene glycol fuel cells (DEGFCs)

5.2 Direct glycerol fuel cells (DGFCs)

5.3 Direct formic acid fuel cells (DFAFCs)

5.4 Direct borohydride fuel cells (DBFCs)

5.5 Overview of different fuel cells

Chapter summary

6: Development of direct alcohol fuel cells components

Abstract

6.1 Electrocatalysts—State-of-the-art, goals, and challenges

6.2 Electrolytes—State-of-the-art, goals, and challenges

6.3 Diffusion layers—Materials and structure

6.4 Other components/layers

Chapter summary

7: Miniaturization of direct alcohol fuel cells: Microfabrication techniques and microfluidic architectures

Abstract

7.1 Microfabrication techniques—Micro-electro-mechanical systems (MEMS)

7.2 Design principles

Chapter summary

8: Direct alcohol fuel cell stacks

Abstract

8.1 Stack design principles

8.2 Mini-micro fuel cell stacks—State-of-the-art

Chapter summary

9: Case studies—Portable applications of direct alcohol fuel cells

Abstract

9.1 Overview on the portable DAFCs systems

9.2 DAFCs prototypes and products

9.3 Economic perspectives

9.4 Technical challenges: Durability/performance degradation

Chapter summary

10: Status and research trends of direct alcohol fuel cell technology

Abstract

10.1 Advanced modeling in DAFCs

10.2 Competing technologies: DAFCs and lithium batteries

10.3 Portable DAFC applications: Codes and standards and environmental effects

10.4 Remaining challenges

10.5 The next decade

Chapter summary

Index

Copyright

Academic Press is an imprint of Elsevier

125 London Wall, London EC2Y 5AS, United Kingdom

525 B Street, Suite 1650, San Diego, CA 92101, United States

50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States

The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom

© 2018 Elsevier Ltd. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher's permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.

This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

Library of Congress Cataloging-in-Publication Data

A catalog record for this book is available from the Library of Congress

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library

ISBN 978-0-12-811849-8

For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Joe Hayton

Acquisition Editor: Raquel Zanol

Editorial Project Manager: Mariana L. Kuhl

Production Project Manager: R.Vijay Bharath

Cover designer: Matthew Limbert

Typeset by SPi Global, India

Preface

Imagine a way of getting rid of all those wired chargers connected to your gadgets and simply plug a small cartridge containing alcohol into all your handheld devices to be powered for a whole week! What about bringing this simple solution to countries with lack of access to reliable modern energy and contribute to fight energy poverty? The massive use of new portable power devices and the conception of small decentralized grid-independent systems are part of the solution to the global energy problem.

Direct alcohol fuel cells (DAFCs) have a great potential in the portable power sector, mainly due to the easy miniaturization of liquid fuel cells technologies. These applications are gaining more and more interest, for example, in developing countries and rural areas where the grids are unreliable and people use mobile phones as a primary device.

This book intends to make the difference among the similar few titles available regarding the DAFC technology and has two main important goals: serve as a teaching tool and be a valuable reference for portable fuel cell researchers, designers, and manufacturers. The first part of the book is mainly directed to undergraduate and graduate students. At undergraduate level, it can be useful both in the electrochemistry and transport phenomena courses and at graduate level in renewable energy courses. The second part is more interesting to PhD students and researchers focused on material sciences for energy production and storage and interest in small fuel cells as portable energy sources, but also developers and policy makers in the renewable energy area.

Following these main ideas, the book is structured in two parts. Part I reviews the fundamental science of direct alcohol fuel cells giving particular attention to methanol and ethanol fuels. It covers, in detail, the thermodynamics, the electrode kinetics, and electrocatalysis of charge-transfer reactions, the mass and heat transfer phenomena, and basic modeling aspects for this type of fuel cells. A detailed description of the experimental characterization and diagnostics techniques, useful to fuel cell research and development, is also provided. The final chapter of Part I deals with small direct alcohol fuel cell stacks.

Part II covers engineering and technological aspects and the applications of the DAFCs in portable devices. It is focused on the state-of-the-art, main goals, and challenges in the areas of materials development, performance, and commercialization, comprising anodic and cathodic electrocatalysts, acid and alkaline membranes, diffusion layers, flow field plates, current collectors, and the other fuel cell components. Part II presents also a detailed chapter on micro-alcohol fuel cells covering microfluidics and microfabrication techniques. The final chapter of the book deals with the status of the portable DAFC technologies, presenting the research and development trends for the next future.

We count on the readers to help us improving the book! Please send any comments, questions, and suggestions to [e-mail]. Your feedback is very important to us and will be considered for the next edition. Thank you.

Acknowledgments

The authors would like to thank their friends and colleagues at Faculty of Engineering of University of Porto, and more specifically, the Chemical Engineering Department and Transport Phenomena Research Center (CEFT), for their support, critiques, comments, and enthusiasm.

Vânia B. Oliveira wants to thank Bruno and her little boy, Daniel, for their unconditional love, patience, and understanding. Without their support, everything would be more difficult! She extended her thanks to her mother and father for the love, education, and encouragement; to her sister, Anita, for the friendship and love and for being the best present she received from her parents!; to her parents-in-law for the support as amazing grandparents and to all of her friends and family.

Daniela S. Falcão is grateful to Carlos and her sweet children, Rafaela and André, for their unconditional love, support, and understanding. They make her laugh even when she is not in the mood of smile! She is thankful to her parents and mother-in-law for their help and encouragement and to all of her very good friends and family.

Alexandra M.F.R. Pinto wants to thank her students for being an inspiration during the long years of teaching. She wishes to acknowledge her family for the strong support in her life. She is grateful to her parents, forever living in her heart, for the education, unconditional love, and support as amazing grandparents; Mario, her life companion, for his friendship and love; her wonderful, sensitive, and encouraging children, Ricardo (and grandchildren Diogo and Mariana), Jú, Inês, João, and Rodrigo, the youngest, who came out in a mature time and helped her gain new energy to follow alternative routes in science. She often calls him the fuel-cell son…

1

Introduction to direct alcohol fuel cells

Abstract

The aim of this chapter is to prepare the reader to the journey into the direct alcohol fuel cells (DAFCs) learning and deeper understanding. Therefore, a broad overview of the DAFC technology, as well as its definition, is provided.

A brief comparison between fuel cells and batteries or combustion engines is made as well as a comparison between the DAFCs and its direct rival—the hydrogen PEMFC. The working principles of the DMFCs and DEFCs are presented together with the description of the two different types of fuel and oxidant supply in active and passive systems. The main advantages and disadvantages of the DAFCs are explained, stressing out the great potential of application in the portable sector. An introduction to the markets and target applications is then offered with the presentation of several examples of products already under commercialization. Finally, the main challenges of this technology are presented.

Keywords

Fuel cell; Direct alcohol fuel cell; Direct methanol fuel cell; Direct ethanol fuel cell; Active DAFC; Passive DAFC; Alcohol crossover; Water management; Portable applications; Stationary applications

The success of fuel-cell-powered vehicles such as Toyota Mirai using proton exchange membrane fuel cells (PEMFCs) shows that this technology has already reached the commercialization readiness level expected for many years. The interest in fuel cells of all types has increased dramatically, due to high efficiencies, nonexistence of gaseous pollutants (sulfur dioxide and various nitrogen oxides), and simple design, making them an attractive alternative to batteries and internal combustion engines. Furthermore, the urgent need of energy storage toward a fully sustainable energy paradigm reinforces the importance of this technology, since fuel cells along with hydrogen production by electrolysis are expected to play a major role linking energy storage and power generation.

A fuel cell (FC) is simply defined as an electrochemical energy converter, transforming the chemical energy of a fuel directly into electrical energy. It works as long as the electroactive chemicals are provided to the cell. Hydrogen usually emerges as the best fuel candidate, but to the date, production, storage and distribution of this fuel are still very complex issues. Alternatively, the Direct Fuel Cells (DFCs) using liquid organic fuels have gained increasing importance. The most commonly used liquid fuels in DFCs are alcohols such as methanol and ethanol, which have a much higher volumetric energy density and are much easier to store, transport, and distribute than hydrogen. DFCs and in particular direct alcohol fuel cells (DAFCs) usually have a compact design and potentially can offer up to 10 times the energy density of rechargeable batteries. In addition, DFCs can be designed to operate at ambient temperature, which significantly reduces thermal management challenges for small systems. These advantages make the technology attractive to the rapid growing need for portable power sources, which should include micro and small DAFCs. In particular, the small cells have market potential in education, auxiliary power systems, and recreational and military applications. Further research and development is needed to achieve the miniaturization needed for small fuel cells be integrated into consumer portable electronics, which will certainly unlock this significant market [1]. Important niche markets for portable applications are in developing countries and rural areas where the grids are unreliable and people use mobile phones as a primary communication device. Small decentralized power systems are seen as a way to keep communications open even when the power goes out.

This chapter is the beginning of a journey to the world of the DAFC technology and its tremendous field of applications. A comparison with the direct rival—hydrogen polymer electrolyte membrane fuel cells (PEMFCs)—is made all over the chapter.

1.1 What is a direct alcohol fuel cell (DAFC)?

A fuel cell is like a factory treating raw materials and delivering products [2]. The plant will be running as long as raw materials are available, generating its main product, electricity. Unlike batteries, fuel cells are not consumed during the energy production, i.e., they do not discharge. Like batteries, fuel cells have a positive and negative electrode and an electrolyte. Fuel cells, like combustion engines, transform the energy stored in a fuel in useful forms of energy, such as electrical, but in a direct conversion process. In the combustion machine, the heat released in the combustion reaction is converted into mechanical and afterwards into electrical energy in a potentially complex and inefficient process. The direct conversion of chemical energy into electrical energy occurring in fuel cells arises from the existence of a physical barrier between reactants (the electrolyte), in a way that the transfer of electrons involved in the bonds reconfiguration through an external trajectory can be harnessed as electrical current.

Fig. 1.1A and B give a schematic representation of a hydrogen-oxygen fuel cell and a direct alcohol fuel cell.

Fig. 1.1 Schematic representation of (A) hydrogen-oxygen fuel cell and (B) direct alcohol fuel cell.

In the hydrogen/oxygen fuel cell, the hydrogen molecules are oxidized producing water and releasing waste heat. Hydrogen is oxidized at the anode producing protons and oxygen is reduced at the cathode. Protons are transported through the electrolyte—the polymer electrolyte membrane (PEM)—and the electrons proceed to the cathode via an external circuit.

Direct alcohol fuel cells produce electricity directly from the electro-oxidation of alcohols such as methanol or ethanol into water and other byproducts such as carbon dioxide (Fig. 1.1B). As in the H2-O2 PEM fuel cells, the heart of the DAFC is the membrane, conducting to the cathode the protons formed at the anode by the oxidation reaction of the alcohol molecules. The most common material used for the electrolyte (Nafion) is a polymer made of persulfonic acid groups with a Teflon backbone, which is not completely impermeable to the alcohol molecules (namely the smaller molecules of methanol), thus resulting in the crossover of some fuel with a consequent loss of performance. This undesirable loss of fuel is a major drawback of the DAFCs technology. Additionally, a fuel cell running on alcohol needs water as an additional reactant at the anode.

1.2 Working principles

1.2.1 How does a DAFC work?

Fig. 1.2 shows schematically a typical alcohol fuel cell, comprising an anode and a cathode physically separated by a PEM.

Fig. 1.2 Operating principle of a DAFC.

The central part of a DAFC is the membrane electrode assembly (MEA) formed by sandwiching the PEM between an anode and a cathode. Upon hydration, the PEM shows good proton conductivity. On both sides of the membrane, there are the catalyst layers (AC and CC) where the reactions take place, and on each side of these, two diffusion layers (AD and CD) have the role of providing the current collection and the distribution of the different species toward the catalyst layers. Finally, on both sides of the MEA, current collector plates conduct the current produced at the anode to the external circuit toward the cathode side and provide structural support to the MEA.

Up to a few years ago, methanol was the most used fuel and much progress has been made in the development and optimization of direct methanol fuel cells (DMFCs) [3–7]. Among the other alcohols available, ethanol appears nowadays as an attractive and promising fuel due to: (i) its nontoxicity, (ii) its natural availability, (iii) its renewability, and (iv) its potentially higher power density. These two alcohols will be, along this book, considered as the most promising fuels for portable applications. Chapter 5 deals with other DFCs.

1.2.2 Direct methanol fuel cell

In a DMFC, methanol or a methanol aqueous solution is fed to the anode compartment. The reactant diffuses through the anode diffusion layer (AD) toward the anode catalyst layer (AC) where it is converted to carbon dioxide, protons, and electrons. As mentioned before, part of the fuel molecules cross through the membrane toward the cathode. The electro-oxidation of methanol occurring at the anode catalyst layer is given by:

   (1.1)

The CO2 generated from the oxidation reaction emerges from the anode baking layer as bubbles and is removed via the outflowing aqueous fuel solution, as the membrane is almost impermeable to gases. As already discussed, the protons and electrons are transported, respectively, through the membrane and through the external circuit to the cathode side.

Simultaneously, air (or oxygen) is fed to the cathode compartment and the oxygen is transported through the cathode diffusion layer (CD) toward the cathode catalyst layer (CC). Here the oxygen combines with the electrons and protons to form water. The reduction reaction taking place at the cathode is given by:

   (1.2)

The water produced moves counter-currently towards the cathode outlet via the cathode diffusion and catalyst layers and also, under some operating conditions, by back diffusion toward the anode.

The two electrochemical reactions occurring at each side are combined to form an overall reaction as:

   (1.3)

1.2.3 Direct ethanol fuel cell

For the direct ethanol fuel cell (DEFC), the two electrochemical half reactions and the overall redox equation are written as follows:

   (1.4)

   (1.5)

   (1.6)

Ideally, in the AC, the electrochemical oxidation of ethanol would generate protons, electrons, and carbon dioxide (Eq. 1.4). However, at temperatures well below 100°C (the target temperature range for portable applications) and with the conventional catalysts used, the reaction is incomplete generating as main products acetaldehyde, acetic acid, carbon dioxide, protons, and electrons [8,9]. On the CC, the oxygen is reduced producing water as in the cathode of a DMFC. Some of the ethanol feed to the anode passes through the membrane to the cathode side where it reacts with oxygen, which will decrease the overall fuel cell performance. Under some operating conditions, the water generated can also, like in the DMFC, move by back diffusion toward the anode.

1.2.4 Active and passive DAFCs

There are two types of fuel and oxidant supply in a DAFC, schematically represented in Fig. 1.3: active and passive.

Fig. 1.3 General operating modes of DAFCs (A) active and (B) passive.

In active cells, the alcohol and oxidant are forced into the anode and cathode flow channels, usually build-up of graphite or stainless steel (Fig. 1.3A). These systems use extra components such as a pump or blower, a fan for cooling, reactant and product control, allowing the operation of a DAFC at favorable conditions with respect to temperature, pressure, concentration, and flow rate. This type of cell supply has greater costs and a lower system energy density and is, therefore, better suited for larger fuel cells.

In passive feed cells, the fuel pump and air blower are eliminated. The fuel is supplied to the anode from a fuel reservoir built in the anode and the air to the cathode (Fig. 1.3B). Passive systems use natural capillary forces, diffusion, and natural convection (air breathing) to achieve all processes without any additional power consumption. The passive cells usually operate at low current densities resulting in reduced cooling loads, less water management issues, less heat production, and lower required fuel delivery rate. Therefore, by using a well-designed compact architecture, a passive system is more suitable for portable power sources. However, this simple design causes lower system performances due to the difficulty in getting a continuous and homogeneous supply of reactants to the anode and cathode. The lack of flowing force to remove the bubbles that constantly build up from the formation of carbon dioxide, in the anode reaction, will also hinder further oxidation of fuel at the anode surface. At the cathode, the water removal is more difficult and water droplets tend to block the active surface, thus reducing the oxygen supply.

1.2.5 Major phenomena occurring under the DAFC operation

The operation of a DAFC relies on several phenomena occurring simultaneously in the cell, as illustrated in Fig. 1.4, which will be studied in detail over this book:

(1)Alcohol and oxidant delivery (and transport)

(2)Electrochemical reactions at the anode and cathode

(3)Ionic transport through the electrolyte and electronic conduction through the external circuit

(4)Product removal from the fuel cell

Fig. 1.4 Cross section of the DAFC illustrating the major phenomena under operation: (1) reactant transport, (2) electrochemical reaction, (3) ionic and electronic transport, (4) product removal.

1.2.6 Scale-up

The basic DAFC consisting of the five-layer MEA (sandwiched Proton Exchange Membrane, catalyst layers and diffusion media) can be repeated, separated by bipolar plates and finished with end-plates. These sandwiched simple units build up a stack, making easy the task of generating more power.

1.3 Advantages and disadvantages

The DAFCs present the same general advantages of fuel cells, namely:

•potential for high efficiency;

•lower emissions when compared to conventional energy conversion technologies;

•simple design with no moving parts, promising low cost and high durability;

•modularity and, therefore, high scalability;

•no need of recharge, continuous power production as long as fuel is supplied to the cell.

Some current limitations of fuel cells that also apply for DAFCs are:

•high cost due to the need of expensive materials such as platinum/ruthenium and other noble metals for the catalysts and Nafion;

•contaminants sensitivity—fuel cells require relatively pure fuel, free of specific contaminants;

•further improvements in power density (gravimetric and volumetric);

•fuel availability and eventual need of reforming, which increases the requirements of ancillary equipment;

•relatively low real durability due to start-stop cycling.

DAFCs present several advantages over their direct competitor H2-O2 fuel cells. The main advantage is the use of a liquid fuel, which strongly simplifies handling and storage. In particular, for portable applications, mostly due to the lack of effective miniaturized hydrogen storage technologies, the use of a liquid fuel, requiring less ancillary equipment, is the best option to achieve a high power density with an attractive cost-to-power ratio. Small or micro-DAFCs can operate at room temperature reducing the thermal management challenges for small systems. The low operation temperature (typically < 95°C) allows an easy start up and a rapid response to changes in load or operating conditions. However, the sluggish low temperature alcohol oxidation reaction prevents the DAFCs from obtaining similar levels of power density than the H2-O2 PEM fuel cell. Another important disadvantage, already pointed out in the previous sections, is the tendency of fuel crossover through the polymer electrolyte membrane.

1.3.1 Methanol or ethanol?

Methanol has been considered as the best option for DAFCs mainly due to its relatively simple oxidation reaction mechanism when compared to other alcohols. However, methanol is toxic for human beings, is highly volatile, and inflammable and is still considered nonrenewable. Furthermore, due to its relatively low molecular size, the methanol crossover is particularly significant in DMFCs that not only lowers the fuel utilization, but also degrades the cathode performance and generates extra heat, as will be explained later in the text.

Ethanol is an attractive fuel for direct fuel cells mainly because it is nontoxic [10] and has a higher mass energy density than methanol (8.0 vs 6.1 kWh kg− 1) [11]. Moreover, ethanol is a potentially renewable fuel source, as it can be easily obtained from the fermentation of sugar-containing agricultural biomass [10]. Also, the carbon dioxide emitted from DEFCs can be recycled by planting, allowing a zero green-house contribution to the atmosphere [10]. However, the cleavage of the Carbon-Carbon bond is very difficult making the ethanol oxidation rate rather low. Platinum (Pt) is the most active catalyst used, but self-inhibition occurs when used alone. An additive such as Tin (Sn) and Ruthenium (Ru) is used to modify the surface of Pt [12]. Nevertheless, the DEFC performance is still poor, due to the incomplete oxidation of ethanol and needs to be improved. A major advantage of using ethanol is the lower crossover of the fuel through the membrane due to its higher molecule size.

1.4 Target applications and markets

The present markets for DAFCs are practically reduced to those for the DMFCs. The DEFC technology could in the end be a cost-effective solution for different applications, but, at the moment, the lack of sizeable cells and commercial factors keeps it still at an incipient stage, however with a great potential to become competitive in the next decade.

The DMFC market is expected to reach around USD 190 Million by 2020 [13]. The DMFC market is still in its initial development phase mainly due to the slow infrastructure development for refueling the fuel cells, some technical limitations, and as was referred, the use of expensive materials for its manufacturing. The global market is nevertheless growing, pushed by Government initiatives and grants for fuel cell research in some regions, together with investments from financial institutions and undoubtedly by the success of Research & Development stimulated by the potential of this technology.

The DMFC actual market can be segmented on the basis of its different target applications: portable, stationary, and niche applications such as military or biomedical. The portable application is the highest growth market for DMFCs. The stationary application is projected to dominate the global market in a near future [13]. Each one of these markets has distinctive demands. For example, the portable applications demand for high system power density and simplicity where efficiency and cost are less important [14]. Chapter 9 of this book provides a detailed description of the main target applications for DAFCs in the portable sector.

Some of the leading players in the DMFC market include SFC Energy AG (Germany), Ballard Power Systems, Inc. (Canada), Oorja Protonics (United States), and Pro-Power Communication Co., Ltd. (Korean) [15–21]. These players have adopted growth strategies such as new product launches, contracts and agreements, mergers and acquisitions, and expansions to capture a larger share in the DMFC market [13].

1.4.1 Portable applications

Some examples of products near or already in the DMFC portable market are:

•Dynario from Toshiba [15], an external power source to deliver power to mobile digital consumer products (Fig. 1.5A);

Fig. 1.5 Examples of DMFC portable applications (A) Dynario from Toshiba and (B) Efoy-confort from SFC Energy AG [15 , 16] .

•Efoy-confort from SFC Energy AG [16], a lightweight portable power pack specifically developed to reliably and conveniently power devices away from the grid. In any outdoor activity, on tenting or boating tours, for fishing trips, at the beach, this mobile power socket is prepared to supply plug and play power to electrical equipment (Fig. 1.5B);

•Direct Methanol Fuel Cell Co. [17], a subsidiary from Viaspace Inc., provides methanol cartridges as the energy source for fuel-cell-powered notebook computers, mobile phones, military equipment, and other applications.

It is expected, for this sector, that the great number of potential users will give a significant help to its growth, along with industry and/or government push.

1.4.2 Stationary applications

Examples of products including DMFC technology for stationary applications are:

•Efoy-Pro 12000 Duo [18], from SFC Energy AG, an off-grid, back-up, and on-board power supply, with a very compact design, which can be clustered to high power levels (Fig. 1.6A);

Fig. 1.6 Examples of stationary DMFC applications (A) Efoy-Pro 12000, (B) Prom-Gen DM 1000—household generator, (C) Prom-Gen DM 1000—communication tower, and (D) Prom-Gen DM 1000—military telegraphic repeater [ 18 – 20 ].

•Oorja Model T-1 [19] from Oorja Protonics (United States) is a methanol fuel cell that operates as a battery charger for a wide variety of stationary applications, including wireless base stations;

•Prom-Gen DM 1000 from Pro-Power Communication Co. [20], a hybrid system including a DMFC stack, in different versions and possible uses, such as a household generator (Fig. 1.6B), a communication tower supplying stabilized energy from a terrestrial radio station (Fig. 1.6C), UPS (uninterruptible power supply), a military telegraphic repeater (Fig. 1.6D), and disaster management systems.

1.4.3 Other applications

Two examples of other applications are:

•Prom-Gen forklift DM 1500 [20], from Pro-Power Communication Co., a lightweight product providing an increased fuel efficiency and performance on transportation and storage (Fig. 1.7);

Fig. 1.7 Other Example of DMFC applications: Prom-Gen forklift DM 1500 [20].

•Hearing-aids running on methanol [21], developed by Danish scientists from the Danish Technological Institute, still in a precommercial stage that, upon general use, will facilitate the life of many hearing-aid users. The great advantage of this device is that the fuel cells should not need to be replaced for 5 years. Instead, the users should simply take the hearing aid from time to time with its in-built fuel cell out and fill it with methanol for 30 s in a recharger.

1.5 Main challenges for DAFCs

Four main drawbacks still affect the DAFCs technology: alcohol crossover (more significant for DMFCs due to the lower size of the methanol molecules), two-phase flow occurring at the anode and cathode (gas-liquid at the anode due to the formation of CO2 bubbles and liquid-gas at the cathode involving water drops), poor catalyst activity, and need of high loads of catalyst. All these topics will be largely covered throughout the book.

The most important requirement for a portable DAFC system to compete with traditional batteries is to reach a higher energy density. It is nowadays accepted that the water management is a critical challenge to accomplish the desirable energy levels. The amount and distribution of water within the fuel cell strongly affect efficiency and reliability. A possible resolution of fuel crossover could be the use of a dilute anode fuel solution, requiring a large amount of water to be carried in the system and thus reducing the energy content of the fuel mixture. However, the presence of a large amount of water tends to flood the cathode and reduce its performance. An important engineering issue is to remove water from the cathode to avoid severe flooding and subsequently supply water to the anode to make up water loss due to water crossover through the membrane. Low water flux through the membrane is desirable for DAFCs, as the anode does not require an excessive amount of water replenishment and the cathode is less susceptible to severe flooding.

In close connection to this requirement is the necessity of working with high concentrations of alcohol, mainly in passive systems, to generate higher electrical power and guaranty acceptable system autonomies. However, high concentrations of alcohol will dramatically increase the alcohol crossover, which, as already discussed, will in turn generate a loss of performance. In this book, the reader will find some strategies to operate DAFCs systems at higher alcohol concentrations and low water fluxes through the electrolyte, while maintaining the fuel crossover rate in acceptable levels.

Cost reduction is also a very important issue. Along with the development of new and less expensive materials and reduction of the amounts of noble metals used, there is an urgent need of including mass production methodologies. The flexibility offered by 3D printing, for example, can be, in a very near future, used to produce designs executed in a single, simple process, reducing the amount of material, labor, and cost. This technology has already been used in some FC applications, but much more work has to be done [22].

Writing this book is itself a major challenge. The technology of fuel cells is continually evolving and writing a text book is a risky task since, probably at the time of publishing, the state-of-the art described to the reader will be somewhat old-fashioned. However, there is a fascinating multidisciplinary science at the heart of a fuel cell, explaining how it works, how to optimize its performance, and how to increase its durability.

The PEM fuel cells in general and the DAFCs, in particular, integrate fundamental science from different engineering disciplines as represented in Fig. 1.8: Thermodynamics, Electrochemistry and Reaction Kinetics, Catalysis and Membrane Separation Processes, Heat and Mass Transfer.

Fig. 1.8 Major engineering disciplines at the basic science of a DAFC.

The first part of this book (Chapters 1–6) is devoted to the explanation of this basic science representing the necessary background to those who want to go deeper in understanding and further developing this technology.

Models play an important role in fuel cell development since they allow a better understanding of the parameters that affect the performance of fuel cells. Mathematical models and simulations are, therefore, major tools for optimization of DAFCs incorporating Numerical Analysis and Computational Fluid Dynamics (CFD) concepts (Fig. 1.8).

Beyond the basic science of an individual DAFC, the stack design relies on manufacturing or microfabrication technologies, on microfluidics architectures, on sensors and system control as well as on heat management subsystems and other technologies. The second part of this book (Chapters 7–10) covers these topics and ends with a review of the status of portable DAFCs and the R&D trends in the near future.

Chapter summary

The aim of this chapter is to prepare the reader for the journey into the direct alcohol fuel cells learning and deeper understanding. A broad overview of the DAFC technology is given.

The fuel cell is presented as a factory treating raw materials and delivering products. A brief comparison between Fuel Cells and batteries or combustion engines is provided, as well as the definition of a DAFC.

A comparison with the direct rival—the hydrogen PEMFC—is made all over the chapter. The working principles of the methanol and ethanol fuel cells are presented together with the description of the two different types of fuel and oxidant supply in active and passive systems. The main advantages and disadvantages of the DAFC are explained, stressing out its great potential of application in the portable sector. An introduction to the markets and target applications is then offered with the presentation of several examples of products already under commercialization. Finally, the main challenges of this technology are presented. The remaining chapters of the book will provide the necessary basic and advanced science, essential in the development of strategies to overcome the main drawbacks of these systems in a near future.

Problems

1.1.Try to find online companies developing and commercializing products using (a) Hydrogen PEM fuel cells and (b) DAFCs.

1.2.Elaborate a list of patents granted for the last year available on (a) PEMFCs and (b) DAFCs.

1.3.Give a comparison of fuel cells with batteries and with combustion engines.

1.4.Identify the main differences between the DAFCs and the hydrogen fuel cells, with respect to the operation principles, losses, and applications.

1.5.Indicate the advantages and disadvantages of using ethanol as fuel instead of methanol.

1.6.Identify the two modes of operation of a DAFC and describe the advantages, disadvantages, and applications of each one.

References

[1] http://www.fuelcelltoday.com/media/1351623/the_industry_review_2011.pdf.

[2] O’Hayre R., Cha S.W., Colella W., Printz F.B. Fuel Cell Fundamentals. New York: John Wiley & Sons; 2009.

[3] Faghri A., Li X., Bahrami H. Recent advances in passive and semi-passive direct methanol fuel cells. Int. J. Therm. Sci. 2012;62:12–18.

[4] Falcão D.S., Oliveira V.B., Rangel C.M., Pinto A.M.F.R. Review on micro-direct methanol fuel cells. Renew. Sust. Energ. Rev. 2014;34:58–70.

[5] Oliveira V.B., Rangel C.M., Pinto A.M.F.R. Modeling and experimental studies on a direct methanol fuel cell working under low methanol crossover and high methanol concentrations. Int. J. Hydrog. Energy. 2009;34:6443–6451.

[6] Achmad F., Kamarudin S.K., Daud W.R.W., Majlan E.H. Passive direct methanol fuel cells for portable electronic devices. Appl. Energy. 2011;88:1681–1689.

[7] Awang N., Ismail A.F., Jaafar J., Matsuura T., Junoh H., Othman M.H., Rahman M.A. Functionalization of polymeric materials as a high performance membrane for direct methanol fuel cell: a review. React. Funct. Polym. 2015;86:248–258.

[8] Andreadis G.M., Podias A.K.M., Tsiakaras P.E. The effect of the parasitic current on the direct ethanol PEM fuel cell operation. J. Power Sources. 2008;181:214–227.

[9] Meyer M., Melke J., Gerteisen D. Modelling and simulation of a direct ethanol fuel cell considering multistep electrochemical reactions, transport processes and mixed potentials. Electrochim. Acta. 2011;56:4299–4307.

[10] Badwal S.P.S., Giddey S., Kulkarni A., Goel J., Basu S. Direct ethanol fuel cells for transport and stationary applications—a comprehensive review. Appl. Energy. 2015;145:80–103.

[11] Abdullah S., Kamarudin S.K., Hasran U.A., Masdar M.S., Daud W.R.W. Modeling and simulation of a direct ethanol fuel cell: an overview. J. Power Sources. 2014;262:401–406.

[12] Antolini E., Gonzalez E.R. Effect of synthesis methods and structural characteristics of Pt-Sn fuel cell catalysts in the electro-oxidation of CH3OH and CH3CH2OH in acid medium. Catal. Today. 2011;160:28–38.

[13] http://www.marketsandmarkets.com/Market-Reports/direct-methanol-fuel-cell-advanced-technologies-and-global-market-research-94.html.

[14] Mench M.M. Fuel Cells Engines. New Jersey: John Wiley & Sons; 2008.

[15] http://www.toshiba.co.jp/about/press/2009_10/pr2201.htm.

[16] http://www.efoy-comfort.com/technical-data.

[17] http://www.viaspace.com/ae_dmfcc.php.

[18] http://sfc:efoy@212.144.238.51/marketing/150205_EFOYPro12000_EN_online.pdf.

[19] https://oorjafuelcells.com/model-t-1/.

[20] http://www.propower.co.kr/en/?c=product/fc/promgen#p03.

[21] http://www.hear-it.org/hearing-aids-running-on-methanol.

[22] Ponce de Leon C., Husseya W., Frazao F., Jonesa D., Ruggeria E., Tzortzatosa S., Mckerrachera R.D., Willsa R.G.A., Yang S., Walsha F.C. The 3D printing of a