Working as a crew, scientists from SIMES and the SUNCAT Heart for Interface Science and Catalysis studied two platinum-rhodium nanostructures, figuring out essentially the most lively websites on the platinum islands and predicting that an optimized platinum-rhodium nanostructure may very well be as much as 5 occasions extra lively than pure platinum.
Researchers from two SLAC-Stanford joint institutes, the Stanford Institute for Supplies and Vitality Sciences (SIMES) and the SUNCAT Heart for Interface Science and Catalysis, lately joined forces to research a catalyst that promotes energy-releasing reactions in gas cells.
They found that the catalyst, manufactured from ultrathin platinum layers grown on a single crystal of rhodium, would work higher and last more if its construction – in addition to its composition – was rigorously engineered.
Steady, extremely lively catalysts are notably wanted in gas cells, which might energy electrical autos with out the vary limitations of present batteries. However the catalysts are sometimes manufactured from scarce and costly supplies like platinum. Makes an attempt to engineer such catalysts have failed, nonetheless, as a result of essentially the most lively catalysts usually are not steady sufficient, and essentially the most steady catalysts aren’t lively sufficient.
The SIMES crew, led by Affiliate Employees Scientist Daniel Friebel, studied two very totally different platinum-rhodium nanostructures: one with platinum deposited on the rhodium crystal in a single, atom-thick layer, and the opposite with the identical quantity of platinum forming thicker islands with naked rhodium in between. They used the high-resolution X-ray spectrometer on the Stanford Synchrotron Radiation Lightsource’s Beam Line 6-2 to look at the floor chemistry that determines the catalytic exercise of each buildings.
The 2 samples confirmed markedly totally different habits: The platinum islands have been significantly better at grabbing and holding oxygen atoms than the platinum monolayer, which captured nearly no oxygen on its floor. In gas cells, atomic oxygen is the important thing middleman between bond-breaking and bond-making chemical reactions on a gas cell’s cathode, the place oxygen molecules, current-carrying electrons and protons which have been generated from hydrogen on the gas cell’s anode are reworked into water.
How strongly oxygen atoms are held by the catalyst is an important consideration when figuring out its efficacy, stated Friebel. “If the oxygen is simply too weakly hooked up to the catalyst, the preliminary bond-breaking by no means will get going. If, nonetheless, oxygen will get caught, it should throttle the bond-making that’s wanted to finish the response.”
Venkat Viswanathan, a graduate pupil at SUNCAT, was capable of clarify the SIMES outcomes utilizing a theoretical instrument known as density purposeful idea. For every platinum floor atom he discovered a easy description of its capacity to seize oxygen, which is determined by what number of platinum and rhodium atoms are in its fast neighborhood. Typically, platinum atoms with fewer neighboring steel atoms can bind oxygen extra strongly, however the place a neighbor atom exists, one other platinum atom is most well-liked. A rhodium neighbor spoils platinum’s urge for food for oxygen greater than a platinum neighbor.
This interplay between platinum and rhodium is why the thicker platinum islands bind oxygen extra strongly than the atom-thick platinum layer, however nonetheless extra weakly than pure platinum.
Researchers have been additionally capable of establish essentially the most lively websites on the platinum islands and predict that an optimized platinum-rhodium nanostructure may very well be as much as 5 occasions extra lively than pure platinum. Furthermore, such a construction is predicted to withstand degradation significantly better than platinum-nickel or platinum-cobalt catalysts with comparable exercise, thus fulfilling necessities for each excessive exercise and stability.
Though rhodium, like platinum, is simply too costly to make use of as a catalyst, the information gained from these research permits novel approaches to cheap catalyst design.
The SIMES-SUNCAT analysis appeared within the Journal of the American Chemical Society.
Picture: Daniel Freibel, et.al.