Andreas Winter

Bio: Andreas Winter is an academic researcher from University of Jena. The author has contributed to research in topics: Graphene & Graphene nanoribbons. The author has an hindex of 11, co-authored 17 publications receiving 2184 citations. Previous affiliations of Andreas Winter include Schiller International University & Bielefeld University.

Three-Dimensional Nitrogen and Boron Co-doped Graphene for High-Performance All-Solid-State Supercapacitors

Abstract: carbide-derived carbon, [ 12 ] carbon nanotubes (CNTs), [ 14–17 ] and graphene, [ 6 , 7 , 10 , 18 , 19 ] possess notable features including high surface area, high electrical conductivity, and good chemical stability, and therefore they have been widely explored as thinfi lm electrode materials for ASSSs. However, the fabrication of ASSSs generally involves complex solution processing, highpressure pressing, high-temperature sintering, and sputtering techniques. [ 11 , 12 , 14–17 ] Moreover, polymer binders and conductive additives are required to enhance the adhesion between electrode materials and substrates as well as to improve the conductivity of the electrode, which unavoidably leads to decreased energy density of the devices. [ 6 , 20 ] Therefore, several challenges remain in developing ASSSs, such as to: i) explore high-performance electrode materials, ii) enhance the interfacial compatibility between electrode and solid-state electrolyte, and iii) simplify the device fabrication process. Graphene aerogels (GAs) represent a new class of ultralight and porous carbon materials that are associated with high

Nitrogen-doped graphene and its iron-based composite as efficient electrocatalysts for oxygen reduction reaction.

Abstract: The high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has hindered the practical application of fuel cells. Thanks to its unique chemical and structural properties, nitrogen-doped graphene (NG) is among the most promising metal-free catalysts for replacing platinum. In this work, we have developed a cost-effective synthesis of NG by using cyanamide as a nitrogen source and graphene oxide as a precursor, which led to high and controllable nitrogen contents (4.0% to 12.0%) after pyrolysis. NG thermally treated at 900 °C shows a stable methanol crossover effect, high current density (6.67 mA cm–2), and durability (∼87% after 10 000 cycles) when catalyzing ORR in alkaline solution. Further, iron (Fe) nanoparticles could be incorporated into NG with the aid of Fe(III) chloride in the synthetic process. This allows one to examine the influence of non-noble metals on the electrocatalytic performance. Remarkably, we found that NG supported with 5 wt % Fe nanoparticles displayed ...

Layer‐by‐Layer Assembled Heteroatom‐Doped Graphene Films with Ultrahigh Volumetric Capacitance and Rate Capability for Micro‐Supercapacitors

Abstract: Highly uniform, ultrathin, layer-by-layer heteroatom (N, B) co-doped graphene films are fabricated for high-performance on-chip planar micro-supercapacitors with an ultrahigh volumetric capacitance of ∼488 F cm(-3) and excellent rate capability due to the synergistic effect of nitrogen and boron co-doping.

All‐Carbon Vertical van der Waals Heterostructures: Non‐destructive Functionalization of Graphene for Electronic Applications

Abstract: We present a route to non-destructive functionalization of graphene via assembly of vertical all-carbon van der Waals heterostructures. To this end, we employ single-layer graphene (SLG) sheets grown by low-pressure methane CVD on Cu foils and large-area dielectric ~1 nm thick amino-terminated carbon nanomembranes (NH 2 -CNMs) generated by electron-beam-induced crosslinking of aromatic self-assembled monolayers. We encapsulate SLG sheets on oxidized silicon wafers with NH 2 -CNMs via mechanical stacking and characterize structural, chemical and electronic proper-ties of the formed heterostructures by Raman spectroscopy and X-ray photoelectron spectroscopy as well as by electric and electromagnetic transport measurements. We show that functional amino groups are brought in close vicinity of the SLG sheets and that their transport characteristics are not impaired by this functionalization; moreo-ver, we demonstrate a functional response of the heterostructure devices to the pro-tonation of the amino groups in water. Due to its relative simplicity, the suggested approach opens broad avenues for implementations in graphene-based electronic devices where non-destructive chemical functionalization of graphene is required (e.g., for engineering electrical transducers for chemical and bio-sensing) or as com-plementary dielectric to graphene in hieratical heterostructures.

Controlled growth of transition metal dichalcogenide monolayers using Knudsen-type effusion cells for the precursors

Abstract: Controlling the flow rate of precursors is essential for the growth of high quality monolayer single crystals of transition metal dichalcogenides (TMDs) by chemical vapor deposition (CVD). Thus, introduction of an excess amount of the precursors affects reproducibility of the growth process and results in the formation of TMD multilayers and other unwanted deposits. Here we present a simple method for controlling the precursor flow rates using the Knudsentype effusion cells [1]. This method results in a highly reproducible growth of large area and high density TMD monolayers. The size of the grown crystals can be adjusted between 10 and 200 μm. We characterized the grown monolayers by optical, atomic force and transmission electron microscopies as well as by X-ray photoelectron, Raman and photoluminescence spectroscopies, and by electrical transport measurements showing their high optical and electronic quality based on the single crystalline nature. The quality of these CVD grown TMDs can be compared to the best quality exfoliated materials [2].

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Abstract: Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Electrochemical capacitors: mechanism, materials, systems, characterization and applications

Abstract: Electrochemical capacitors (i.e. supercapacitors) include electrochemical double-layer capacitors that depend on the charge storage of ion adsorption and pseudo-capacitors that are based on charge storage involving fast surface redox reactions. The energy storage capacities of supercapacitors are several orders of magnitude higher than those of conventional dielectric capacitors, but are much lower than those of secondary batteries. They typically have high power density, long cyclic stability and high safety, and thus can be considered as an alternative or complement to rechargeable batteries in applications that require high power delivery or fast energy harvesting. This article reviews the latest progress in supercapacitors in charge storage mechanisms, electrode materials, electrolyte materials, systems, characterization methods, and applications. In particular, the newly developed charge storage mechanism for intercalative pseudocapacitive behaviour, which bridges the gap between battery behaviour and conventional pseudocapacitive behaviour, is also clarified for comparison. Finally, the prospects and challenges associated with supercapacitors in practical applications are also discussed.

Design and Mechanisms of Asymmetric Supercapacitors.

Abstract: Ongoing technological advances in diverse fields including portable electronics, transportation, and green energy are often hindered by the insufficient capability of energy-storage devices By taking advantage of two different electrode materials, asymmetric supercapacitors can extend their operating voltage window beyond the thermodynamic decomposition voltage of electrolytes while enabling a solution to the energy storage limitations of symmetric supercapacitors This review provides comprehensive knowledge to this field We first look at the essential energy-storage mechanisms and performance evaluation criteria for asymmetric supercapacitors to understand the wide-ranging research conducted in this area Then we move to the recent progress made for the design and fabrication of electrode materials and the overall structure of asymmetric supercapacitors in different categories We also highlight several key scientific challenges and present our perspectives on enhancing the electrochemical performance of future asymmetric supercapacitors

Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

Abstract: Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

Metal-free catalysts for oxygen reduction reaction.

Abstract: Liming Dai,*,†,‡ Yuhua Xue,†,‡ Liangti Qu,* Hyun-Jung Choi, and Jong-Beom Baek* †Center of Advanced Science and Engineering for Carbon (Case4Carbon), Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, United States Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, Department of Chemistry, School of Science, Beijing Institute of Technology, Beijing 100081, People’s Republic of China School of Energy and Chemical Engineering/Center for Dimension-Controllable Covalent Organic Frameworks, Ulsan National Institute of Science and Technology (UNIST), 100 Banyeon, Ulsan, 689-798, South Korea