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Fuel Cell Development Managing the Interfaces John R. Wallace, Ford Motor Company INTRODUCTION The development of a commercially viable fuel cell system for transporta- tion has been one of the largest problems that the automobile industry has faced in the past 50 years. Its solution will require the coordination and interaction of many different disciplines. Although the fuel cell stack is fundamentally an electrochemical device, the surrounding air and water management systems inter- act significantly with the stack design. Fluid dynamics, mechanical engineering, and control systems skills are required to develop a properly optimized system. The interaction of the complete vehicle with the fueling infrastructure adds further to the overall complexity of this emerging technology. Any organization or set of organizations with a goal of successfully commercializing fuel cells in transpor- tation must reflect these interactions and manage these complex interfaces. Sir William Robert Grove invented the fuel cell or "gas battery" in the 1 840s, but the discovery of the "fuel cell effect" by Christian Friedrich Schoenbein dates back to 1838. The first practical fuel cells were not built until the Gemini and Apollo space programs in the 1960s and are still used in space today. The differ- ence between building a successful fuel cell and a commercially successful fuel cell, however, is the same difference between putting a man on the moon and putting 10,000 men on the moon every day at an affordable price. Despite all of the challenges associated with fuel cell technology, vehicles powered by fuel cells promise zero tailpipe emissions with improved fuel efficiency and fuel flex- ibility. Alternative fuel sources in the transportation technology portfolio are pre- ferred, so that no matter what changes occur in the fuel industry, people and goods can move around. As it currently stands, an enormous industrial pyramid rests on a single transportation fuel. 18
FUEL CELL DEVELOPMENTMANAGING THE INTERFACES FUEL CELLS 19 For vehicles, proton exchange membrane fuel cells are probably the most practical design (Figure 3.1~. The most important part of a fuel cell is the mem- brane, which must be an ion conductor, an electronic insulator, an impermeable gas barrier and also possess good mechanical strength. However, the key issues in making a practical fuel cell are nonelectrochemical. These include the acts of delivering the gases to the fuel cell membrane, removing the water, removing the heat from around the system, and controlling humidity and pressurization of gases. There are still many challenges for electrochemists, chemists, and chemical engineers. For example, a membrane that is more tolerant of environmental con- ditions for gases of varying pressures will allow for the elimination of various system components, which can be very expensive due to their use of stainless steel. The technical challenge is in fabricating a membrane to be thin enough so that the hydrogen side of the gas supply does not need to be humidified. How- ever, as membranes get thinner, reliability over long periods of time becomes an issue due to faradaic losses. If the membrane is too thick, additional components must be added to humidify the hydrogen. In a vehicle fuel cell stack, which has over 400 cells in series, the situation is even more complicated. Well over 90 percent of fuel cell industry funds are not spent on the membrane but on moving these gases in and out of the fuel cell stack, FIGURE 3.1 Configuration of a typical proton exchange membrane (PEM) fuel cell. Source: National Fuel Cell Research Center.
20 ENERGY AND TRANSPORTATION managing the system, and creating the environment where the membrane can do its job. Fuel cell research, however, is mainly performed in a lab where gases are supplied at exactly the right humidity, pressures, and so on. The actual commer- cial problem, development of a fuel-cell-powered vehicle that has a life of 15 years and 150,000 miles under terrible external environmental conditions, has not been approached. Fuel cell technology may be developed to permit its use for power generation in the near future, but the cost is prohibitive for vehicle trans- portation. Tolerances are also not well understood. A fuel cell stack with over 400 cells operating in this environment contains sealant, which is literally miles long. Seals will start to fail after the fuel cell is bumped and jostled on the highway and while temperature shifts between hot and cold, and the cell is turned off and on. With zero tolerance for safety failures, hydrogen leaks cannot occur with these vehicles. Additionally, every cell has to be identical or the system cannot be managed. Unfortunately, that kind of tolerance control is not yet available. An ideal fuel cell system will have minimal components outside of the stack and will operate using ambient, unhumidified hydrogen. Although fuel cells are very efficient, they do not release much heat through the exhaust. Even though they generate less heat than an internal combustion engine, the system requires the addition of cooling components due to the generated heat in the cooling stack. However, if this stack can generate less heat, then radiators, pumps, and coolant will not be required. The standard for a modern vehicle requires it to start within 2 seconds at worst. A fuel cell starts well within 1 second. However, fuel cells, including hydrogen fuel cells, do not operate well at subfreezing temperatures. This is because fuel cells are basically a liquid interface device and need liquid-phase water to operate. Running the system under the conditions of a highway environ- ment is possible, but the current cost is too great for commercialization. HYBRIDIZATION Hybridization is the optimization of two different power plants with two different characteristics and blending them together into a system that is better than either of the two components alone. In the case of transportation, hybridiza- tion involves a fuel cell and a battery or a battery and an internal combustion engine. The stacks, its fuel cell system, and the battery are completely different devices with different characteristics, so a tradeoff needs to occur. Fortunately, energy can be recaptured, transient capability can be improved, and the fuel cell can be put into its most efficient operating mode to literally use a battery to carry out all the operating modes that are detrimental to the fuel cell and to only allow the fuel cell to operate in a benign environment. The two devices working together can also help improve the start time. With hybridization, the size of the stack can be reduced, in turn reducing overall costs.
FUEL CELL DEVELOPMENTMANAGING THE INTERFACES 21 Of course, the negative tradeoff is that an extra component is added. The battery has its costs with benefits that need to be quantified. However, the addi- tion of a hybrid battery up to the peak of 60 percent of a 60/40 battery/fuel cell stack yields a 50 percent improvement in fuel efficiency. While the battery has no ability to provide independent primary energy, hybridization is still an amazing new technology, especially since speed, start-up launch, and performance improve for the customer. INSTITUTIONAL STRUCTURE More is gained by going out to the interfaces and solving problems as a system rather than trying to solve everything one component at a time for example, at the membrane or at the fuel cell stack. This is also true for corporate structures. DaimlerChrysler and Ford have a partnership in the fuel cell area. Until fairly recently, it was a rather complex corporate partnership with other companies. For example, Ballard had responsibility for the stack, Xcellsis for the fuel cell system, Ecostar for the power electronics and drive train, and Ballard Automotive for trying to integrate it to some extent and sell it as a unit. This corporate structure added corporate and cultural interfaces into the system's engineering tasks. In the recent reorganization, all of the system inter- faces are now contained inside one corporation, which solved a lot of issues in terms of development interfaces and a lot of business issues as well. The message here is that interfaces need to be addressed not just in terms of processes but also in terms of the vital institutional structure that surrounds it. HYDROGEN STORAGE Practical use of hydrogen in vehicles may never happen until there is a better method to store hydrogen, especially since onboard reforming of hydrogen at a reasonable cost may not be a possibility. The U.S. Department of Energy has worked with the auto industry and has ranked the options for hydrogen storage. The best candidate so far is compressed gas at pressures of about 700 bar. While not an ideal solution, it is probably marketable. The use of hydrogen requires additional infrastructure for production and transportation. One method is to use electrical energy to produce hydrogen, but power grids are very inefficient. Another is the use of a natural gas pipeline, which is also wasteful since it involves the liquefying and re-evaporation of gases. The issues that need to be addressed in terms of fueling are the required number of fueling stations, the amount of money it will cost, how the oil industry will react, and how the auto industry will manage this emerging technology.
22 ENERGY AND TRANSPORTATION THREE-WAY INTERFACE Renewable energy is the ultimate goal. Over the very long term, there must be a sustainable energy system that does not require a depletable resource. Unfor- tunately, at this time there are no systems that are economically competitive and renewable. The Department of Energy supports this goal, but it will be universi- ties or the private sector that reach it. Fuel flexibility and new infrastructures in fuels are three-way issues between the auto industry, the energy providers, and the federal government. Dealing with this three-way interface will be a problem, especially since each institution is used to having its own way. Fortunately, there is an institution like the California Fuel Cell Partnership, which is not just localized to California but is the world's fuel cell partnership. It is the only institution in the world that involves major public sector players, the major energy providers, and the major auto companies of the world. This is the only forum where they can all interact and struggle with the fuel cell problem. The partnership is actually working. An initial report on the infrastructure problem has been issued recently. Although it really raises more questions than it provides answers, it puts forth a common language for all involved parties to use to talk about the problem. Recently, there has been an announcement that Toyota has created a new organization inside the company. A fuel cell technology center has been created that includes vehicle development, fuel cell system development, fuel cell stack development, and manufacturing. Toyota also has run into this interface problem in its development efforts and consequently has created an organizational answer to it that allows the company to solve this giant interface issue across all these areas. DaimlerChrysler and Ford have both reached the same conclusion. There needs to be more openness toward creating new institutions to solve fuel cell problems. Fuel cell development is a major systems engineering issue, and the problems involved will not be solved simply by applying current processes. Fuel cell issues need to be solved now even if the solutions are not needed immedi- ately. Waiting until fuel cells are needed may be too late to solve the problem.
