1. Catalytic Materials

2. Why do we care about catalysts?
“…at least one third of the material gross national product in the US involves a catalytic process somewhere along the production chain.“
Examples:
Haber-Bosch process
Cracking of petroleum
Catalytic converters
Pharmaceuticals
Just in the US, “catalyst technologies provide revenues exceeding $1 trillion”

3. What is a catalyst? According to the Arrhenius equation,
Rate constant
Energy of
Activation
Catalysts increase the rates of chemical reactions by lowering the activation energy
How?
Stabilization of reaction intermediates
Activation/destabilization of the starting  mat erials
Emergence of alternate reaction pathways
Reaction energy diagrams of a catalyst changing the activation energy of a reaction

4. The Goal of Catalysis
The development of dirt cheap, highly active and stable catalysts that provide near-100% selectivity to a target product with limited production of chemical waste and with minimal use of energy

5. Broderick, Peters, PNAS 2010, 107, 10448-10453
Diversity in Catalysis
Functional HER catalysts include homogeneous (molecular), biological (enzyme), and heterogeneous (solid-state) systems
Science, 2012, 335, 698
Science, 2011, 333, 863
[FeFe] hydrogenase
Broderick, Peters, PNAS 2010, 107,
J. Am. Chem. Soc., 2005, 127 (15), 5308

6. 2H2O(l) → O2(g) + 4H+(aq) + 4e-
Application: Hydrogen through Water Splitting
Oxygen Evolution Reaction
OER
2H2O(l) → O2(g) + 4H+(aq) + 4e-
Hydrogen Evolution Reaction
HER
2H+(aq) + 2e- → H2(g)
2H2O(l) → 2H2(g) + O2(g)
Load
Cathode O2 H+
Electrolyzers produce hydrogen from the electrochemical decomposition of H2O
Endothermic reaction
ΔGo = 1.23 eV/electron
Seen as promising alternatives to batteries and internal combustion engines
Anode H2 H+
Electrolyte
Membrane

7. Oxygen Evolution Reaction
The oxygen evolution reaction (OER) produces oxygen gas from the electrochemical oxidation of water
2H2O → O2(g) + 2H+ + 4e-
Catalyzed most effectively by noble metals like iridium
Scarce and expensive
There is a need to develop electrocatalysts that is:
Highly active
Stable
Earth-abundant
Fe: $72/kg
Ir: $54,000/kg

8. Work at Caltech