This dissertation the syntheses of Pt-based binary and ternary alloy electrocatalysts using the transition metals of Co and Ni are presented. These electrocatalysts were synthesised by an impregnation-reduction procedure at high temperature whereby Pt supported on carbon, (Pt/C (40 percent), was impregnated with the various metal and mixtures thereof and reduced at high temperatures in a H2 atmosphere. The procedure was also designed in such a way so as to prevent the oxidation of the support material (carbon black) during the alloy formation. The resultant nanoparticles (9-12 nm) of Pt3Co/C, Pt3Ni/C and Pt3Co0.5Ni0.5/C were also subjected to a post treatment procedure by acid washing (denoted AW) to produce electrocatalysts of Pt3Co/C-AW, Pt3Ni/C-AW and Pt3Co0.5Ni0.5/C-AW to study the effect of acid treatment on these electrocatalysts. The synthesised electrocatalysts were then characterised by a number of physical and electrochemical techniques and compared to that of commercial Pt/C (Pt/C-JM, HiSpec 4000) as well as Pt/C catalysts (Pt/C-900 and Pt/C-900-AW) treated under the same conditions used for the alloy synthesis. The electrocatalysts were then used to fabricate MEAs that were loaded into commercial single test cells and characterised by means of polarisation curves and Electrochemical Impedance Spectroscopy (EIS). The extensive physical characterisation included Powder X-Ray Diffraction (PXRD) analysis, Transmission Electron Microscopy (TEM), elemental analysis by Energy Dispersive Spectroscopy (EDS) and metal loading by Thermo-Gravimetric Analysis (TGA). These studies showed that Pt-based alloy electrocatalysts were successfully synthesised with particle sizes ranging from 9 - 12 nm, within their respective atomic ratios and whereby no significant loss of carbon support occurred. This indicated that significant sintering or electrocatalyst particles occurred when compared to that of the starting Pt/C catalyst (3 – 4 nm). From the combined results of the physical characterisation procedures, it was also shown that leaching as a result of acid washing was catalyst dependent with Ni containing catalysts showing a significant degree of leaching compared to that of Co containing catalysts. Electrochemical characterisation in terms of Electrochemical Active Surface Area (ECSA) by Cyclic Voltammetry (CV) and ORR activity by Rotating Disc Electrode (RDE) analysis revealed that a significant decrease in the ECSA resulted from the increase in particle size and this had a major influence on the ORR activity. Furthermore it was found that a significant improvement in the ORR activity was achieved by the synthesis of Pt-based alloys. It was also found that catalytic properties of the acid washed electrocatalysts were substantially different from that of non-acid washed electrocatalysts. The experimental data confirmed that it was possibly to achieve better catalytic performance as compared to that of Pt/C at a lower material cost when Pt is alloyed with base transition metals. The trend observed from the ORR activity studies by RDE was successfully repeated in the in-situ fuel cell testing in terms of mass activity of the electrocatalysts. Of the electrocatalysts studied under „real‟ fuel cell conditions Pt/C-JM had the best performance compared to the others, with the ternary Pt3Co0.5Ni0.5/C showing better catalytic performance compared to the Pt3Co/C electrocatalyst. This was found to be due to a higher charge transfer resistance observed in Pt3Co/C as compared to that of Pt3Co0.5Ni0.5/C which was similar than that of the commercial Pt/C-JM catalyst with both Pt3Co/C and Pt3Co0.5Ni0.5/C-AW having similar but higher ohmic resistances than that of Pt/C-JM as determined by electrochemical impedance spectroscopy. The results showed that a great potential exist to improve the catalytic performance of low temperature PEM fuel electrocatalysts at a reduced cost as compared to that of pure Pt provided a method of controlling the particle size was established.

Electrochemical promotion (EP) is a new way of controlling catalytic performance. It is implemented by depositing porous thin film metal catalysts on solid electrolyte supports where they act as both a catalyst and a working electrode of an electrochemical cell. The technique entails electrochemical pumping of ions from the solid electrolyte to the surface of the catalytically active metal film with which it is in contact. In short, controlling the potential difference of the electrochemical cell controls the coverage of promoters on the catalyst while a catalytic reaction is taken place. Thus, it provides a unique method for studying promotion in heterogeneous catalysis. My research has focused on elucidating the phenomena that underlie the EP effect. The resulting advances in fundamental understanding have been used to exploit EP as a tool to study alkali promotion in new applications in heterogeneous catalysis and to diversify the catalytic chemistry that can be addressed by EP. Thus, we have used conventional and spatially resolved in situ photoelectron spectroscopic data to demonstrate that EP of thin film metal catalysts deposited on solid electrolyte supports is the result of the spillover phenomena at the three phase boundary between the electrolyte, the catalyst and the gas phase. Ions from the electrolyte are discharged at the catalyst/ electrolyte interface and migrate to cover the catalyst surface whose properties are thereby strongly altered. This is the first time that such advanced spectroscopic techniques have been brought to bear on this fascinating and complex problem. Reactor measurements along with post-reaction photoelectron spectroscopies were used in order to: (i) establish the mechanism of reaction, (ii) determine the mode of promoter action and (iii) identify the chemical state of the promoter phase, in the Na-promoted catalytic control of toxic emissions. Very large increases both in activity and in selectivity of the catalysts were achieved and point the way towards further developments and possible applications. Finally, the use of EP as a mechanistic probe in surface catalysed polymerisation reactions has been demonstrated for the first time, broadening the range of utility of the extraordinary phenomenon of EP.

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate in the same cell was investigated. The alkaline hydrogen peroxide was obtained by the electroreduction of oxygen in NaOH on a fixed carbon bed while the chlorate was obtained by the reaction of anodic electrogenerated hypochlorite and hypochlorous acid in an external reactor. An anion membrane, protected on the anode side with an asbestos diaphragm was used as the separator between the two chambers of the cell. The effects of superficial current density (1.2 - 2.4 kA m⁻²), sodium hydroxide concentration (0.5 - 2.0 M) and catholyte flow (0.1 x 10⁻⁶ - 0.5 x 10⁻⁶ m³ s⁻¹) on the chlorate and peroxide current efficiencies were measured. The effect of peroxy to hydroxy mole ratio on the chlorate current efficiency was measured too. The cell was operated at fixed anolyte flow of 2.0 x 10⁻⁶ m³ s⁻¹, inlet and outlet temperatures of 27/33°C (anode side), 20/29°C (cathode side), cell voltages of 3.0 - 4.2 V (current density of 1.2 - 2.4 kA -m⁻²) and a fixed temperature of 70°C in the anolyte tank. Depending on the conditions, alkaline peroxide solution and sodium chlorate were cogenerated at peroxide current efficiency between 20% and 86%, chlorate current efficiency between 51.0% and 80.6% and peroxide concentration ranging from 0.069 M to 0.80 M. The cogeneration of the two chemicals was carried out at both concentrated (2.4 - 2.8 M) and dilute (0 - 0.5 M) chlorate solutions. A relative improvement on the current efficiencies at concentrated chlorate was observed. A chloride balance indicated negligible chloride loss to the catholyte. The results are interpreted in terms of the electrochemical and chemical kinetics and the hydrodynamics of the cell . / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The interaction between Pt and its carbon support was investigated by a model electrochemical system. This entailed aggressively oxidising a two-dimensional carbon substrate, i.e. highly orientated pyrolytic graphite (HOPG) and mirror finish graphite (MFG) quartz crystal, to incorporate oxygen terminated groups into the graphitic matrix. This study focusses on potential cycling to determine the mobility of Pt across these carbon surfaces and the effect of the Pt anchoring to carbon on the electrocatalyst durability. This work incorporates both a conventional three electrode electrochemical setup and the use of the electrochemical quartz crystal nano-balance (EQCN). The objectives of this study were to better understand the Pt mobility across the carbon substrate surface and to gain insight into the solid-liquid interface of Pt dissolution due to potential cycling. Initial results on HOPG as discussed in chapter 2, indicated minimal Pt dissolution of between 13% and 15% of total electrochemical active surface area loss. These results, however, did not provide adequate evidence to conclusively determine the extent of Pt mobility on the carbon surface and the effect of oxygen terminated groups in hindering Pt dissolution. In order to gain a more thorough understanding of the Pt dissolution processes, the use of the EQCN technique was utilised. Firstly, it was shown that the mirror finished graphite quartz crystals used in the EQCN technique, are qualitatively comparable to the electrochemical measurements recorded with the HOPG samples. Secondly, potential cycling under the same conditions as HOPG produced similar electrochemical results. The frequency response curves from the EQCN yielded the most promising results. This study showed, qualitatively, that the surface of Pt is non-monotonic, and that the surface charge changes with increased potential cycling. Pt/MFG-A had consistent frequency responses over the entire potential range during Pt dissolution, thus, with the above understanding of surface charge, it is concluded that acid treated carbon substrates show a stronger affinity for Pt anchoring.

Miniaturization, integration and intelligence are the developing trends for sensor,especially for biosensors. The development of microelectronics technology is a powerful engine to full this objective. It is well known that the microelectronic fabrication process in proven technology for fabrication of integrated circuits. Advances in the field of micro-electronics and micro-mechanical devices combined with medical science have led to the development of numerous analytical devices in monitoring of a wide range of analytes. The unique properties of nanoscale materials offer excellent prospects for interfacing biological recognition events with electronic signal transduction and for designing a new generation of bio-electronic devices exhibiting novel functions. Biosensor development has the potential to meet the need for rapid, sensitive, and specic detection of pathogenic bacteria from natural sources. This work focuses on development of one such electrochemical biosensor platform and discusses dierent aspects related to the design of biosensor and biodetection systems. A new transducer for bio sensor applications based on 3-dimensional, comb structured interdigitated electrode arrays was chosen mainly for two reasons. Firstly, this geometry allows the monitoring of both resistivity and dielectric constant of solution, thus making interdigitated electrodes more versatile tools than other kind of transducers. Second, they present short electric eld penetration depths, which make them more sensitive to changes occurring close to their surface (20 - 100 nm above the surface). This fact enables the monitoring of local changes in the vicinity of interest. Binding of analyte molecules to the chemically modied transducer surface induces important changes in the conductivity between the electrodes. Interdigitated electrodes have been employed to detect the presence of Anti-Transglutaminase (TG) antibodies, that are established biomarkers for Celiac disease which is due to gluten allergy. The biosensor was optimized for specific and sensitive detection of this biomarker. The sensor showed a sensitivity down to picomolar(pM) concentration of the biomarker. Gold nanoparticles were further used for signal enhancement so as to bring the sensor performance closer to Enzyme linked immunosorbant assay (ELISA).

Indiana University-Purdue University Indianapolis (IUPUI) / For the past decade, many microfluidic paper-based analytical devices have been developed and used in different research fields. These devices are low-cost, portable, flexible, sterilizable, disposable, and easy to manufacture. The microfluidic paper-based analytical devices offer good alternatives to measurements and assays commonly performed in laboratories for analytical and clinical purposes, especially in diagnostics. In this work, we developed an electrochemical paper-based pH sensor. The determination of pH is essential in applications in areas as diverse as in the food industry, agriculture, health care or water treatment. The method presented in this work is an electroanalytical method that involves quantification of pH using stencil-painted graphite electrodes. Preliminary tests showed that pH can be determined on paper-based devices, thus indicating the presence of electroactive elements sensitive to pH on the surface of our electrodes (Chapter 4). Chemical modification of the electrode by adsorption with sodium carbonate and modification of the surface of the electrode was accomplished via: oxygen (ambient air) plasma treatment and pure oxygen plasma treatment. These treatments were to attempt to improve the definition of redox peaks on the CVs (Chapter 5). The changes made to the design of the paper-based device and the addition of a conditioning step improved the definition of the redox peaks on the CVs and increased the pH-sensing ability of our method (Chapter 6). The pH-sensing ability of our method was evaluated by testing solutions over a wide pH range. Adding sodium chloride to samples adjust the solution for accurate pH determination. The pH was successfully measured for solutions with values ranging from 1 to 13 and for artificial saliva samples prepared with pH values in the cavity-prone range (Chapter 7). This work offers a method that uses electroactive elements sensitive to pH on the surface of the PBD electrodes for pH-sensing.

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No description available.

On-site sensing systems provide fast and timely information about a myriad of applications ranging from chemical and biological to physical phenomena in the environment or the human body. Such systems are embedded in our daily life for detecting pollutants, monitoring health, and diagnosing diseases. Especially in the field of health care, the development of portable and affordable diagnosing systems, also known as point-of-care (PoC) devices, is a major challenge. Moreover, to this day, systems for therapeutic drug monitoring (TDM) have remained bulky and highly expensive, mostly due to the need for exceptionally precise, rapid, and highly accurate real-time on-site measurements. This dissertation focuses on the design, development, and implementation of miniaturized PoC devices for achieving high sensitivity, selectivity, and reliability through a combination of hardware and software strategies at the edge. The first part of the dissertation introduces the design of single and multi-channel electrochemical readout platforms with a high voltage range, fast scan rates, and with nano-ampere resolution, covering a broad range of electrochemical excitation techniques. These platforms were paired with electrochemical-based sensors to detect SARS‑CoV‑2, bisphenol A, and ascorbic acid. The low power feature of the proposed platforms is demonstrated by powering the complete detection system with energy harvested from natural and artificial ambient light. The second part of the dissertation introduces the design and development of a miniaturized wearable device with a pico-ampere resolution, high-speed electrochemical frequency interface, and highly stable sensing circuitry. A complete in-vivo system is demonstrated for long-term (>4 hours) measurement, wherein molecules are detected and monitored directly from a probe inserted in the subcutaneous abdomen region of a Sprague-Dawley rat. A solution for sensor drift due to biofouling and interference is demonstrated thought to the integration with real-time processing software. Furthermore, integrating the aforementioned platforms with highly reduced dense neural network models is demonstrated to increase the robustness of the sensors, allowing the detection of contaminants in complex samples, improving the sensor selectivity, and providing timely diagnoses in-situ.

Ultramicroelectrodes (UMEs) have gained considerable attention over the few past decades due to the important roles they play in electrochemical studies. Electrodes with dimension less than 25 mm can generally be classified as UMEs. These electrodes exhibit enhanced electrochemical properties as their dimensions get smaller hence making nanoelectrode (production of electrodes with limiting dimensions less than 100 nm) a continuing area of interest in research. Nanometer size electrodes have advantages of high sensitivity which enables them to be used in fields such as single particle characterization and single cell analysis, and fast electron and mass transport which permits use for studying short-lived and transient electrochemical reactions such as those involved in neurochemistry. Nanoelectrodes can be fabricated via a few different strategies which include but are not limited to electrochemically etching a thin metal wire down to a cone shape or flame-etching a carbon fiber, and chemical vapor deposition of carbon in nanopipette. This work seeks to employ the use of the laser-assisted pulling method to fabricate carbon fiber electrodes sealed in glass capillary tubes. Effects of various pre- and post- treatment techniques on electrode size and stability are explored. Key words: Electrodes, Electrochemical, carbon fiber.