Ennetech by Erasmus and Kinkajou Authors

 

 

Erasmus and Kinkajou share their vision of technologies that will help us on our way.

Batteries vs Fuel Cells

 

KinkajouKinkajou

 

Fuel Cell expense precludes their use except in niche special circumstances- notably where recharging the battery is not a viable course of action.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Kinkajou : What’s the Best Battery?

ErasmusErasmus : I think in the distorted words of an old song,
“Different things for different people, that’s what the Best battery is”.

On another note, one of the new exciting developments in battery technology is the development of Smart batteries. These batteries have a chip which communicates with a charger. This enables intelligent and optimised maintenance of the battery based on the pre-programmed performance characteristics and life expectancy of the battery. Of course unfortunately battery chargers would be specific to the brand of battery, which creates new maintenance issues.

Best Battery Best Battery

 

 

 

Fuel Cells In Batteries

KinkajouKinkajou : so what are the issues in the development of fuel cells?

ErasmusErasmus : Much of our technology is based on “economies of scale”. In short “bigger is better”.  This is based on the premise that for a given investment or size of a machine, more product or output can be produced per unit of time. This means the product or output is cheaper per volume or unit. Generally, because capital investment and operational costs do not increase linearly with scale, the cheapest costs are obtained with larger machines with greater output.

Hydrocarbon Fuel Stored for Fuel Cells Hydrocarbon Fuel Stored for Fuel Cells

These economies of scale are not necessarily always desirable. For example, the current trend in the development of nuclear reactors is to develop smaller reactors. This reduces the financial risk of capital investment for many companies in the power industry, so be by reducing the amount of capital investment required to build a facility.

However miniaturisation allows for a new range of applications or benefits. These include:

  • Portability.
  • Operation in inaccessible environments such as within the human body.
  • Remote areas.
  • Economies of scale in production automation.

Modular design for example many of the most powerful modern computers are based on a combination of CPU chips working in parallel to achieve a task. Alternatively, even single chips have multiple pipelines for processing. This is proving to be a better solution to scalable performance than ever faster and ever bigger chips.

Allowing the combination of a range of microprocessor controllers that are able to work in tandem. This also allows for easier maintenance or replacement of damaged or faulty components. In such an environment failure of a single microprocessor, is unlikely to cause shutdown of the entire network. This leads to a more robust and stable function.

The development of miniaturised fuel cell is a good example of the advantages of the process miniaturisation. There are many applications were a small power cell is much more advantageous or suitable than a larger power supply.

 

 

 

KinkajouKinkajou : So what’s stopping us from charging out there and developing small or miniaturised fuel cells?

Erasmus Erasmus : Batteries translate chemical energy into electrical power by harvesting the alteration in potential of chemicals changing their chemical state. It is a much more difficult proposition to translate “thermal” chemical energy into electrical power. Fuel cell technology is approximately twice as efficient as the internal combustion engine in turning a carbon based fuel into energy. However, much of this energy (up to 50%) is lost as heat. In addition, fuel cells can take advantage of fuels with energy densities up to 10 times greater than the energy capacity that exists within a battery.

Fuel cells work by combining a fuel with oxygen in aqueous combustion chamber to create heat. In this fashion, they function much the same as the internal combustion engine.

The efficiencies of this thermal electricity generation process in fuel cells are currently substantially less than for batteries. However the “holy Grail” of fuel cells lies in the very high energy density of fuels.  Potentially they could produce more energy and for longer than a battery. Potentially they could use much simpler chemicals such as simple organic molecules for fuel. Also, they produce chemical by-products much less toxic to the environment than the waste materials generated by discharged batteries.

The fuel cell is closest to commercialisation are freestanding systems functioning as power supply units in the 10 to 100 Watt range. As freestanding systems they are not configured to fit within specific spaces within appliances at this stage of our technology. The greatest demand for fuel cells probably lies within cell phones and laptops. The limited energy density of batteries means that these appliances must be constantly recharged. A power source with a longer lifetime and the faster “recharge” time would be desirable.

Much innovation is also driven by military necessities. Military radios, powered night vision equipment for soldiers, signalling equipment, and sensor arrays would benefit from the provision of fuel cell power units in the several hundred Watt range.

Stationary fuel cells in Europe have begun to evolve into the consumer market. By using a fuel cell, claims have been made that up to 30% to 40% less carbon dioxide emissions are produced each year when compared to modern gas condensing boilers operating via the grid power supply. Nitrate and sulphate pollution is substantially reduced.

Finally energy delivered by batteries is expensive and potentially has a much more limited lifespan than the achievable by fuel cells. (Depends on the Technology and application : of course). This means that remote and inaccessible sites would benefit from the use of fuel cell technology applications include: sensors, signalling systems, medical appliances such as pacemakers, backup power systems and security devices and cameras in remote areas.

Fuel cell technology will require substantial investment in research and development before it reaches a stage of market penetration compatible with that of the rechargeable battery.

 

HowHydrogenFuelCellsWork HowHydrogenFuelCellsWork

 

KinkajouKinkajou : So how does the hydrogen fuel cell work?

ErasmusErasmus : The fuel cell uses two electrodes separated by an electrolyte. The electrolyte allows the unidirectional transmission of charged Ions. Hydrogen directs to the anode (negative electrode). Oxygen directs to the cathode (positive electrode). A catalyst at the anode facilitates the dissociation of the hydrogen into positively charged hydrogen ions and electrons. The electrons migrate through the wire linking the anode and cathode. The oxygen becomes ionised by these electrons at the cathode and then under the influence of an electric field migrates across to electrode to the anodic compartment where it combines with hydrogen. The chemical fuel for this reaction is the supplied hydrogen.

Essentially the reaction operates like electrolysis in reverse. To break down the water molecules using electrolysis requires energy, to energise the chemical reaction as well as to provide the activation energy for the chemical reaction. Noble metals (such as platinum) are used to reduce the activation energy and to facilitate electrolysis.

Hydrogen Fuel Car Hydrogen Fuel Car

A hydrogen based fuel cell typically produces .7 to .8 V. High voltages are obtained by linking fuel cells in series. Fuel cell technology is typically twice as efficient as combustion in turning fuel into electrical energy. The theoretical maximum voltage of fuel cell derived from burning hydrogen with oxygen to form water sports to 1.23 eV (electron volts). This is somewhat less than battery derived voltages.

Hydrogen was initially favoured in  the development of fuel cells because is the ultimate clean green fuel. Combustion of hydrogen generated water. Hydrogen as a fuel source however has many disadvantages.

It needs to be stored under pressure. This requires energy to extract and compress the hydrogen into a high-pressure storage container.

Hydrogen is a very reactive chemical and combines easily with many other atoms.

Hydrogen is unstable and is always at risk of exploding. Witness the Hindenburg disaster in the early 1900s. The Hindenburg zeppelin used hydrogen as a lift technology. A single spark can create an instant disaster.

Other fuels such as liquefied petroleum are much more stable and much more energy dense.

Require substantial energy for its production. Typical production methods would involve industrial processes and extracting hydrogen from feedstocks such as methanol, propane, butane or natural gas. Alternatively photoelectric electrolysis can be used as a production technology.

 

 


ILLUSTRATION : Concept of a fuel cell

The anode (negative electrode) receives the hydrogen and the cathode (positive electrode) collects the oxygen.

 

Fuel Cell Structure Fuel Cell Structure

 

 

 

KinkajouKinkajou : What is the fuel cell of the future?

ErasmusErasmus : Currently, the most promising miniature fuel cell technology is the direct methanol fuel cell (DMFC). However, advances in technology may result in the solid oxide fuel cell (SOFC) and being the technology of the future.

There are many technical challenges blocking the path to the implementation of fuel cell technology. Miniaturised devices to start and stop the fuel supply are essential. Fuel flow rate must be controlled. In the case of hydrogen, fuel pressure will require regulation via pressure reducers. Air supply to the cathode and for system cooling are also essential, necessitating the presence of valves pumps and fans. A control system is required to integrate these separate subsystems, including safety features.

Batteries are a very safe technology even in hostile environments, (physical movement, vibration, position change). Fuel cells must match the safety of batteries to be a viable alternative technology. Maintenance must be minimised to refuelling, and this must occur in a safe fool proof protocol.
Methanol fuel cells have the highest energy density. However hydrogen based fuel cells have the highest power density. The solid oxide fuel cell perhaps promises the greatest efficiency of output.

Some authors have suggested that the cost per fuel cell system would be of the same order of magnitude as battery technology if mass production were to be undertaken. To meet the criteria of minimum cost, fuel cells must minimise the incorporation of noble metals in the catalyst layer, incorporate mass production methods such as fire hot pressing or injection moulding, and take advantage of cheaper automated mounting and bonding systems.

Fuel Cells In Future CarFuel Cells In Future Car

 


ErasmusErasmus : Here are the most common fuel cell technologies.

  • Proton Exchange Membrane Fuel Cell (PEMFC)
  • Alkaline Fuel Cell (AFC)
  • Solid Oxide Fuel Cell (SOFC)
  • Direct Methanol Fuel Cell (DMFC)

 

 

ErasmusErasmus :Other Fuel cell technologies include:

  • Molten Carbonate (MCFC)
  • Phosphoric Acid (PAFC)
  • Butane
  • Formic acid
  • Organic or microbial or enzyme based systems
  • hydride fuel cells
  • Air breathing laminar fuel cells (some with membranes, some membraneless).

 

Solid Oxide Fuel Cell Solid Oxide Fuel Cell

KinkajouKinkajou : I think tell us about the solid oxide fuel cell (SOFC), which at the moment appears to be the most exciting kid on the block.

ErasmusErasmus :Solid Oxide Fuel Cell (SOFC)

Electric utilities use three types of fuel cells, which are molten carbonate, phosphoric acid and solid oxide fuel cells. Among these choices, the solid oxide (SOFC) is the least developed but has received renewed attention because of breakthroughs in cell material and stack design. Rather than operating at the very high operating temperature of 800–1,000°C (1,472–1,832°F), a new generation of ceramic material has brought the core down to a more manageable 500–600°C (932–1,112°F). This allows the use of conventional stainless steel rather than expensive ceramics for auxiliary parts.

High temperature allows direct extraction of hydrogen from natural gas through a catalytic reforming process. Carbon monoxide, a contaminant for the PEM, is a fuel for the SOFC. Being able to accept carbon-based fuels without a designated reformer and delivering high efficiency pose significant advantages for this type of fuel cell. Cogeneration by running steam generators from the heat by-product raises the SOFC to 60 per cent efficiency, one of the highest among fuel cells. As a negative (disadvantage), high stack temperature requires exotic materials for the core that adds to manufacturing costs and reduces longevity.

We provide the fuel cell with hydrogen gas on the anode side and oxygen (usually the oxygen in air) on the cathode side. In the cathode, the oxygen molecule splits apart and doubly charged negative oxygen ions are formed. The electrons needed to form the oxygen ions come from the anode of the cell through an electrical load.

The cross-section of the Nectar MEMS fuel cell above gives a bit better idea of the way it functions. Fresh air is pumped into port 2 to provide the fuel cell with a source of oxygen. A mixture of air and butane is pumped into port 1, where it goes into a miniaturized fuel reformer. There, the fuel mixture is partially oxidized to convert the mixture into hydrogen gas and carbon monoxide. In area 3, the fuel and oxidizer react across the YSZ cell membrane, providing electrical power output, water, and carbon dioxide. Finally, the exhaust still has a bit of fuel mixed in, so it is sent through a catalytic converter 4 before being released to the atmosphere.

Those electrons are released in the anode by the reaction of the hydrogen fuel with the oxygen ions to form water.

The role of the electrolyte here is key as it allows the oxygen ions to easily pass between the cathode and the anode, but blocks electrons from passing. This forces these electrons to pass through the external electrical load, where their energy can do work. In the end, the properties of the electrolyte allow a fuel cell to generate electricity. A typical electrolyte for an SOFC is ceramic, a common example of which is yttrium-stabilized zirconia (YSZ).

Fuel Cell Example Fuel Cell Example

KinkajouKinkajou : Let’s talk next about the fuel used within fuel cells such as the SOFCBiodiesel Hydrocarbon Fuel Biodiesel Hydrocarbon Fuel

ErasmusErasmus : Hydrocarbon or Butane

Hydrocarbon-based liquid fuels such as petrol (gasoline), diesel or butane are easily available throughout the world. However to use these in a fuel cell and convert them into a hydrogen rich gas mixtures requires temperatures above 700°C.

By contrast methanol is the only fuel this class which can be converted at intermediate temperatures of 250 to 300°C into a hydrogen rich gas mixture.

This gasification process can be very rapid in miniaturised systems, requiring contact times in the range of 20 to 50 ms. The suppression of carbon monoxide formation is critical, both to reduce the risk to the public and to improve the efficiency of the fuel cell. Catalysts are routinely used to accelerate this process, but must be able to cope with such common problems as sulphur contamination of fuels such as diesel.

 

 

 

KinkajouKinkajou : Have any hydrocarbon fuel cells been built?

ErasmusErasmus :There do exist butane based fuel cells using a SOFC (solid oxide fuel cell) combustion chamber format.

Miniaturised butane based fuel cell systems have been developed, based on solid oxide fuel cell technology. Butane has a large energy density (approximately 7400 Wh/l {Watt hours per litre}). It requires temperatures of approximately 400° to auto ignite. Butane can operate in a SOFC at temperatures between 500 to 1,000°C. This creates thermal insulation problem as heat losses can approach 200 W with an electric power output of between 2 to 3 W.


The fuel cell is built on silicon slab silicon is an excellent thermal insulator. This dovetails with the use of a multilayered and engineered silicon die to achieve the desired operating voltages and power output. A Vacuum containing containment vessel must be used to limit convection losses and to increase the efficiency of the fuel cell by minimising losses. Radiation is limited through the use of internal highly reflective surfaces which re-radiate the heat back to the combustion chamber. This resulted in a fuel cell with a thermal loss of approximate 3 W at and operating temperature of 600°C, increasing to a thermal loss of approximately 7 W and operating temperature of 800°C.

ErasmusErasmus :  Problems in the creation of the structure are caused by different thermal expansion coefficients of the silicon and the Yttria-stabilized zirconia (YSZ) ceramic using the combustion chamber. If the YSZ membrane cracks, oxygen and fuel can mix. This causes cracking of the silicon die, resulting in failure of the fuel cell. The engineering approach to solving this problem involves engineering the silicon to crack in specific harmless locations which can be pre-sealed by other materials. This means the YSZ ceramic membrane remains intact in the active combustion regions.

Biodiesel Fuel Storage Plant Biodiesel Fuel Storage Plant

 

ErasmusErasmus : The design of fuel cells also involves a small air pump, a mini carburettor, and a temperature controller which regulates fuel input to the combustion chamber to maintain a constant temperature. To be useful the unit has incorporated electronics to provide a USB compatible output. USB2 standard devices give an output of 5 V and 500 mA. USB3 three standard devices have been engineered to provide an output of 5 V and 900 mA. The resulting fuel cell provides a recharge rate of approximately 2.5 W with the voltage adjusted to match battery voltages with an internal DC converter. A Small AA battery sized butane container provides approximately 55 Wh of electrical energy which is enough to recharge a laptop battery once and other devices such as mobile phones to 10 times. The example we have looked at here, the “nectar” unit has a volume of approximately 144 cubic centimetres and weighs approximately 200 g. It required years to develop and approximately one hundred million dollars of funding.

Consumer level cost was projected to be in the range of $300-$400 for a 2.5 W output. Most consumers would regard this is excessively expensive. Also the unit is a limited lifespan due to deterioration of combustion chamber, so it is likely to provide an expensive alternative to battery technology.

KinkajouKinkajou : I think we can start to see the barriers to the development of miniaturised mobile fuel cells.



Car Fuel Cell Car Fuel Cell




ErasmusErasmus ::  Hydride Fuel Cells

Hydride fuel cells are available in several different configurations.

  • Firstly, Chemical compounds like CaH2 can be used. These release hydrogen upon addition of water.
  • Secondly metallic alloys can be used which are able to absorb and desorb hydrogen reversibly upon changes of pressure and temperature.

If implemented on portable systems, the temperature and pressure for the desorption process must operate at ambient temperature and pressure. The temperature of these hydride materials is known to decreasing typically during discharging. This decelerates the hydrogen release is a significant safety feature. Hydride alloys can be charged and discharged several thousands of times, depended mainly upon the purity of the hydrogen used for charging.

  • A third approach is based on a hydrous NaBH4-solution, which releases hydrogen upon contact with a Ru-catalyst.

Microscopic View Fuel Cell Base Plate Microscopic View Fuel Cell Base Plate

Explaining Fuel Cell Microstructure Explaining Fuel Cell Microstructure

 

 

 

KinkajouKinkajou : Are there any other any other types of Fuel Cell?

ErasmusErasmus : Proton Exchange Membrane Fuel Cell (PEMFC)

The proton exchange membrane, also known as PEM, uses a polymer electrolyte. PEM is one of the furthest developed and most commonly used fuel cell systems; it powers cars, serves as a portable power source and provides backup power in lieu of stationary batteries in offices. The PEM system allows compact design and achieves a high energy-to-weight ratio. Another advantage is a relatively quick start-up when using hydrogen. The stack runs at a moderate temperature of 80°C (176°F) and is 50 per cent efficient. (The ICE is 25–30 per cent efficient.) [ICE = internal combustion engine].

The PEM fuel cell has high manufacturing cost and a complex water management system. The stack contains hydrogen, oxygen and water. If dry, water must be added to get the system started; too much water causes flooding. The stack requires pure hydrogen. Lower fuel grades can cause decomposition and clogging of the membrane. Testing and repairing a stack is difficult, given that a 150V stack requires 250 cells.

Freezing water can damage the stack and heating elements may be added to prevent ice formation. Start-up is slow when cold and the performance poor at first. Excessive heat can also cause damage. Controlling temperatures and supplying oxygen requires compressors, pumps and other accessories that consume about 30 per cent of the energy generated.

If operated in a vehicle, the PEMFC stack (Proton Exchange Membrane Fuel Cell) has an estimated service life of 2,000–4,000 hours. Wetting and drying caused by short distance driving contributes to membrane stress. Running continuously, the stationary stack is good for about 40,000 hours. Stack replacement is a major expense.

A critical point is the transport of hydrogen or methanol in aeroplanes since they are classified as hazardous materials (Department of Transportation) or dangerous goods (UN). (3).

 Among the techniques for the storage of pure hydrogen - gaseous at high pressure, liquid at -253 degrees Celsius and chemically bound in hydrides - the latter is the only suitable way to store hydrogen with an appropriate energy density in small units. Containers for high pressure or with super-isolation do not fit to the requirements for portable applications.

 

Examples Proton Exchange Fuel Cells Examples Proton Exchange Fuel Cells

 

KinkajouKinkajou : Are there any other any other types of Fuel Cell?

ErasmusErasmus : Alkaline Fuel Cell (AFC)

The alkaline fuel cell has become the preferred technology for aerospace, including the space shuttle. Manufacturing and operating costs are low, especially for the stack. While the separator for the PEM costs between $800 and $1,100 per square meter, the same material for the alkaline system is almost negligible. (The separator for a lead acid battery costs $5 per square meter.) Water management is simple and does not need compressors and other peripherals. A negative is that AFC is larger in physical size than the PEM and needs pure oxygen and hydrogen as fuels. The amount of carbon dioxide present in the air in a polluted city can poison the stack.

 

 

 

 

KinkajouKinkajou : Are there any other any other types of Fuel Cell?

ErasmusErasmus :Direct Methanol Fuel Cell (DMFC)

Portable fuel cells have gained attention and the most promising development is the direct methanol fuel cell. This small fuel cell is inexpensive to manufacture, convenient to use and does not require pressurized hydrogen gas. The DMFC has good electrochemical performance and refilling is by squirting in liquid or replacing the cartridge. This enables continued operation without downtime.

Manufacturers of small fuel cells admit that a direct battery replacement is years away. To bridge the gap, micro fuel cell serves as a charger to provide continuous operation for the onboard battery.

Furthermore, methanol is toxic and flammable and there are limitations as to how much fuel passengers can carry on an aircraft. In 2008 the Department of Transportation issued a ruling to permit passengers and crew to carry an approved fuel cell with an installed methanol cartridge and up to two additional spare cartridges of 200 ml (6.76 fl. Oz.). This provision does not yet extend to bottled hydrogen.

ILLUSTRATION

Micro Fuel Cell Refuelling Micro Fuel Cell Refuelling


Figure illustrates a portable fuel cell made by SFC Smart Fuel Cell. The EFOY fuel cell comes in different capacities that ranges from 600 to 2160 watt hours per day.

 

Figure: Micro fuel cell. This prototype micro fuel cell is capable of providing 300mW of continuous power.

Figure: Toshiba fuel cell with refuelling cartridge. The fuel in a 10ml tank is 99.5 per cent pure methanol.

Improvements are being made and Toshiba unveiled prototype fuel cells for laptops and other applications generating 20 to 100 watts. The units are compact and the specific energy is comparable with that of a NiCad battery. Toshiba has given no indication as to when the product could be available. Meanwhile, Panasonic claims to have doubled the power output from 10 watts to 20 watts with similar size. Panasonic specifies a calendar life of 5,000 hours if the fuel cell is used intermittently for eight hours per day. The low longevity of these fuel cells has been an issue to be reckoned with.

Attempts are made with small fuel cell running on stored hydrogen. Increased efficiency and smaller size are the advantages of pure hydrogen over methanol. These miniature systems have no pumps and fans and are totally silent. A 21cc cartridge is said to provide the equivalent energy of about 10 AA alkaline batteries with a runtime between refuelling of 20 hours.

Military and recreational users are also experimenting with the miniature fuel cell.

 

 

Methanol, the simplest alcohol, is a liquid fuel which can be oxidised electrochemically in the presence of water. Methanol has a high energy density (3450 Wh/kg and 3000 Wh/l in 1:1 molar ratio with water, excluding efficiency losses), is easy to handle, is completely miscible with water and can be generated from a variety of sources such as natural gas, coal and even biomass.

 Furthermore, it is available in pharmacies at a low price. However, it is toxic and there is a certain leakage of methanol through the polymer electrolyte membrane (crossover) resulting in a poisoning of the cathode catalyst by the formation of a mixed potential. Another material problem is the slow anode electrocatalysis of methanol which requires significantly more costly noble metal catalyst than the direct hydrogen fuel cell. As a result of this, the power density of the fuel cell stack at room temperature is currently at least a factor of 5 smaller than that of hydrogen fed fuel cells.

 

 


ILLUSTRATION

Figure: Portable fuel cell for consumer market

the fuel cell converts hydrogen and oxygen to electricity and clean water is the only by-product. Fuel cells can be used indoors as an electricity generator.


ErasmusErasmus : This Table describes the applications and summarizes the advantages and limitations of common fuel cells. The table also includes the Molten Carbonate (MCFC) and Phosphoric Acid (PAFC), classic fuel cell systems that have been around for a while and have unique advantages.

Type of Fuel Cell

Applications

Core temp.
Efficiency

Advantages

Disadvantages

Proton Exchange Membrane(PEMFC)

Portable, stationary and automotive

50–100°C;
80°C typical;
35–60% efficient

Compact design, long operating life, quick start-up, well developed

Expensive catalyst, needs clean fuel, complex heat and water control

Alkaline
(AFC)

Space, military,  submarines, transport

90–100°C;
60% efficient

Low parts and, operation costs; no compressor; fast cathode kinetics

Large size; sensitive to hydrogen and oxygen impurities

Molten Carbonate
(MCFC)

Large power generation

600–700°C;
45–50% efficient

High efficiency, flexible to fuel, co-generation

High heat causes corrosion, long start-up, short life

Phosphoric Acid
(PAFC)

Medium to large power generation

150–200°C;
40% efficient

Good tolerance to fuel impurities; co-generation

Low efficiency; limited service life; expensive catalyst

Solid Oxide(SOFC)

Medium to large power generation

700–1000°C;
60% efficient

Lenient to fuels; can use natural gas, high efficient

High heat causes corrosion, long start-up, short life

Direct Methanol
(DMFC)

Portable, mobile and stationary use

40–60°C;
20% efficient

Compact; feeds on methanol; no compressor

Complex stack; slow response;
low efficiency

Butane, Diesel, Other Hydrocarbon

 

Will not auto ignite below 400°C so operating temp of butane fuelled SOFC is at least 500°C

   

Formic acid

       

Organic or microbial or enzyme based systems

 

Efficiency limited due to low concentrations of oxygen in blood

   

Hydride fuel cells

       

Air breathing laminar fuel cells

       

Table : Advantages and disadvantages of various fuel cell systems

 


ErasmusErasmus : The development of the fuel cell has not advanced at the same pace as batteries; a direct battery replacement is not yet feasible.


KinkajouKinkajou : Can you make any other comments on future developments in fuel cell technology?

 

 

 

ErasmusErasmus : Developments In Fuel Cell Technology

The fuel cell requires improvements to resolve slow start-up times, low power output, sluggish response on power demand, poor loading capabilities, narrow power bandwidth, short service life and high cost. Similar to batteries, the performance of all fuel cells degrades with age, and the stack gradually loses efficiency. Such performance losses are not visible with the ICE.

The relatively high internal resistance of fuel cells poses a challenge. This means that fuel cells may be unable to sustain applications drawing heavy load power current. Each cell of a stack produces about one volt in open circuit. A heavy load causes a notable voltage drop. Fuel cells also suffer from short lifespan. Output begins to fade with use at timescales compatible with the life of an average battery. As a technology, fuel cell development lags substantially behind battery technology. It becomes obvious that fuel cells are more likely to be used in combination with batteries as a trickle power support for battery operation. Hybrid power systems may well be the path of the future.

Use of micro integrated circuit technology and construction of fuel cells has been an exciting development.

Nanotechnology supplies a method to bypass reaction kinetics issues. However fuel sources and chemical catalyst need to be compatible with integrated chip fabrication, need to minimise fluid flow in deal with water production, and achieve performance criteria such as acceptable performance at room temperature, power density greater than 10 mW per square centimetre and cell voltage greater than .4 V under load conditions.

The most critical operations in the functioning of a portable fuel cell are:

  • Stopping and starting the fuel supply.
  • Air supply.
  • Water management in chemical systems requiring water for the reaction phase.
  • Miniaturising devices such as valves, pumps and fans or pressure reducers and optimising their power usage.
  • Smart operational technology which can adjust load and output and maintain safety.
  • Minimal maintenance requirements.

Humans have lower experience with fuel cell technologies than with battery technologies. Fuel cell development requires expertise in areas such as modelling, catalyst technology (especially focusing on noble metal such as platinum or more exotic combinations such as a Ruthenium Barium) system design microactuators, conductive polymers, power management, micro-machining, laminar flow techniques for substrate combination, mounting (the integration of electrodes and porous membranes on silicon chips), and bonding technology.

 

Power Characteristics Portable Fuel Cell Power Characteristics Portable Fuel Cell

 

ILLUSTRATION

Figure: Power band of a portable fuel cell

High internal resistance causes the cell voltage
to drop rapidly with load. The power band is limited to between 300 and 800mA.

Fuel cells operate best at a 30 per cent load factor; higher loads reduce efficiency. A load factor approaching 100 per cent, as is common with a battery and the ICE is not practical with the fuel cell. In addition, the fuel cell has poor response characteristics and takes a few seconds to react to power demands. Rather than serving as a stand-alone engine, as the developers had hoped, the fuel cell works in a support function, or a charger, to keep the batteries charged.


 

Erasmus Erasmus :
There is renewed interest for the fuel cell in the automotive field in Japan. Large 40,000kW fuel cells are in operation to generate electricity in remote locations. Fuel cells also replace battery banks and diesel generators in office buildings, as they can be installed in tight storage places without exhaust and on rooftops with minimal maintenance. Fuel cells also allow continuous and pollution-free operation of forklifts.