The main objective of this doctoral thesis is explore the origin of the nanoporous carbons photoactivity for studying their applications in different fields of research covering their use as photocatalysts for pollutants degradation as well as photoelectrodes for water photooxidation reaction, either by themselves or as additives coupled to a semiconductor in hybrid electrodes. The first stage of this study mainly consisted in investigating the photoactivity of carbon materials by themselves (in the absence of semiconductors) towards different reactions, aiming at linking their photochemical response with the carbon material nature in terms of porosity, surface chemistry, composition and structure. The exploration of the photoassisted degradation of phenol nanoconfined in the pore voids of several nanoporous carbons showed a positive effect of the tight packing of the molecule in the carbon material porosity. This indicated the role of confinement to boost fast interactions between the photogenerated charge carriers at carbon material surface and the molecule adsorbed inside pores. The irradiation wavelength was found as a key variable upon phenol photooxidation reaction, with the best optimum performance at low and high wavelengths, and a minimum photodegradation yield at ca. 400 nm for all tested carbon materials. Another parameter strongly influencing the photoactivity of the nanoporous carbons was the surface functionalisation. When sulphur was incorporated to a carbon matrix, the light conversion towards the phenol photooxidation became more efficient and it was dependent on the nature of the S-containing groups. Further on, the analysis of photocurrent transients obtained by irradiating several nanoporous carbon electrodes exhibited different responses, with either anodic or cathodic photocurrent, and transient shapes, thus demonstrating the distinct nature of the catalysed reaction occurring onto electrode/electrolyte interface. The second stage deals with hybrid nanoporous carbon/semiconductor (i.e. WO3) electrodes which allowed to explore the role of nanoporous carbon as additive towards water oxidation reaction. The presence of carbon material had a notable effect on the hybrid electrode performance, in terms of conversion efficiency (IPCE), likely due to the improved collection of the photogenerated electrons by carbon matrix. An optimal amount of carbon additive of ca. 20 wt.% was obtained for the best performing hybrid electrode, with a twofold IPCE compared to that obtained for bare WO3 electrode. The effect of carbon matrix on WO3 performance was found dependent on semiconductor crystalline structure.

The society profits from a variety of electronic devices, which rely on electrons and holes as the charge carriers for information transmission and processing. In contrast, biological systems operate via ions of varying size to handle complicated tasks, including massive parallel information sensing, processing, storing, and behavior controlling in nature, which inspire the development of iontronics (such as ionic transistors, ionic diodes, and ionic resistive memristors) for further bioelectronic interface, in-memory computing, and artificial intelligence hardware.[1] In recent years, the electric double layer (EDL) formation has proven a powerful tool for the coupling of ions and electrons in iontronics. EDL electrically adsorbs/desorbs ions on the surface of electrodes to balance and store opposite charges in a controllable manner, which enables to operate ions and build iontronic devices. Nanoporous carbons with higher specific surface areas compared to widely-used metal electrodes in iontronics feature the higher volume and specific capacitances along with fine compatibility with biological systems, which are promising for ion manipulation in iontronics.[2,3] In recent years, a series of carbon-based capacitive iontronics were developed to realize the functions of conventional diodes and transistors.[4,5] Due to the demand of high performance (energy and power density) in above devices, toxic electrolytes were applied as the electrolytes,[4,5] which limits the implementation in biological applications. Various functionally bioactive ions are a requisite for complicated psychological, physiological, and behavioral processes, such as neurotransmitters (ranging from amino acids (e.g., glycine (Gly) and gamma-aminobutyric acid (GABA)), biogenic amines (e.g., dopamine and acetylcholine), to peptides (e.g., vasopressin and somatostatin)).[6] Moreover, some bioactive ions such as sodium ibuprofen (NaIbu) and sodium salicylate (NaSal) are common analgesic and inflammation drugs for the human health.[7,8] So far, there have been few reports about applying bioactive ions as the charge carriers in carbon-based EDL iontronics. A deep molecular-level mechanism of the adsorption of bioactive ions and the deliberate concentration control via nanoporous carbons with and without polarization remain unclear and unsolved, but are crucial for the design of neuromorphic devices, neurotransmitter sensors, and transmitter delivery. Given the varying sizes and structures of bioactive ions and the varying porosity structures of nanoporous carbons, there are some open questions for the interaction mechanism of bioactive ions and nanoporous carbons in the EDL devices as shown in the following: a) the influence of porosity structures of nanoporous carbons for the adsorption kinetics and thermodynamics of bioactive ions; b) the difference of the electrosorption and physisorption and their roles for manipulating ion behaviors; c) the influence of bioactive ion structure for the adsorption process; d) the adsorption mechanisms for electroneutral and charged neurotransmitters; e) the effects of the surface polarity and functional groups of nanoporous carbons for the bioactive ion adsorption process. This thesis focuses on revealing the interaction behaviors of bioactive ion electrolytes and nanoporous carbon electrodes from four main parts, with the aid of electrochemical methods and spectroscopic analyses. In Chapter 5.1, the adsorption kinetics of bioactive choline chloride (ChCl) in ACC with a narrow pore size distribution (PSD) and ROX with a broad PSD is explored. The comparison indicates a faster diffusion process of ChCl in ROX with a broad PSD. The evaluation of physisorption and electrosorption of ChCl in ROX with a broad PSD is conducted, which show that the amount of physically adsorbed ChCl in ROX is less than 6 μmol/g, while the amount of electrosorption-induced concentration changes in the polarized ROX electrode is up to 30 μmol/g. Electrosorption dominates the adsorption process for ChCl. Consequently, it can be concluded that the capture and release of ChCl in aqueous solutions can be easily manipulated via electrochemical techniques. Chapter 5.2 builds on the investigation of the ChCl interaction behavior in the ROX carbon. The investigation is extended to a series of ammonium-based ionic liquid salts with different alkyl chain lengths paired with Cl- anions (CxAmOMCl, where x=2, 6, and 12). The increasing physisorption of these cations in the ROX carbon is observed with the alkyl chain length increasing. The role of alkyl chain is clarified in bioactive cations for the adsorption in nanoporous carbons. However, the bioactive anions with long alkyl chains showed a quite weaker adsorption in the ROX carbon, compared with bioactive cations with long alkyl chains. These results illustrate the synergistic effect of the hydrophobic interaction and electrostatic attraction for the bioactive ions strong adsorption in nanoporous carbons. In Chapter 5.3, the adsorption and charge balancing mechanism of electroneutral amino acids are further explored in ROX carbon electrodes. The weak physisorption of four amino acids (with linear structures) is observed, which results from the hydrophilic end groups and electroneutral properties. The charge balance mechanism of these electroneutral zwitterions (with amine and carboxylic acid groups) is clarified as the dissociation reaction of amino acid zwitterions, which produces anions to balance positive charges and cations to balance negative charges. In the buffered environment, the deliberate uptake and release of inhibitory neurotransmitters (Gly and GABA) are achieved by polarizing porous carbon electrodes, which implies the powerful abilities of electrosorption for controlling the concentration of neurotransmitters in aqueous and phosphate-buffered saline (PBS) solutions. In Chapter 5.4, we investigate the impurity effects for the carbon properties and bioactive ion adsorption processes. The impurity contents are very high in some commercial porous carbons. The washing process leads to the decrease of O and N contents, and reduces wettability of porous carbons. Moreover, some O, N, and other non-carbon contents, which are commonly considered as surface functional groups of carbons, are not bonded but adsorbed inorganic impurities on the carbon surface. In-situ UV-Vis experiments clarify that the adsorbed ionic impurities play a role in the charge balance process during the electric polarization, which partly explains the capacitances of porous carbons in pure water electrolytes. The questions addressed in this thesis provide a fundamental basis for the understanding of the interaction of various bioactive ions with nanoporous carbons, which benefit the development of EDL iontronics. Based on two different interaction modes (weak and strong adsorption), the interaction theory is further applied in the construction of iontronic devices. For weak adsorption, EDL transistors are deeply explored using bioactive ions (ChCl, NaIbu, Gly, and GABA). The capacitance switching behavior is confirmed in a 3D printed carbon-based ionic transistor. The concentration manipulation of bioactive ions in aqueous environments are promising for various potential applications, such as toxic ion removal, drug delivery, plant regulation, and bioelectronic devices. For strong adsorption, the confined cations with long alkyl chains (cations of C12AmOMCl) are irreversibly adsorbed and fixed on the porous carbon surface. The electric polarization cannot desorb confined cations, causing anion depletion and anion enrichment during electric polarization, which leads to the favorable memristive behavior for promising ionic memristors and in-memory computing applications in the future. References [1] C. Wan, K. Xiao, A. Angelin, M. Antonietti, X. Chen, Advanced Intelligent Systems 2019, 1, 1900073. [2] S. Z. Bisri, S. Shimizu, M. Nakano, Y. Iwasa, Advanced Materials 2017, 29, 1607054. [3] Y.-Z. Zhang, Y. Wang, T. Cheng, L.-Q. Yao, X. Li, W.-Y. Lai, W. Huang, Chemical Society Reviews 2019, 48, 3229. [4] S. Lochmann, Y. Bräuniger, V. Gottsmann, L. Galle, J. Grothe, S. Kaskel, Advanced Functional Materials 2020, 30, 1910439. [5] E. Zhang, N. Fulik, G.-P. Hao, H.-Y. Zhang, K. Kaneko, L. Borchardt, E. Brunner, S. Kaskel, Angewandte Chemie International Edition 2019, 58, 13060. [6] S. E. Hyman, Current Biology 2005, 15, R154. [7] S. A. Hawley, M. D. Fullerton, F. A. Ross, J. D. Schertzer, C. Chevtzoff, K. J. Walker, M. W. Peggie, D. Zibrova, K. A. Green, K. J. Mustard, B. E. Kemp, K. Sakamoto, G. R. Steinberg, D. G. Hardie, Science 2012, 336, 918. [8] N. Azum, A. Ahmed, M. A. Rub, A. M. Asiri, S. F. Alamery, Journal of Molecular Liquids 2019, 290, 111187.:Table of Contents I Abbreviations IV 1. Motivation 1 2. Background and Introduction 5 2.1. Biology and Ion-controlled Devices 5 2.2. Ion-related Biological Processes 5 2.2.1. Sensing and Signaling 5 2.2.2. Memory and Computing 7 2.2.3. Actuation Components 9 2.3. Bioinspired Iontronics 10 2.3.1. Ionic Diodes 11 2.3.2. Ionic Transistors 12 2.3.3. Ionic Resistive Memristors 14 2.4. Carbon-based Capacitive Iontronics 15 2.4.1. The Mechanism of Carbon-based Supercapacitors 15 2.4.2. Electrolytes for Supercapacitors 18 2.4.3. Nanoporous Carbons 22 2.4.4. Carbon-based Ionic Diodes 23 2.4.5. Carbon-based Ionic Transistors 24 2.4.6. The Interaction Mechanism of Bioactive Ions with Porous Carbons 26 3. Electrochemical Methods 28 3.1. Linear Sweep Voltammetry (LSV) 28 3.2. Cyclic Voltammetry (CV) 30 3.3. Electrochemical Impedance Spectroscopy (EIS) 31 4. Experimental Section 35 4.1. List of Used Chemicals 35 4.2. List of Used Materials 36 4.3. Preparation and Characterizations 37 4.3.1. Carbon Preparation 37 4.3.2. Electrode Preparation 38 4.3.3. 2-electrode Cells 38 4.3.4. 3-electrode Cells 38 4.3.5. 4-terminal Setups 39 4.3.6. Local pH Measurement 39 4.3.7. EIS Measurement 40 4.3.8. In-situ UV-Vis Measurement 40 4.3.9. Raman Spectroscopy 41 4.3.10. NMR and MS Measurement 41 4.3.11. Ninhydrin Reaction 42 4.3.12. Nitrogen Physisorption 42 4.3.13. Electrosorption Evaluation 42 5. Results and Discussion 43 5.1. Pore Structure and Ion Adsorption Kinetics 43 5.1.1. Introduction 43 5.1.2. Physiochemical Properties of Two Nanoporous Carbons 43 5.1.3. ChCl Physisorption Mechanism in Nanoporous Carbons 45 5.1.4. ChCl Electrochemical Stability and Performance 48 5.1.5. ChCl Electrosorption Mechanism in Nanoporous Carbons 52 5.1.6. Switchable Capacitive Transistor Analogues in Printed Structures 60 5.1.7. Summary 63 5.2. Ion Structures and Adsorption Kinetics 64 5.2.1. Introduction 64 5.2.2. Synthesis and Characterization of Ammonium-based ILs 65 5.2.3. Adsorption Behavior of Ammonium-based ILs in Nanoporous Carbons 67 5.2.4. Electrochemical Performance of Ammonium-based ILs 76 5.2.5. Adsorption Behavior of Organic Salts in Nanoporous Carbons 78 5.2.6. Strong Interaction and Ionic Memristor Behaviors 82 5.2.7. Weak Interaction and Ionic Transistor Applications 86 5.2.8. Summary 89 5.3. Electroneutral Neurotransmitter Adsorption Mechanism 90 5.3.1. Introduction 90 5.3.2. Amino Acid Physisorption Mechanism in Nanoporous Carbons 92 5.3.3. Amino Acid Electrochemical Behaviors in Electrically-polarized Nanoporous Carbons 96 5.3.4. Mechanism Investigation of Zwitterions in Electrically-polarized Nanoporous Carbons 99 5.3.5. Local pH Measurement of Amino Acid Electrolytes during Electric Polarization 105 5.3.6. Electrosorption-induced Capture and Release of Amino Acid Neurotransmitters 109 5.3.7 Neurotransmitter-based Bioinspired Iontronic Devices 113 5.3.8. Summary 115 5.4. Porous Carbon Impurities for Bioactive Ion Adsorption 116 5.4.1. Introduction 116 5.4.2. Qualitative Analysis of the Impurity Release from Porous Carbons 118 5.4.3. Electrochemical Evaluation for Ionic Impurities in Porous Carbons 121 5.4.4. The Effect of Adsorbed Ionic Impurities for Carbon Properties 126 5.4.5. The Charge Balance Mechanism of Ionic Impurities for Bioactive Ion Controlling 135 5.4.6. Summary 137 6. Conclusion and Outlook 139 7. References 142 A. Bibliography 152 B. List of Publications 154 C. Acknowledgements 155 D. Appendix 157 E. Versicherung und Erklärung 161

Monolithic integration of iontronic devices is a key challenge for future miniaturization and system integration. The G-Cap, a novel iontronic element, is a switchable supercapacitor with gating characteristics comparable to transistors in electronic circuits, but switching relies on ionic currents and ion electroadsorption. The first monolithic in-plane G-Cap integration through 3D-inkjet printing of nanoporous carbon precursors is reported. The printed G-Cap has a three-electrode architecture integrating a symmetric “working” supercapacitor (W-Cap) and a third “gate” electrode (G-electrode) that reversibly depletes/injects electrolyte ions into the system, effectively controlling the “working” capacitance. The symmetric W-Cap operates with a proton-conducting hydrogel electrolyte PVA/H₂SO₄ and shows a high capacitance (1.6 mF cm⁻²) that can be switched “on” and “off” by applying a DC bias potential (-1.0 V) at the G-electrode. This effectively suppresses AC electroadsorption in the nanoporous carbon electrodes of the W-Cap, resulting in a high capacitance drop from an “on” to an “off” state. The new monolithic structures achieve high rate performance, reversible on-off switching with an off-value reaching 0.5 %, which even surpasses recently reported values. Establishing technologies and device architectures for functional ionic electroadsorption devices is crucial for diverse fields ranging from microelectronics and iontronics to biointerfacing and neuromodulation.

L'objectif de la thèse présentée ici est l'optimisation de matériaux carbonésnanoporeux au moyen de la “conception de matériaux virtuels”. En ce qui concerne cette échelle de travail (~ 10nm), la Nanotomographie FIB-SEM est la seule technique d'imagerie donnant accès à une information sur la géométrie tridimensionnelle. Cependant, pour l'optimisation du comportement, l'espace des pores doit être reconstruit à partir des données tirées des images obtenues. Jusqu'à présent ce problème n'était pas résolu. Pour pouvoir le maîtriser, on a développé une simulation d'images FIB-SEM. Les images FIB-SEM simulées peuvent être utilisées pour la vérification et la validation des algorithmes de segmentation. En utilisant les données d'image simulées, un nouvel algorithme pour la reconstruction de l'espace des pores à partir des données FIB-SEM a été développé.Deux études de cas avec des carbones nanoporeux utilisés pour le stockage d'énergie sont présentées, en utilisant les nouvelles techniques pour la caractérisation et l'optimisation des électrodes Li-ion de type EDLC'S (« electric double-layer capacitors », soit supercondensateurs). L'espace des pores reconstruit est modélisé géométriquement à l'aide de la géométrie stochastique. Enfin, on a simulé les propriétés électriques des matériaux enutilisant des structures modélisées et simulées. / The aim of the work presented here is to optimize nanoporous carbon materials by means of 'virtual material design'. On this length scale (~ 10nm) Focused Ion Beam – Scanning Electron Microscopy Nanotomography (FIB-SEM) is the only imaging technique providing three dimensional geometric information. Yet, for the optimization, the pore space of the materials must be reconstructed from the resulting image data, which was a generally unsolved problem so far.To overcome this problem, a simulation method for FIB-SEM images was developed. The resulting synthetic FIB-SEM images could then be used to test and validate segmentation algorithms. Using simulated image data, a new algorithm for the morphological segmentation of the highly porous structures from FIB-SEM data was developed, enabling the reconstruction of the three dimensional pore space from FIB-SEM images.Two case studies with nanoporous carbons used for energy storage are presented, using the new techniques for the characterization and optimization of electrodes of Li-ion batteries and electric double layer capacitors (EDLC's), respectively. The reconstructed pore space is modeled geometrically by means of stochastic geometry. Finally, the electrical properties of the materials were simulated using both imaged real and modeled structures.