MoS2 is a potential catalyst for hydrogen production through water electrolysis. It is cheaper than platinum, which is currently used. The document summarizes recent work studying how a catalyst support and applied voltage can lower the activation energy and increase the reaction rate of hydrogen evolution using MoS2 catalysts. Results showed unsupported MoS2 had a higher activation energy than when supported on gold, and activation energies decreased with increasing voltage. Together, the results suggest tuning a catalyst's support and the applied voltage could optimize hydrogen production from MoS2 for more economical clean energy applications.

1. Hydrogen Production
Using Molybdenum
Disulfide Electrocatalysts
OERC Symposium 2017
Charlie Ruffman
Department of Chemistry, U. Otago

2. Uses of Hydrogen
• Hydrogen (H2) is an alternative to fossil
fuels (hydrocarbons)
• Harmless byproducts – No CO2
• High energy density by weight
• Efficient ignition
Fossil Fuels → Energy + CO2
H2 → Energy + water
• H2 is also an industrial
reactant used in the
making of fertiliser

3. Hydrogen Production
• Steam reformation:
• Electrolysis:
Methane
Steam reformation plant
H2
H2O CO
Electricity
H2O
H2
O2

4. Electrolysis - Water Splitting
• Water splitting:
• Two separate but linked processes:
Oxygen Evolution
Hydrogen Evolution
H2O → H2 + ½O2
H2O → ½O2 + 2H+ + 2e-
2H+ + 2e- → H2

5. Electrolysis - Catalysis
• Platinum is effective but expensive
• Search for Earth-abundant materials to catalyse H2 production
$$$
Platinum (Pt) surface catalyst
Pt
Nørskov, J. K.; Bligaard, T.; Rossmeisl, J.; Christensen, C. H., Nat. Chem. 2009, 1 (1), 37-46.

6. Transition Metal Sulfides: MoS2
• Molybdenum disulfide (MoS2) cheap and
abundant – in biological systems
• Forms layered sheets and nanoparticles
• Catalytically active towards H2 evolution
Lauritsen, J. V., et al., Nat. Nanotechnol. 2007, 2 (1), 53-58.
Jaramillo, T. F., et al., Science, 2007, 317 (5834), 100-102.
Key: Molybdenum – green, Sulfur – yellow
MoS2 nanoparticles
1 nm

7. Studying a Catalyst
• Energy is important in any chemical
reaction
– Energy of products and reactants
– The activation energy – Ea
• The lower Ea the faster the reaction
• A catalyst lowers Ea, reducing the energy
cost and speeding up the reaction
Huang, Y.; Nielsen, R. J.; Goddard III, W. A.; Soriaga, M. P., J. Am. Chem. Soc. 2015, 137 (20), 6692-6698.

8. Further Lowering Ea
• Catalyst support
• Applied voltage
Huang, Y.; Nielsen, R. J.; Goddard III, W. A.; Soriaga, M. P., J. Am. Chem. Soc. 2015, 137 (20), 6692-6698.

9. Catalyst Support Applied Voltage
Efficient hydrogen evolution
catalysis
Tuning of catalyst

10. Our Recent Work
Unsupported
Low applied
voltage
Unsupported
High applied
voltage
Gold-supported
Low applied
voltage
Gold-supported
High applied
voltage
 Looked at activation barriers (Ea) to hydrogen evolution

11. Unsupported Ea
• Reaction goes
faster at higher
voltage
• More H atoms
on the surface at
higher voltages
• Crowding
makes leaving
as H2 easier
Ea = 0.76 eV
Ea = 0.70 eV

12. Gold-supported Ea
Ea = 0.61 eV
Ea = 0.67 eV
• Overall
lowering of Ea
with gold
• Reaction goes
faster at lower
voltage

13. Summary
• Together, applied voltage and catalyst
support may tune the activity of a
catalyst
• Can be used to optimise hydrogen
evolution on cheap MoS2 catalysts
• More economically viable hydrogen
production?

14. Acknowledgments
The Garden Group
Left to right: Steph, Caitlin,
Charlie, Anna, Ray, Geoff

15. Acknowledgments
The Garden Group
Left to right: Steph, Caitlin,
Charlie, Anna, Ray, Geoff