Development of Efficient Nanostructured Electrocatalyst for the Synthesis of Ammonia as Clean Energy Alternative from Atmospheric Nitrogen Fixation

Abstract

Ammonia (NH3) is a versatile chemical that is critical to agriculture and various industries. Today, ammonia is further regarded as one of the most promising carbon-free energy carriers in the net-zero hydrogen economy as well as potential green fuel. Conventionally, the energy-intensive Haber Bosch process has been the major route for producing ammonia by the thermocatalytic blending of nitrogen and hydrogen, but its enormous greenhouse gas signature has generated concerns about its sustainability. The electrochemical nitrogen reduction reaction (e-NRR) is an attractive alternative roadmap to achieving clean and sustainable ammonia production under ambient conditions that can be powered by renewable energy sources. Accordingly, the development of efficient electrocatalysts for e-NRR is essential to the realization of this emerging technology. Among various types of promising materials, earth-abundant Fe element presents a competitive edge for developing high-performance N2 reduction catalysts owing to its intrinsic activity, low cost, and ease of modification with other elements to form compounds with distinguished catalytic activity.
This dissertation focuses on the development of novel Fe nanomaterials with attractive features for e-NRR. The dissertation begins by establishing the state of the art in e-NRR research in chapters 1 and 2, highlighting its chemistry, fundamentals, mechanisms, and experimental procedures. A detailed review of state-of-the-art Fe-based catalysts was conducted encompassing various classes of nanomaterials including oxides, bimetallic catalysts, single atom catalysts (SACs), metal organic frameworks (MOFs), and chalcogenides, providing critical insight into research trends and gaps over the last decade. Subsequently, the research work focused on the development of efficient Fe catalysts with enhanced catalytic activity towards e-NRR. In chapter 4, bioinspired FeVO4 nanoparticles (NPs) were synthesized and supported on Fe foam for catalytic e-NRR. The bimetallic catalyst exhibited favorable synergistic interactions between Fe and V and a coupling interaction with Fe support which enabled faster electron donation and charge transfer for superior catalysis. The catalyst achieved a significant catalytic performance, delivering an impressive NH3 yield of 22.5 µg-1 mg-1 and Faradaic Efficiency (FE) of 20.74% at –0.2 versus reversible hydrogen electrode (VRHE) in 0.1 M Na2SO4. Chapter 5 presented a unique pyrochlore FeF3/C catalyst fabricated from a two-step synthetic protocol, characterized and evaluated for catalytic activity. The pyrochlore FeF3/C nanocomposite combined key structural properties including a distinct open framework, carbon coating, and a large surface area that conferred improved electronic conductivity, abundant active sites, enhanced electrolyte diffusion, and favorable interfacial interactions for optimal electrocatalytic activity. Electrocatalytic results showed that the FeF3/C electrocatalyst achieved the highest ammonia yield of 15.75 µg h-1 mg-1 along with FE of 3.9% at –0.4 VRHE. The highest FE of 8.63% was attained at –0.1 VRHE with a total yield rate of 5.34 µg h-1 mg-1 . In chapter 6, a novel nanocomposite of fluorine doped β-FeOOH nanoparticles on a carbon matrix was fabricated via a facile one-pot synthetic protocol. The catalyst featured dual attributes of support anchoring and heteroatom doping to enhance surface area and boost surface N2 adsorption, respectively. An outstanding electrochemical performance was recorded on the F-β-FeOOH/C electrocatalyst with an optimal ammonia yield of 11.36 µg h-1 mg-1 and FE of 9.32% at –0.2 VRHE. This research contributes to the quest for rational design of effective e-NRR catalysts and promotes the development of efficient, low-cost Fe catalysts with significant catalytic activity for the electrochemical nitrogen fixation.

Date of Award	2025
Original language	American English
Supervisor	Ahsan Ul Haq Qurashi (Supervisor)