Real-time ammonia quantification in electrochemical nitrogen reduction
File(s)
Author(s)
Khobnya, Artem
Type
Thesis
Abstract
Ammonia synthesis is a cornerstone of global agriculture, yet the conventional Haber–Bosch process relies on high temperatures and pressures, operates at large centralised facilities, and is a major contributor to global CO₂ emissions. Electrochemical approaches, particularly lithium-mediated nitrogen reduction, offer a promising and potentially sustainable alternative, enabling ammonia production under ambient conditions with decentralised, renewable-powered operation. However, despite recent advances, the lithium-mediated system remains limited by key challenges, including electrolyte instability, parasitic side reactions, and low ammonia yields, all of which hinder its commercial viability. This thesis aims to enhance the accuracy and consistency of ammonia quantification techniques, specifically UV–Vis colorimetry and electrochemistry–mass spectrometry (ECMS), and apply them to investigate the mechanisms of electrolyte degradation and acidification, as well as their impact on system performance and stability. This work demonstrates that conventional calibration curves are unsuitable for colorimetric detection of ammonia in lithium-mediated electrolytes due to large variations in calibration curve gradients. Additionally, real-time detection of gas-phase ammonia using ECMS was found to be highly sensitive to electrolyte acidity, which primarily arises from anodic solvent oxidation. This work establishes a rigorous methodology for real-time ammonia quantification using ECMS, addressing a critical gap in literature for standardisation and technique development. Through this framework, the project provides new mechanistic insight into electrolyte decomposition processes in lithium-mediated nitrogen reduction, highlighting the role of solvent breakdown and gas evolution. Furthermore, it elucidates how electrolyte acidification, driven by anodic reactions, affects ammonia yield & distribution and system stability. Together, these contributions advance the analytical and mechanistic understanding of the lithium-mediated system and inform the design of more robust, efficient electrochemical ammonia synthesis platforms.
Version
Open Access
Date Issued
2025-04-02
Date Awarded
01/06/2025
License URL
Advisor
Stephens, Ifan
Ryan, Mary
Titirici, Magda
Davies, Bethan
Winiwarter, Anna
Publisher Department
Department of Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)