SUBJECT: Ph.D. Proposal Presentation
BY: Mohammadreza Nazemi
TIME: Monday, April 29, 2019, 1:30 p.m.
PLACE: MoSE, 1226
TITLE: Investigation of (Photo) Electrocatalytic Conversion of Dinitrogen to Ammonia Using Hybrid Plasmonic Nanostructures
COMMITTEE: Dr. Mostafa El-Sayed, Co-Chair (Chem)
Dr. Todd Sulchek, Co-Chair (ME)
Dr. Younan Xia (Chem)
Dr. Paul Kohl (ChBE)
Dr. Ting Zhu (ME)
Dr. Matthew McDowell (ME)


As the cost of renewably derived (e.g., solar and wind) electricity continues to decrease given the rapid progress in technology and economies of scale, there is a growing interest for ammonia electrosynthesis from nitrogen and water under ambient conditions. This approach can provide an alternative pathway to the Haber-Bosch process for an energy-efficient, clean, and distributed ammonia synthesis. To date, most studies have shown low electrocatalytic efficiency for ammonia production mainly due to the high energy required for N≡N cleavage and to the competition with the hydrogen evolution reaction (HER). Gold (Au) has been known as one of the best catalysts for the electrochemical nitrogen reduction reaction (NRR) through an associative mechanism where the breaking of the triple bond of N2 and the hydrogenation of the N atoms occur simultaneously.

For the preliminary studies, we showed that the nanoscale confinement of N2 near the electrocatalyst’s surface enhances the conversion of N2 to NH3 remarkably using hollow Au nanocages (AuHNCs). This increases the residence time of N2 molecules on the nanoparticle inner surface, which facilitates the conversion of N2 to NH3. The interdependency between the pore size/density, the localized surface plasmon resonance (LSPR) peak position, the silver content in the cavity, and the total surface area of hollow nanoparticles was investigated for further optimization of hollow plasmonic nanocatalysts in electrochemical NRRs, leading to empirical structure-activity trends for ammonia synthesis by an array of hollow nanocatalysts with tunable plasmonic properties.

It has been demonstrated that electrochemical N2 reduction for NH3 production using Pd nanoparticles requires lower overpotential and results in higher electrocatalytic efficiency for NH3 compared with Au nanoparticles. The central hypothesis is the incorporation of the second metal in double-shell hollow nanoparticles can further enhance the ammonia yield and Faradaic efficiency. We propose to synthesize hollow Pd nanocages and Au-Pd double shell nanocages and determine their electrocatalytic activities for NH3 production. The results are further complemented by in-situ surface-enhanced Raman spectroscopy (SERS) and ex-situ 1H NMR to monitor the trace amount of NH3 over the course of the experiment and elucidate the possible differences in the reaction mechanism for electrosynthesis of NH3 on Pd and Au surfaces.