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Fuel Cells – A Review

 

Fuel Cells

Illustration 1: How it works?Adapted from http://www.fuelcelltoday.com/technologies/pemfc 

By Behlol Nawaz

             You might have heard of “fuel cells” or the term “hydrogen economy”. Governments, private companies and research institutions are continuously conducting research on different aspects of fuel cells, at the cost of billions, to make the mass use of fuel cells feasible. But what exactly are fuel cells? How do they work? What advantages do they offer over conventional power generation/conversion systems? What are the challenges that inhibit their mass use? And what is being done to overcome them?

What are they?

            Fuel cells are systems that convert chemical energy into electrical, just like batteries. The main difference between the two is that a battery has all the chemicals it needs to generate electricity, while in a fuel cell, the fuel (generally Hydrogen(H) and Oxygen(O)) has to be continuously supplied. And as long as the fuel is supplied, it will generate electricity (you can say it is similar to an internal combustion engine (ICE) in this respect).

How do they work?:

            There are many different types of fuel cells, usually the difference being in the electrolyte and the operating temperature. But they all do the same thing. With the help of a catalyst, the hydrogen and oxygen are facilitated to react and form water and the released chemical energy of the reaction is utilized as electrical energy to do the required work (e.g. spin a motor, light a bulb etc). This is done through an electrolyte which allows only a specific ion type to flow in it, forcing electrons to flow through the external circuit, in order to complete the reaction.

The fuel, by-products, type of ions and their direction of movement depends on the exact type of fuel cell.

The Fuel: the most abundant element, still too expensive:

Illustration 2: A molecule of Hydrogen

Illustration 2: A molecule of Hydrogen

            Hydrogen is considered the most abundant element in the universe, but it is not found in nature in its elemental form, which is needed for most fuel cells. It has to be formed or extracted from different compounds that contain hydrogen. The main methods of doing so are through reformation of hydrocarbons (usually from natural gas) or through electrolysis of water, which makes it very expensive compared to fossil fuels.

            Reforming hydrocarbons releases carbon dioxide, carbon monoxide and a small amount of other pollutants.

            Carbon emissions can be eliminated entirely if hydrogen is produced through the electrolysis of water, which is meaningful only if the electrolysis is done by electricity from sources like solar, wind or nuclear power.

Rocket fuel everywhere?

            You might have performed an experiment with hydrogen in school or college. Remember pouring acid onto zinc pieces and collecting the released gas (hydrogen) in an inverted jar? The next step was usually to stick a match stick at the mouth of the gas jar and poof! Even that uncompressed, small amount of hydrogen made a scary pop.

            Hydrogen is highly inflammable, being used as rocket fuel for its almost explosive combustion. And considering most hydrogen is stored under pressure, this means that there will be a lot of safety issues with hydrogen’s widespread use. New protocols are being developed for reacting to accidents or malfunctions in devices related to hydrogen and experts say stricter quality standards will have to be adopted. We certainly don’t want hydrogen to act as rocket fuel in our cars!

 

Comparison to internal combustion engines:

Minimal to no pollution!

            The greatest advantage that fuel cells have over combustion engines is that there are no carbon emissions or the other fossil fuel pollutants of the core fuel cell itself (e.g oxides of sulphur or nitrogen). The net by-products of a fuel cell are usually just water and a comparatively small amount of heat.

            Fuel cells are also a lot more efficient than combustion engines. They can have efficiencies between 40% to 70%, compared to 30% of the most efficient combustion engines. They are even more efficient than hybrid vehicles. Theoretically, fuel cell/battery powered hybrids offer the best combination for efficiency.

            Although the mainstream procedure for producing hydrogen today (reforming of hydrocarbons) releases carbon dioxide and carbon monoxide, the environmental impact of fuel cells powered by such hydrogen is still very small compared to the combustion of fossil fuels in combustion engines. (approximately 55% less CO2 emissions than combustion engines and 25% less than combustion/electric hybrid vehicles, according to a United States Department of Energy report.)

            Carbon emissions can be eliminated entirely if hydrogen is produced through the electrolysis of water by energy sources like solar, wind or nuclear energy generated electricity. And we have plenty of water, so it can be a sustainable source if we can overcome the different challenges which include the efficiency, reliability and cost of the technologies, tapping into the renewable energy sources.

But then, money makes the mare go……

            Despite the advantages mentioned, we don’t see widespread use of fuel cells. That is because fuel cells are very expensive as many types use some very rare and expensive material.

            Furthermore its fuel, hydrogen, has plenty of challenges of its own. Making hydrogen is itself very expensive (4 times as expensive as gasoline, from hydrogen’s cheapest source). The cost of fuel cells and hydrogen make their mass use impossible.

            And as mentioned before, mass use of hydrogen has safety issues as well as the storage capacity problem of its storage systems.

 

Fuel Cells car

Illustration 3: A fuel cell car 
 From http://www.illustratoren.be/technicsweb/cutaway.htm

 

Fuel cells vs batteries:

            Fuel cells can be used indirectly, as storage devices. Instead of charging a battery, the energy can be used to produce fuel for fuel cells. Although batteries are cheaper, easier to charge and a lot more efficient in energy conversion than fuel cells, there are some advantages in favour of fuel cells, particularly in some cases.

Battery Woes:

            Batteries have roughly 1/10th the energy density (by weight) of a hydrogen fuel cell, which greatly affects the range of current electric vehicles (EV). Furthermore, if a fuel cell is used instead of a battery, it would take the few minutes to refuel with hydrogen, rather than the hours required to charge an EV.

            Batteries also have limited charge/recharge cycles and their regular replacements in case of large scale use make them very costly. Most batteries have hazardous material and so, their disposal is also an environmental concern. Despite efficiency improvements in electronics, the power requirements of most hand-held devices are continuously increasing and soon they will not be met satisfactorily by batteries.

            Capacity and limited lifetime are glaring limitations of batteries. Improvements in battery technologies have been slowing in the recent past. Fuel cells can overcome these limitations of batteries.

Rivals or tag-team partners?

            It has been devised that fuel cells be used to augment batteries, minimize the capacity issue and get the best of both worlds. There are fuel-cell/battery powered hybrid vehicle designs which promise great efficiency, miniature fuel-cell powered chargers for hand-held devices exist, which can run a USB 2.0 device continuously for more than a month, with a single finger sized canister of hydrogen. But price remains a major issue with fuel-cells and hydrogen.

            Future developments in fuel-cell and battery technologies will determine whether one might replace another entirely or both will be used to support each other for maximum benefits.

Current Research:

            For obvious reasons, fuel cells are being actively researched worldwide. Many partnerships have been formed, from corporate level like the Honda and General Motors partnership, to the international level, like the International Partnership for Hydrogen and Fuel cells in Economy (IPHE) which has 18 countries, mostly technologically advanced. Space agencies have been using fuel cells in their equipment for a long time and they continue to work on improving them.

            Research is being carried out to address various issues, some of which we’ve already seen. But what directions are being taken?

Less costly, reliable and efficient cells:

          Currently, fuel cells are very expensive. One important part that is really expensive is the catalyst. Finding and forming inexpensive catalysts has been the focus of research for some time. Similarly improving the efficiency of catalysts is also being worked on. So that a smaller amount of its material is required.

            Fuel cells are not very durable in varying environments. Some types are durable in certain environments, but not others. Some catalysts (usually the more expensive ones) are relatively tolerant to contaminants, while others become useless even with traces of contamination. Finding ways of increasing tolerance to contaminants and improving general durability in harsher conditions is being investigated so that fuel cells may be more reliable.

Stuffing an elephant into a shoe-box:

             Hydrogen has a very low density at standard temperature and pressure (STP). If you want to store hydrogen for a 200 mile trip at STP, you will need a volume of approximately 33000 litres!  So in real life they store it compressed under immense pressure.

            But even then, storing it is challenging as simply keeping it under pressure doesn’t cut the volume enough for portable use.

            So most of the current storage systems are large, heavy and very expensive for use in portable devices and vehicles (vehicle being an important target of fuel cells). Whether for stationary, portable, or automobile applications, cheaper and  high-density energy storage systems are required to make them practical for mass use.

            Different hydrogen storage materials (e.g metal hydrides, the famous carbon nanotubes and graphene), their properties and different storage system configurations are being studied and devised to store more hydrogen in a smaller volume, with lesser extra weight and at reduced costs than the current storage systems.

Illustration 4: A graphene based structure devised for storage of Hydrogen promises three times as much storage per unit mass as the current best method. http://www.newscientist.com/article/dn14867-hightech-sponge-could-take-hydrogen-cars-further.html

Illustration 4: A graphene based structure devised for storage of Hydrogen promises three times as much storage per unit mass as the current best method.
 
http://www.newscientist.com/article/dn14867-hightech-sponge-could-take-hydrogen-cars-further.html

Cleaner and cheaper hydrogen:

            Currently, most of our hydrogen is being produced from natural gas. While not environmentally as damaging as burning it and other fossil fuels, we still need long term, sustainable and pollution free methods of producing hydrogen that are practically and economically feasible.

            Scientists are working on microbes that actually split water into hydrogen and oxygen during their metabolic processes using sunlight. Natural solar power electrolysis!

            There are also a large number of techniques being studied and developed that aim at making hydrogen from different types of bio-mass.

            Another interesting method being investigated is photo-electrolysis, with the use of Photo-electro-chemical (PEC) cells. Similar to electrolysis, but more efficient as the light’s energy is used to directly split water into hydrogen and oxygen.

            Use of renewable energy sources like solar, water, biomass etc to produce electricity and electrolyse water into hydrogen is also being actively studied.

 

Illustration 5: Photo-electro-chemical cell : Free hydrogen from water and sunlight From http://www.che.udel.edu/research_groups/chen/photoelectrochemical_cells.html

Illustration 5: Photo-electro-chemical cell : Free hydrogen from water and sunlight 
http://www.che.udel.edu/research_groups/chen/photoelectrochemical_cells.html

 

Supplying hydrogen:

            The current infrastructure to supply fuel all over cannot be used for hydrogen. So in case hydrogen becomes the primary fuel in the future, a completely new infrastructure will be needed for delivery, tailored specifically to hydrogen. Currently devised, experimental solutions are being continuously analysed, to determine improvements in cost and safety that become possible with advancements in technology, like newer storage solutions, safer dispensing systems etc.

What next?

          Although fuel cells have existed for quite some time now, they have been used mostly in extreme cases, where costs or the other challenges of fuel cells don’t count, e.g. in satellites, exploration rovers, at facilities in extreme locations and there are those rare hydrogen fueling stations (about 100 worldwide) and a handful of hydrogen powered vehicles that they supply.

            Fuel cells and hydrogen have a lot of practical hurdles to overcome related to cost and feasibility, that have to be overcome before a “Hydrogen Economy” can be possible. Current fuel cells and hydrogen production methods are not at all feasible for large scale use, especially in comparison to the well-established power related technologies.

            And although there are some who argue that the effort and resources being spent to develop fuel cells might not match the benefits we may achieve at the end, many experts think fuel cells and hydrogen might be where the future lies. It is a direction, in which breakthroughs can bring about some very great changes. Imagine a world where the wind, sun and water can give us the energy we need!

            To what extent, if any, will hydrogen and fuel cells will really be able to fulfill tomorrow’s power needs, cleanly and economically? Only meticulous research over an extended period of time will tell.

Interesting links:

 

–        http://americanhistory.si.edu/fuelcells/index.htm

–        http://www.fuelcells.org/

–        http://www.fuelcelltoday.com/about-fuel-cells

–        http://www.nasa.gov/centers/glenn/technology/fuel_cells.html

–        http://www.nrel.gov/hydrogen/

–        http://www.nfcrc.uci.edu/3/default.aspx

–        https://www.fueleconomy.gov/feg/fcv_challenges.shtml

–        http://www.iphe.net/

–        http://www.aps.org/policy/reports/occasional/upload/fuelcell.pdf (a relatively old, but simple report)

–        http://www.plugpower.com/AboutUs/Technology.aspx (a very helpful animation)

–        http://auto.howstuffworks.com/fuel-efficiency/alternative-fuels/fuel-cell.htm

 

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Comments on: "Fuel Cells – A Review" (2)

  1. Isha Lodhi said:

    This is by far the best article I have read on this blog! I have got to know a lot about fuel cells! I especially love the idea of using bio-mass (microorganisms) to split water into hydrogen and oxygen! It’s fascinating because it’s green and genius!

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