Viktória B. Kovács| Fuel cells| © 2015 BMEGEENAG51 | D218 | 2015-16-1 | 1 FUEL CELLS Viktória Barbara KOVÁCS.

Viktória B. Kovács| Fuel cells| © 2015 BMEGEENAG51 | D218 | 2015-16-1 | 1

FUEL CELLS

Viktória Barbara KOVÁCS


INTRODUCTION

Fuel cell is a device which use hydrogen or hydrogen rich fuel and oxygen to produce electricity through electrochemical process.

Byproducts: water and heat Present use: vehicles, energy supply of

buildings, PC.


WHY FUEL CELLS?

Decrease pollution Decrease fossil energy source dependence Slowing down global warming Prevent energy crisis


FUEL CELLSAdvantages

High and size independent efficiency (40..70%).

The heat (byproduct) can be used in cogeneration.

Low specific mass: 1 kg/kW. No moving parts → long

lifetime, silent, reliable. Very low GHG emission. No toxic /harmful pollutants for

health or for the environment In case of pure hydrogen

operation only water and heat emission.

Disadvantages

New technology → averseness in the beginning.

High costs in the beginning of market introduction → high risk

Missing or undeveloped hydrogen infrastructure.


PRINCIPLE OF OPERATION The fuel cell produces electric power from hydrogen and

oxygen through electrochemical process. An ordinary fuel cell consists of two fine and porous

electrode (anode and cathode) and the electrolyte between the electrodes. The hydrogen or hydrogen rich

fuel dissociates to e- and p+ on the anode by the help of the catalyst.

The oxygen with the electrons and protons (or other ions) form water (or something else) on the cathode.

The electrons are not allowed to penetrate through the membrane, they are forced to the cathode through the current circuit.

The drift of the electrons produces electrical direct current.

an

od

e cath

od

e


PRINCIPLE OF OPERATION

oxygen

protons

electrons

membrane

DC

ee

water

heat

H2 2H+ + 2e- 1/2O2 + 2e- 1/2O2 2 -

~1,23 Volt

ee e

e

an

od

e

cath

od

e


FUEL CELL SYSTEM

1. Fuel reforming unit (cleaner) 2. Energy conversation unit (fuel cell) 3. Transformer (DC/AC converter) 4. Heat recovery (mainly in case of high temperature)

3. INVERTER

H2-rich gasfuel

4. Heat recoveryfuel reforming

2.Fuel CELL

1. thermal reformer

oxygen (air)

ACDC

water

cogeneration

heat


1. FUEL REFORMING UNIT

Fuel reforming and cleaning. If the fuel is hydrogen only cleaning is

needed. Liquid fuel (methanol, ethanol, gasoline...)

are changed by thermal reforming to gaseous hydrocarbons.


2. ENERGY CONVERSATION UNIT (FUEL CELL)

Chemical energy → electrical power. DC is produced through chemical reaction.


3. TRANSFORMER AND REGULATOR

Keep regulated and constant electrical connection between the fuel cell and network (consumer).

Transform DC to AC. Regulates the current intensity, potential,

frequency, and other parameters according to the demands.


4. HEAT RECOVERY UNIT

Not always added, because heat is not the main product.

In case of high temperature:– steam production for combined power

generation – direct use in steam turbine.

The overall efficiency is higher with heat recovery.


CLASSIFICATION OF FUEL CELLS

By Fuel

Direct: hydrogen to anode Indirect: Hydrogen rich fuel

reformatted to anode Regenerative: products are

decomposed and reused

By Electrolyte

polymer electrolyte membrane (PEMFC) ~80 °C

phosphoric acid (PAFC) ~200 °C alkaline (AFC) 80..100 °C molten carbonate (MCFC) ~650

°C solid oxide (SOFC)

– tubular (TSOFC) 800 °C– intermediate temperature (ITSOFC)

1000 °C


POLYMER ELECTROLYTE MEMBRANE- PEMFC

Other name: SPEFC (Solid Polymer Electrolyte Fuel Cells)

Electrolyte: proton exchange membrane

Low temperature (85..105 °C) Nafion® membrane (DuPont

development) which is bed in poli-tetra-fluorethilen (PTFE, Teflon) based composition

Anode: H2 → 2H+ + 2e-

Cathode: 1/2O2+ 2H+ + 2e- → H2O High power density (Power/mass) Fast stand-up Mainly in vehicles disadvantage: low CO tolerance (Pt

poison)


POLYMER ELECTROLYTE MEMBRANE - PEMFC

Fuel cell stack explained.mp4:https://www.youtube.com/watch?v=w5E_MAZdO-k

anode cathode


PHOSPHORIC ACID ELECTROLYTE - PAFC

100% concentration of H3PO4 in SiC matrix with Pt catalyst

Anode: H2 → 2H+ + 2e-

Cathode: 1/2O2+ 2H+ + 2e- → H2O High temperature is needed,

because H3PO4 is bad conductor CO<3..5 vol% or Pt is poisoned


ALKALINE ELECTROLYTE - AFC

high concentration KOH (35..85 m%) in asbestos matrix Anode: H2 + 2OH- → 2H2O + e- Cathode: 1/2O2 + H2O + 2e- →

2OH- CO2 is poison: CO2 + KOH →

K2CO3

because the electrolyte changes High efficiency (~60%) Disadvantage: expensive


MOLTEN CARBONATE ELECTROLYTE - MCFC

Mixture of alkali carbonates LiAlO2 in ceramic matrix,

High temperature (600..800 °C) Anode: H2 + CO3

2- → H2O + CO2 + 2e-

CO + CO32- → 2CO2 +

2e-

Cathode: 1/2O2+ CO2 + 2e- → CO3

2-

Ni (anode) and NiO (cathode) High efficiency (70..80% !!!!!) fuel: H2, CO, NG, propane and

even diesel oil


SOLID OXIDE ELECTROLYTE - SOFC

solid ceramic: ZrO2 stabilized by Y2O3

Anode: H2 + O2- → H2O + 2e-

CO + O2- → CO2 + 2e-

CH4 + 4O2- → 2H2O + CO2 + 8e-

Cathode: 1/2O2 + 2e- → O2-

Co-ZrO2 or Ni-ZrO2 (anode) and LaMnO3 mixed with Strontium (cathode)

two types:– tubular (1 m tube bundles)– laminated plates

high power: (electricity supply)SOFC Brennstoffzelle.mp4:https://www.youtube.com/watch?v=Itz2hJPP9l4


COMPARISON - REACTION I.

Type of fuel cell

Name Electrolytetoperation

(°C)Fuel

OxidizerAnode and cathode

reaction

alkaline AFC30% KOH,

Liquid or gel60-90

- pure H2

- O2

A: H2+2OH- 2H2O +2e-

C: 1/2O2+H2O+2e-2OH-

solid polymer

SPFC, PEMFC

Proton exchange membrane

70-90- pure H2- O2, air

A: H2 2H+ +2e-

C: 1/2O2+2H++2e-2H2O

direct methanol

DMFCProton

exchange membrane

60-120- methanol- O2, air

A: CH3OH + H2OCO2++6H+ +6e-

C: 3/2O2+6H++6e-3H2O

phosphoric acid

PAFCundiluted

phosphoric acid

~220- pure H2- O2, air

A: H2 2H+ +2e-

C: 1/2O2+2H++2e-2H2O

molten carbonate

MCFC

lithium-carbonate,potassium- carbonate

~650- H2, NG, biogas, coal-gas- air, O2

A: H2+CO32- H2O +CO2+2e-

C: 1/2O2+CO2+2e-CO32-

Solid oxide

SOFCyttrium-Zircon cheramic oxid

~1000- H2, NG, biogas, coal-gas- air, O2

A: H2+O2- H2O +2e-

C: 1/2O2+2e-O2-


COMPARISON - REACTION II.

Not used fuel

fuel O2 / air

not used O2 / air

SOFC

MCFC

PAFC

DMFC

PEMFC

AFC

H2/CO

H2/CO

H2

CH3OH

H2

H2

O2

O2

O2

O2

O2

O2

H+

H+

H+

OH-

CO32-

O2-solid oxide

molten carbonatephosphoric acid

direct methanol

polymer electrolyte

alkaline

hig

h

tem

pera

ture

low

tem

pera

tire

>800°C

650°C

200°C

60 – 120°C

< 90°C

< 80°C


COMPARISON - ENERGY

Type of fuel cellOperation

temp., °C

Pressure,kPa

Current density, A/cm2

Potential, V

alkaline 70 1 (101) 0,2 0,8

Phosphoric acid 190 1 (101) 0,324 0,62

Phosphoric acid 205 8 (808) 0,216 0,73

molten carbonate 650 1 (101) 0,16 0,78

solid oxide 1000 1 (101) 0,2 0,66


USE, POWER, EFFICIENCY

Type of fuel cell Use PowerEfficiency

actual (theoretical)

AFC (alkaline)

vehiclesSpace program

Military purposesEnergy storage

low power 5..150 kW

62% (70%)

PEMFC (polymer electrolyte)

low power 5..250 kW

50% (68%)

DMFC (direct methanol)

low power 5 kW

26% (30%)

PAFC (phosphoric acid)

Combined cycle power plant

Low - medium power

50 kW..11 MW60% (65%)

MCFC (molten carbonate)

Combined cycle power plantAnd traffic

(railway, ship, …)

low power 100 kW..2 MW

62% (65%)

SOFC (solid oxide)

low power 100..250 kW

62% (65%)


EFFICIENCY OF A FUEL CELL

H2 52,5 kW (100%) Net Power

25,1 kW (47,8%)

System loss 4,5 kW (8,6%)

H2 loss 0,5 kW

(1%)

Gross power

29,6 kW (56,4%)

Heat loss

22,4 kW (42,6%)

25 kW PEMFC efficiencies in case of DC production


USE AND POWER RANGES

Methanol Alkaline Molten carbonate

Phosphoric acid

Solid oxide

Polymer electrolyte / Proton exchange

Portable devices,

high energy density

Mobile, home use

zero emission

Industrial use,

higher efficiency

silent, environmental

friendly operation


USE

Energy storage

Road transport

Small scale power plants

Analytics


PEMFC IN VEHICLES


QUESTIONS

What is the working principle of fuel cells (PEMFC)?

What are the advantages and disadvantages of fuel cells?

Describe fuel cell system for power generation!

What type of fuel cells do you know? Describe one of them in detail: type of electrolyte, fuel, operating temperature, efficiency!


THANK YOU FOR YOUR ATTENTION!

Viktória Barbara KOVÁCS

Build. D room 207B06 1 463 2592

[email protected]

Viktória B. Kovács| Fuel cells| © 2015 BMEGEENAG51 | D218 | 2015-16-1 | 1 FUEL CELLS Viktória Barbara KOVÁCS.

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