Fuelling a greener economy

Transcription

1 Materials Foresight Making the future work for you Fuelling a greener economy The importance of materials for fuel cells and related technologies Foresight Fuel Cells Taskforce

2 Members of the Foresight Materials Panel Professor Graham Davies (Chairman) Dr Alan Begg Professor David Bott Dr Paul Butler Dr Steve Garwood Dr Clive Hayter Dr Alan Hooper Mr Gerry Miles Dr John Patterson Dr Bernie Rickinson Dr Alan Smith Professor George Smith Professor Pankaj Vadgama Professor John Wood Mr D Arthur (Secretary) The views expressed in this report are the personal opinions of the Panel and Task Force members and do not represent the official views of the Department of Trade and Industry or the organisations they represent.

3 Contents Foreword from the Foresight Materials Panel 2 Chairman s introduction 3 Executive summary 5 1 Introduction 7 2 The technology Systems and components Materials and applications 11 3 Geographical distribution 12 4 Current activity key developments 14 5 Technical issues Solid oxide fuel cells (SOFCs) Polymer electrolyte membrane fuel cells (PEMFCs) 16 6 Future development Electrolysis Fuels Hydrogen generation and distribution Electrocatalysis Gas separation membranes 19 7 Conclusions 20 8 Recommendations 21 Task Force members 22 1

4 Foreword from the Foresight Materials Panel The development and application of new materials has a significant effect on our use of energy and our health, our use of communications technology and our security. In short, materials play an increasingly important role in our everyday lives. It is clear that a manufacturing and innovation strategy which highlights advanced materials development is more likely to provide wealth creation and commercial success. Foresight is an essential part of the process to identify new opportunity for industry, government and academia. It stands as a signpost to the future. In this new series of reports, the third phase of Materials Foresight, new thinking is provided for the benefit of national stakeholders. The Materials Panel wish to record their thanks to the many individuals and companies who have contributed to the development of these reports, and to the Institute of Materials, Minerals and Mining who provided the secreteriat for this work. Foresight Fuel Cells Taskforce 2

5 Chairman s introduction Fuel cell technology has been much heralded in recent years as a keystone of the future energy economy. Fuel cells offer very high chemical to electrical conversion efficiency and can achieve such efficiency in a wide range of application scales. In the short to medium term fuel cell technology promises to greatly reduce CO 2 emission through enhanced conversion efficiency of conventional hydrocarbons and in the longer term fuel cell technology provides the means of Professor John Irvine implementation for the hydrogen economy or, indeed, the utilisation of clean biofuels. The technology offers immense benefit to society and the potential of very significant economic gain for the UK. Professor Gary Acres Whilst fuel cell technology seems certain to be implemented the scale of this implementation will strongly depend on a number of materials dominated factors. These are improvements in durability and lifetime performance and, most importantly, cost reduction. It is very clear that the most cost-effective solutions will dominate the future market. The UK has a very significant track record in fuel cell technology and excellent capability. There are huge opportunities if we can maintain our current technological capability and translate our leading edge ideas into new market opportunities. Professor John T.S. Irvine Chairman of the Foresight Fuel Cells Taskforce Professor Gary J.K. Acres OBE 3

6 Executive summary Greater concern about the greenhouse effect, its impact on climatic change and the need to reduce carbon dioxide (CO 2 ) emissions has prompted an increased interest in the application of fuel cells and related technologies. In fact, the rate at which the technology has grown in the past few years puts the potential market at millions of pounds per annum. In the long-term, fuel cells will be an essential component of any hydrogen or similar clean energy economy. In the short-term, they promise large reductions in CO 2 emissions by greatly enhancing the conversion efficiencies of more conventional fuels. The UK has an admirable record of achievement in fuel cell technology, both in industry and academia, and should be in an excellent position to capitalise on these new opportunities. Unfortunately, this can only become a commercial reality if money spent on research in the UK can match that of its competitors. Several countries are rapidly increasing national spend in this important area. Annual government spend in Japan and Germany, for example, is currently around 140 million and 70 million, respectively, on fuel cell technology EU spend is about 30 million. The US is also increasing its commitment to research, spending 55 million in 2003 and an estimated 120 million in Compared to these figures typical UK spend in recent years has been around 1.5 million (although some care needs to be exercised in comparing different countries figures, as fuel cell and fuel cell related spends are difficult to differentiate). Fuel cells have a broad range of applications and have been demonstrated in a variety of commercial appliances from battery replacements in consumer products to power systems for vehicles and cogeneration plant, ranging in output from a few watts to several megawatts. It is quite likely that the impact of fuel cells upon society will be revolutionary, with materials science having a pivotal role to play, particularly if the technology is to achieve anything like its full potential. 5

7 1 Introduction In recent years, fuel cell technology has been promoted as a foundation for the energy economy of the future, becoming the preferred means of power generation. Together with the hydrogen economy, fuel cell technology is being strongly promoted by the governments of most of the world s leading industrialised nations, most recently the FreedomCAR and Fuel Initiative in the US, as a means of increasing fuel economy. Hydrogen can be used in conventional combustion equipment such as the internal combustion engine or gas turbine, but for increased efficiency and the elimination of emissions, the majority of people prefer fuel cell technology, particularly with respect to NOx emissions. There is now a phenomenal commercial interest in fuel cell technology with new start-up companies being established and major players in the energy market turning their attention to this technology. Daimler Chrysler, for example, has declared an intention to spend 1,000 million on its Necar fuel cell vehicle programme during the period Figure 1: Daimler Chrysler Necar 5 fuel cell demonstration car (copyright DaimlerChrysler) 7

8 It is unlikely that a single fuel cell technology alone will meet all the requirements for fuelling a greener economy because there are distinct advantages for different electrolyte systems and temperatures of operation. Extensive reviews of recent developments in fuel cells and the associated materials technology have been published, including the need for further developments to make fuel cells more cost effective, particularly for transport applications. In short, there is now no technical reason why fuel cells should not replace traditional fossil fuel-based combustion systems in land-based applications its scale will depend on the success of researchers in improving performance and cost. Fossil Fuels Biofuels Hydrocarbons Renewable Electricity External Reforming Internal Reforming Hydrogen Electrolysis CO + H 2 Fossil Fuels Fuel Cell Figure 2: Schematic of the future fuel cell economy strategies Foresight Fuel Cells Taskforce 8

9 2 The technology Even with the invention of the fuel cell by Grove and its development as a power source by Bacon, materials have played a major role in the growth of today s fuel cell technology. Grove chose to use platinum as the electrode material in his historic experiment in 1839, which demonstrated that hydrogen and oxygen produced by the electrolysis of water could be recombined to produce electricity. Water electrolysis Fuel Cell e - Direct current power Load e - e - e - H 2 gas O 2 gas H 2 gas O 2 gas Electrode (Pt) Electrode (Pt) Electrode (Pt) Catalyst Carbon particle Pt Water + Electrolyte Water + Electrolyte Figure 3: Schematic of Grove fuel cell Bacon, in his ground breaking experiments at Cambridge in the 1940s and 1950s had significantly more information on the catalytic activity of materials and chose to use nickel electrodes in the development of his alkaline fuel cell (AFC). Operating at elevated temperature and pressure, Bacon achieved power densities approaching 1 watt per cm 2, which is similar to today s advanced systems. 2.1 Systems and applications Fuel cells are in essence batteries powered by an external source of hydrogen or hydrogen rich gas fuel, either supplied directly or by in-situ reforming of hydrocarbons (only methanol of the readily available liquid fuels can be used directly). Each fuel cell is characterised and defined by the composition of its electrolyte. 9

10 In addition to the alkaline fuel cell (AFC), which formed the basis of the systems used by the US manned space vehicles to provide electrical power, heat and drinking water, a further four systems have now been developed phosphoric acid fuel cells (PAFCs), molten carbonate fuel cells (MCFCs), solid oxide fuel cells (SOFCs) and polymer electrolyte membrane fuel cells (PEMFCs). Direct methanol fuel cells (DMFCs) and regenerative fuel cells (RFCs) are also beginning to attract attention. DMFCs generally use sulphuric acid or a proton-conducting polymer as the electrolyte. Type Electrolyte Operating temperature ( C) Alkaline Potassium hydroxide Proton exchange Polymeric membrane Direct methanol Sulphuric acid or polymer Phosphoric acid Orthophosphoric acid Molten carbonate Lithium/potassium carbonate mixture Solid oxide Stabilised zirconia Table 1: Types of fuel cell technology Today, fuel cells have a broad range of applications where cleaner energy is required, such as corrosion protection, uninterruptible power supplies, remote generation, domestic appliances and even consumer electronics. The most publicised examples are in the automotive sector where companies such as Ford and Renault are looking at high-temperature fuel cells for auxiliary power generation and other companies such as Daimler Chrysler are looking at low-temperature polymer-based fuel cells for complete electrical generation. Even aircraft propulsion systems are the subject of current research. Foresight Fuel Cells Taskforce 10

11 2.2 Components and materials All fuel cell systems now employ the flat plate configuration for the polymer electrolyte membrane (PEM) cell. The exception is the tubular SOFC system developed by Siemens Westinghouse and Adelan, in the UK. The performance of a fuel cell is conventionally defined by a cell voltage versus current density plot. Other fuel cell systems, with the Figure 4: Schematic of a membrane electrode assembly used in PEMFCs possible exception of the AFC, have similar performance characteristics even though their operating conditions and cell materials are different. Materials technology has made a significant contribution to reducing the onset of mass transport limitations, reducing anode activation and cell resistance. Despite extensive research on cathode catalyst materials, this remains an area where significant improvements in cell performance are sought Theoretical cell voltage Cathode activation Cell voltage/v Cell performance Cell Resistance Anode activation Mass transport Current density/ma cm -2 Figure 5: Current density plot for a PEM cell 11

12 3 Geographical distribution Since the invention of the fuel cell by Grove and the work of Bacon, the UK s involvement in fuel cell development has been particularly influential with new concepts in design and functional materials being developed in recent years. Extensive programmes led by BP and Shell in the 1960s provided much of the technology upon which subsequent programmes were based, particularly in the US. Although Shell were not successful in developing a methanol fuel cell powered car owing to the limitations of anode catalyst materials, they did develop a fuel cell powered demonstration car using hydrazine as the fuel, which is now in the Science Museum in London, UK. Following this development, there was no significant fuel cell programme in the UK for the next 20 years, other than the involvement of companies such as BG plc and Johnson Matthey in American and Japanese programmes. Renewed interest in fuel cell technology started with the American NASA programme for manned space vehicles followed by the American DOE and Japanese MITI programmes to develop fuel cells for commercial applications. The AFCs used in the US space programme were significantly modified to meet the demanding requirements of weight and volume. Of notable importance was the development of platinum and platinum/gold electrode catalysts, and lightweight durable stack materials. Figure 6: Space shuttle Foresight Fuel Cells Taskforce 12

13 Current interest in fuel cells in the UK was stimulated by the introduction of a fuel cell materials research programme by the Department of Trade and Industry in 1992 and the Engineering and Physical Sciences Research Council (EPSRC) in It was decided to focus limited resources on solid oxide and solid polymer systems. This decision was made with the benefit of information from America and Japan, as well as taking into account the strengths of UK industry and academia in this field at this time. While encouraged by renewed government interest, the UK position in fuel cell and hydrogen technology is weak in relation to that of America and Japan, as well as in EU member states such as Germany, particularly in relation to spending and fuel cell operation in the UK. Since 1992, the average UK government spend per annum on fuel cells and hydrogen technology has been around 2.5 million. Annual government spend in Japan and Germany, for example, is currently around 140 million and 70 million, respectively, on fuel cell technology EU spend is about 30 million. Furthermore, the UK s fuel cell programme was a research initiative primarily concerned with materials and components systems development and demonstrations were given a low priority. As a result, there is only one stationary fuel cell demonstration unit in everyday operation in the UK, and three fuel cell vehicles. This compares with some 1,600 stationary and 325 vehicle demonstrations worldwide. Of little encouragement is the UK s portfolio of intellectual property in this area. UK industry and academia has so far been granted 49 patents out of a worldwide total of 4,619. However, the news is not all bad. Stimulated by the UK s substantial renewable resources, commitments to reduce CO 2 emissions and the launch of the UK s Low Carbon Vehicle Initiative by the DTI, interest and opportunities in the UK are growing rapidly. Development agencies such as those in the North East, Midlands and London are participating in launching programmes reflecting their industrial interests and opportunities to improve their sustainable aims. The Scottish Executive, with its substantial renewable energy resources, is supporting a collaborative university/industry programme to develop and exploit fuel cell and hydrogen technology. The UK s strengths are limited but significant. It now has both solid oxide and solid polymer stack technology and the associated materials and components, which are seen as prime candidates for both stationary and mobile applications. It also has a leading position in advanced reformer technology for producing hydrogen from fossil fuel sources. 13

14 4 Current activity key developments Today, a number of UK companies, including Rolls-Royce, Johnson Matthey, Morgan Crucible and Advantica have significant activities and an involvement in international fuel cell collaborative programmes. Johnson Matthey, for example, has been particularly successful in the development of electrocatalysts and gas reformers for PEMFC systems. Air Products, BP and BOC have active programmes in the production and distribution of hydrogen, with BP developing hydrogen refuelling and distribution technology, as well as having interests in CO 2 sequestration and renewable energy. In SOFCs a number of innovative processing techniques have been applied to develop new concepts, such as the microtubular system (Keele/Birmingham), the integrated planar concept (Rolls-Royce) and the SOFCRoll (St Andrews). The Rolls-Royce activity has grown substantially and they are now working towards a 2007 demonstration of its combined cycle 1MW SOFC gas turbine system. e - e - O 2 Air Side Porous support substrate H 2 Cathode Fuel Side Anode H 2 O Electrolyte Interconnect Cathode Electrolyte Anode Figure 7: Innovative SOFC concepts a) Rolls-Royce integrated tubular, b) St Andrews SOFCRoll New companies have also sprung up from university activities. Loughborough University, now Intelligent Energy has built up a strong activity in polymer fuel cell development. Imperial College has championed the intermediate temperature fuel cell concept based upon ceria as opposed to zirconia, which recently led to the launch of Ceres Power. While the University of Birmingham is leading both an EC and UK research programme on solid-state hydrogen storage. Foresight Fuel Cells Taskforce 14

15 5 Technical issues and materials development Solid oxide and solid polymer fuel cells are seen as prime candidates for both stationary and mobile applications. However, there are a number of important areas to be addressed in any future development. 5.1 Solid oxide fuel cells (SOFCs) Fuel electrode The key development issues are to achieve new SOFC anodes capable of operating in natural gas without suffering from carbon build-up owing to catalytic cracking. Nickel-based electrodes are favoured at present and work well with hydrogen or steam reformed fuels. However, major efficiency improvements could be realised if reforming was carried out internally, or better still, if oxidation was achieved with minimal steam additions. For many applications it is essential to heat up and cool down the fuel cell and there are major risks of failure from oxidation of the nickel. Developing new anodes that are much more redox tolerant, more resistant to coking problems and also more tolerant of sulphur would allow a much broader range of hydrocarbon fuels to be used in simpler systems, and certainly facilitate the implementation of ecofuels. Most importantly it would assist the implementation of this energy efficient technology into current infrastructures. Air electrode There are many advantages to reducing the operating temperature of high-temperature fuel cells, in particular ease of sealing, improved long-term stability and the ability to use lower cost steel interconnected cells. At low operating temperatures, the major performance limitations are high over potential losses at the cathode. Therefore, there is considerable interest and activity in improving the efficiency of the present cathode materials based on (La,Sr)MnO 3 with new materials that show much better electrocatalytic activity, particularly through improved mixed ionic and electronic conductivity. Electrolyte Most current designs are based on yttria-stabilised zirconia, which can only operate effectively at very high temperatures owing to its non-ideal ionic conductivity. There is significant effort directed at developing new thin film technologies, which reduce the resistance of this and related materials. In addition there is also a great deal of interest in finding new, alternative oxide ion conducting electrolytes, such as ceria or lanthanum gallate that can be used at lower temperatures, for example 600 C, but with improved stability. 15

16 Interconnected materials Historically, lanthanum chromate interconnects have been previously considered. However, there are a number of problems, mainly associated with cost and corrosion. Therefore, interest is now turning towards finding new interconnects based on steel, especially if lower temperature electrolytes can be developed. The search is focused largely on corrosion resistance and avoidance of chromium contamination of electrodes, which arises from the degradation of the interconnect material. Fuel processing An important area, especially for higher hydrocarbon fuels, is the processing of fuels through steam reforming or partial oxidation reforming to allow hydrocarbons to be used more effectively in the fuel cell. Other important approaches in fuel processing relate to sulphur scrubbing, deliberate cracking to provide hydrogen for the fuel cell with carbon sequestration and cogeneration systems to generate useful feedstocks as well as electricity. System development There are a number of very important processing issues relating to co-firing of components that are key to the development of high-temperature fuel cell technology. Interest in alternative geometries also continues. Contrary to the search for lower temperature systems, designs such as those that couple SOFCs with gas turbines require higher temperatures to optimise efficiency. 5.2 Polymer electrolyte membrane fuel cells (PEMFCs) Polymer electrolyte membrane fuel cell (PEMFC) technology is essentially hydrogen-based and is more mature than SOFCs. There are still a number of important areas of materials development that will further advance the technology, particularly relating to electrolyte and catalysts for electrodes and reformers. Of fundamental importance is the achievement of higher temperature membranes to replace the present-day fluoro-sulphonic acid membranes. This would allow the tolerance of carbon monoxide and other impurities to be dramatically improved. If this cannot be achieved, then further improvements in carbon monoxide electrode tolerance and better reforming characteristics are required. Further advances would result from lower cost systems, especially with regard to the membranes and also bipolar planes. Foresight Fuel Cells Taskforce 16

17 6 Future development 6.1 Electrolysis Fuel cell technology may also be used in reverse for electrolysis of water or steam to produce hydrogen and oxygen. This offers one of the most promising routes for generating hydrogen from renewable electricity by providing a source of much needed clean fuel. A related process is combined electrolysis of steam and carbon dioxide to produce synthesis gas. From synthesis gas several valuable compounds, such as methanol or dimethyl ether, can be produced. This technology could also be developed for transportation of renewable energy from remote areas, or for better distribution of energy from gas fields to urban areas. Although not a major application in the short-term, electrolysis of steam or carbon dioxide has also been frequently proposed to produce oxygen for manned space stations on Mars, for example. 6.2 Fuels Fuel choice is critical to the widespread implementation of fuel cell technology. All fuel cell technologies work well with hydrogen, but this is not a fuel that is readily available at present. Clean hydrogen, that is hydrogen produced from non-fossil fuel resources is unlikely to be available in large quantities much before 2020, unless nuclear energy is used to drive electrolysis. Therefore, in the short-term hydrocarbon fuels will continue to be used, either directly or reformed in-situ to produce hydrogen for fuel cell use. Furthermore, it is worth noting that the energy density from liquid hydrocarbon fuels is unlikely to be approached by hydrogen. It is of considerable importance to find new means of storing hydrogen to bring the mass density towards 10% w/w achieved either by improved low-rate, highstrength pressure containment vessels or perhaps through the development of hydrogen storage media. In view of the high hydrogen content of chemical fuels such as methane, 25% w/w, the possibility of converting atmospheric or waste carbon dioxide into hydrocarbon fuels as a means of storing hydrogen should certainly be explored with greater energy. Alternative CO 2 free or CO 2 neutral fuels for hydrogen transport, such as ammonia, should also be explored. 6.3 Hydrogen generation and distribution Materials technology has an ongoing role in improving renewable sources of energy such as solar, wind and wave, and the associated electrolytic systems for hydrogen generation and distribution. Today, merchant hydrogen and that produced in the chemical and oil industry is largely obtained from natural gas by steam reforming. In areas such as Scandinavia and Canada where extensive 17

18 hydroelectric power is available, hydrogen is produced by water electrolysis. The ultimate goal is to produce hydrogen from renewable sources, but in the mean time other fossil fuel sources, including coal are expected to be used by steam reforming combined with CO 2 sequestration to provide a clean, zero emissions source of energy. In the short- to medium-term, local hydrogen distribution centres are being set up notably in Germany, California and Japan using a variety of storage, small scale electrolytic and reformer systems. It is widely agreed that the development of a solid-state hydrogen store would bring the aim of a hydrogen economy that much closer, notably for vehicle and consumer applications. In the absence of such a system, both liquefied hydrogen containers and very high-pressure cylinders have been developed and used on current demonstration vehicles. Figure 8 - Munich refuelling centre in Germany Early claims for carbon nanotube-based systems have not been reproduced and attention is now focused on light metal systems using metals such as magnesium or lithium promoted with other metals. A major worldwide research effort is now underway to find and develop a material and the associated system compatible with the needs of a low temperature fuel cell such as the PEM. Foresight Fuel Cells Taskforce 18

19 6.4 Electrocatalysis Intimately linked with fuel cell technology is electrocatalysis. In developing new fuel cell anodes, catalytic activity for hydrocarbon oxidation is very important. Electrocatalysis at solid electrolytes is a topic of growing importance and is potentially an excellent tool for the partial oxidation of hydrocarbons in the preparation of olefins from alkanes, for example. Catalytic processes at solid electrolytes are of great interest to the chemical industries as they offer improved yields and selectivity. Such processes are also of considerable interest for the generation of alternative fuels such as dimethyl ether or even ammonia. 6.5 Gas separation membranes These membranes are based upon mixed ionic and electronic conducting oxides or composites, and they are very closely allied to electrode materials for hightemperature fuel cells in terms of functionality and properties. They are used for chemical separation, such as removal of hydrogen from a gas stream or for controlled partial oxidation in the preparation of dimethyl ether from methane. These are extremely important applications in energy conversion. The ability to convert gaseous hydrocarbons into liquid fuels greatly facilitates the transport of energy from remote sites to population centres, as well as having obvious transport applications. It is important to overcome a number of technological barriers for the implementation of these materials. In particular it is essential to optimise hydrogen or oxygen flux through the membrane, and to provide mechanically sound redox stable membranes. 19

20 7 Conclusions Fuel cells have been successfully demonstrated in applications ranging from a few watts to megawatts, for stationary and mobile appliances. While many materials and engineering challenges have been met, few if any fuel cell systems have yet to be fully commercialised. Further improvements in power density and cell efficiency are sought, together with developments in the associated fuel and hydrogen supply systems. Balance of plant components such as heat exchangers and power electronics remain as challenges, particularly for mobile applications. Overall, the cost of fuel cells has to be reduced to compete with established technology. The UK has a technology base and incentives to build upon the existing national and international interests of academia and industry. Materials technology, together with a broad involvement of the engineering community from both industry and academia, would be beneficial in the future development and implementation of fuel cell technology. 20 Figure 9: Fuel cell applications

21 8 Recommendations Fuel cell technology is an area of considerable importance and one that is certain to make an impact on society. The extent and rate of this impact will largely depend upon the optimisation of certain material properties and the ability to reduce the cost of the components while ensuring their long-term stability. The most important amongst these are cost issues. For the introduction of this technology, there is a need to reduce current costs by almost an order of magnitude bringing cost down to 300/kW, or even lower if widespread implementation in the transport sector is to be achieved. Some of the main materials requirements for the introduction of an effective fuel cell economy are: fuel flexibility and impurity tolerance must be improved lower cost fabrication routes need to be developed for optimisation of performance and stability, micro-engineering of the gas electrode/electrolyte interfaces is required better current collecting materials with good stability under fuel cell conditions are required for stack development. There are also a number of important national and regional initiatives coming on stream, so the spending profile is likely to increase. Therefore, perhaps the most important recommendation is that these opportunities to bring forward UK fuel cell technology are strongly grasped, both by government and UK industry, using the platform of knowledge and talent already available. 21

22 Members of the Fuel Cells Taskforce Professor John Irvine, Chairman University of St Andrews, Fife Professor Gary Acres OBE Johnson Matthey/ University of Birmingham Profs Gary Acres and John Irvine both have extensive research experience and knowledge of both polymer and solid oxide fuel cells and such fuel cell systems. Foresight Fuel Cells Taskforce 22

23 Images Necar fuel cell vehicle, copyright DaimlerChrysler Copyright Pacific Northwest National Laboratories Smart methanol fuel cell, copyright Smart Fuel Cell zbt bipolar, copyright ZBT PSI high power detail, copyright Paul Scherrer Institute MTU HotModule, detail of stack, copyright Justin Sutcliffe 2003 Necar 5, copryight DaimlerChrysler World s first fuel cell powered electric aeroplane, copyright FASTec Fuel cell bus, copyright DaimlerChrysler 23

24 1 Carlton House Terrace, London SW1Y 5DB Tel: +44 (0) Fax: +44 (0) Website: Report no. FMP/03/02/IOM3