Researchers have been designing catalysts inspired by hydrogenase cores and testing them. In this work, an important step in breaking a hydrogen molecule so the bond's energy can be captured as electricity is to break the bond unevenly. Instead of producing two equal hydrogen atoms, this catalyst must produce a positively charged proton and a negatively charged hydride.
The physical shape of a catalyst along with electrochemical information -- can reveal how it does that. So far, scientists have determined the overall structure of catalysts with cheap metals using X-ray crystallography, but hydrogen atoms can't be located accurately using X-rays. Based on chemistry and X-ray methods, researchers have a best guess for the position of hydrogen atoms, but imagination is no substitute for reality.
Bullock, Tianbiao "Leo" Liu and their colleagues at the Center for Molecular Electrocatalysis at PNNL, one of DOE's Energy Frontier Research Centers, collaborated with scientists at the Spallation Neutron Source at Oak Ridge National Laboratory in Tennessee to find the lurking proton and hydride. Using a beam of neutrons like a flashlight allows researchers to pinpoint the nucleus of atoms that form the backbone architecture of their iron-based catalyst.
To use their iron-based catalyst in neutron crystallography, the team had to modify it chemically so it would react with the hydrogen molecule in just the right way. Neutron crystallography also requires larger crystals as starting material compared to X-ray crystallography.
"We were designing a molecule that represented an intermediate in the chemical reaction, and it required special experimental techniques," Liu said. "It took more than six months to find the right conditions to grow large single crystals suitable for neutron diffraction. And another six months to pinpoint the position of the split H2 molecule."
Crystallizing their catalyst
|Contact: Mary Beckman|
DOE/Pacific Northwest National Laboratory