Dr. Harry Gray (the Arnold O. Beckman Professor of Chemistry and the Founding Director of the Beckman Institute at the California Institute of Technology) is this years speaker for the Engaging Chemistry: Edmonton Distinguished Lecture Series in Chemistry. He will be speaking at Edmonton City Hall on October 22nd, and at the University of Alberta on October 23rd (details below). [Pamphlet PDF]
The sun is a boundless source of clean energy, but it goes down every night. We and many others are trying to design solar-driven molecular machines that could be used on a global scale to store solar energy by splitting water into its elemental components, hydrogen and oxygen. Hydrogen is a clean fuel that could be used directly or combined with carbon dioxide to produce methanol, a liquid fuel. We are investigating the structures and mechanisms of hydrogen evolving catalysts made from Earth abundant elements such
as cobalt, iron, nickel, and molybdenum. We also are employing pulsed laser ablation for synthesis of metal- oxide nanoparticles that will be deployed as catalysts on photoanodes such as tungsten oxide. To aid our research, we have recruited hundreds of students to join a Solar Army whose mission is the discovery of mixed- metal oxides for
testing on the photoanodes of our solar water splitters.
Molecular hydrogen has emerged as an attractive candidate for a clean, renewable fuel to meet the world’s skyrocketing demand for energy. Hydrogenase enzymes that contain iron and nickel cofactors evolve H2 catalytically from water with turnover frequencies as high as 9000 s-1 at 30 °C. However, the relative instability of these enzymes under aerobic conditions has led to the search for robust inorganic catalysts that can produce hydrogen from water. Platinum is an excellent catalyst for proton reduction and hydrogen oxidation, but scarcity and high cost limit its widespread use. Our emphasis is on heterogeneous and homogeneous catalysts made from earth-abundant elements that could be part of scalable solar fuel devices. Promising heterogeneous catalysts include MoS2 and Ni–Mo, which reduce protons in aqueous solutions with catalytic efficiencies near that of platinum. While homogeneous catalysts typically degrade faster than their heterogeneous counterparts, molecular systems are much easier to study mechanistically. Cobalt complexes enable
electrocatalytic production of H2 from solutions with high turnover frequencies, and kinetics investigations have established that the reactive intermediate is a Co(II)-hydride. The challenge of water oxidation in many ways eclipses that of proton reduction. The oxidation reaction involves the rearrangement of more protons and electrons, and fewer good catalysts for the reaction exist that are made of earth-abundant materials. We have found that 3 to 5 nm metal-oxide particles made by pulsed laser ablation of precursors in water are very active water oxidation catalysts. We hope to elucidate the electronic structures of these very small nanoparticles as part of a program with the goal of understanding their mechanisms.