Probing functionalized interfaces for carbon capture using spectroelectrochemistry

This dissertation has advanced both the mechanistic understanding and methodological capabilities necessary for studying electrochemically mediated carbon capture (EMCC) at functionalized gold and carbon electrode interfaces using electrochemical attenuated total reflectance surface-enhanced infrared absorption spectroscopy (EC-ATR-SEIRAS). The motivation arises from the urgent global need to decarbonize and sequester already-emitted CO₂ from the atmosphere to meet the targets of the Paris Climate Agreement. While thermochemical carbon capture approaches (e.g., amine scrubbing, alkaline sorbents) have been dominant, their inherent inefficiencies, high regeneration costs, and limited scalability make them unsuitable for widespread deployment, particularly for direct air capture (DAC). EMCC is a promising alternative due to its ability to operate under ambient conditions with theoretically lower energy costs. In Chapter 2, a systematic investigation of the electrochemical stability of aromatic self-assembled monolayers (SAMs) on gold across a range of solvents and pH conditions was accomplished. The stable potential windows (SPWs) for these monolayers were found to be highly dependent on both the electrolyte composition and the surface chemistry of the interface. In aqueous media, the boundaries of the SPW were primarily defined by reductive desorption at negative potentials and oxidative desorption at positive potentials which in turn determined by the pH of the electrolyte. In non-aqueous systems, desorption occurred more gradually and was less discrete, with solvent polarity playing a dominant role. A clear trend was observed that the SPW increased as the polarity index of the solvents decreased. These results highlight the importance of selecting appropriate solvent and potential conditions for maintaining the structural integrity of functionalized surfaces in electrochemical applications. In Chapter 3, a graphene-on-gold hybrid electrode was developed and validated as a platform that enables EC-ATR-SEIRAS measurements at graphitic carbon interfaces. This innovation addresses a major limitation in current SEIRAS studies, which have largely focused on plasmonic metals like Au, Cu, or Ag. The graphene-on-gold substrate allows for the direct observation of molecular-level changes at carbon surfaces, which are highly relevant to scalable EMCC systems. The utility of this platform was demonstrated by monitoring the real-time electrografting of diazonium-functionalized molecules such as 4-amino-2,2,6,6-tetramethyl-1-piperidine N-oxyl and 4-nitrobenzene diazonium. These experiments showcased well-resolved vibrational features and the electrochemical responses corresponding to the grafted species, thereby validating the platform. This work lays a foundation for using this platform in a wide range of electrochemical studies involving functionalized carbon materials. In Chapter 4, the graphene-on-gold electrodes were used to track the real-time, reversible capture and release of carbon dioxide at electrodes modified with two RAO capture agents: anthraquinone (AQ) and a riboflavin-derived flavin motif (MFD). Using in situ EC-ATR-SEIRAS, the spectral responses of CO₂ capture was differentiated from those of the CO₂ reduction reaction (CO₂RR). Under continuous polarization at reducing potentials, both AQ and MFD produced the CO₂RR byproducts, that masked the vibrational signatures of surface-bound CO₂ capture intermediates. In contrast, when the electrodes were reduced and then exposed to CO₂ under open-circuit conditions, distinct spectral features emerged consistent with the formation of surface-bound CO₂ adducts. This work highlights relevant considerations for performing CO2 capture studies under polarization, illuminates key surface intermediates, and demonstrates the ability to screen novel RAO capture agents using EC-SEIRAS on novel graphene-on-gold electrodes.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Siddiqui, Abdur-Rahman

Contributors dc:contributor

• Rodríguez-López, Joaquín
• Shen, Mei
• Kenis, Paul J. A.
• Murphy, Catherine J.

• Spectroelectrochemistry
• Atr-seiras
• Carbon
• Carbon Dioxide
• Carbon Capture
• Graphene
• Anthraquinone
• Riboflavin
• Co2 Reduction Reaction
• Self-assembled Monolayer
• Electrochemical Stability
• Non-aqueous
• Aromatic Thiols
• Adsorption
• Desorption
• Tempo
• 4-amino Tempo
• 4-nitrobenzene Diazonium
• Cyclic Voltammetry
• Electrografting
• Time-resolved

Statement dc:rights

• Copyright 2025 Abdur-Rahman Siddiqui

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129903

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129903