Let’s face it; hydrogen fuel cells are really awesome. In goes some hydrogen — which just happens to be the most abundant element in the universe — and out comes a bunch of electricity. In one brush-stroke the troublesome range, battery lifespan and charging problems associated with today’s electric cars would be wiped out. The only problem? To make hydrogen you currently either need to spend a lot of money or make a lot of pollution, neither of which will be tolerated by consumers.
A new paper in the International journal of hydrogen energy, titled: “challenges for renewable hydrogen production from biomass,” written by U of M’s David Levin, looks at sustainable ways to meet the future demand for hydrogen.
Hydrogen might be the most abundant element in the universe, but on our planet hydrogen really likes hanging out with other atoms, such as sulfur, carbon and oxygen. The reason why hydrogen is constantly found associated with other elements is partially because hydrogen is lighter than air, meaning that free hydrogen floats right out of the atmosphere and into space, and partially because it is energetically favorable for hydrogen to be bonded to other atoms. Put another way, energy is released when hydrogen bonds to another atom, and is required to break that bond. It is for this reason that a fuel cell — which harnesses the energy released from the bonding of hydrogen and oxygen — works.
Hydrogen gas (H2) exists as two hydrogen atoms bonded to one another. It is extremely flammable, and very useful in industry. At 3.4 million tonnes per year, Canada produces more H2 than any other member of the Organization for Economic Co-operation and Development (OECD) — an organization which helps governments develop sustainability policies.
At 3 million tonnes annually, Canada also uses more. One of the most common uses of H2 is for the purification of low quality crude oil, such as that refined from oil sands. It is estimated that over the next decade Canada’s demand for H2 will continue to grow, with the potential to reach 6-7 million tonnes per year by 2020.
This estimated increase in demand is partially due to new laws that demand cleaner petroleum products, partially because of a need to develop petroleum products from lower quality crude oil reserves, and partially due to the projected demand from hydrogen fuel cell vehicles.
Traditional methods of hydrogen gas production
Currently 59 per cent of the 38 million tonnes of H2 produced annually is made via a process called steam methane reforming (SMR) where methane (a molecule consisting of one carbon atom surrounded by four hydrogen atoms [CH4]) or other suitable hydrocarbon is heated with steam to 700-1,100C. The result is that for each molecule of methane and water put into the system a molecule of carbon monoxide (CO) and three molecules of H2 are produced.
The CO, a byproduct of the reaction, can then be reacted with more water, producing a carbon dioxide (CO2) molecule and another molecule of H2.
According to Levin’s paper, SMR is responsible for the release of 30 million tonnes of CO2 per year, or the equivalent of burning 13 billion litres of gasoline, or about one third the amount burned by cars in Canada in 2004.
Electrolysis is another method for producing H2, where water — which has been contaminated with conductive impurities — since pure water will not conduct electricity — has an electric charge passed through it. This method frees the hydrogen from dihydrogen monoxide, more commonly known as H2O. For each two molecules of water reacted, a single molecule of oxygen gas (O2) is produced along with two molecules of H2. While this reaction does not directly create any harmful emissions, and produces very clean H2, free of contaminants — something SMR cannot boast, and something that is required for fuel cells — it is more expensive than SMR and indirectly creates emissions through its use of electricity which is not necessarily generated from a renewable source.
Renewable methods of Hydrogen gas production
As was stated earlier, hydrogen is everywhere. It makes up two thirds of the atoms in each molecule of water, one half of the atoms in glucose (C6H12O6) and is an essential molecule for life, driving the molecular pumps powering your cells. As such, the challenge isn’t finding the hydrogen, but freeing it from the molecular bonds holding it in place.
According to Levin’s paper, one such source of hydrogen could be cellulose, the woody material that makes up the structure of many plants. One tonne of cellulose, from a source such as cornhusks, which would otherwise be discarded, has the potential to yield 150 kg of H2.
One such method of H2 production is biomass gasification, where cellulose is mixed with sodium hydroxide (a powerful base) and steam at relatively low temperatures (200-300C as opposed to more than 1,000C required for SMR). The result is H2 and sodium carbonate (NA2CO3), also known as washing soda.
Another method of H2 production that also relies on cellulose is fermentation, the same process used to produce beer and bread. Instead of producing CO2, as occurs with the kind of fermentation we’re used to, the microorganisms used in the process produce H2. One potential pitfall of fermentation is that the final product can be contaminated with CO2, methane and hydrogen sulfide. However because fermentation is cheap and efficient, the cost and difficulty associated with purifying the H2 could be completely offset.
If hydrogen fuel cell cars, like the one Honda is currently leasing in California, are a solution to our dependence on fossil fuels and the greenhouse gasses that the burning of said fuels release, then it makes little sense to cause the same environmental damage in hydrogen fuel cell production. Levin explains that none of the renewable technologies outlined above are without fault, however the increasing demand for hydrogen requires that we find an inexpensive and clean way to produce it. And while the current methods for the renewable production of H2 leave something to be desired, each is a step in the right direction, a step toward sustainability and a step towards our freedom from fossil fuels.