Electrochemistry Of Bubbles: Developing New Sensors, Promoting Gas Evolution Reactions, And Extraction Of Rare Earth Elements
Open Access Dissertation
Date of Award
This dissertation presents new analytical, electrocatalysis, and separation strategies that utilize bubble behaviors in different electrochemical systems. The first part of this dissertation focuses on the method development for PFAS preconcentration and detection. First, we present the bubble-nucleation-based electrochemical method for the selective and sensitive detection of surfactants. Our method utilizes the high surface activity of surfactant analytes to affect the electrochemical bubble nucleation and then transduces the change in nucleation condition to an electrochemical signal for determining the surfactant concentration. Using this method, we demonstrate the quantitation of perfluorinated surfactants in water, a group of emerging environmental contaminants, with a remarkable limit of detection (LOD) down to 30 μg/L and a linear dynamic range of over 3 orders of magnitude. The experimental results agree with our theoretical model derived from classical nucleation theory. Our method also exhibits an exceptional specificity for the surfactant analytes even in the presence of 1000-fold excess of nonsurfactant interference. Next, we present a highly efficient method that uses anodically generated shrinking gas bubbles to preconcentrate PFAS via aerosol formation, achieving ~1400-fold enrichment of PFOS and PFOA—the two most common PFAS—in 20 min. This new method improves the enrichment factor by 15% to 105% relative to the previous method that uses cathodically generated H2 bubbles. The shrinking gas bubbles are in situ electrogenerated by oxidizing water in an NH4HCO3 solution. H+ produced by water oxidation reacts with HCO3- to generate CO2 gas, forming gas bubbles containing a mixture of O2 and CO2. Due to the high solubility of CO2 in aqueous solutions, the CO2/O2 bubbles start shrinking when they leave the electrode surface region. A mechanistic study reveals two reasons for the improvement: (1) shrinking bubbles increase the enrichment rate, and (2) the attractive interactions between the positively charged anode and negatively charged PFAS provides high enrichment at zero bubble path length. Based on this preconcentration method, we demonstrate the detection of ≥70 ng/L PFOA and PFOS in water in ~20 min by coupling it with our bubble-nucleation-based detection method, fulfilling the need of the U.S. Environmental Protection Agency. The second part of the dissertation describes the development of a facile strategy to precisely control the dissolved-gas concentration at the electrode/gas/electrolyte interface for enhanced HER and HzOR. With PFOS modulation, a lowered dissolved-hydrogen concentration at the catalytic interface and sufficient exposure of the active surface area can be achieved. Accordingly, the PFOS-modulated Pt possesses remarkable HER performance relative to pure Pt. With CFPS modulation, the interfacial dissolved-nitrogen concentration was effectively lowered while CFPS still ensured a sufficient exposure of the active sites during HzOR. As a result, relative to pure Pt, the CFPSmodulated Pt exhibited a 2.1-fold higher current density and a lower overpotential for HzOR. This work provides a convenient approach to realizing high-performance electrocatalysis based on precisely controlling the dissolved-gas concentration at the catalytic interface. The last part of the dissertation describes a proof-of-concept design for extracting Gd from hospital wastewater effluents. We achieved a Gd extraction efficiency of 75% from water samples containing ppb-level Gd using electrochemically generated bursting bubble aerosol with the help of an amphiphilic Gd-binding ligand. We also successfully separated Gd and its ligand using an origami paper-based electrophoresis device. This environmental-friendly extraction process opens a new avenue to fulfill the Gd demand in the USA.
Ranaweera, Ruchiranga R., "Electrochemistry Of Bubbles: Developing New Sensors, Promoting Gas Evolution Reactions, And Extraction Of Rare Earth Elements" (2022). Wayne State University Dissertations. 3692.