For a set of graphs H, we call a graph G H-free if G-S is non-isomorphic to H for each S⊆V(G) and each H∈H. Let f_H^* ∶N_(>0)↦N_(>0 )be the optimal χ-binding function of the class of H-free graphs, that is, f_H^* (ω)=max⁡{χ(G): ω(G)=ω,G is H-free} where χ(G),ω(G) denote the chromatic number and clique number of G, respectively. In this thesis, we mostly determine optimal χ-binding functions for subclasses of P_5-free graphs, where P_5 denotes the path on 5 vertices. For multiple subclasses we are able to determine them exactly and for others we prove the right order of magnitude. To achieve those results we prove structural results for the graph classes and determine colourings. We sometimes obtain those results by researching the prime graphs and combining the two decomposition methods by homogeneous sets and clique-separators. Additionally, we use the Strong Perfect Graph Theorem and analyse the neighbourhood of holes. For some of these subclasses we characterise all graphs G with χ(G)>χ(G-\{u\}), for each u∈V(G) and use those to determine the function.

A novel strategy for the intercalation of antimony (Sb) under the (6√3 × 6√3)R30° reconstruction, also known as buffer layer, on SiC(0001) is reported. Using X-ray photoelectron spectroscopy, low-energy electron diffraction, and angle-resolved photoelectron spectroscopy, it is demonstrated that, while the intercalation of the volatile Sb is not possible by annealing the Sb-coated buffer layer in ultrahigh vacuum, it can be achieved by annealing the sample in an atmosphere of Ar, which suppresses Sb desorption. The intercalation leads to a decoupling of the buffer layer from the SiC(0001) surface and the formation of quasi-freestanding graphene. The intercalation process paves the way for future studies of the formation of quasi-freestanding graphene by intercalation of high-vapor-pressure elements, which are not accessible by previously known intercalation techniques, and thus provides new avenues for the manipulation of epitaxial graphene on SiC.

Emerging contaminants represent newly identified organic chemical pollutants that are not yet covered by routine monitoring and regulatory programs. Current research on these contaminants is greatly hindered by the shortage of analytical methods due to the complex matrices, extremely low concentration and their “emerging” nature. In this study the innovative analytical and monitoring methods have been developed and validated for determination of emerging pollutants in water (including pharmaceutical and personal care products, pesticides and artificial sweeteners) based on graphene-silica composite as the solid-phase extraction (SPE) sorbent and as the receiving phase in passive sampler. Graphene, a new allotropic member in the carbon family, has been considered to be a promising candidate for sorption material with high loading capacity because of its ultra-high specific surface area and large delocalized π-electron-rich structure. The composite employed in this work was synthesized by using the cross-link agent to covalently combine carboxylic acid groups of graphene-oxide with the amino groups of the modified silica gel. Afterwards, graphene-silica composite was obtained after treated with hydrothermal reaction in the microwave autoclave, which was demonstrated by X-ray diffraction (XRD). The analytical procedure entails SPE followed by high performance liquid chromatography equipped with tandem mass spectrometers (HPLC-MS/MS). Several crucial parameters were optimized to improve recovery of the analytes, including the amount of sorbents, the ratio of graphene oxide/amino-silica and pH value of water samples. The best recovery results were achieved with 100 mg 10 % (w/w) graphene-silica composite, which were over 70 % except four artificial sweeteners, ranitidine and triclosan. Compared with its commercial counterpart Oasis HLB, pH value variation of water samples has less effect on the recoveries, making graphene composite to be a potential receiving phase of monitoring tool. The batch-to-batch reproducibility was verified on six independently SPE cartridges with graphene-silica composites from two repeatable synthetic batches, showing relative standard deviations (RSDs) in the range of 8.3 % to 19.1 %, except ibuprofen and saccharin. The cartridges proved to be reusable for at least 10 times consecutive extractions, with RSD < 14.9 %, except ibuprofen and diclofenac. The Chemcatcher® passive sampler is frequently used for monitoring polar organic chemicals in surface water. Uptake kinetics is necessary to be quantified to calculate time-weighted average (TWA) concentration. A series of calibration experiments were conducted in the beaker renewal experiments as well as in the flow-through system with styrenedivinylbenzene-cross connect (SDB-XC) disks and graphene-silica composite as the receiving phase. The results obtained from the beaker renewal experiments showed that the uptake kinetics of accumulated compounds with all Chemcatcher® configurations can keep linear within 2 weeks. The innovative configuration using graphene-silica composite powder placed between two PES membranes was able to accumulate eleven of the selected compounds with uptake rate (Rs) from 0.01 L/day (acesulfame K and sucralose) to 0.08 L/day (chlothianidin), while its commercial counterpart SDB-XC disks with polyethersulfone (PES) membranes can accumulate seven substances with Rs from 0.02 L/day (sucralose and chlothianidin) to 0.15 L/day (carbamazepine). In the flow-through system, when Chemcatchers® were equipped with SDB-XC disks without PES membranes, the linear uptake range for the majority of compounds was only in one week, except atrazine. The Rs of accumulated compounds were from 0.16 L/day (chloramphenicol) to 1.04 L/day (metoprolol) that are higher than the same substances in the beaker renewal experiments, in which the Rs of chloramphenicol and metoprolol were 0.09 L/day and 0.56 L/day respectively. However, if the PES membranes were employed, the uptake kinetics in both calibration experimental designs were comparable: the Rs of accumulated compounds from the configuration with SDB-XC disks covered by PES membranes were from 0.035 L/day (sucralose) to 0.17 L/day (carbamazepine) and from the configuration with graphene-silica composite were from 0.01 L/day (gemfibrozil) to 0.08 L/day (chlothianidin). Moreover, the uptake range can keep linear within two weeks. The developed Chemcatcher® method was successfully applied in real surface waters. 1-H benzontriazole, tolyltriazole and caffeine were the main contaminants in Elbe River and the Saidenbach drinking water reservoir. The investigated results between summer and autumn monitoring period were not significantly different.:Acknowledgement I Abstract III Zusammenfassung V Content IX List of Figures XIII List of Tables XVII Table of Abbreviations XIX 1. Motivation 1 2. Introduction 3 2.1 Emerging contaminants 3 2.1.1 Definition 3 2.1.2 Sources 3 2.1.3 Concern about the adverse impacts 5 2.2 Analysis of the emerging contaminants 7 2.2.1 General analytical process 7 2.2.2 Enrichment techniques 8 2.2.2.1 Liquid-liquid extraction (LLE) 8 2.2.2.2 Solid-phase extraction (SPE) 9 2.2.2.3 Innovative type of solid-phase extraction 13 2.2.3 Analytical methods 15 2.3 Graphene and its application in analytical chemistry 19 2.3.1 Introduction 19 2.3.2 Synthesis methods of graphene 20 2.3.3 Application in sample pre-treatment 21 2.3.3.1 Graphene-based material as SPE sorbent 21 2.3.3.2 Graphene-coated fibers as SPME sorbent 22 2.3.3.3 Magnetic graphene as MSPE sorbent 23 2.3.3.4 Graphene-based MIPs 24 2.4 Chemcatcher®—a passive sampling technique 25 2.4.1 Introduction 25 2.4.2 Theory 26 2.4.2.1 Equilibrium passive sampling 27 2.4.2.2 Kinetic passive sampling 28 2.4.3 Concept of Chemcatcher® 28 2.4.4 Calibration of Chemcatcher® 33 2.4.5 Performance and reference compounds 36 3. Study objectives and hypotheses 39 3.1 Study objectives 39 3.2 Hypotheses 41 4. Material and methods 43 4.1 Materials 43 4.1.1 Chemicals and solutions 43 4.1.2 Consumable materials and instruments 44 4.2 Synthesis of graphene-silica composite 46 4.3 SPE experiments 49 4.3.1 Packing method 49 4.3.2 SPE procedure 49 4.3.3 Optimization of SPE procedures 51 4.3.4 Repeatability and reusability test 52 4.4 Chemcatcher® experiments 53 4.4.1 Preparation and precondition 53 4.4.2 Calibration of Chemcatcher® 55 4.4.2.1 Preliminary test 55 4.4.2.2 Experimental design of the beaker batch tests 56 4.4.2.3 Experimental design of the flow-through system 57 4.4.3 Monitoring application of Chemcatcher® in surface water 59 4.4.4 Elution process 60 4.4.5 Statistic data evaluation 61 4.5 HPLC-MS/MS analysis 62 5. Results and discussion 63 5.1 Preparation and characterization of graphene-silica composite 63 5.2 SPE performance of the graphene-silica composite 67 5.2.1 Preliminary test of packing methods 67 5.2.2 Optimization of SPE procedures 68 5.2.2.1 The amount of sorbent 68 5.2.2.2 Graphene ratio in the composites 68 5.2.2.3 pH value of the water sample 69 5.2.3 Repeatability and reusability test 72 5.2.3.1 Performance of the off-line SPE 72 5.2.3.2 Repeatability and reusability test results 75 5.2.4 Summarized discussion of the SPE performance 76 5.3 Calibrating results of Chemcatcher® 86 5.3.1 Pre-test results 86 5.3.1.1 Feasibility test of commercial disks as receiving phase 86 5.3.1.2 Stability test 88 5.3.1.3 Elution optimization. 88 5.3.1.4 Recovery of the filters 92 5.3.2 Calibration results of renewal experiments 93 5.3.2.1 SDB-XC disks without and with membranes 93 5.3.2.2 Graphene-silica composite as receiving phase 97 5.3.3 Calibration results of the flow-through system experiments 101 5.3.3.1 Determination of experimental parameters 101 5.3.3.2 Concentration control 103 5.3.3.3 Calibration results 105 5.3.3.4 Preliminary evaluation of performance and reference compounds 112 5.4 Application of Chemcatcher® in surface water 114 5.5 Discussion about problems of commercial disks as receiving phase in Chemcatcher® 118 5.5.1 Deformation of commercial disks 118 5.5.2 The particles in the solution after elution 119 6. Conclusion and perspective 121 7. Annex 125 7.1 Material and methods 125 7.1.1 Chemicals 125 7.1.2 Silica gel and graphene oxide 144 7.1.3 Microwave reduction program 144 7.1.4 Working schedule of the calibration experiments in flow-through system 144 7.1.5 HPLC-MS/MS conditions 146 7.2 Experimental results 149 7.2.1 Stability of the colloid solution of graphene oxide 149 7.2.2 EDX analysis results 149 7.2.3 HPLC-MS/MS results 152 7.2.4 Calibrating results of the beaker renewal experiment 153 7.2.5 Calibrating results of the flow-through system experiments 157 7.2.6 Monitoring results in the Elbe River 161 Reference 163

Nach der Entwicklung des Nicht-Kontakt-Rasterkraftmikroskops (NC-AFM) konnten dessen Leistung, Empfindlichkeit und Anwendungsmöglichkeiten deutlich gesteigert und somit neue grundlegende physikalische Eigenschaften von Festkörperoberflächen mit hoher Auflösung und Präzision untersucht werden. Dabei gibt es jedoch immer wieder neue Errungenschaften, die die Technik noch weiter verbessern können – sei es auf dem Gebiet der Signalverarbeitung, der -detektion oder der prinzipiellen Funktionsweise des Mikroskops. So wird in der vorliegenden Arbeit das theoretische Verständnis der Regelkreise und des Rauschverhaltens des NC-AFMs im Messbetrieb verbessert. Die Regelkreise verhalten sich – anders als im freischwingenden System – in Wechselwirkungsnähe mit der Probe hochgradig dynamisch, sodass die ursprünglich gewählten Parameter der Regelkreise sich nicht eins zu eins auf den echten Messbetrieb übertragen lassen und suboptimale Einstellungen die Bildqualität dadurch beeinträchtigen können. Mithilfe der korrekten Modellierung der Regelkreise in Probennähe kann diese Störquelle nun minimalisiert werden, was durch experimentell bestimmte Spektren bestätigt wird. Bei der Exfoliation von Graphen auf CaF2 an der Raumluft werden Wassermoleküle eingeschlossen, die nicht durch Heizen entfernt werden können, ohne dass das Graphen Blasen schlägt und reißt. Unterschiedliche Mengen an Wasser zwischen den Graphenflocken und dem Substrat haben einen großen Einfluss auf das elektrische Kontaktpotenzial, das mithilfe der Kelvin-Sonden-Kraftmikroskopie vermessen werden kann. Ergebnisse der Kapitel sind die berechnete Adhäsionsenergie von Graphen auf CaF2, inwieweit das Wasser das Graphen dotieren kann und die Erklärung des großen Unterschieds des Kontaktpotenzials.

Spectral graph theory widely increases the interests in not only discovering new properties of well known graphs but also proving the well known properties for the new type of graphs. In fact all spectral properties of proverbial graphs are not acknowledged to us and in other hand due to the structure of nature, new classes of graphs are required to explain the phenomena around us and the spectral properties of these graphs can tell us more about the structure of them. These both themes are the body of our work here. We introduce here three models of random graphs and show that the eigenvalue counting function of Laplacians on these graphs has exponential decay bound. Since our methods heavily depend on the first nonzero eigenvalue of Laplacian, we study also this eigenvalue for the graph in both random and nonrandom cases.

We give a strongly polynomial time combinatorial algorithm to minimise the largest eigenvalue of the weighted Laplacian of a bipartite graph. This is accomplished by solving the dual graph embedding problem which arises from a semidefinite programming formulation. In particular, the problem for trees can be solved in time cubic in the number of vertices.

On Cu(111) surface and in interaction with a single hexa-tert-butylphenylbenzene moleculegear, the rotation of a graphene nanodisk was studied using the large-scale atomic/molecular massively parallel simulator molecular dynamics simulator. To ensure a transmission of rotation to the molecule-gear, the graphene nanodisk is functionalized on its circumference by tertbutylphenyl chemical groups. The rotational motion can be categorized underdriving, driving and overdriving regimes calculating the locking coefficient of this mechanical machinery as a function of external torque applied to the nanodisk. The rotational friction with the surface of both the phononic and electronic contributions is investigated. For small size graphene nanodisks, the phononic friction is the main contribution. Electronic friction dominates for the larger disks putting constrains on the experimental way of achieving the transfer of rotation from a graphene nanodisk to a single molecule-gear.

In memory of François Diederich. / Nanographenes (NGs) with open-shell character have gained intense attention due to their potential applications in future organic nanoelectronics and spintronics. Among them, NGs bearing a pair of parallel zigzag edges, such as acenes and periacenes (PAs) bestow unique (opto)electronic and magnetic properties owing to their localized non-bonding π-state. However, their reactive zigzag edges impart intrinsic instability, leading to the challenging synthesis. The recent development of synthetic strategies provided access to several π-extended PAs, which were considered unrealistic for decades. Notably, their laterally π-extended structures of zigzag-edged graphene nanoribbons was realised via on-surface synthesis. However, synthesis of π-extended PAs in solution is still in its infancy, more intensive scientific efforts are needed to surpass the existing challenges regarding stability and solubility. This Review provides an overview of recent progress in the synthesis and characterization of PAs through a bottom-up synthetic strategy, including on-surface and solution-phase chemistry. In addition, views on existing challenges and the future prospects are also provided.

The choice of suitable materials influences the sensor properties. Carbon materials such as graphene are promising for electrochemical sensors. Laser-induced graphene (LIG) offers a cost-effective alternative to conventional methods. This work investigates the potential of LIG to improve electrochemical sensors by optimizing the synthesis parameters. We develop LIG-based sensors for the measurement of nitrite and 4-aminophenol in water samples. The working electrode of the 4-aminophenol sensor was fabricated from LIG and multi-walled carbon nanotubes with polyaniline (MWCNT-PANI), which improves sensitivity and stability. For the detection of nitrite, the LIG was modified with carbon nanotubes and gold nanoparticles (f-MWCNT-AuNPs). The LIG sensors show excellent properties. The 4-aminophenol sensor on bare LIG reaches a detection limit of 9.23 nM, with MWCNT-PANI 6 nM. The nitrite sensor on LIG/f-MWCNT-AuNPs shows linear behavior from 10 to 140 μM, with a detection limit of 0.9 μM. The results show that LIG is suitable for versatile electrochemical sensors. The fabrication approach simplifies production and reduces costs. For the first time, an unmodified LIG electrode was used to detect 4-AP in contaminated water samples.:CHAPTER 1. INTRODUCTION CHAPTER 2. THEORETICAL BACKGROUND ON ELECTROCHEMICAL SENSORS CHAPTER 3. LASER-INDUCED GRAPHENE CHAPTER 4. ENHANCEMENT OF LIG ELECTROCHEMICAL SENSORS CHAPTER 5. 4-AMINOPHENOL DETECTION IN PARACETAMOL AND WATER SAMPLES USING LIG MODIFIED BY MWCNT-PANI CHAPTER 6. NITRITE DETECTION IN WATER SAMPLES USING LIG FUNCTIONALIZED BY F-MWCNT AND AUNPS CHAPTER 7. CONCLUSION APPENDIX

Mit der Entdeckung von Graphen begann ein neuer Zeitabschnitt für die Entwicklung von Elektronik und Sensoren aufgrund der einzigartigen elektronischen Struktur Graphens. Graphen ist breit vertreten, beispielsweise in Anwendungsbereichen von Sensorik, Energiespeicherung und Katalyse. Elektronentransferprozesse sind fundamentale Prozesse für eben solche Anwendungen. Die Eigenschaften des heterogenen Elektronentransfers von Graphen sind sehr umstritten und es gibt immer noch kein einheitliches Bild, um eben jenen zu verstehen, da oft voneinander abweichende Eigenschaften in der Literatur dargestellt werden. Diese Arbeit präsentiert systematische Untersuchungen der Elektronentransfereigenschaften von einlagigen Graphenelektroden. Als weiterer Teil dieser Arbeit werden die Elektronentransfereigenschaften durch den Entwurf einer neuen Graphen-Hybridelektrode gezielt verändert. Der erste Teil ist auf die Verbesserung der Herstellungsschritte und der anschließenden Untersuchung des Einflusses von Kupferrückständen auf die Kinetik des Elektronentransfers von einlagigen Graphenelektroden fokussiert. Die Kupferrückstände kommen von der Herstellung und dem Transfer von Graphen. Die Elektronentransferkinetik von klassischen Redoxmediatoren mit inner-sphere Elektronentransfermechanismus nimmt nach erfolgreichen Entfernen von Kupferrückständen ab. Im Gegensatz dazu bleibt die Kinetik von outer-sphere Redoxmediatoren unberührt. Hier wird gezeigt, dass die Elektronentransferkinetik von solchen Redoxmediatoren vom pH-Wert der Lösung abhängig ist, obwohl bei dem Elektronentransfer Protonen nicht involviert sind. Weiterhin wird hier festgestellt, dass der Elektronentransfer von Kationen an Graphen am schnellsten in neutralem pH stattfindet, während der Elektronentransfer von Anionen am schnellsten in saurem Millieu abläuft. Diese pH-Abhängigkeit wird den elektrostatischen Wechselwirkungen zwischen den dissoziierten Redoxmediatoren und der Ladung der Graphen-Flüssigkeit-Grenzschicht zugeschrieben. Dieses Verhalten wird auch für Graphenelektroden auf anderen isolierenden Substraten und sogar mit einer unter dem Graphen liegenden Schicht von hexagonalem Bornitrid (hBN) gefunden. Basierend darauf ist die Schlussfolgerung, dass diese pH-Abhängigkeit für den Elektronentransfer von geladenen Redoxmediatoren an Graphenelektroden intrinsisch und spezifisch für Graphen ist. Mit Metallsubstraten unter dem Graphen kann dieser pH-Effekt unterdrückt werden, was für einen verstärkten elektrokatalytischen Effekt vom darunterliegenden Metall spricht, welcher dem vorher diskutierten elektrostatischen Effekt, vermutlich durch die Zunahme der gesamten Elektronendichte, überwiegt. Basierend darauf wurde eine neue Art von Graphenelektrode entwickelt: die Graphen-Sandwichelektrode. Diese Elektrode besteht aus zwei aufeinanderliegenden Graphenschichten mit dazwischenliegenden Metallpartikeln. Diese Sandwichelektrode nutzt die elektrochemischen Eigenschaften der in der Mitte liegenden Metallpartikeln aus, obwohl das Metall durch eine Graphenschicht bedeckt ist und nicht in Kontakt mit der Lösung kommt. Bei der Verwendung von Platinpartikeln wird die obere Graphenschicht mit elektrokatalytischen Eigenschaften versehen. Als Ergebnis wird die Bildung von Wasserstoff (HER) und die Reduktion von Sauerstoff (ORR) an dieser Elektrode katalysiert. Des Weiteren wird dieser Effekt hier dafür genutzt um Wasserstoffperoxid zu messen, auch wenn eine solche Reaktion an einer „normalen“ Graphenelektrode nicht beobachtet werden kann. Hierdurch wird eine neue Klasse von optimierten Elektroden mit maßgeschneiderten elektrokatalytischen Eigenschaften realisiert. Diese Ergebnisse heben den Einfluss eines unter Graphen liegenden Metalls auf die Elektrochemie von Graphen hervor. Der zweite Teil dieser Arbeit konzentriert sich auf die Untersuchungen von Ladungen an der Graphen-Flüssigkeit-Grenzschicht auf einem lokalen und räumlich aufgelösten Niveau mit Hilfe von Rasterionenleitfähigkeitsmikroskopie (Scanning Ion Conductance Microscope - SICM). Dafür sind weiche Trägerflächen benötigt, die die Spitzen von Glaskapillaren nicht beschädigen. Diesbezüglich werden drei Protokolle für den Transfer von Graphen auf ein weiches Polymersubstrat, dem Polydimetyhlsiloxan (PDMS), entwickelt. Die dadurch erhaltenen Graphenproben werden mit Hilfe von optischer und Rasterkraftmikroskopie charakterisiert. Anhand von Annäherungskurven aus der SICM kann die Oberflächenladung qualitativ charakterisiert werden. Die Oberflächenladung einer Graphenoberfläche kann als negativ geladen in einem pH-Wert von 7 entschlüsselt werden. Zusätzlich werden Herausforderungen und Hindernisse beim Arbeiten mit SICM zu Grenzflächenuntersuchungen von einlagigem Graphen diskutiert. Diese Ausarbeitung zeigt die Bedeutung von Grenzflächenladungen und den Einfluss von unter dem Graphen liegenden Metall auf Graphen und graphenverwandte Elektroden auf. Dieses Wissen kann genutzt werden, um neue graphenbasierte Sensoren und auch hybride Elektroden für Elektrokatalyse zu entwickeln. / The discovery of graphene initiated a new era of electronic and sensor development due to graphene's unique electronic structure. Graphene covers a wide range of applications including sensing, energy storage and catalysis. The heterogeneous electron transfer (ET) is the most fundamental and most important process happening at devices in such applications. However, the ET properties of graphene are highly debated and still no coherent picture can be drawn to understand them since differing ET rates are presented in literature. This work presents systematic investigations of the ET characteristics of graphene monolayer electrodes. Furthermore, the ET properties are engineered by the fabrication of a novel graphene-based hybrid electrode. The first part focusses on the improvement of the fabrication steps and subsequent investigation of the influence of Cu trace residues on the ET kinetics of graphene monolayer electrodes. The residual Cu traces come from the fabrication process of graphene as well as from the transfer process of graphene monolayer electrodes. The ET kinetics of a classical inner-sphere redox probe decreases after a successful removal of Cu particles. In contrast to this, the ET kinetics for outer-sphere redox probes stay unaffected. Most importantly, the ET kinetics of both kinds of redox probes are found to be dependent on the solution pH, although these reactions are proton independent. ET at graphene with cations is found to be fastest in neutral pH, while the ET kinetics of anions are fastest in acidic media. This pH dependency is attributed to electrostatic interactions between the dissociated redox probes and the interfacial charge at the graphene-liquid interface (GLI). This behavior is further observed for graphene monolayer electrodes on other insulating substrates. Even with an underlying hexagonal boron nitride (hBN) layer that shields the graphene monolayer from the substrate, the same pH effect can be observed. Based on this, it can be concluded that the pH dependency of ET at graphene for charged redox species is intrinsic to graphene. By using a subsurface metal substrate, the pH effect is suppressed, indicating an enhanced electrocatalytic effect from the metal underneath that dominates the afore discovered electrostatic effect, most likely due to an increase of the overall electron density. By exploiting this effect, a new kind of graphene electrode is designed: the graphene sandwich electrode. This electrode consists of two graphene monolayers, with electrodeposited metal particles between both layers. This sandwich electrode exploits electrochemical properties of the metal in between, even though the metal is covered by a graphene monolayer and hence not exposed to the liquid. By using Pt particles, the upper graphene layer gets rendered with electrocatalytic properties. As a result, the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR) are found to be clearly catalyzed at this electrode. Furthermore, this effect is exploited for hydrogen peroxide sensing, while this reaction is not observable on pristine graphene. Thus, a new kind of engineered electrode with rendered novel electrocatalytic properties was designed. These findings highlight the influence of a subsurface metal on to the electrochemistry of graphene. The second part of this work focusses on using scanning ion conductance microscopy (SICM) to investigate interfacial charges at the GLI at a local and spatially resolved level. First, for investigations using an SICM, soft samples are needed for avoiding damage of SICM tips. For this, three different protocols are developed and discussed for transferring a graphene monolayer on a soft poly(dimethylsiloxane) (PDMS) substrate. The obtained graphene samples are characterized using optical and atomic force microscopy. By utilizing approach curves in SICM, the surface charge can be characterized qualitatively. At a graphene surface in pH 7, an overall negative surface charge can be deciphered. In addition, challenges and obstacles are discussed when using SICM for interfacial investigations of graphene monolayers. Taken together, this work presents systematic investigations of the ET of graphene monolayer and graphene sandwich electrodes. These findings improve the understanding of graphene electrochemistry and highlights the importance of interfacial charge and the influence of a subsurface metal on graphene and graphene-related electrodes. This knowledge can be used to design new graphene-based sensors and hybrid electrodes for electrocatalysis.