氫能源

Hydrogen energy材料系 蔡文達 教授

Dec 31th 2009

二十一世紀前五十年 人類將面臨之十大問題

ENERGY

WATER

FOOD

ENVIRONMENT

POVERTY

TERRORISM & WAR

DISEASE

EDUCATION

DEMOCRACY

POPULATION

Greenhouse Effect

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Global warming – mean surface temperature 1850-2006

Needs of New Type of Energy -- Renewable energy

Renewable energy is energy generated from natural resources—such as sunlight, wind, rain, tides and geothermal heat—which are renewable (naturally replenished). In 2006, about 18% of global final energy consumption came from renewables

wind turbines Monocrystalline solar cell

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Types of Energy

Biomass Fossil energy Electricity

Hydropower Natural gas Coal Nuclear energy Wind Geothermal

Renewable energy Biomass Solar energy Batteries Fuel cells Wind energy Hydrogen energy Wide and tidal power

Efficiency

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To achieve comparable driving range may require larger amount of H2.

On a weight basis, hydrogen has nearly three times the energy content of gasoline. However, on a volume basis the situation is reversed and hydrogen has only about a quarter of the energy content of gasoline.

Why Challenge

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For the successful commercialization and market acceptance of hydrogen powered vehicles, the performance targets developed are based on achieving similar performance and cost levels as current gasoline fuel storage systems for light-duty vehicles.

Gasoline or Hydrogen.

氫能經濟的意義 由來：

1970 年：「 Hydrogen Economy （氫能經濟）」首次由美國通用汽車公司提出。

2000 年：美國通用汽車公司在國家石油化學與煉製協會的年會上說：「我們的長期遠景是氫能經濟」。

意義：主要為描繪未來氫取代石油成為支撐全球經濟之主要能源後，整個氫能源生產、輸送、貯存及使用之市場運作體系。

Building Hydrogen Economy

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H2 utilization (Fuel cell)

A fuel cell is an electrochemical conversion device. It produces electricity from fuel (on the anode side) and an oxidant (on the cathode side), which react in the presence of an electrolyte.

Fig. Direct-methanol fuel cell Fig. Scheme of fuel cell

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H2 on-board vehicle application A hydrogen vehicle is a vehicle that uses hydrogen as its on-board fuel for motive power. The term may refer to a personal transportation vehicle, such as an automobile, or any other vehicle that uses hydrogen in a similar fashion, such as an aircraft.

Fig. Hydrogen station

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To achieve comparable driving range may require larger amount of H2.

On a weight basis, hydrogen has nearly three times the energy content of gasoline. However, on a volume basis the situation is reversed and hydrogen has only about a quarter of the energy content of gasoline.

Why Challenge

?

For the successful commercialization and market acceptance of hydrogen powered vehicles, the performance targets developed are based on achieving similar performance and cost levels as current gasoline fuel storage systems for light-duty vehicles.

Gasoline or Hydrogen.

• Overview of hydrogen energy

Hydrogen Energy

If the energy used to split the water were obtained from renewable or Nuclear power sources, and not from burning carbon-based fossil fuels, a hydrogen economy would greatly reduce the emission of carbon dioxide and therefore play a major role in tackling global warming.

2H2O → O2 + 4H+ +4e- 2H+ + 2e- → H2

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H2 Hydrogen is the only chemical energy carrier that has the potential to used without generating pollutants to the atmosphere.

Environmentally friendly.

Hydrogen fueled heat engines can be optimized by the manufacturer to operate at much higher thermal efficiencies than heat engines powered with traditional hydrocarbon fuels.

Efficient combustion.

Clean , Renewable and Sustainable .

“ The choice for the future .”

Why hydrogen ?

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H2 production Hydrogen is commonly produced by extraction from hydrocarbon fossil fuels via a chemical path. Hydrogen may also be extracted from water via biological production in an algae bioreactor, or using electricity (by electrolysis), chemicals (by chemical reduction) or heat (by thermolysis)

Biological production : Biohydrogen can be produced in an algae bioreactor. In the late 1990s it was discovered that if the algae is deprived of sulfur it will switch from the production of oxygen, i.e. normal photosynthesis, to the production of hydrogen.

Fig. An algae bioreactor for hydrogen production.

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H2 production Electrolysis : Hydrogen can also be produced through a direct chemical path using electrolysis. With a renewable electrical energy supply, such as hydropower, wind turbines, or photovoltaic cells, electrolysis of water allows hydrogen to be made from water without pollution.

Chemical production : By using sodium hydroxide as a catalyst, aluminum and its alloys can react with water to generate hydrogen gas.

Al + 3 H2O + NaOH → NaAl(OH)4 + 1.5 H2 Solar Energy

Fig. Photoelectrochemical cell

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Methods for Hydrogen Storage

• Gas form

• Liquid form

• Solid form

Hydrogen storage methods

High pressure gas cylinders (up to 800bar)

Liquid hydrogen in kryogenic tanks(at 21 K)

Absorbed hydrogen on materials with a large specific surface area(T<100 K)

Adsorbed on interstial sites in a host metal(at ambient pressure and temperature)

Chemically bond in covalent and ionic compounds (at ambient pressure, high activity)

Oxidation of reactive metals, e.g. Li,Na, with waterRef: A. Zu¨ttel, P. Wenger, S. Rentsch, P. Sudan,Ph. Mauron, Ch. Emmenegger,Journal of Power Sources 118 (2003) 1–7.

儲氫方法 優點 缺點壓縮儲氫 成本低，應用廣泛。

充放氣速度快，且在常溫下就可進行運輸和使用方法方便。

能量密度低,壓力高，消耗較多的壓縮功。氫氣易泄漏和容器爆破等不安全因素，使用和運輸有危險。

液化儲氫 能量密度最大，是一種輕巧緊湊的儲氫方式。

能量損失大，成本高。液氫貯存需要極好的絕熱裝置來隔熱貯存容器龐大。

金屬氫化物儲氫

壓力平穩，充氫簡單、方便

單位體積的儲氫密度大運輸和使用安全。

儲氫量小。金屬氫化物易破裂且材料成本高。

吸附儲氫 碳奈米管的儲氫能力可達 10％以上。

生產奈米碳管的技術尚不成熟，且價格昂貴。

H2 storage High pressure gas cylinders (up to 800bar)

Liquid hydrogen in cryogenic tanks(at 21 K)

Fig. Liquid hydrogen tank for a hydrogen car Fig. gas cylinders

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H2 storage Adsorbed hydrogen on materials with a large specific surface area (T<100 K) : carbon materials or zeolite

Adsorbed on interstitial sites in a host metal (at ambient pressure and temperature) : metal hydride

Chemically bond in covalent and ionic compounds (at ambient pressure, high activity) : complex metal hydride

Fig. Hydrogen in metal matrixFig. Carbon nanotube

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Gasoline or Hydrogen

The 2015 targets represent what is required based on achieving similar performance to today’s gasoline vehicles (greater than 300 mile driving range) and complete market penetration.

US DOE H2 storage system targets

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6 wt% 9 wt%

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Current approaches include:1. High pressure H2 cylinders (Gas)2. Cryogenic and liquid hydrogen (Liquid)

3. High surface area sorbents (Solid)4. Metal hydrides (Solid)

Hydrogen Storage

Methods

Conventional Storage

Advanced Solid Materials Storage

Increasing H2 density by Pressure and Temp. control.

Using little additional material to reach high H2 density.

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The materials science challenge of hydrogen storage is to understand the interaction of hydrogen with other elements better, especially metals.

Hydrogen production, storage, conversion has reached a technological level, although plenty of improvements and new discoveries are still possible.

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Thank you for your kind attention.

Department of Materials Science and Engineering

National Cheng Kung UniversityCorrosion Prevention Laboratory