Electrocatalytic Oxygen and Nitrate Reduction Reactions Using Cu-Based Electrodes
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Authors
Mondol, Profulla
Issue Date
2024
Type
Dissertation
Language
Keywords
Current Density , Electrochemistry , Faradaic Efficiency , Nitrate Reduction Reaction , Oxygen Reduction Reaction , Selectivity
Alternative Title
Abstract
There has been a resurgence of interest in electrocatalysis because interesting chemistry frequently happens at the electrochemical interface between electrodes and electrolytes that are relevant to energy conversion processes. The focus of this dissertation is on the electrocatalytic reduction of oxygen (O 2 ) and nitrate (NO 3 -) to water (H 2 O) and ammonia (NH 3 ), respectively, using molecular- and surface-based Cu electrocatalysts. The oxygen reduction reaction (ORR) is important due to its application in the cathode of fuel cells. The nitrate reduction reaction (NRR) can be used to generate NH 3 as an alternative to the traditional Haber-Bosch process. The first part (chapter 1) of this thesis discusses the importance of electrocatalysis in the field of energy conversion and storage technologies. The second part of this thesis (chapters 2 and 3) focusses on the ORR. Due to the high reduction potential and slow kinetics of the ORR, fuel cells are not being fully commercialized. This part discusses efforts to understand the ORR reaction mechanism and develop new ORR electrocatalysts using Cu tripeptide complexes. Laccase is a well-known Cu-containing ORR enzyme with a low overpotential, but it is only stable in a narrow pH range. Here, we synthesized Cu-tripeptide complexes and investigated their ORR activities in a wide pH range from 2.5 to 10 and determined the effect of peptide aggregation and Cu-peptide binding constant on ORR performance. In the last parts of chapter 2 and 3, we discuss some future prospects of the ORR using non-precious Cu-based electrocatalysts. The third part (chapters 4 and 5) of this thesis discusses the NRR. Here, we fabricated Nafion-modified metals electrodes and tested the activity of theses electrodes for the NRR to produce NH 3 electrochemically. We interrogate the mechanism of NH 3 production from NO 3 - reduction using electrochemical experiments, surface-enhanced Raman spectroscopy, and density functional theory calculations. We also explore this NO 3 - reduction reaction for Nafion-modified electrodeposited Cu electrodes to increase the current density and NH 3 Faradaic efficiency. Lastly, we discuss the future prospect of this electrocatalytic NRR using different fluoropolymers instead of Nafion and propose methods to increase the durability of the catalysts.