- Adam Rondinone, Center for Nanophase Materials Science, Oak Ridge, TN
The arrangement of active sites on a nanostructured catalyst can yield new ways to influence complex reaction mechanisms. The Center for Nanophase Materials Sciences has developed a textured carbon comprised of 50-80nm graphene spikes with ~5% nitrogen dopants for electrochemical catalysis. Two reactions for this electrocatalyst will be discussed: first, when co-doped with ~50 nm copper nanoparticles, the electrocatalyst converts CO2 to ethanol with high Faradaic efficiency (63% at -1.2V vs reversible hydrogen electrode (RHE)) and high selectivity (84%) in aqueous bicarbonate and at ambient temperature and pressure. Electrochemical analysis and density functional theory calculations suggest a mechanism in which active sites on the Cu nanoparticles and the carbon nanospikes work in tandem to control the electrochemical reduction of carbon monoxide dimer to alcohol.
Second, the sharp tips of the nanospikes, which typically reach a radius of ~1 nm, achieve very high electric fields over a large number of active sites. When coupled to the proper electrolyte, and without a metal co-catalyst, the carbon nanospikes are active for nitrogen electroreduction to ammonia with an average Faradaic efficiency of 12.5% at –1.19 V vs RHE. Theoretical calculations and modeling of the tip-enhanced field indicate an electric field that exceeds 10 V/nm within the Stern layer, a field strength high enough to alter the energy of the lowest unoccupied molecular orbital of dissolved N2 thereby allowing electron injection into the molecule. The reaction rate is also dependent on the counterion type, suggesting a role in increasing N2 concentration within the Stern layer.
Refreshments served at 9:30 am.