Hydrogen in Transportation

The development of a hydrogen infrastructure, besides the difficulties discussed earlier, is facing the "chicken and egg dilemma". As long as there is no adequate hydrogen distribution infrastructure, there will be only a limited demand for hydrogen-powered cars and other applications, despite its obvious attractiveness as an energy storage material. On the other hand, there is no real incentive for investing hundreds of billions of dollars in a hydrogen infrastructure unless there is a solid and sustained demand for it. The question is: how can the demand for hydrogen be stimulated, and will the hydrogen economy become real? Today, the fate of the hydrogen economy seems to be tightly connected with the development of fuel cells which offer the promise of very efficient and zero-emission vehicles. Unfortunately, however, the questions raised about generation, handling and distribution of hydrogen are often neglected. Due to significant technical and economic challenges, the road to commercialization has still a long way to go. Currently, most prototype vehicles have very high price tags, and even using optimistic assumptions the U.S. Department of Energy has estimated that future fuel cell vehicles (FCV) would likely be 40-60% more expensive than conventional ones [95]. Thus, it may take decades before FCVs begin seriously to replace internal combustion engines (ICE) -powered cars and trucks. In aiming to accelerate the transition to a hydrogen economy, the use of hydrogen fuel in a conventional ICE has also been suggested. Except for replacing the fuel tank with a hydrogen tank, only minor and relatively inexpensive changes would be necessary to run an ICE vehicle on hydrogen. Safety precautions, however, must be seriously considered, and a number of automobile makers are heading down this pathway. BMW, in particular, has been conducting research on hydrogen-powered engines since 1978, testing the first prototype motor car a year later. The company's sixth-generation hydrogen-powered car, planned to be produced in limited series within a few years, has a bivalent engine which is able to run either on hydrogen or gasoline. This will allow the motor car to move on today's road network, where hydrogen filling stations are still few and far between. The liquid hydrogen tank, with a capacity of 170 L, will allow the car to cover a distance of about 300 km, with a secondary gasoline tank extending this range to 800 km (Fig. 9.9) [100]. In addition to BMW, Ford (hydrogen-powered model U concept car) and Mazda are also planning to introduce hydrogen ICE cars. These vehicles have the advantage of

producing almost no pollutants (except for small amounts of NOx) and can be introduced relatively soon in the market compared to FCVs. In order to significantly increase its efficiency, the hydrogen ICE could also be coupled with an electric hybrid system, as found in Toyota's Prius (an ICE engine running on gasoline also charges batteries, which take over to provide an electric drive in slow city traffic). The efficiency, however, is expected to remain lower than for fuel cell vehicles. Despite the advantages of hydrogen ICE, the problem of on-board hydrogen storage, which presently limits the driving range, also remains. Besides fueling cars with hydrogen produced at central locations and in delocalized small units using electrolysis of water at filling stations, it should also be possible to fuel these cars with hydrogen produced by on-board reforming of a variety of hydrocarbon fuels. This would, however, bring no advantage over conventional hydrocarbon-burning ICEs. Carbon monoxide must be carefully separated from the generated syngas, so as not to poison the fuel cells. If the CO were to be oxidized to CO2 and with no CO2 sequestration, the CO2 emission would only be relocated to the hydrogen-generating facilities or devices, but not eliminated.

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