Catalytic Materials

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”

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

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

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, 10448-10453 J. Am. Chem. Soc., 2005, 127 (15), 5308

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

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

Work at Caltech