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ECN publication
Hydrogen production and fuel cells as the bridging technologies towards a sustainable energy system
Published by: Publication date:
ECN Hydrogen and Clean Fossil Fuels 22-6-2007
ECN report number: Document type:
ECN-B--07-013 Book
Number of pages: Full text:
53 Download PDF  

Published in: Catalysis for Renewables: From feedstock to Energy Production, 299, 336, Wiley-VCH Verlag, Weinheim.

Today's energy use, based on the conversion of fossil fuels, is not sustainable on the long term. Global warming, security of supply and local air quality are strong driving forces to change the present energy system. Given the huge global demand for energy, no single solution can be imagined to make this energy supply more efficient, less carbon intensive and more sustainable, i.e. using renewable sources to a large extent. Hydrogen plays a pivoting role in all strategies to lower CO2-emissions, improve the air quality of urbanised areas and increase the possibilities of covering the energy demand with energy sources other than petroleum. In the European Union, the Hydrogen and Fuel Cell Platform has set up a Strategic Research Agenda [1]aiming at the development of technologies needed for hydrogen production, storage, transport and application in stationary and mobile systems. In addition, a Deployment Strategy [1] has been made for the market introduction of these technologies. A program of over 2 billion euros is foreseen in the 7th Framework Programme. In the United States, the Freedom Car Initiative [2] and the FutureGEN [3] projects are just two examples of a huge program on hydrogen and fuel cell technologies. The Department of Energy has a well-organised program in which clear technology development targets are set, and progress is frequently assessed. In California, demonstration fleets of fuel cell vehicles are on the road, and state legislation on emissions pose a strong driving force to clean vehicles. In Japan, being completely dependant on fossil fuels imports, a long tradition exists in developing stationary and mobile fuel cell applications. Programs funded by the NEDO and METI departments have already resulted in hundreds of small scale micro Combined Heat and Power Units as well as fuel cell vehicles running in road demonstrations [4]. The hydrogen energy chain The energy chain for hydrogen is schematically drawn in Figure 1. For each step in the chain, several options exist or are in development. The energy efficiency and CO2 emission of the complete hydrogen energy chain should be taken into account when considering the introduction of hydrogen into certain applications. Optimisation of each step will be necessary to maximise the benefit of this fuel for the future. At the same time the energy use and CO2 emissions in society as a whole must be minimised. The consequence is that selection of a primary energy source for in this case the hydrogen energy chain alone is not sufficient. The optimal selection of the use of that primary energy source is as important as well. From the perspective of hydrogen in transport for instance, hydrogen obtained by using wind power in combination with an electrolyser leads to a near zero-emission hydrogen chain. When this wind power can be used directly to substitute fossil fuel powered electricity generation, while the hydrogen for transport is generated by methane steam reforming, the benefit for society in terms of CO2 reduction and energy savings is two times larger. Hydrogen Sources and Production Hydrogen can be produced by reforming natural gas and petroleum derived fuels, by gasification of biomass and coal, and by using renewable electricity to power water electrolysers. Longer term options as thermo-chemical splitting of water, bacteriological hydrogen production and photo-electrochemical splitting of water are investigated as well. In this chapter we limit ourselves to a number of mid-term options that can be used when the large scale use of hydrogen needs to be supplied by cost effective production routes using available sources, being reforming of natural gas, with CO2 capture, and the use of electrolysers which can be powered by renewable electricity. The use of hydrogen in stationary and mobile applications For road transport, fuel cells are the most efficient conversion devices for using hydrogen. For the average drive cycle, which is dominated by a power demand which is only a fraction of the maximum available power, hybrid fuel cell systems offer a clear advantage in comparison to Internal Combustion Engines, hybridised or not, when energy use, CO2 emissions and non-greenhouse pollutants are considered. For stationary power production, small systems (1 – 200 kWe) in which heat and power demand can be provided by fuel cells provide an opportunity to save large amounts of energy in comparison to central electricity production, where waste heat is in general not used. These systems would preferably run on natural gas, which is converted on site to hydrogen. For large scale power production, the CO2-free production of hydrogen from natural gas and coal, with the subsequent burning of this hydrogen in the power plant, can offer the first step to reduce the CO2 emissions from power production significantly. We discuss both the Proton Exchange Membrane as well as the Solid Oxide Fuel Cell in this chapter (PEMFC and SOFC). Both types are in full development, the PEMFC for mobile and stationary applications, the SOFC for stationary applications as well as for auxiliary power generation for transport as well.

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