Photoelectrochemical Photoelectrochemical Photoelectrochemical - - PowerPoint PPT Presentation

Photoelectrochemical Photoelectrochemical H 2 Production Production Photoelectrochemical Photoelectrochemical H 2 Production Production

Advisor: Professor Eric McFarland

Kimberly Kaufman

Chemical Engineering, AHC

Graduate Mentor: Scott Roney, UCSB

Clean renewable fuel source High fuel value of 142 kJ/g Reduces the use of fossil fuels Combustion produces H2O Little H2 in nature decomposed H2O or hydrocarbons, fossil fuels cost more energy to make expensive materials for solar energy Gas-storage

H 2 Production Production H 2 Production Production

Photovoltaic + Electrochemistry

Photovoltaic

Solar Energy Chemical Energy

1972 Fujishima and Honda Photo-Electrochemical Cell

2h+ 2e- 2 H+

H2

H2O ½ O2 + 2 H+

Cathode anode

TiO2

• Pure high quality H2

Required expensive Pt catalyst Band gap too large for efficiency Poor solar absorption (UV only)

must be inexpensive and stable semiconductors with bandgaps in the energy range of visible light potential cathode materials is Cu2O Cu2O is prone to “photocorrosion”

Practical H2 from Photoelectrodes

Cu2O-based heterojunction photocathode

Deposit Cu2O on FTO substrates Cu2O easily reduces or oxidized Current proportional Cu2O deposited

Data Plate Digital Hotplate/stirrer Target Plate Hot Plate Probe PMC 50ºC

1 2 3 4 5 6 7 8 9 10 11 12

Ref Gnd Cntr Wkg

Model 273A Diff. Electrometer EXT Dummy

Sense

Scan set up EG &G Princeton Applied Research I= E= Charge= Control Mode Cell On OFF Current range Output Reset Integral Potentiostat/galvanostat

Synthesis of Materials

Cu Lactate

Protect integrity w/ Spray Pyrolysis

• f Zn acetate solution

Approximate thickness 200nm- 400nm Annealing time 6-12 minutes

Data Plate Digital Hotplate/stirrer Target Plate Hot Plate Probe PMC 250˚

1 2 3 4 5 6 7 8 9 10 11 12

AIR

Photocatalyst Screening

70 80 90 100 110 120 130 140 150

• 2.5
• 2.0
• 1.5
• 1.0
• 0.5

0.0

Light Off ("dark" current) Light On (anodic current)

Full Xe spectrum UV Cut-off Filter

Current (mA/cm

2)

Time (sec)

Zero-bias photocurrent as a function of time

h+ e- A D D+ A- Photo-cathode h+ e- A A- i

H2O

½ O2 + 2 H+

2 H+

H2

Xen Xenon La n Lamp

COLEMAN

Filter wheel control

Variable Flow

Chemical Pump

Thermo Oriel

Warning!

Potentiostat/Galvanostat 237A

HP Multimeter

N 2

computerized drive

Na

acetate

Photocurrent System

3 7 10 13

• 100
• 80
• 60
• 40
• 20

20 40 60 80 100

Current (µA) Time (min) .4C .8C

Controlled Spray Pyrolysis Parameters:

Cu2O only Cu2O w/ ZnO 9.0 pH Annealed 175˚C, 4hrs

• 300 mV bias
• ------ .4C --------.8C

2 4 6 8 10

• 100
• 80
• 60
• 40
• 20

20 40 60 80 100

Current (µA) Time (min)

.4C .8C

Controlled Spray Pyrolysis Parameters:

3 7 10

• 200
• 150
• 100
• 50

50 100

Current (µA) Time (min)

3 7 10

• 200
• 150
• 100
• 50

50 100

Current (µA) TIme (min)

Cu2O w/ ZnO Cu2O only 9.0 pH Annealed 175˚C, 4hrs

• 300 mV bias

Post annealed, 300˚C. 4hrs

• ------ .4C --------.8C

Our Findings…

ZnO films can be synthesized on electrodeposited Cu2O by spray pyrolysis Oxidation improved the photocurrent of the Cu2O ZnO may protect Cu2O from photocorrosion, depending on thickness Thicker ZnO layer causes anodic behavior Thicker Cu2O layer reduced the amount of photocurrent, electrons have too far to travel Annealing after spray pyrolysis improved the conductivity of the Cu2O

Special Thanks To:

Scott Roney Kelsey Gorter Nick Tovar Alan Kleiman-Shwarcstein Eric McFarland Nick Arnold Mike Northen Trevor Hirst Liu-Yen Kramer Julie Niles & Judy

Future Works:

Use applied potential during photocurrent between - 0.3V and -0.425V Make thinner ZnO layers (e.g. use more dilute spray solution) Try higher annealing temperature for Cu2O Refine higher-pH electrodeposition Measure thickness of ZnO and Cu2O layers using profilometer Characterize ZnO/Cu2O made by Atomic Layer Deposition (collaboration with Prof. Steve George at University of Colorado)