Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electro-Chemistry, 1917. / Includes bibliographical references (leaf 25). / by Frederick William Dodson. / B.S.

The experimental work discussed in this thesis examines the effect of voltammetry of nanoparticle arrays with a specific focus on the effect of nanoparticle size and surface coverage on the substrate electrode. These effects are investigated in relation to the reduction of hydrogen peroxide, 4-nitrophenol and the hydrogen evolution reaction. In each case, the experimental data obtained is subsequently fitted using numerical simulations to extract quantitative kinetic data. Distinct differences are noted between macro – and nano – scale. The reduction of H₂O₂ reveals the absence of autocatalysis at the nano – scale. Furthermore, peak potential shifts positively with surface coverage under Case 3 diffusion conditions. On the other hand, at essentially isolated particles (Case 1) E_p varies logarithmically with nanoparticle radius. By decreasing nanoparticle size, we promote convergent diffusion and enhance irreversibility of the process. The shift in E_p with surface coverage can be accounted for as the diffusion layers begin to overlap heavily, tending towards more macro – disk type behaviour. We also study the hydrogen evolution reaction at an array of AgNPs. By fitting of the experimental data with numerical simulations we demonstrate altered kinetics between the macro – and nano – scale. Voltammetry at AgNP – arrays also display dependence between surface coverage and current. We attribute this to increased electro – active surface area and decrease in irreversibility of the process, with increasing surface coverage. Numerical simulations are also used to fit experimental data obtained for the reduction of 4 – nitrophenol in acidic media. The AgNP – arrays exhibit significantly different electrode kinetics compared to a macro – disk. Examination of the data obtained for AgNP – arrays at two different acid concentrations implies the rate - determining step is likely the electron transfer process. We therefore infer a change in α the mechanism of the rate – determining step between macro – and nano – scale. An unusually low value of α at the NP – array may indicate that adsorption plays some role in the process. Furthermore, we discuss the size – dependent adsorption behaviour exhibited by silver nanoparticle arrays, such that small particles with diameters below ~ 50 nm do not display the typical underpotential deposition characteristics of corresponding bulk materials or larger nanoparticles. This phenomenon is reported for the deposition of heavy metals (thallium, lead and cadmium) at silver nanoparticle arrays. The stripping voltammetry of arrays of silver nanoparticles has also been investigated. The stripping peak potential is dependent on the degree of surface coverage. Modelling of this system has shown that a one – dimensional diffusion model is appropriate for high surface coverage; essentially it is experiencing planar diffusion. However, for an array of widely dispersed particles, the individual nanoparticle size and convergent diffusion begin to dominate behaviour. A detailed overview of the literature is first discussed, relating to the synthesis of a wide variety of metallic nanoparticles and their practical applications, such as the determination of pH using platinum nanoparticles as covered in Chapter 7. We also discuss the fundamental principles governing the voltammetric behaviour of nanoparticles.

Depuis de nombreuses années des chercheurs imitent le vivant afin d'obtenir des systèmes capables de s'adapter à des environnements de plus en plus complexes. Aujourd'hui aucune des technologies classiques n'est capable de rivaliser complètement avec le fonctionnement d'un muscle. L'objectif de ce travail est de synthétiser et d'intégrer une nouvelle génération d'actionneurs-capteurs à base de réseaux interpénétrés de polymères conducteurs dans des systèmes de perceptions biomimétiques. Nous avons tout d'abord réalisé la synthèse et la caractérisation d'une nouvelle matrice hôte à base de réseaux interprétés de polymères (RIP) combinant de bonnes propriétés mécaniques du caoutchouc nitrile (NBR) et de conductivités ioniques du poly (oxyde d'éthylène). Nous avons ensuite incorporé dans cette matrice hôte un polymère conducteur électronique, le poly (3,4-éthylènedioxythiophène), par polymérisation in situ. Nous avons caractérisé les effets de différents paramètres de synthèse sur la localisation et la morphologie du polymère conducteur au sein de la matrice. Puis nous avons caractérisé les propriétés d'actionneurs et de capteurs de ces matériaux électroactifs. Enfin nous avons réalisé l'intégration de ces matériaux dans deux prototypes de systèmes de perceptions biomimétiques, le premier tactile imitant les vibrisses du rat et le deuxième visuel imitant les muscles oculomoteurs. Finalement, nous concluons que les propriétés et performances de cette nouvelle génération d'actionneurs-capteurs permettent leurs intégrations dans des systèmes de perceptions spécifiques pouvant être utilisés sur un robot mobile. / For many years researchers mimic the living in order to obtain systems that can adapt to complex environments. Today no conventional technology is able to fully compete with the functioning of a muscle. The objective of this work is to synthesize and integrate a new generation of actuators and sensors based on interpenetrating polymer networks of conductive polymers in biomimetic perceptions systems. We first carried out the synthesis and characterization of a novel host matrix based on interpreted polymer networks (IPN) combining good mechanical properties of nitrile rubber (NBR) and ionic conductivities of poly(ethylene oxide ) (PEO). Then, We incorporated into this host matrix an electronically conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), by in situ polymerization. We characterized the effects of various synthesis parameters on the location and morphology of the electrically conductive polymer within the matrix. Then, we characterized the actuation and sensing properties of these électroactive materials. Finally, we completed the integration of these materials into two prototypes of biomimetic perceptions. The first one tactile is imitating and emulating tactile perception of the rat vibrissae. The second one visual is imitating the extraocular muscles. Finally, we conclude that properties and performances of this new generation of sensor-actuators allow their integration into specific perception system that can be used on a mobile robot.

This thesis develops diffusion models for modern electrochemical experiments involving the transport of particles to electrodes and adsorbing surfaces. In particular, the models are related to the 'impact' method where particles stochastically arrive at an electrode and detected electrochemically. The studies are carried out using numerical simulations and also analytical methods. Chapter 1 is introductory and outlines some fundamental concepts in mass transport and kinetics, and their relation to electrochemical measurements which are of importance for the reader. Chapter 2 describes the numerical methods which are used for electrochemical simulations. Chapter 3 focuses on a specific two dimensional simulation system and the development of a high performance voltammetry simulation. Chapters 4 and 5 study the stochastic impacts of particles at an electrode surface. In Chapter 4, a 'diffusion only' model is developed using a probabilistic study and random walk simulations in order to provide expressions that can be used in so-called `impact' experiments. In Chapter 5, the practical cases of microdisc and microwire electrodes are investigated. Expressions for the number of impacts are developed and the concept of the lower limit of detection in ultra-dilute solutions is introduced. Then, a comparison study between the microwire electrode and the microdisc electrode explores a geometrical effect and its implications for experimental setups. In Chapter 6, a numerical and analytical study is developed to examine the effect of hindered diffusion as a particle moves close to an adsorbing surface. The study identifies the conditions under which this hindered diffusion is signiffcant even in a non-confined space. The study shows that the domination of hindered diffusion is strongly dependant on the sizes of both the particle and the target. The study focuses on a variety of target shapes and allows the number of hits/impacts to be estimated in practical 'impact' experiments. Moreover, a drastic effect on the calculation of the mean first passage time is observed for a sub-micron sized target, showing the importance of this effect not only for electrochemistry but also in biological systems. Chapters 7 and 8 investigate the properties of an adsorbing insulating surface adjacent to an electrode. In Chapter 7, a numerical study of the effect of 'shielding' by the insulating sheath is carried out. The study examines the in uence of this effect on the magnitude of the current in chronoamperometry experiments. Chapter 8 explores the case of reversible adsorption on the insulating surface for voltammetric enhancement by pre-concentration on the sheath surface. The results identify the conditions under which enhancement of the voltammetric signal can be observed. Finally, Chapter 9 looks at geometrical effects on the current response of insulating particles modified with an electroactive surface layer. Numerical models are developed to model the diffusion of charge transfer between electro-active sites on a modified surface of insulating particles. The current-time responses are simulated for particles with the shape of a sphere, a cube/cuboid, and a cylinder on an electrode. The characteristic currenttime responses are calculated for the various shapes. The observations show that the model can be utilised in experiments to determine the coverage or the diffusion coeficient of charge dissipation on modified insulating particles and, in some situations to identify the particle shape.

Miniature electrochemical sensors can be produced by thick-film technology. The optimal properties of thick-film electrode system, the production technology optimization of thick-film sensors and the adjustment of optimal technological properties are main problems of sensor design. An area of working electrode and an electrode topology design is the important parts in design of electrode system optimization. The rules for optimization of electrode systems in classical electrochemistry exist. The design of standard thick-film electrode construction is limited (2-D construction, substrate dimensions, resolution, paste parameters …). Therefore rules for classical electrode systems cannot be used fully in this case and larger electrode area can be making by 3D structure only. One of resolutions is unconventional method. The increase of working electrode surface by unconventional method – ball and wire bonding is discussed in this work.

This thesis concerns the development and the study of Iron-based water oxidation catalysts (WOCs) and how to immobilize them onto the hydrophobic surface of a carbon paste electrode. In the introductory chapter a general background of the field of water splitting and this thesis is given. In the second chapter, experimental performance is described from synthesis to measurements of a complete complex-doped electrode. The third chapter deals with the results and the discussion of the performed experiments. In chapter four, a descriptive conclusion of the obtained data is held. / Det här arbetet berör studien och utvecklingen utav järnbaserade katalysatorer, speciellt framtagna för för delning utav vatten. Utöver detta undersöks även om dessa katalysatorer (WOCs) kan immobiliseras på den hydrofoba ytan hos elektroder gjorda på kol-pasta. I det inledande kapitlet ges en generell bakgrund till området som berör delning utav vatten. I det andra kapitlet presenteras det experimentella utförandet utav synteser samt elektrokemiska mätningar som berörts under arbetets gång i jakten på en komplexdopad elektrod. I det tredje kapitlet diskuteras resultaten från mätningarna samt möjliga framtidsutsikter. I det fjärde kapitlet presenteras slutsatserna utav studien.

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Diabetic ketoacidosis (DKA) is a life-threatening condition that can appear in patients with diabetes. High ketones in the blood lead to acidity of the blood. For DKA diagnosis and management, ketones such as hydroxybutyrate (HB) can be used to quantify the severity of the disease. The fabrication of electrochemical biosensors for the detection of HB is attractive since their capability to deliver fast response, high sensitivity, good selectivity and potential for miniaturisation. In this thesis, an integrated electrode system was prepared for the detection of HB. Laser-induced graphene (LIG) with a 3D porous structure was used as the flexible platform. Poly (toluidine blue O) (PTB) was electro-deposited on LIG (PTB/LIG) under the optimised conduction (pH of 9.7 and from 0.4 to an upper cyclic potential of 0.8 V). The single PTB/LIG working electrode demonstrated excellent performance towards the detection of NADH with a linear range of 6.7 M to 3 mM using chronoamperometry, high sensitivity of detecting NADH and excellent anti-fouling ability (94 % response current retained after 1500 s). Further integration of the 3-electrode system realised the static amperometric detection of NADH over the range of 78 M to 10 mM. Based on the excellent performance of PTB/LIG to NADH sensing, hydroxybutyrate dehydrogenase was immobilised via encapsulation with chitosan and polyvinyl butyral (PVB) which was used for HB biosensing over the linear range of 0.5 M to 1 mM with NAD+ dissolved in solution. In addition, the co-immobilisation of NAD+ and HBD on PTB/LIG was conducted by optimisation of enzyme and NAD+ amount per electrode, which shows excellent reproducibility and satisfactory HB biosensing performance. Further experiments to improve the long-term stability of the enzyme electrode is expected in the future. The proposed integrated electrode system also possesses the potential to extend to a multichannel sensor array for the detection of multiple biomarkers (e.g. pH and glucose) for diagnosis and management of DKA.