Slayt Basligi Yok

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UNIDO-ICHET United Nations Industrial
Development Organization International Centre
for Hydrogen Energy Technologies
HYDROGEN PRODUCTION FROM SOLAR ENERGY
NATO Advanced Research Workshop (ARW) On
"Assessment of Hydrogen Energy for Sustainable
Development Energy Environmental Security"
I. Engin TÜRE 7-10 August 2006 Istanbul,
TURKEY
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UNIDO-ICHET United Nations Industrial
Development Organization International Centre
for Hydrogen Energy Technologies

• OUTLINE
• Hydrogen From Solar Energy General
  
• PV How it works?
• Electrolyzers Alkaline, Solid polymer (PEM),
  
  
  
  
  Solid Oxide
• Photoproduction Methods Semiconductor
  
  
  
  
  (photoelectrochemical), Photochemical,
  
  
  
  
  Photobiological, Hybrid and other
  systems
• New Technologies (rectenna etc.)

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UNIDO-ICHET United Nations Industrial
Development Organization International Centre
for Hydrogen Energy Technologies
Pathways to Hydrogen
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UNIDO-ICHET United Nations Industrial
Development Organization International Centre
for Hydrogen Energy Technologies

• Methods of Hydrogen Production Using Solar Energy
• Electrolysis of Water
• Thermochemical Hydrogen Production
• Photochemical Hydrogen Production
• Photoelectrochemical Hydrogen Production
• Direct Thermal Decomposition of Water
• Biological Biochemical Hydrogen Production

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SEMICONDUCTORS PHOTOVOLTAIC CELLS

• PARAMETERS AFFECTING THE EFFICIENCY OF A PV CELL
• BAND GAP OF THE SEMICONDUCTOR
• THE VOLTAGE DROP AT THE P-N JNCTION
• LIFE TIME ( ? ) AND MOBILITY ( ? ) OF CARRIERS
  

IDEAL P-N JUNCTION SOLAR CELL EFFICIENCY vs
BANDGAP
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SOLAR SPECTRUM
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• KEY PHOTOVOLTAIC TECHNOLOGY ISSUES
• SI WAFER-BASED PHOTOVOLTAIC TECHNOLOGY IS
  
  
  
  
  CURRENTLY THE MOST WIDELY DEPLOYED, WELL-
  
  
  
  
  DEVELOPED, AND COST-EFFECTIVE
  TECHNOLOGY.
• THIN-FILM PHOTOVOLTAIC TECHNOLOGY HAS YET TO
  
  
  
  
  REALIZE ITS LOW-COST PROMISE.
• NOVEL PHOTOVOLTAIC TECHNOLOGIES BASED ON
  
  
  
• TANDEM CELL CONCEPTS, NANO-STRUCTURED
• MATERIALS, AND POLYMERS MAY BE IMPORTANT
  
  
  
  
• TECHNOLOGIES IN THE LONG-TERM, BUT WILL NOT BE
• PRACTICAL FOR SOME TIME.
• REAL PROGRESS IN PHOTOVOLTAIC TECHNOLOGY
• WILL OCCUR THROUGH CONTINUED APPLICATION OF
• HIGH-EFFICIENCY CONCEPTS TO LOW-COST
  
  
  
  
• PRODUCTION ENVIRONMENTS.

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UNIDO-ICHET United Nations Industrial
Development Organization International Centre
for Hydrogen Energy Technologies
ELECTROLYSIS

• ALKALINE WATER
• SOLID POLYMER ELECTROLYTE
• SOLID OXIDE ELECTROLYZER

Solar powered electrolysis Photovoltaics
Solar Thermal Power (Concentrators) New
Developments Nano Rectenna Conversion (3rd
Gen. PV) Combined Power/Cooling cycle
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UNIDO-ICHET United Nations Industrial
Development Organization International Centre
for Hydrogen Energy Technologies
ALKALINE WATER
Cathode (positive voltage) 2H 2e- ? H2 Anode
(negative voltage) H2O ? ½ O2 2H 2e-
ELECTROLYSIS
FOR THE CONTINUITY OF REACTIONS

• No net build-up of charge at either electrode
• H2 and O2 must be physically separeted

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ELECTROLYSIS COMPLETE CELL REACTION H2O H2 ½
O2 THE NERNST EQ. FOR THE CATHODE THE
NERNST EQ. FOR THE ANODE
Ec -0.828-0.059 log aOH- Ea 0.401-0.059
log aOH- THE POTENTIAL REQUIRED TO SPLIT WATER
INTO H2 AND O2 Ea Ec 1.23 V
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SOLID POLYMER ELECTROLYZER (SPE)
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SOLID POLYMER ELECTROLYZER (SPE)-1

• The efficiency of SPE is dependent on
• Polyelectrolyte membrane (PEM)
• Electroctalyst performance
• The membrane consists of a solid fluoropolymer
  (contains
  
  
  
  sulphonic acid groups, SO3H, which
  easily release their
  
  
  
  hydrogen as
  positively-charged atoms or protons H
• SO3H -gt SO3- H
• Water can penetrate into the membrane structure
  but not hydrogen H2 and oxygen O2.
• H2O H H3O (hydrated proton)

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• The hydrated proton H3O i s free to move
  whereas the SO3-
• remains fixed to the polymer side-chain.
• When an electric field is applied across the
  membrane
• the hydrated protons are attracted to the
  cathode,
• Thus the membrane acts as a conductor of
  electricity since moving
• H3O is identical with electric current. It is
  called protonic Conductor.
• Typical membrane material is sold by Du Pont
  under
• the trade name nafion.
• It has several advantages over conventional
  electrolyzers
• Because nafion is a solid, its acidity is
  self-contained and so
• chemical corrosion of the electrolyzer housing
  is much less.
• It is an excellent gas separator,

SOLID POLYMER ELECTROLYZER (SPE)-2
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• It can be made very thin (around 100 ?m).
• BUT IT IS EXPENSIVE
• Electrocatalysts
• About 1.5V DC is supplied to the metal plate
  electrodes
• Protons are drawn to the cathode and are
  discharged as H atoms
• by combination with electrons (e-) at the metal
  cathode surface (M).
• Pairs of adsorbed H atoms then combine to make
  molecules of H2 gas
• which escape, freeing the electrode surface for
  more proton discharge
• 4H 4e- -gt 4M-H
• 4M- H -gt 4M 2H2

SOLID POLYMER ELECTROLYZER (SPE)-3
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• At the positive electrode or anode, electrons
  are lost by incoming
• water molecules creating O ad-atoms, and
  protons.
• The electrons are shunted to the cathode,
  protons enter the membrane,
• and two O atoms combine to release O2 gas
• 2H2O -gt 2M-O 4 H 4 e-
• 2M-O -gt 2M O2
• The balance of overall process is hydrogen and
  one molecule of
• oxygen from two molecules of water
• 2H2O -gt 2H2 O2

SOLID POLYMER ELECTROLYZER (SPE)-4
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• The minimum energy required to drive the process
  
• is about 1.23V.
• In reality required voltage is always larger
  than 1.23 due to the IR loss
• and the speed of the process at the electrode
  surface.
• A solid catalyst (M) speeds up chemical
  reactions due to its surface
• action. As a simple example, two H atoms held
  loosely on a surface
• are much more likely to collide and make H2 gas
  than if they are
• dispersed in a liquid with billions of water
  molecules in-between.
• This is a spatial or localized concentration
  effect.

SOLID POLYMER ELECTROLYZER (SPE)-5
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SOLID POLYMER ELECTROLYTE

• ADVANTAGES OF SOLID POLYMER ELECTROLYTES
• High productivity (current density up to 1
  A/cm2)
• Efficiency with respect to power consumption
  (4.0-4.2 kWh per cubic
  
  
  
  meter of hydrogen)
• No hazard to the environment (absence of alkali
  and asbestos)
• Noiseless operation
• Considerable reduction in mass and overall
  dimensions
• Non-explosiveness and non-flammability
• High purity of produced gases (over 99.99 for
  hydrogen and over
  
  
  
  99.8 for oxygen)
• Possibility to produce compressed gases (with
  the pressure no less than
  
  
  
  30 atm).

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• COMPARISON OF ELECTROLYZERS
• ALKALINE ELECTROLOYTE
• ADVANTAGES
• DURABLE AND MATURE TECHNOLOGY
• NICKEL PLATED STEEL AND STEEL ELECTRODES
• KOH SOLUTION
• DISADVANTAGES
• INABILITY TO PRODUCE HIGH PRESSURE H2 FOR STORAGE

• PROTON EXCHANGE MEMBRANE
• SOLID STATE TECHNOLOGY
• HIGHLY POROUS NETWORK OF GRAPHITE LIKE MATERIAL
  WITH EXTREMELY
  
  
  
  SMALL PLATINUM PARTICLES EMBEDDED INSIDE
  IT ARE USED AS ELECTRODES
• GRAPHITE MATERIAL SERVE S CONDUCTIVE ELECTRODE
• PLATINUM PARTICLES SERVE TO CATALYZE THE
  ELECTROCHEMICAL
  
  
  
  REACTIONS
• SOLID POLYMER ELECTROLYTE (NAFION)

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ELECTROLYTE TYPE STRENGTHS
WEAKNESSES ALKALINE -HIGH VOLTAGE
EFFICIENCY -HIGH PARASITIC POWER
CONSUMPTION -DURABLE -COMPLEX GAS
HANDLING -LIQUID ELECTROLYTE SOLID
POLYMER -COMPACT -LOW PARASITIC POWER -HIGH
PURITY WATER CONSUMPTION
NEEDED -HIGH OVERALL EFFICIENCY - HIGH
OVERPOTENTIAL SOME
ELECTROLYERZS -PRESSURE DIFFERENCE ALLOWED
BETWEEN H2 AND O2 SIDES
STRENGTH AND WEAKNESS OF ALKALINE AND PEM
ELECTROLYZERS
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PROJECTED PRICE PER kW FOR PEM ELECTORLYZER
TECHNOLOGY
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• SOLID OXIDE ELECTROLYZERS-1
• A solid ceramic material is used as the
  electrolyte, such as fully
  
  
  
  stabilized Zirconia doped with
  Yttrium(YSZ), that is sandwiched
  
  
  
  between two porous
  electrodes,
• At the cathode, water combines with electrons
  from the external
  
  
  
  circuit to produce hydrogen gas and
  negativly charged ions,
• The oxygen ions move through the solid oxide
  membrane and
  
  
  
  release electrons to the external
  circuit,
• The solid oxide membrane must be between 500-800
  C,
• At elevated temperatures, solid oxide
  electrolyts become oxygen
  
  
  
  ion conductors ,

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• SOLID OXIDE ELECTROLYZERS-2
• The oxygen ion is conducted through the
  vacancies in the crystal
  
  
  
  structure of the electrolyte to
  the anode,
• At the anode, the oxygen donates the electrons
  to the external
  
  
  
  circuit to form an oxygen atom,
• Two oxygen atoms combine to form an oxygen
  molecule at the
  
  
  
  anode side of the cell.

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SOLID OXIDE ELECTROLYZER
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• SOLID OXIDE ELECTROLYZERS
• CAN PRODUCE HYDROGEN AT HIGH
  
  
  
  
  TEMPERATURES (FROM STEAM)
• THEY ARE ENERGY EFFICIENT (90 ) (REDUCTION
  
  
  
  
  IN OHMIC LOSSES)
• ELECTROLYTE THICKNESS CAN BE MINIMIZED
• SIZE CAN BE REDUCED UP TO 3 TIMES
• TECHNICAL BARRIERS
• DURABLE TO HIGH TEMPERATURE MATERIALS ARE
  
  
  
  
  REQUIRED
• COST OF SOLAR ENERGY AND SOLAR
  
  
  
  
  CONCENTRATORS MUST BE REDUCED
• METHOD OF ENGINEERING AND MANUFACTURING OF
  
  
  
  
  THESE SYSTEMS HAVE NOT BEEN FULLY
  EVALUATED

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HIGH TEMPERATURE ELECTROLYZER

• Overall efficiency is around 50

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• PHOTO-ELECTRCHEMICAL (PEC) CELL-1
• (DIRECT HYDROGEN PRODUCTION)
• PEC is the integration of PV and electrolyzer
  into a single device
• PEC consists of a light absorbing semiconductor
  (PV) structure coated
  
  
  
  with catalytic films, a metal counter
  electrode and an electrolyte
  
  
  
  

Structure of a PEC cell (Fujishima and Honda)
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• PHOTO-ELECTRCHEMICAL (PEC) CELL
• PV structre produces electric current in order to
  drive , hydrogen and
  
  
  
  oxygen evolution reactions (HER OER) at
  the respective surfaces,
• High bangap semiconductor materials are used as
  the light absorbing
  
  
  
  electrodes due to
  
  
  
  
  a) losses in the system
  (resistance electrode overpotential)
  
  
  
  b) unstability of
  small bandgap materials
  
  
  
  
  (electrochemical corrosion during PEC operations)
  
• For the reduction of losses,
  Catalyst material must
• Provide a low energy reaction pathway,
• Adsorb intermediate reaction products
  sufficiently strongly to hold
  
  
  
  them long enough for reaction
  to occur
• Simultaneously holding them loosely enough that
  the electrode does
  
  
  
  not get saturated with the intermediate
  products.

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A Schematic Illustrating the Operating Principles
of a Photoelectrochemical Cell Producing Hydrogen
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Integrated Planar Photoelectrode for Hydrogen
Production
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Planar Photoelectrodes for Solar-to-Hydrogen
Conversion
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HYBRID PHOTOELECTROCHEMICAL CELL
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A Schematic Illustrating the Sequence of Charge
Transfer Processes for a Dye Sensitized Solar
Cell (DSSC)
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• PHOTOELECTROCHEMICAL HYDROGEN CELL TECHNOLOGY KEY
  ISSUES
• STABILITY AND DURABILITY OF PHOTOELECTRODE
• MATERIALS
• HYBRID PHOTOELECTRODES SEEM TO BE PROMISING
• LOW-COST TANDEM CELL DESIGN
• EFFICIENCY COST

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Next Generation High-Efficiency Hybrid
Photoelectrode for Hydrogen Production Based on
Monolithically-Stacked CIGS Tandem Device
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Large Scale PEC Hydrogen Production System
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PHOTOCHEMICAL SYSTEM-1

• Photocemical Water Splitting Mechanism
• Any photochemical process must involve a
  sensitizer
• The absorbtion of a single photon can cause the
  transfer of one electron
• in a photoredox process.

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PHOTOCHEMICAL SYSTEM-2

• Photocemical Water Splitting Mechanism
• Visible Light Absorption
• Hydrogen Oxygen Evolution Reactions Involved
• 2H2O ? 4H4e- O2 Oxidation reaction (OER)
• 4H4e- ? 2H2 Reduction reaction (HER)

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• THERMOCHEMICAL HYDROGEN PRODUCTION FROM SOLAR
  ENERGY
• Thermochemical Water-splitting Promises
  Efficient
• Hydrogen Production From Heat
• Requires High Temperatures
• For Solar Process matching and Selection of
  Appropriate
• Cycle is Needed

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THERMOCHEMICAL HYDROGEN
Chemical Cycle
High Temperature Heat
Low Temperature Heat
Hydrogen
Hydrogen
Water
Oxygen

• UTILIZE A SERIES OF CHEMICAL REACTIONS TO
• PRODUCE HYDROGEN
• MOST COMMON REACTONS
• Iodine-Sulfur processes, ZnO/Zn,
  Fe3O4/FeO ,

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THERMOCHEMICAL ROUTES FOR THE PRODUCTION OF
HYDROGEN
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THERMOCHEMICAL HYDROGEN PRODUCTION SULPHUR /
IODINE PROCESS

• Thermochemical processes require
  high-temperature (800-1000C),
• Low-pressure endothermic (heat absorbing)
  decomposition of sulfuric
• acid produces oxygen and sulfur dioxide
• H2SO4 gt H2O SO2 1/2O2
• In the iodine-sulfur (IS) process iodine
  combines with the SO2 and
• water to produce hydrogen iodide which then
  dissociates to hydrogen
• and iodine. This is the Bunsen reaction and is
  exothermic, occurring at
• low temperature (120C)
• I2 SO2 2H2O gt 2HI
  H2SO4

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THERMOCHEMICAL HYDROGEN PRODUCTION SULPHUR /
IODINE PROCESS

• The HI then dissociates to hydrogen and iodine
  at about 350C,
• endothermically
• 2HI gt H2 I2
• This can deliver hydrogen at high pressure.
• The net reaction is then
• H2O gt H2 1/2O2
• All the reagents other than water are recycled,
  there are no effluents.

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SULPHUR / IODINE PROCESS
Reaction Steps and Key Process Parameters
Temp. Heat Flow Purpose Step I2 SO2 2 H2O ? 2
HI H2SO4 120C Exothermic Produce HI
(1) H2SO4 ? SO2 H2O 0.5 O2 850C
Endothermic Crack (2)

H2SO4 2 HI I2 H2
350C Endothermic Crack HI (3)
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BIOLOGICAL HYDROGEN

• HYDROGEN PRODUCING ORGANISMS
• ALGAE Uses the reversible hydrogenase enzyme to
• generate hydrogen from protons
  in anaerobic
• conditions
• CYANOBACTERIA Uses nitrogenase enzymes to
• generate
  hydrogen in anaerobic
  
  
  
  
  conditions

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BIOLOGICAL HYDROGEN
Schematic of an Indirect Photo-biological
Hydrogen production System
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BIOLOGICAL HYDROGEN
Process General reaction
Microorganisms

Used Direct
Biophotolysis 2 H2O light 2 H2 O2
Microalgae Photo-fermentation CH3COOH 2
H2Olight 4 H2 2 CO2 Purple bacteria


Microalgae Indirect a) 6H2O6CO2 light
C6H12O6 6O2 Microalgae biophotolysi
s, b) C6H12O6 2H2O 4H2
2CH3COOH 2CO2 Cyanobacteria
c) 2CH3 COOH4H2O light 8 H2 4CO2
Overall reaction 12 H2O light
12 H2 6 O2
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HYBRID SOLAR CONCENTRATOR SYSTEM

• CONSISTS OF 4 MAJOR COMPONENTS
• Concentrator Photovoltaic (CPV)
• Spectral Splitter
• Light Pipe
• Solid Oxide Electrolyzer Cells (SOEC)

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HYBRID SOLAR CONCENTRATOR SYSTEM
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Other Techniques (Recent developments)-1
Sandia Lab News, February 3, 2006
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• NANO RECTENNA CONVERSION
• NANOSCALE RECTENNAS FOR DIRECT SOLAR ENERGY
• CONVERSION TO ELECTRICITY
• 3

Relies on quantum nature of light. A
revolutionary concept suggested by UF Prof.
Bailey in 1968, based on wave nature of light.
Concept has been demonstrated for microwave
(2.45 GHz) reception and rectification to DC at
over 80 efficiency With the advent of
nanotechnologies the concept can be extended
to solar frequencies
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Freiburg Solar-Hydrogen House
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Freiburg Solar-Hydrogen House
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Freiburg Solar-Hydrogen House
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THANK YOU www.unido-ichet.org eture_at_unido-ichet.
org
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