1. A Novel Design of Electrode Surface
Morphology to Improve Water Electrolysis
Efficiency
Jaehyeong Lee
Sangmin Lee, Myra Halpin
North Carolina School of Science and
Mathematics

2. Introduction
• Fuel economy still hydrocarbon dominant
– Air, water, and soil pollution
– Unsustainable
• Alternatives
– Electrolysis
• Has the potential to be cost competitive against
hydrocarbon fuels, sustainable (It’s just water!)
• Two ways to improve, use different metal to improve
catalytic effect
• Or increase effective surface area of the electrode

3. Surface Area Calculation: Aspect Ratio or Height?
•Equation to find effective
surface area:
*d = side length of structure
*a = space between structures
*h = thickness
•Constant Aspect Ratio Model
•Peaks
•Nanoparticle Surfaces
•Constant Thickness Model
•Increases exponentially
•Smaller d/a

4. The “Mushroom Top” Concept
•(Left) – Pyramid
Structure, Additional Surface
Area: A-B
•(Center) – Mushroom
Structure, Additional Surface
Area: A+B
•(Right) – Straight
Sidewall, Additional Surface
Area: A
•Effective surface area difference
between mushroom structure and
straight sidewall structure
•Shows as much as 13.4%
increase in surface area in
additional surface area vs.
aspect ratio graph

5. Electroplating
•Electroplating selected
•Ease of control
•Applied current
•Plating time
•Low operating temperature
•Wide market available
•Plate thickness directly
proportional to plating time and
applied current

6. Photoresist Patterning/Developing
•AZ2070 Photoresist, 9um thick:
•2000rpm for 30 second spin
•1 min, 100°C bake
•Developing Procedure
•400nm UV Exposure
•2.5 minutes
•150°C Heat Treatment
•1.5 minutes
•MIF300 developing
•1.5 minutes

7. Butler Volmer Equation
Butler Volmer Equation
with Ohmic Component
1
0
log(Ja)( A/cm2)
-1
Fit of Voltammogram using
-2 above Butler Volmer
Equation
-3 Ohmic fit data-0.5M Buttler Volmer fit
-4
0 1 2 3 4 5 6 7 8
E-E0 (V)

8. Modifications to Butler Volmer

9. Optimal KOH Concentration
•Different KOH concentrations tested in Pt-Pt system
•0.5M, 1.0M, 1.5M, 2.0M
•Cyclic Voltammetry
•Analysis using modified Butler Volmer Equation
•Resistance values compared versus concentrations
•Between 0.5M and 1.0M, large resistance drop
•Tapers off past 1.0M, 1.0M selected

10. Electrode Mounting Fixture
*Kelvin Probe Method used to remove voltage drop through the wire.

11. Surface Area Dependence on I-V Characteristics

12. Impact of New Surface Morphology on System

13. Conclusion
• The new surface morphology shows significant
improvement compared to smooth surfaces
• SEM photos verify new structure’s mushroom
sidewall gives 4 times more effective surface
area than straight side wall
• Linear approximation:
– Average Resistance Reduction from approximation
• 20.4%
– Translates into 25.6% increase in efficiency.

14. Questions?

15. Future Works
• Find trend of electrolysis efficiency as function of
pattern size and spacing
– Photolithography techniques with higher controllability
– Smaller pattern size
– Further increased effective surface area
• Apply mushroom top surface morphology with high
aspect ratio materials (nanowires/nanotubes)
• Other nonnoble metals with greater catalytic effect
than Ni
– Cobalt/Manganese
High efficiency electrolysis may become a prominent
source of fuel in the future.