--------- #1477 - Hydrogen to fuel cars?
- If our people technology could work like plant technology the world would be a nicer place. Plants soak up the sun to extract their fuel and expel pure oxygen which we like to breath. People technology disrupts the earth to collect fossil fuels and expels CO2 that causes Global Warming.
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- The Sun’s energy is enormous. More energy hit’s the Earth in one hour then the entire world consumes in one year.
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- Another great thing about plant technology is that plants have the ability to store energy when the Sun doesn’t shine. Plant technology has evolved and been perfected over 3,500,000,000 years. No wonder people technology is having great difficulty in duplicating it in the last several decades. Although we are trying; the desire is there.
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- Plant technology uses the Sun’s energy to split water, H2O, into its components hydrogen and oxygen. Plants then breath carbon dioxide and rearrange the chemistry to produce carbohydrates which store the energy. However, plants are not terribly efficient. Only about 2% of the Sun’s energy ends up stored in the carbohydrates. Also, plants are not especially robust. Too much Sun and they burn. Too little Sun and they wilt. To compensate robustness plant processes constantly reproduce and are renewed.
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- Carbohydrates are not a very efficient fuel either. Pure hydrogen would be much better fuel if it were used directly. Hydrogen produces 2.5 times more energy per pound than gasoline. A Fuel Cell can use hydrogen to produce electricity and expel drinking water. What is stopping Fuel Cells from being our ideal power source? They are 10 times more expensive then today’s alternatives. Fuel Cell development needs to create a cheap, efficient , robust technology that we have yet to achieve.
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- The problem starts with receiving the Sun’s energy. Silicon does a good job absorbing the Sun’s high energy photons. It can split out electrons with 1.1 electron volts of energy. To split water into hydrogen and oxygen it requires 1.23 electron volts of energy. So, why not stack silicon substrates together to get the higher electron volts. When silicon reacts with oxygen ( rusts) it creates an insulating layer of silica which stops the electron flow. Gallium Arsenide and Gallium Indium Phosphide semiconductors absorb the Sun’s energy at different wavelengths but they also oxidize. Metal - oxide semiconductors are another alternative being investigated.
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- The second part of the problem is that when you separate electrons and holes you have to keep them separated or they just recombine and become neutral in the atoms. When you split water into hydrogen and oxygen you have to suck away the electrons before they can recombine in the atoms. What we want to produce is free molecular oxygen and free protons. At a separate side of the process we want to produce molecular hydrogen.
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- To accomplish these chemical reactions two separate catalysts are required for hydrogen and for oxygen. Platinum works well but it is too expensive, it is like gold. Nickel and Molybdenum Sulphide are the other catalysts being studied for hydrogen.
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- For oxygen separation plants use Manganese atoms. People technology has found something more efficient in Indium Oxide. More efficient but again too expensive.
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- An “ artificial leaf ” has been developed that works in battery acid. Not good. Newer developments work in water and require Nickel, Molybdenum, and Zinc catalyst for the hydrogen and Cobalt-borate for the oxygen. But, the efficiency of the leaf is only 2.5% and it degrades with a couple weeks of use.
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- Using the triple-junction silicon is also too expensive. The hydrogen produced would cost $7 per kilogram. We can get hydrogen from methane for $2.50 per kilogram. The design goal for the “ artificial leaf” is to achieve $3 per kilogram at 5% efficiency.
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- An artificial leaf design is especially suited for regions where sunlight is abundant and access to clean water is a problem. A secondary benefit often in these regions is that they would replace paraffin lamps and diesel generators that are major polluters.
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- How soon will we be making hydrogen fuel as the sun shines? An announcement will be made shortly, stay tuned.
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(1) To learn more: Review #528 - The hydrogen economy will take awhile. Written in 2004
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707-536-3272, Saturday, May 26, 2012
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