Prof. R. Shanthini Mar 03, 2012 Module 08 (subjected to continual revision) New and Emerging Energy...

Prof. R. Shanthini Mar 03, 2012

Module 08(subjected to continual revision)

New and Emerging Energy Technologies

Fuel cells

Energy storage

Hydrogen economy

Other alternatives to energy use


It combines hydrogen and oxygen to produce electricity via an electrochemical process.

Fuel Cell

Exhaust is water (not CO2) It works quietly.

H2 is split at anode

O2 is split at cathode (hard)

H2 2H+ + 2e- 2H+ + 2e- + ½ O2 H2O


- Individual fuel cells can be placed in a series to form a fuel cell stack.

- The stack can be used in a system to power a vehicle or to provide stationary power to a building.

Fuel Cell


Fuel Cell Car

- At a steady cruising speed, the motor is powered by energy from the fuel cell.

- When more power is needed, for example during sudden acceleration, the battery supplements the fuel cell’s output.

- At low speeds when less power is required, the vehicle runs on battery power alone.

- During deceleration the motor functions as an electric generator to capture braking energy, which is stored in the battery.


Fuel Cell Hybrid


Fuel Cell

- All fuel cells have the same basic configuration - an electrolyte and two electrodes.

- Fuel cells are classified by the kind of electrolyte used.

- The type of electrolyte used determines the kind of chemical reactions that take place and the temperature range of operation.


Fuel Cell Type

PEMFC - Polymer Electrolyte Membrane Fuel Cells (or Proton Exchange Membrane Fuel Cells )

DMFC - Direct Methanol Fuel Cells

AFC - Alkaline Fuel Cells

PAFC - Phosphoric Acid Fuel Cells

MCFC - Molten Carbonate Fuel Cells

SOFC - Solid Oxide Fuel Cells


- H2 is the fuel for PEMFC.

- Proton exchange polymer membrane (PEM) is used as electrolyte.

- Platinum particles on carbon (Pt/C) is used as electrodes.

- At the anode, a platinum catalyst causes the H2 to split into positive hydrogen ions (protons) and negatively charged electrons.

Proton Exchange Membrane Fuel Cell (PEMFC)


- PEM allows only the positively charged hydrogen ions to pass through it to the cathode.

-The negatively charged electrons must travel along an external circuit to the cathode, creating an electrical current.

- At the cathode, the electrons and positively charged hydrogen ions combine with oxygen to form water, which flows out of the cell.



- Suited for applications where quick startup is required making it popular for automobiles

- Used in the NASA Gemini series of spacecraft



- Pt/C electrodes are too expensive to replace internal combustion engines.

- H2 (produced from light hydrocarbons) contains 1-3% CO, 19-25% CO2 and 25% N2.

- Even 50 ppm of CO poisons a Pt catalyst.

- Pure H2 is used as fuel, which is costly.




- Electrolytes were sulfonated polystyrene membranes

- Nafion is used as electrolytes now

- Nafion is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by DuPont.


Direct Methanol Fuel Cell (DMFC)

CH3OH + H2O 6H+ + 6e- + CO2

6H+ + 6e- + 1½ O2 3H2O

Methanol + water

Air

CO2

Water + Excess air

H+

- Polymer membrane is used as electrolyte as in PEMFC.

- Pt/C is used as electrodes as in PEMFC.

- Anode is able to draw hydrogen from methanol directly, unlike in PEMFC.


- Operates at about 50-90oC

- Efficiency is about 40%

- Used more for small portable power applications, possibly cell phones and laptops

Direct Methanol Fuel Cell (DMFC)

Toshiba Corporation


Alkaline Fuel Cell (AFC)

- Potassium hydroxide in water is used as the electrolyte

- A variety of non-precious metals can be used as catalyst at the electrodes

- Can reach up to 70% power generating efficiency

- Used mainly by military and space programs

- Used on the Apollo spacecraft to provide electricity and drinking water


- Pure H2 and O2 because it is very susceptible to carbon contamination

- Purification process of the H2 and O2 is costly

- Susceptibility to poisoning affects cell’s lifetime which also affects the cost

- Considered to costly for transportation applications

Alkaline Fuel Cell (AFC)


- Uses highly concentrated or pure liquid phosphoric acid as electrolyte

- This acid is saturated in a silicon carbide matrix (SiC)

- Uses Pt/C electrodes

- Most commercially developed fuel cell

- Installed and currently operating in banks, hotels, hospitals and police stations.

Phosphoric Acid Fuel Cell (PAFC)


- Efficiency is about 40%

- Operates at about 150-220oC

- One main advantage is that it can use impure hydrogen (with less that 1.5% CO) as fuel

Phosphoric Acid Fuel Cell (PAFC)


- Uses an electrolyte composed of a molten carbonate salt mixture

- Require carbon dioxide and oxygen to be delivered to the cathode

- Operates at extremely high temperatures

- Primarily targeted for use as electric utility applications

Molten Carbonate Fuel Cell (MCFC)


- Because of the extreme high temperatures, non-precious metals can be used as catalysts at the anode and cathode which helps reduces cost

- Disadvantage is durability

- The high temperature required and the corrosive electrolyte accelerate breakdown and corrosion inside the fuel cell

Molten Carbonate Fuel Cell (MCFC)


Solid Oxide Fuel Cell (SOFC)

- Uses a hard, non-porous ceramic compound as the electrolyte

- Can reach 60% power-generating efficiency

- Operates at extremely high temperatures

- Used mainly for large, high powered applications such as industrial generating stations, mainly because it requires such high temperatures


Fuel cell type

Operating Temp (oC)

Effici-ency

Suitable applications

Domestic power

Small-scale power

Large-scale

Trans-port

PEMFC 50-120 40-50 X

AFC 50-90 50-70 X

PAFC 150-220 40-45 X X X

MCFC 600-650 50-60 X X

SOFC 800-1000 50-60 X

Fuel Cell Type


Fuel Cell Where do we get the hydrogen from?


Fuel Cell Hydrogen from steam reforming:95% of the usage

HTS – High temperature shift

LTS – Low temperature shift


Fuel Cell

Bulk hydrogen is usually produced by the steam reforming of natural gas (70-80% efficiency) or methane (lower efficiency): Steam reforming at high temperatures (700–1100°C) with nickel catalyst:

CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol

Shift conversion at 130°C:

CO + H2O → CO2 + H2 - 40.4 kJ/mol

Hydrogen from steam reforming:95% of the usage

http://en.wikipedia.org/wiki/File:Hydrogen.from.Coal.gasification_tampa.jpg


Fuel Cell

http://www.nrel.gov/hydrogen/energy_analysis.html

per kg of H2 produced:

GHG emissions: 10621 g CO2, 60 g CH4 and 0.04 g N2O

GWP : 11.88 kg CO2 eq.

Resource required : 159 g coal, 10.3 g Fe (ore),

11.2 g Fe (scrap),16.0 g CaCO3,

3642 g natural gas and 16.4 g of oil

Water consumption: 19.8 litres

Energy consumption: 183.2 MJ

Solid waste generated: 201.6 g

0.66 MJ of H2 is produced per MJ of fossil fuel consumed.

Hydrogen from natural gas steam reforming:95% of the usage


Fuel Cell Hydrogen from electrolysis:5% of the usage


Fuel Cell Hydrogen from electrolysis:

Where does the power come from?

WindSolar PVOther..

5% of the usage


Fuel Cell


per kg of H2 produced:

GHG emissions: 950 g CO2, 0.3 g CH4 and 0.05 g N2O

GWP : 0.97 kg CO2 eq.

Resource required : 214.7 g coal, 212.2 g Fe (ore),

174.2 g Fe (scrap),366.6 g CaCO3,

16.2 g natural gas and 48.3 g of oil

Water consumption: 26.7 litres

Energy consumption: 9.1 MJ

Solid waste generated: 223 g

13.2 MJ of H2 is produced per MJ of fossil fuel consumed.

5% of the usage

Hydrogen from electrolysis of water using wind electricity:


Regenerative Fuel Cell


Fuel Cell Hydrogen from water-splitting:

Solar water splitting is the process by which energy in solar photons is used to break down liquid water into molecules of hydrogen and oxygen gas.

Hydrogen produced through solar water does not emit carbon into the atmosphere.



Highly dense vertical arrays of nanowires made from silicon and titanium oxide and measuring 20 microns in height show promise for the efficient production of hydrogen through solar water splitting.


Fuel Cell


Fuel Cell Hydrogen from waste:

Concept of the gasification

system

HyPR-MEET demonstration

plant


Fuel Cell


Hydrogen from waste:


Fuel Cell

Researchers have designed a microbial electrolysis cell in which bacteria break up acetic

acid (a product of plant waste fermentation) to produce hydrogen gas with a very small electric

input from an outside source.

Hydrogen can then be used for fuel cells or as a fuel additive in vehicles that now run on natural

gas.

http://www.solutions-site.org/node/294

Hydrogen from waste:

Prof. R. Shanthini Mar 03, 2012 Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG

Microbial Fuel Cells


anode

cathode

Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG



An anode and a cathode are connected by an external electrical circuit,

and separated internally by an ion exchange membrane.



Microbes growing in the anodic chamber metabolize a carbon substrate (glucose in this case) to produce energy and hydrogen.



Hydrogen generated is reduced into hydrogen ions (proton) and electrons.

C6H12O6 + 2H2O → 2CH3COOH + 2CO2 + 4H2 or

C6H12O6 → CH3CH2CH2COOH + 2CO2 + 2H2



Electrons are transferred to the anodic electrode, and then to the external electrical circuit.

The protons move to the cathodic compartment via the ion exchange channel and complete the circuit.



The electrons and protons liberated in the reaction recombine in the cathode.

If oxygen is to be used as an oxidizing agent, water will be formed.

An electrical current is formed from the potential difference of the anode and cathode, and power is generated.



The anode and cathode electrodes are composed of graphite, carbon paper or carbon cloth.

The anodic chamber is filled with the carbon substrate for the microbes to metabolize to grow and produce energy.

The pH and buffering properties of the anodic chamber can be varied to maximize microbial growth, energy production, and electric potential.

The cathodic chamber may be filled with air in which case oxygen is the oxidant.



Laboratory substrates are acetate, glucose, or lactate. Real world substrates include wastewater and landfills.

Substrate concentration, type, and feed rate can greatly affect the efficiency of a cell.



Microbes should be anaerobic (fermentative type) because anodic chamber must be free of oxygen.

Microbes tested are: E. coli Proteus vulgaris Streptococcus lactis Staphylococcus aureus Psuedomonas methanica Lactobacillus plantarium



Some bacteria, likeClostridium cellulolyticum, are able to use cellulose as a substrate to produce an electrical output between 14.3-59.2 mW/m2, depending on the type of cellulose.


Microbes should be anaerobic (fermentative type) because anodic chamber must be free of oxygen.


Proton Exchange Membrane (PEM)

The PEM acts as the barrier between the anodic and cathodic chambers.

It is commonly made from polymers like Nafion and Ultrex.

Ideally, no oxygen should be able to circulate between the oxidizing environment of the cathode and the reducing environment of the anode.

The detrimental effects of oxygen in the anode can be lessened by adding oxygen-scavenging species like cysteine.



Real-life MFC


Real-life MFC

The MFC shown in this tabletop setup can take common sources of organic waste such as human sewage, animal waste, or agricultural runoff and convert them into electricity (Biodesign Institute).


Real-life MFC

Fuel cells like this are now used by a leading UK brewery to test the activity of the yeast used for their ales.


Real-life MFC

The black boxes arranged in a ring of the robot are MFCs, each generating a few

microwatts of power, enough to fuel a simple brain and light-seeking behaviour in

EcoBot-II.


Storing the Hydrogen

Developing safe, reliable, compact and cost-effective hydrogen storage is one of the biggest challenges to widespread use of fuel cell technology.

http://www.kentlaw.edu/ faculty/fbosselman/class es/EnergyLawSp07/Pow erPoints/BonnettFuelCell PresentationFinal.ppt



- Hydrogen has physical characteristics that make it difficult to store large quantities without taking up a great deal of space.


- Hydrogen has a very high energy content by weight (3 times more than gasoline) and a very low energy content by volume (4 times less than gasoline).


Storing the Hydrogen- If the hydrogen is compressed and stored at room temperature under moderate pressure, too large a fuel tank would be required.


- Researchers are trying to find light-weight, safe, composite materials that can help reduce the weight and volume of compressed gas storage systems.




- Liquid hydrogen could be kept in a smaller tank than gaseous hydrogen, but liquefying hydrogen is complicated and not energy efficient. - Liquid hydrogen is also extremely sensitive to heat and expands significantly when warmed by even a few degrees, thus the tank insulation required affects the weight and volume that can be stored. - If the hydrogen is compressed and cryogenically frozen it will take up a very small amount of space requiring a smaller tank, but it must be kept supercold (-120oC to -196oC).


How can Fuel Cell Technology be used?


Transportation

- All major automakers are working to commercialize a fuel cell car.

- fuel cell buses are currently in use in North and South America, Europe, Asia and Australia

- Trains, planes, boats, scooters, and even bicycles are utilizing fuel cell technology as well



http://www.treehugger.com/aviation/boeing-flies-first-ever-hydrogen-fuel-cell-plane.html

Boeing Flies First Ever Hydrogen Fuel Cell Plane:

The experimental airplane climbed to an altitude of 1,000 m above sea level using a combination of lithium-ion battery power and power generated by hydrogen fuel cells.

After reaching the cruise altitude, batteries were disconnected, and the plane flew straight and level at a cruising speed of 100 km/h for about 20 min on power solely generated by the fuel cells.



First Commercial Fuel Cell Powered Aircraft:

Airbus and the German Aerospace Center (DLR) presented the first commercial aircraft powered by fuel cells at the ILA Berlin Air Show 2008. The fuel cells cannot replace the plane's jet engines for powering the heavy plane through the air. Fuel cells replace the

auxiliary power units which meet the plane's power demands when the plane is on the ground.



Fuel Cell Powered Trains:

Visit http://hydrail.org/



Fuel Cell Powered Buses:

28 litres of Hydrogen /100 km(compared to 52 litres diesel /100 km)


How can Fuel Cell Technology be used?Stationary Power Stations:



Telecommunications:



Micro Power:


- Platinum as cathode catalyst is strong enough to break the oxygen bonds (molecule dissociation) but does not bind to the free oxygen atoms too strongly (catalyst binding).

- But, cost is high.

- Platinum was combined with copper to create a copper-platinum alloy, and then the copper was removed from the surface region of the alloy.

- Dealloyed platinum-copper catalyst was found to be more reactive because the interatomic distance is changed by dealloying.

- Thereby efficiency is increased.

Nanotechnology in Fuel Cells

http://www.understandingnano.com/fuel_cells-platinum-reactivity-lattice-strain.html


- Depositing one nanometer thick layer of platinum and iron on spherical nanoparticles of palladium.

- In laboratory scale testing, it was found that a catalyst made with these nanoparticles generated 12 times more current than a catalyst using pure platinum, and lasted ten times longer.




- The researchers believe that the improvement is due to a more efficient transfer of electrons than in standard catalysts.

- Increasing catalyst surface area and efficiency by depositing platinum on porous alumina

- Allowing the use of lower purity, and therefore less expensive, hydrogen with an anode made of platinum nanoparticles deposited on titanium oxide.




Hydrogen Economy

http://www.nap.edu/catalog/10922.html

The vision of the hydrogen economy is based on twoexpectations:

(1) that hydrogen can be produced from domestic energy sources in a manner that is affordable andenvironmentally benign, and

(2) that applications using hydrogen—fuel cell vehicles, for example—can gain market share in competition with the alternatives.


Hydrogen Economy


National Academy of Sciences, 2004. The hydrogen economy: opportunities, costs, barriers, and R&D needs. Washington: The National Academies Press. Available from http://www.nap.edu/catalog/10922.html


Prof. R. Shanthini Mar 03, 2012 Module 08 (subjected to continual revision) New and Emerging Energy...

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