President George W Bush believes that hydrogen is the fuel of the future. In 2003 he announced an initiative worth $1.2 billion over a period of five years to fund research into the use of hydrogen fuel cells. The EU and Member States agree and are estimated to have supported activities in this field to the tune of 600 million euros for the 2002-2006 period.
The biggest driving force (no pun intended) behind the massive investment is the auto industry, which relies on oil-fuelled cars, but the electronics industry, which currently uses limited-life lithium ion batteries, is also making significant contributions.
There are many disadvantages associated with running internal combustion engines, not least economic issues. The price of oil is extremely volatile and the last 12 months have seen the cost per barrel rocket. In today's political climate the trend looks likely to continue upwards. Furthermore, burning gasoline releases carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), and hydrocarbons, amongst other gases, and particulate matter into the atmosphere, which cause serious environmental damage. But it is not just the environmental effects of harmful emissions - public health is also being compromised. For example, nitrogen oxides can react with volatile organic compounds in the atmosphere to form smog, which is known to increase respiratory problems in humans and carbon dioxide is a "greenhouse gas" that contributes to global warming.
Electronic devices such as laptops, cell phones, mp3 players, etc. are powered by lithium batteries, but these also have inherent problems. Lithium ion batteries operate using salts of lithium to provide conductivity, they can then be recharged by introducing an electric current in the opposite direction. The system returns to its charged state. However, because recharging does not completely return the cell to its previous charged state, the battery deteriorates with time, i.e. lithium ion batteries have a limited lifespan.
The rising cost of oil, a more environmentally-conscious public, and fears that oil supplies will dry up within 50 years are forcing change. Fuel cell technology is seen as a viable alternative.
Fuel cells are essentially electrochemical cells and operate following the same basic mechanism as everyday batteries. However, unlike batteries, where all of the chemicals used in the cell are contained and when the reaction is complete the battery is dead, fuel cells have a constant flow of fresh chemicals into the cell and so in theory have an unlimited life.
At the anode, hydrogen is forced through a catalyst (usually platinum powder) where it is ionized: 2H2 ==> 4H+ + 4e-. The electrons then pass through an external circuit, where their flow can be harnessed as electricity, on their way to the cathode.
At the cathode, oxygen reacts with the products from the anode (the protons and electrons) to produce water: O2 + 4H+ + 4e- ==> 2H2O. Along with heat, this is the only by-product of the hydrogen fuel cell: the reactants are normally fully utilized.
Aside from electricity and heat, which itself can be captured and used, water is the only product from a hydrogen fuel cell. Of course, this is harmless and so the process has huge environmental advantages over polluting combustion engines. However, water builds up in the cell and so it must be removed periodically otherwise it will saturate. This is usually achieved through a water pump or separator.
As explained, fuel cells generate electricity through a chemical process. This means that they are not subject to the Carnot Limit (a theoretical limit on the efficiency of an engine based on the flow of heat between two reservoirs), and that they can effectively extract more energy from fuel than combustion-based methods. Traditional internal combustion engines typically have efficiencies of around 30%, whereas fuel cells can achieve 40-70% efficiency.
There is considerable progress being made, and governments and organisations are beginning to see the results from the huge amount of research they have supported into fuel cell technologies.
Typically cars need 15,000 watts to run - achieving this wattage at an acceptable temperature has proved a significant challenge for those working in this area. However, in the autumn of 2005, engineers sponsored by Honda at Stanford University announced that they had produced a fuel cell, which delivers a power density of 400mW/cm2 at around 400°C, i.e. a fuel cell stack with a total membrane surface area of 4m2 could produce sufficient power to run a car.
Stanford University's solid oxide membrane-based hydrogen fuel cell effectively cut the operating temperature of the fuel cell in half without compromising on any power making the likelihood of a commercially-viable fuel cell-driven car much more of a possibility.
Also in 2005 Honda's second-generation fuel cell vehicle (FCV) was certified by both the US Environmental Protection Agency and the California Air Resources Board for commercial use and is the world's most advanced FCV in daily operation. Other auto makers are hot on the heels of Honda in terms of their fuel cell vehicles and so it is likely that we will see more FCVs on the roads in coming years.
Another exciting development in the application of fuel cell technology is the use of fuel cell power plants for electric power generation. Siemens, Ballard, and FuelCell Energy Inc, among others, are all developing these, albeit in some cases on a small scale (e.g. for home power generation). Most fuel systems convert natural gas or biofuels into hydrogen for processing with oxygen to generate multiple megawatts of useable electricity.
While existing fuel cell technology is already being applied in the auto industry and by power plant operators, electronics manufacturers are nearing commercialization of their products. For example, Panasonic and Toshiba both demonstrated a direct methanol fuel cell for laptop computers at the International Consumer Electronics Show earlier this year, and MTI Micro has recently signed an agreement with Samsung to develop a series of prototypes for Samsung's cell phones operating using a methanol fuel cell.
Along with the hydrogen fuel cells' high efficiency (from 40-70%), the possibility of utilizing both heat and electricity from them will make a significant contribution to reducing atmospheric emissions. For example, a fuel cell operating at 60% efficiency would emit 35-60% less CO2 at the fossil fuel stage and 80% less from hydrogen.
Energy sources of the future will have to be cleaner and more efficient than current sources - fuel cells fulfill these requirements. Several challenges remain before we will see wide-spread commercialization, mainly because of restrictions with size, cost, reliability and safety, but an environmentally-friendly source of power is definitely on its way.
If you need to cite this page, you can copy this text:
Dr Lisa Bushby. Hydrogen Fuel Cells. EnvironmentalChemistry.com. Aug 22, 2006. Accessed on-line: 9/21/2020