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The hydrogen economy is a proposed system of delivering energy using hydrogen. The term ''hydrogen economy'' was coined by John Bockris during a talk he gave in 1970 at General Motors (GM) Technical Center. The concept was proposed earlier by geneticist J.B.S. Haldane.〔(''Daedalus or Science and the Future'', A paper read to the Heretics, Cambridge, on February 4th, 1923 – Transcript 1993 )〕 Proponents of a hydrogen economy advocate hydrogen as a potential fuel for motive power〔(A portfolio of power-trains for Europe: a fact-based analysis )〕 (including cars and boats) and on-board auxiliary power, stationary power generation (e.g., for the energy needs of buildings), and as an energy storage medium (e.g., for interconversion from excess electric power generated off-peak). Molecular hydrogen of the sort that can be used as a fuel does not occur naturally in convenient reservoirs; nonetheless it can be generated by steam reformation of hydrocarbons, water electrolysis or by other methods. The spike in attention for the concept during the 2000s has been repeatedly described as a hype by critics, neutral observers and advocates of further research and development. Some small-scale initiatives from that period are still trying to enable hydrogen-fuelled land transport. However, this application faces many issues, given fundamentally low conversion efficiencies and competition from other sources. == Rationale == A hydrogen economy was proposed by the University of Michigan to solve some of the negative effects of using hydrocarbon fuels where the carbon is released to the atmosphere. Modern interest in the hydrogen economy can generally be traced to a 1970 technical report by Lawrence W. Jones of the University of Michigan. In the current hydrocarbon economy, transportation is fueled primarily by petroleum. Burning of hydrocarbon fuels emits carbon dioxide and other pollutants. The supply of economically usable hydrocarbon resources in the world is limited, and the demand for hydrocarbon fuels is increasing, particularly in China, India, and other developing countries. Proponents of a world-scale hydrogen economy argue that hydrogen can be an environmentally cleaner source of energy to end-users, particularly in transportation applications, without release of pollutants (such as particulate matter) or carbon dioxide at the point of end use. A 2004 analysis asserted that "most of the hydrogen supply chain pathways would release significantly less carbon dioxide into the atmosphere than would gasoline used in hybrid electric vehicles" and that significant reductions in carbon dioxide emissions would be possible if carbon capture or carbon sequestration methods were utilized at the site of energy or hydrogen production. Hydrogen has a high energy density by weight but has a low energy density by volume when not highly compressed or liquified. An Otto cycle internal-combustion engine running on hydrogen is said to have a maximum efficiency of about 38%, 8% higher than a gasoline internal-combustion engine.〔BMW Group Clean Energy ZEV Symposium. September 2006, p. 12〕 The combination of the fuel cell and electric motor is 2-3 times more efficient than an internal-combustion engine. However, the high capital costs of fuel cells, about $5,500/kW in 2002, are one of the major obstacles of its development, meaning that the fuel cell is only technically, but not economically, more efficient than an internal-combustion engine. Other technical obstacles include hydrogen storage issues〔(R&D of large stationary hydrogen/CNG/HCNG storage vessels )〕 and the purity requirement of hydrogen used in fuel cells – with current technology, an operating fuel cell requires the purity of hydrogen to be as high as 99.999%. On the other hand, hydrogen engine conversion technology is more economical than fuel cells. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hydrogen economy」の詳細全文を読む スポンサード リンク
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