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Showing posts with label Hydrogen Generation. Show all posts
Showing posts with label Hydrogen Generation. Show all posts
Tuesday, January 12, 2010
Horizon Hydrofill Hydrogen Refueling and Storage Solution
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Thursday, January 7, 2010
Water electrolysis explained
Electrolysis - when coupled with renewable energy sources (solar panels, wind turbines...), it is one of the cleanest methods of hydrogen production. It is being utilized in hydrogen on demand applications - e.g HHO fuel for cars. Here are some basic knowledge related with electrolysis.
Electrolysis of water
Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an
electric current being passed through the water. This electrolytic process is rarely used in industrial
applications since hydrogen can be produced more affordably from fossil fuels.
An electrical power source is connected to two electrodes, or two plates, (typically made from some inert
metal such as platinum or stainless steel) which are placed in the water. In a properly designed cell
Hydrogen will appear at the cathode (the negatively charged electrode, where electrons are pumped into the
water), and oxygen will appear at the anode (the positively charged electrode). The generated amount of
hydrogen is twice the amount of oxygen, and both are proportional to the total electrical charge that was sent
through the water. However, in many cells competing side reactions dominate resulting in different products.
Electrolysis of pure water requires a great deal of excess energy in the form of over potential to overcome
various activation barriers. Without the excess energy the electrolysis of pure water occurs very slowly if at
all. This is in part due to the limited self-ionization of water. Pure water has an electrical conductivity about
one millionth that of seawater. Many electrolytic cells may also lack the requisite electrocatalysts. The
efficacy of electrolysis is increased through the addition of an electrolyte (such as a salt, an acid or a base)
and the use of electrocatalysts.
Thermodynamics of the process
Decomposition of pure water into hydrogen and oxygen at standard temperature and pressure is not
favorable in thermodynamical terms.
Thus, the standard potential of the water electrolysis cell is -1.23 V at 25 °C at pH 0 (H+ = 1.0 M). It is also
-1.23 V at 25 °C at pH 7 (H+ = 1.0x10-7 M) based on the Nernst Equation.
The negative voltage indicates the Gibbs free energy for electrolysis of water is greater than zero for these
reactions. This can be found using the G=-nFE equation from chemical kinetics, where n is the moles of
electrons and F is the Faraday constant. The reaction cannot occur without adding necessary energy,
usually supplied by an external electrical power source.
Electrolyte selection
If the above described processes occur in pure water, H+ cations will accumulate at the anode and OH−
anions will accumulate at the cathode. This can be verified by adding a pH indicator to the water: the water
near the anode is acidic while the water near the cathode is basic. These charged ions will repel the further
flow of electricity until they have diffused away, a slow process. This is why pure water conducts electricity
poorly and why electrolysis of pure water proceeds slowly.
If a water-soluble electrolyte is added, the conductivity of the water rises considerably. The electrolyte
disassociates into cations and anions; the anions rush towards the anode and neutralize the buildup of
positively charged H+ there; similarly, the cations rush towards the cathode and neutralize the buildup of
negatively charged OH− there. This allows the continued flow of electricity.
Care must be taken in choosing an electrolyte, since an anion from the electrolyte is in competition with the
hydroxide ions to give up an electron. An electrolyte anion with less standard electrode potential than
hydroxide will be oxidized instead of the hydroxide, and no oxygen gas will be produced. A cation with a
greater standard electrode potential than a hydrogen ion will be reduced in its stead, and no hydrogen gas
will be produced.
The following cations have lower electrode potential than H+ and are therefore suitable for use as
electrolyte cations: Li+, Rb+, K+, Cs+, Ba2+, Sr2+, Ca2+, Na+, and Mg2+. Sodium and lithium are frequently
used, as they form inexpensive, soluble salts.
If an acid is used as the electrolyte, the cation is H+, and there is no competitor for the H+ created by
disassociating water. The most commonly used anion is sulfate (SO42-), as it is very difficult to oxidize, with
the standard potential for oxidation of this ion to the peroxodisulfate ion being −0.22 volts.
Strong acids such as sulfuric acid (H2SO4), and strong bases such as potassium hydroxide (KOH), and
sodium hydroxide (NaOH) are frequently used as electrolytes.
A solid polymer electrolyte can also be used such as NAFION and when applied with a special catalyst on
each side of the membrane can efficiently split the water molecule with as little as 1.8 Volts.
Applications
About four percent of hydrogen gas produced worldwide is created by electrolysis. The majority of this
hydrogen produced through electrolysis is a side product in the production of chlorine. This is a prime
example of a competing side reactions.
2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH
The electrolysis of brine (saltwater), a water sodium chloride mixture, is only half the electrolysis of water
since the chloride ions are oxidized to chlorine rather than water being oxidized to oxygen. The hydrogen
produced from this process is either burned, used for the production of specialty chemicals, or various other
small scale applications.
The majority of hydrogen used industrially is derived from fossil fuels. One example is fossil fuel derived
hydrogen used for the creation of ammonia for fertilizer via the Haber process and for converting heavy
petroleum sources to lighter fractions via hydrocracking. The production of this hydrogen usually involves
the formation of synthesis gas a mixture of H2 and CO. Synthesis gas can be hydrogen enriched through
the water gas shift reaction. In this reaction the carbon monoxide is reacted with water to produce more H2
with CO2 byproduct.
Efficiency
Water electrolysis does not convert 100% of the electrical energy into the chemical energy of hydrogen. The
process requires more extreme potentials than what would be expected based on the cell's total reversible
reduction potentials. This excess potential accounts for various forms of overpotential by which the extra
energy is eventually lost as heat. For a well designed cell the largest overpotential is the reaction
overpotential for the four electron oxidation of water to oxygen at the anode. An effective electrocatalyst to
facilitate this reaction has not been developed. Platinum alloys are the default state of the art for this
oxidation. The reverse reaction, the reduction of oxygen to water, is responsible for the greatest loss of
efficiency in fuel cells. Developing a cheap effective electrocatalyst for this reaction would be a great
advance.
The simpler two-electron reaction to produce hydrogen at the cathode can be electrocatalyzed with almost
no reaction overpotential by platinum or in theory a hydrogenase enzyme. If other, less effective, materials
are used for the cathode then another large overpotential must be paid.
The energy efficiency of water electrolysis varies widely with the numbers cited below on the optimistic side.
Some report 50–80% These values refer only to the efficiency of converting electrical energy into hydrogen's
chemical energy. The energy lost in generating the electricity is not included. For instance, when
considering a power plant that converts the heat of nuclear reactions into hydrogen via electrolysis, the total
efficiency may be closer to 30–45%.
Source: Link
Electrolysis of water
Electrolysis of water is the decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an
electric current being passed through the water. This electrolytic process is rarely used in industrial
applications since hydrogen can be produced more affordably from fossil fuels.
An electrical power source is connected to two electrodes, or two plates, (typically made from some inert
metal such as platinum or stainless steel) which are placed in the water. In a properly designed cell
Hydrogen will appear at the cathode (the negatively charged electrode, where electrons are pumped into the
water), and oxygen will appear at the anode (the positively charged electrode). The generated amount of
hydrogen is twice the amount of oxygen, and both are proportional to the total electrical charge that was sent
through the water. However, in many cells competing side reactions dominate resulting in different products.
Electrolysis of pure water requires a great deal of excess energy in the form of over potential to overcome
various activation barriers. Without the excess energy the electrolysis of pure water occurs very slowly if at
all. This is in part due to the limited self-ionization of water. Pure water has an electrical conductivity about
one millionth that of seawater. Many electrolytic cells may also lack the requisite electrocatalysts. The
efficacy of electrolysis is increased through the addition of an electrolyte (such as a salt, an acid or a base)
and the use of electrocatalysts.
Thermodynamics of the process
Decomposition of pure water into hydrogen and oxygen at standard temperature and pressure is not
favorable in thermodynamical terms.
Thus, the standard potential of the water electrolysis cell is -1.23 V at 25 °C at pH 0 (H+ = 1.0 M). It is also
-1.23 V at 25 °C at pH 7 (H+ = 1.0x10-7 M) based on the Nernst Equation.
The negative voltage indicates the Gibbs free energy for electrolysis of water is greater than zero for these
reactions. This can be found using the G=-nFE equation from chemical kinetics, where n is the moles of
electrons and F is the Faraday constant. The reaction cannot occur without adding necessary energy,
usually supplied by an external electrical power source.
Electrolyte selection
If the above described processes occur in pure water, H+ cations will accumulate at the anode and OH−
anions will accumulate at the cathode. This can be verified by adding a pH indicator to the water: the water
near the anode is acidic while the water near the cathode is basic. These charged ions will repel the further
flow of electricity until they have diffused away, a slow process. This is why pure water conducts electricity
poorly and why electrolysis of pure water proceeds slowly.
If a water-soluble electrolyte is added, the conductivity of the water rises considerably. The electrolyte
disassociates into cations and anions; the anions rush towards the anode and neutralize the buildup of
positively charged H+ there; similarly, the cations rush towards the cathode and neutralize the buildup of
negatively charged OH− there. This allows the continued flow of electricity.
Care must be taken in choosing an electrolyte, since an anion from the electrolyte is in competition with the
hydroxide ions to give up an electron. An electrolyte anion with less standard electrode potential than
hydroxide will be oxidized instead of the hydroxide, and no oxygen gas will be produced. A cation with a
greater standard electrode potential than a hydrogen ion will be reduced in its stead, and no hydrogen gas
will be produced.
The following cations have lower electrode potential than H+ and are therefore suitable for use as
electrolyte cations: Li+, Rb+, K+, Cs+, Ba2+, Sr2+, Ca2+, Na+, and Mg2+. Sodium and lithium are frequently
used, as they form inexpensive, soluble salts.
If an acid is used as the electrolyte, the cation is H+, and there is no competitor for the H+ created by
disassociating water. The most commonly used anion is sulfate (SO42-), as it is very difficult to oxidize, with
the standard potential for oxidation of this ion to the peroxodisulfate ion being −0.22 volts.
Strong acids such as sulfuric acid (H2SO4), and strong bases such as potassium hydroxide (KOH), and
sodium hydroxide (NaOH) are frequently used as electrolytes.
A solid polymer electrolyte can also be used such as NAFION and when applied with a special catalyst on
each side of the membrane can efficiently split the water molecule with as little as 1.8 Volts.
Applications
About four percent of hydrogen gas produced worldwide is created by electrolysis. The majority of this
hydrogen produced through electrolysis is a side product in the production of chlorine. This is a prime
example of a competing side reactions.
2 NaCl + 2 H2O → Cl2 + H2 + 2 NaOH
The electrolysis of brine (saltwater), a water sodium chloride mixture, is only half the electrolysis of water
since the chloride ions are oxidized to chlorine rather than water being oxidized to oxygen. The hydrogen
produced from this process is either burned, used for the production of specialty chemicals, or various other
small scale applications.
The majority of hydrogen used industrially is derived from fossil fuels. One example is fossil fuel derived
hydrogen used for the creation of ammonia for fertilizer via the Haber process and for converting heavy
petroleum sources to lighter fractions via hydrocracking. The production of this hydrogen usually involves
the formation of synthesis gas a mixture of H2 and CO. Synthesis gas can be hydrogen enriched through
the water gas shift reaction. In this reaction the carbon monoxide is reacted with water to produce more H2
with CO2 byproduct.
Efficiency
Water electrolysis does not convert 100% of the electrical energy into the chemical energy of hydrogen. The
process requires more extreme potentials than what would be expected based on the cell's total reversible
reduction potentials. This excess potential accounts for various forms of overpotential by which the extra
energy is eventually lost as heat. For a well designed cell the largest overpotential is the reaction
overpotential for the four electron oxidation of water to oxygen at the anode. An effective electrocatalyst to
facilitate this reaction has not been developed. Platinum alloys are the default state of the art for this
oxidation. The reverse reaction, the reduction of oxygen to water, is responsible for the greatest loss of
efficiency in fuel cells. Developing a cheap effective electrocatalyst for this reaction would be a great
advance.
The simpler two-electron reaction to produce hydrogen at the cathode can be electrocatalyzed with almost
no reaction overpotential by platinum or in theory a hydrogenase enzyme. If other, less effective, materials
are used for the cathode then another large overpotential must be paid.
The energy efficiency of water electrolysis varies widely with the numbers cited below on the optimistic side.
Some report 50–80% These values refer only to the efficiency of converting electrical energy into hydrogen's
chemical energy. The energy lost in generating the electricity is not included. For instance, when
considering a power plant that converts the heat of nuclear reactions into hydrogen via electrolysis, the total
efficiency may be closer to 30–45%.
Source: Link
Tuesday, January 5, 2010
The Toilet That Can Help Solve Our Water and Energy Problems
There is a 'toilet revolution' taking shape -- and it may be coming just in time.
Upwards of 3 million people die annually from diarrhea, dysentery, and parasitic diseases -- all for the want of clean water. Meanwhile, each year in the water-rich United States, 2.1 billion gallons of the world's most precious liquid are used, not to water thirsty crops or slake parched throats, but to flush human waste from home toilets to municipal sewers. While harvesting rainwater and recycling graywater are fine strategies, it's time to get to the seat of the problem. We need a Toilet Revolution.
As frequently happens, the solution to this modern problem can be found in the recent past -- and the Third World present. Jeff Conant, author of The Community Guide to Environmental Health, has traveled the world in search of the perfect "waterless toilet." He found it in the Mexican town of Tepotzlan, which boasts hundreds of "non-traditional waterless" eco-loos. In the 1980s, Tepotzlan's innovators got a boost when former UNICEFworker Ron Sawyer settled in to help the locals design a new generation of "eco-san" toilets.
While the practice of using human waste as fertilizer is as old as humanity itself, Tepotzlan's eco-sanistas marked an engineering watershed when they found a way to separate feces from urine. A locally designed toilet seat harvests the fluids while allowing the solid wastes to fall into a dry compost toilet. (Not such a strange idea: The human body is designed to send solid and liquid wastes in opposite directions.) One immediate result of separating pee from poo is the elimination of the unpleasant aromas associated with the traditional outhouse.
While installing waterless toilets in high-rise apartments might raise certain engineering challenges, "urine-separating dry toilets" are being adopted around the world -- from South Africa, Peru, Cuba, and India to the United States, where composting waterless toilets can be purchased online. There are several to choose from, including Biolet, Envirolet, Sun-Mar, the venerable-sounding Clivus Multrum, and the EcoJohn (an "incinerating toilet" that's being used in US homes and military camps). Most sell for around $1,500. Home Depot lists a Biolet for $1,400 (about the price of a new fridge). The Nature's Head urine-separating dry toilet (designed by sailors for onboard use) is a bargain, priced at $850.
Dry-compost toilets not only conserve water, they also protect rivers and oceans. By circumventing modern sewers, dry-compost toilets avoid diverting nitrogen, potassium, and phosphate-rich wastes from the land (where they would enrich the soil) to rivers and oceans, where they cause algal blooms, oxygen-robbing eutrophication, and oceanic "dead zones."
The first flush of the Toilet Revolution was heard in Orange County, of all places. In 1997, San Diego announced plans to have a "Toilet-to-Tap" system up and running by 2001. In 1998, California's governor signed a law directing the state to evaluate the potential of recycling the post-toilet flow to "ensure that any water produced by these systems meets the identical standards that our drinking water does now." While San Diego's filtration system successfully reduced contaminants to the same level as "untreated fresh water," many people had trouble swallowing the idea of sipping treated waste water, even though toilet-to-tap is a proven, Space-Age technology. For decades, America's orbiting astronauts have thrived by drinking their own urine, recycled endlessly through space shuttle filtration systems.
There's another powerful reason to separate and recycle urine. It turns out that urine -- the world's most abundant waste -- could become the "fuel of the future." Ohio University researcher Geradine Botte has developed a catalyst that can extract hydrogen fuel from urine. While it takes 1.23 volts to split two hydrogen atoms from H2O, it only takes 0.37 volts to strip four hydrogen atoms from a urea molecule. That's twice as much hydrogen for one-third the effort. The Royal Society of Chemistry's journal, Chemical Communications, confirms Botte's discovery: "While water is an increasingly limited essential resource," the journal notes, "there will never be a lack of urine."
Existing nickel electrode technology can be easily scaled up to produce hydrogen from the effluent of today's sewage treatment plants. As Botte notes: "We do not need to reinvent the wheel." But tomorrow's water-smart homeowners will need to adapt. There will be one more container to add to the line-up for weekly curbside pick-up -- the urine bin.
Solving two problems for the price of one is a rare deal, especially when tankless toilets will start paying back the investment immediately as household water use falls by one-third. Sometimes, relief can come from surprising places. If this all pans out, we may need to replace the phrase "piss-poor" with "urine-rich."
Source: Link
Thursday, December 31, 2009
Can Aluminum Make Hydrogen Real?
Hydrogen may not be dead after all. Keep that hate mail coming.
Hydrogen is a dream fuel that's a nightmare to make.
Most companies currently produce it by cracking methane molecules, a process that requires large amounts of energy and generates 9.3 kilograms of carbon dioxide for every kilogram of hydrogen. Cracking water molecules with electricity also consumes a lot of power. Transporting hydrogen, the smallest molecule out there, is also difficult.
Some researchers, though, believe that hydrogen could be economically generated through chemical catalysis and the latest one is AlumiFuel Power. AlumiFuel says it can generate 1,000 liters of hydrogen in 20 minutes by mixing water with two 32-ounce cans of aluminum powder and other additives. The reaction between the water and the aluminum and chemical powders creates the hydrogen. (Aluminum has a strong urge to react with oxygen, which is why aluminum powder gets used as an accelerant in rocket fuel.) Carbon dioxide does not get produced in the reaction.
AlumiFuel will begin delivering its PBIS-1000 generator to customers in early 2010.
The PBIS generator was originally created to inflate weather balloons, but the hydrogen can also be used in fuel cells, according to the company. As an added bonus, the cans of catalysts don't need to be pressurized and external power sources are not required to generate the reaction. That cuts down distribution headaches: cans of aluminum powders can be delivered to filling stations instead of raw hydrogen gas.
The catalyst crowd is small but determined. Purdue University professor Jerry Woodall has discovered a way to make hydrogen out of a reaction of water and an alloy of aluminum and gallium. Mixing water and pellets made up of the alloy in a tank can produce fuel for a small engine or a car. Woodall discovered the process in 1967 and started to move toward commercialization two years ago. Signa Chemistry has a hydrogen catalyst based around sodium. Other researchers have identified microbes that can produce hydrogen with sunlight and water. The downside: some species of bugs die in the presence of the oxygen. Oxygen, of course, gets released when water breaks down into hydrogen and oxygen.
Is it an uphill battle? Yes. Critics of government-funded initiatives often hold up he hydrogen car program sponsored by the Department of Energy as an example of why the government shouldn't get involved in sponsoring technologies.
"The present hydrogen fuel cells are losers," Nobel prize winner Burton Richter told us earlier this year and he provided a list of cogent, sound reasons.
The cost of generating hydrogen in mass production through catalysis also must be established. Woodall has said it could be competitive with $3 a gallon gas, but cheap hydrogen is a big part of his life's work.
Still, many car companies, particularly Toyota, still hold out the idea that hydrogen could play an essential role in transportation in the 2020s. That's further out that earlier estimates, but the technology is not simple and the potential benefits remain large. Fuel cell cars can be recharged in minutes (compared to hours for a battery-powered car) and the fuel cell stack weighs far less than a lithium ion battery pack, increasing range and performance.
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