11/02/2026
By Marley O'Neil

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a doctoral dissertation defense by Snigdha Rajendra Rashinkar for “Optimizing Green Ammonia Production through Coupled Non-Thermal Plasma and Electrocatalysis: Experimental and Computational Studies.”

Defense Details

  • Date: Thursday, November 19, 2026
  • Time: 11 a.m. – 2 p.m.
  • Location: Perry 315

Committee

  • Advisor: Dr. Fuqiang Liu, Associate Chair, Professor, Mechanical and Industrial Engineering, UMass Lowell
  • Juan P. Trelles, Director, Professor, Mechanical and Industrial Engineering, UMass Lowell
  • Ertan Agar, Associate Professor, Mechanical and Industrial Engineering, UMass Lowell
  • KwokFan Chow, Associate Professor, Chemistry, UMass Lowell

Abstract

Ammonia is essential to global agriculture as the primary nitrogen fertilizer, and it is a promising carbon-free energy carrier. Its industrial production via the Haber-Bosch process, however, requires high temperature, high pressure and fossil-derived hydrogen. Plasma-electrochemical synthesis offers a carbon-free route to ammonia from nitrogen and water under ambient conditions, enabling decentralized, renewable-powered production of green ammonia. Realizing this potential requires understanding the coupling between gas-phase plasma chemistry, the plasma-liquid interface, and electrode surface processes.

This dissertation investigates plasma-electrocatalytic ammonia synthesis through complementary experimental and computational approaches. A plasma-driven H-cell was first designed, fabricated, and characterized under direct-current (DC) operation, establishing how applied voltage, catalyst selection, electrode composition (with PtIr as the primary working electrode), and electrolyte conditions determined ammonia yield and Faradaic efficiency. The study was then extended to alternating-current (AC) operation, which consistently outperformed DC. This advantage is explained by a depletion-versus-replenishment charge-transport framework, supported by electrochemical impedance spectroscopy, linear sweep voltammetry, and chronoamperometry.

Quantification of nitrate, nitrite, and ammonia concentrations across operating conditions further resolves the relationship between plasma-derived reactive nitrogen species and ammonia formation at the electrode. Comparative studies of electrolyte type and concentration, pH, voltage type and magnitude, catalyst type and composition, plasma type, purge-gas identity and humidification, and NOₓ speciation establish the mechanisms governing system performance.

A two-dimensional computational fluid dynamics model was also developed to investigate the coupled transport and reaction mechanisms governing plasma-assisted electrochemical ammonia synthesis. The model incorporates plasma-derived reactive nitrogen inputs, plasma-jet and N₂-purge-induced liquid convection, and effective electrochemical nitrogen-reduction pathways. Three complementary numerical studies systematically evaluated the factors controlling ammonia production. N₂-purge-induced convection dominated liquid-phase circulation, substantially enhancing nitrogen-precursor delivery to the electrode and increasing electrochemical ammonia production by approximately 19-fold compared with plasma-induced convection alone.

Increasing the plasma-derived nitrogen-precursor supply enhanced ammonia production, while N(III)-enriched conditions promoted greater electrochemical NH₄⁺ formation than nitrate-enriched conditions at the same nominal nitrogen input, although competing N₂O accumulation also increased. Activating electrode reduction increased the final mean NH₄⁺ concentration by approximately 60%, with electrochemical pathways contributing 37.6% of total modeled NH₄⁺ formation.

Collectively, the experimental and computational findings highlight the interconnected roles of electrolyte environment, plasma operation, liquid-phase convection, nitrogen-precursor availability and composition, and electrode-mediated conversion. The results provide a mechanistic basis for rationally designing green ammonia systems and suggest that improving precursor transport and electrochemical conversion can enhance reactor performance, while quantitative predictions remain dependent on effective kinetic assumptions and prescribed plasma-source conditions.