EML4930L12

EML4930L12 - Sustainable Energy Science and Engineering...

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S ustainable E nergy S cience and E ngineering C enter Hydrogen Production
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S ustainable E nergy S cience and E ngineering C enter Hydrogen Production Source:
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S ustainable E nergy S cience and E ngineering C enter Feedstocks Usage in Hydrogen Production Source: NAS Study, 2004
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S ustainable E nergy S cience and E ngineering C enter Sustainable Paths to Hydrogen Source:
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S ustainable E nergy S cience and E ngineering C enter Hydrogen Production Methods Most methods of producing hydrogen involve splitting water (H 2 O) into its component parts of hydrogen (H 2 ) and oxygen (O). The most common method involves steam reforming of methane (from natural gas), although there are several other methods. Steam reforming converts methane (and other hydrocarbons in natural gas) into hydrogen and carbon monoxide by reaction with steam over a nickel catalyst Electrolysis uses electrical current to split water into hydrogen at the cathode (+) and oxygen at the anode (-) Steam electrolysis (a variation on conventional electrolysis) uses heat, instead of electricity, to provide some of the energy needed to split water, making the process more energy efficient Thermochemical water splitting uses chemicals and heat in multiple steps to split water into its component parts Photoelectrochemical systems use semi-conducting materials (like photovoltaics) to split water using only sunlight Photobiological systems use microorganisms to split water using sunlight Biological systems use microbes to break down a variety of biomass feed stocks into hydrogen Thermal water splitting uses a very high temperature (approximately 1000°C) to split water Gasification uses heat to break down biomass or coal into a gas from which pure hydrogen can be generated
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S ustainable E nergy S cience and E ngineering C enter Chemical Hydrogen Production
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S ustainable E nergy S cience and E ngineering C enter Electrolysis
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S ustainable E nergy S cience and E ngineering C enter Electrolysis
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S ustainable E nergy S cience and E ngineering C enter Electrolysis of Water By providing energy from a battery, water (H 2 O) can be dissociated into the diatomic molecules of hydrogen (H 2 ) and oxygen (O 2 ). This process is a good example of the the application of the four thermodynamic potentials (internal energy, U, Helmoltz free energy, F = U-TS; Enthalpy, H = U+pv and Gibbs free energy, G =U+pv-TS. The electrolysis of one mole of water produces a mole of hydrogen gas and a half a mole of oxygen gas in their normal diatomic forms. A detailed analysis of this process makes use of the thermodynamic potentials and the first law of thermodynamics. This process is presumed to be at 298K and atmospheric pressure.
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S ustainable E nergy S cience and E ngineering C enter Quanitity H 2 OH 2 0.5O 2 Change Enthalpy -285.83kJ 0 0 H = -285.83kJ Entropy 69.91 J/K 130.68J/K 0.5x205.14J/K T S = 48.7 kJ System work: W = P V = (101.3 kPa)(1.5 moles)(22.4x10 -3 m 3 /mol)(298K/273K) = 3715 J U = H-P V = 285.83kJ-3.72 kJ = 282.1 kJ G = H-T S = 285.83 kJ-48.7 kJ = 237.1 kJ Electrolysis of Water
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S ustainable E nergy S cience and E
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EML4930L12 - Sustainable Energy Science and Engineering...

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