A novel approach is reported for obtaining ambipolar electroactive polymers via in situ electropolymerization for vertical organic electrochemical transistor (vOECT) applications. It is shown that electropolymerization is a practical and efficient method to obtain copolymers without contamination from chemical polymerization processes. To this end, two monomers, G-DTP-Bu-NDI and G-DTP-G-NDI, are proposed, comprising naphthalene diimide (NDI) as the acceptor core and dithienopyrrole (DTP) as the donor unit, capable of forming carbon-carbon bonds under the influence of an electric current. The incorporation of oligo(oxyethylene) (OEG) side groups ensures their amphiphilicity. Both compounds underwent successful electrochemical polymerization, resulting in thin, porous, uniform polymer layers on the electrode surface. The synthesized polymers are further examined using electrochemical and spectroelectrochemical techniques in both organic and aqueous electrolytes. Regardless of the electrolyte medium (aqueous or non-aqueous), poly(G-DTP-Bu-NDI), and poly(G-DTP-G-NDI) exhibit stable electroactivity, as demonstrated by numerous scans showing ambipolar redox behavior. Both polymers are tested as components of vertical OECTs, following in situ electrochemical deposition within a 350 nm channel. The recorded transfer characteristics suggest that the fabricated donor-acceptor (D-A) compounds hold promise for developing a new generation of ambipolar ECT devices.

Platinum is the most widespread electrode material used for implantable biomedical and neuroelectronic devices, motivating exploring ways to improve its performance and understand its fundamental properties. Using reactive magnetron sputtering, PtOx is prepared, which upon partial reduction yields a porous thin-film form of platinum with favorable properties, notably record-low impedance values outcompeting other reports for platinum-based electrodes. It is established that its high electrochemical capacitance scales with thickness, in the way of volumetric capacitor materials like IrOx and poly(3,4-ethylenedioxythiophene), PEDOT. Unlike these two well-known analogs, however, it is found that PtOx capacitance is not caused by reversible pseudofaradaic reactions but rather due to high surface area. In contrast to IrOx, PtOx is not a reversible valence-change oxide, but rather a porous form of platinum. The findings show that this oxygen-containing form of Pt can place Pt electrodes on a level competitive with IrOx and PEDOT. Due to its relatively low cost and ease of preparation, PtOx can be a good choice for microfabricated bioelectronic devices. Platinum is used in many medical implants, but lags behind next-generation electrode materials in performance. How sputtered platinum oxide is a microfabricatable thin film material that provides bioelectronics electrodes with volumetric capacitance and low impedance that tweaks platinum to compete at the level of conducting polymers and IrOx is shown. image

Organic electrochemical transistors (OECTs) have emerged as promising candidates for various fields, including bioelectronics, neuromorphic computing, biosensors, and wearable electronics. OECTs operate in aqueous solutions, exhibit high amplification properties, and offer ion-to-electron signal transduction. The OECT channel consists of a conducting polymer, with PEDOT:PSS receiving the most attention to date. While PEDOT:PSS is highly conductive, and benefits from optimized protocols using secondary dopants and detergents, new p-type and n-type polymers are emerging with desirable material properties. Among these, low-oxidation potential oligomers are highly enabling for bioelectronics applications, however the polymers resulting from their polymerization lag far behind in conductivity compared with the established PEDOT:PSS. In this work we show that by careful design of the OECT geometrical characteristics, we can overcome this limitation and achieve devices that are on-par with transistors employing PEDOT:PSS. We demonstrate that the vertical architecture allows for facile electropolymerization of a family of trimers that are polymerized in very low oxidation potentials, without the need for harsh chemicals or secondary dopants. Vertical and planar OECTs are compared using various characterization methods. We show that vOECTs are superior platforms in general and propose that the vertical architecture can be expanded for the realization of OECTs for various applications.

Reactive oxygen species (ROS) are an integral part of many anticancer therapies. Fenton-like processes involving reactions of peroxides with transition metal ions are a particularly potent and tunable subset of ROS approaches. Precise on-demand dosing of the Fenton reaction is an area of great interest. Herein, we present a concept of an electrochemical faradaic pixel that produces controlled amounts of ROS via a Fenton-like process. The pixel comprises a cathode and anode, where the cathode reduces dissolved oxygen to hydrogen peroxide. The anode is made of chromium, which is electrochemically corroded to yield chromium ions. Peroxide and chromium interact to form a highly oxidizing mixture of hydroxyl radicals and hexavalent Cr ions. After benchmarking the electrochemical properties of this type of device, we demonstrate how it can be used under in vitro conditions with a cancer cell line. The faradaic Fenton pixel is a general and scalable concept that can be used for on-demand delivery of redox-active products for controlling a physiological outcome.

Bioelectronic devices such as neural stimulation and recording devices require stable low-impedance electrode interfaces. Various forms of nitridated titanium are used in biointerface applications due to robustness and biological inertness. In this work, stoichiometric TiN thin films are fabricated using a dual Kaufman ion-beam source setup, without the necessity of substrate heating. These layers are remarkable compared to established forms of TiN due to high degree of crystallinity and excellent electrical conductivity. How this fabrication method can be extended to produce structured AlN, to yield robust AlN/TiN bilayer micropyramids, is described. These electrodes compare favorably to commercial TiN microelectrodes in the performance metrics important for bioelectronics interfaces: higher conductivity (by an order of magnitude), lower electrochemical impedance, and higher capacitive charge injection with lower faradaicity. These results demonstrate that the Kaufman ion-beam sputtering method can produce competitive nitride ceramics for bioelectronics applications at low deposition temperatures.

Increasing the electrochemical surface area of noble metal electrodes is vital for many applications, including catalysis and bioelectronics. Herein, a method is presented for obtaining porous noble metal thin films via reactive magnetron sputtering of noble metal oxides, MOx, followed by their reduction using chemical reducers or electrochemical current. Variation of reduction conditions yields a range of different electrochemical and morphological properties. This method for obtaining porous noble metals is rapid, facile, and compatible with microfabrication processes. The resulting metallic films are porous and have competitively high capacitance and low impedance.

The approach of using polyether, aka glycol, side chains to afford amphiphilicity to conducting polymers has recently emerged as a powerful technique for next-generation materials for bioelectronics and electrochemical devices. Herein we apply this synthetic logic to the archetypical conducting polymer poly(3,4-ethylenedioxythiophene), PEDOT, to generate a glycolated PEDOT analogue, G-PEDOT. We report on the electropolymerization of this material, and its electrochemical properties: including spectroelectrochemistry, electrochemical capacitance, and operation of microelectrodes and electrochemical transistors. While in many respects performing like PEDOT, G-PEDOT has electrochemical switching within lower potentials with complete de-doping at lower potentials, affording transistors with higher on/off ratios than PEDOT, and electrochromic switching within a smaller electrochemical window. Overall, G-PEDOT emerges as a useful, functional alternative to other PEDOT derivatives, and could be a building block in copolymers.

Hydrogen peroxide (H₂O₂) is an important oxidant, used in various fields of industry, such as paper manufacturing, production of polymers, detergents, and cosmetics. Considering that the molecule degrades only to H₂O and O₂, it is regarded as a green chemical. Unfortunately, the incumbent method of H₂O₂ synthesis, based on anthraquinone oxidation, although efficient, is not environmentally friendly, as it requires fossil fuels and significant energy input. Therefore, there are efforts underway to reduce the ecological impact of hydrogen peroxide production. Some of the most promising approaches involve catalytic reduction of O₂ to H₂O₂ in an aqueous environment. This can be coupled with water oxidation. As the required energy could be delivered in different ways, hydrogen peroxide synthesis can be achieved by electrocatalysis, photoelectrocatalysis, or photocatalysis.

This thesis explores the possibility of using organic electronic materials as catalysts for H₂O₂ evolution in oxygenated water solutions. Organic electronics is a field of materials science focused on conducting and semiconducting organic molecules. These materials offer many possible advantages, related to low cost, flexibility, and good optoelectronic properties. Huge progress in the field over the last years led to their commercial applications in e.g. organic light emitting diodes and photovoltaics. Only very recently have organic electronics begun to be considered from the point of view of catalysis.

In the first two papers, we investigate electrocatalytic activity of an organic pigment (PTCDI) and a conducting polymer (PEDOT) towards oxygen reduction to hydrogen peroxide. Both types of catalysts are chemically stable and able to operate in a wide pH range. In paper 3, we demonstrate that H₂O₂-evolving photocathodes can be based on an organic PN heterojunction, giving devices of a record-breaking performance. In the first part of paper 4, the same concept was tested for a naturally-occurring semiconductor, eumelanin, leading to a first report of photoelectrocatalytic properties of this material. In the second part of paper 4, as well as in papers 5 and 6, we explore, respectively, photochemical hydrogen peroxide synthesis with eumelanin, organic semiconductors, and organic dyes. We show that the photostability of catalysts is higher for materials with low-lying HOMO level and it can be increased by an addition of a reducing agent to the reaction system. Our findings prove that already existing organic electronic materials can be successfully applied in H₂O₂ evolution for environmentally friendly chemical synthesis, suggesting their use in harvesting of solar energy and in situ generation of hydrogen peroxide for biomedical applications.

Väteperoxid (H₂O₂) är en viktig oxidant som används inom olika industrier, såsom papperstillverkning och produktion av polymerer, tvättmedel och kosmetika. Med tanke på att molekylen bryts ner till vatten (H₂O) och syre (O₂) betraktas den som en grön kemikalie. Tyvärr är den befintliga metoden för framställning av H₂O₂ baserad på oxidation av en antrakinon, en metod som är effektiv, men inte miljövänlig eftersom den kräver fossila bränslen och betydande energitillförsel. Det pågår därför ansträngningar för att minska den ekologiska effekten av väteperoxidproduktionen. Några av de mest lovande metoderna involverar katalytisk O₂ till H₂O₂-reduktion i vattenlösning, kombinerat med vattenoxidation. Eftersom den nödvändiga energin kan levereras på olika sätt kan väteperoxidsyntesen uppnås genom elektrokatalys, fotoelektrokatalys eller fotokatalys.

Denna avhandling undersöker möjligheten att använda organiska elektroniska material som katalysatorer för framställning av H₂O₂i syresatta vattenlösningar. Organisk elektronik är ett område inom materialvetenskap med fokus på ledande och halvledande organiska molekyler. Dessa material erbjuder många fördelar, såsom låg kostnad, flexibilitet och goda optoelektroniska egenskaper. Enorma framsteg på området har under de senaste åren lett till deras kommersiella tillämpningar i till exempel organiska ljusemitterande dioder och fotovoltaik. Nyligen har också organisk elektronik börjat övervägas ur katalysens synvinkel.

I de två första artiklarna undersöker vi en elektrokatalytisk aktivitet av ett organiskt pigment (PTCDI) och en ledande polymer (PEDOT) i respekt till syrereduktion och väteperoxidproduktion. Båda typerna av katalysatorer är kemiskt stabila och kan arbeta inom ett brett pH-område. I artikel 3 visar vi att H₂O₂-producerande fotokatoder kan baseras på en organisk PN-gränsyta, vilket ger enheter med en rekordbrytande kapacitet. I den första delen av artikel 4 testades samma koncept för en naturligt förekommande halvledare, eumelanin, vilket ledde till en första rapport om fotoelektrokatalytiska egenskaper hos detta material. I den andra delen av artikel 4, samt i artikel 5 och 6, undersöker vi fotokemisk väteperoxidsyntes med eumelanin, organiska halvledare och organiska färgämnen. Vi visar att fotostabiliteten hos katalysatorer är högre för material med lågt liggande HOMO-nivå och att den kan ökas genom en tillsats av ett reduktionsmedel till reaktionssystemet. Våra fynd visar att redan befintliga organiska elektroniska material framgångsrikt kan tillämpas i H₂O₂-utvecklingen för miljövänlig kemisk syntes, vilket antyder att de kan användas för att ta tillvara på solenergi och för produktion av väteperoxid inom biomedicin.

Electrocatalysis for energy‐efficient chemical transformations is a central concept behind sustainable technologies. Numerous efforts focus on synthesizing hydrogen peroxide, a major industrial chemical and potential fuel, using simple and green methods. Electrochemical synthesis of peroxide is a promising route. Herein it is demonstrated that the conducting polymer poly(3,4‐ethylenedioxythiophene), PEDOT, is an efficient and selective heterogeneous catalyst for the direct reduction of oxygen to hydrogen peroxide. While many metallic catalysts are known to generate peroxide, they subsequently catalyze decomposition of peroxide to water. PEDOT electrodes can support continuous generation of high concentrations of peroxide with Faraday efficiency remaining close to 100%. The mechanisms of PEDOT‐catalyzed reduction of O2 to H2O2 using in situ spectroscopic techniques and theoretical calculations, which both corroborate the existence of a chemisorbed reactive intermediate on the polymer chains that kinetically favors the selective reduction reaction to H2O2, are explored. These results offer a viable method for peroxide electrosynthesis and open new possibilities for intrinsic catalytic properties of conducting polymers.

Photochemical generation of hydrogen peroxide via oxygen reduction is a critical component of emerging sustainable energy conversion concepts. Light‐absorbing semiconductors as well as electrodes modified with sensitizers typically catalyze oxygen photoreduction to hydrogen peroxide. Here, it is reported that, in contrast to these heterogeneous systems, a homogeneous solution of a metal‐free organic dye can perform the whole catalytic cycle of hydrogen peroxide photoevolution itself. This cycle can proceed with simultaneous oxidation of various organic molecules as electron donors, or even water. In the three water‐soluble dyes that are experimented with, photoevolution of peroxide occurs favorably at neutral to basic pH. The reaction is first order with respect to dye concentration, and evidence implicates a single‐electron reduction pathway with superoxide as an intermediate. Photostability of the dyes over time correlates with increased oxidation potential of the molecule. The finding that hydrogen peroxide can be produced in aqueous solution with single fully organic molecules performing the entire photocatalytic cycle creates a new avenue for the peroxide carbon free energy cycle.