Novel Non-Kekulé and Kekulé Hydrocarbons
Intense research efforts have been dedicated to inducing magnetism in carbon-based nanomaterials owing to their improved magnetic performance, such as lower spin-orbit couplings and larger spin correlation lengths, than many inorganic materials. Non-Kekulé polycyclic hydrocarbons (PHs) (or nanographenes (NGs)) belong to the class of carbon-rich molecules for which no Kekulé valence structures can be drawn without leaving unpaired electrons, which makes such compounds inherently magnetic and attractive for exploring their fundamental physicochemical properties. Here we are interested in the synthesis of novel non-Kekulé molecules and open-shell Kekulé PHs, which exhibit unique electronic and magnetic properties as well as the potential applications for organic electronics and spintronics.
Graphene nanoribbons (GNRs) are considered to be next-generation carbon materials for the fabrication of nanoscale electronic devices owing to their high electrical conductivity and tunable bandgaps. We are particularly interested in synthesizing structurally well-defined GNRs with different topologies through solution-mediated or surface-assisted methods. Programming the shape, width, length, and edge structures of GNRs by the bottom-up organic synthetic methods, allows us to achieve unique insights into their structure-property relationships. Solution processability of GNRs is an important concern for us to readily transfer them on the substrate for reliable device fabrications, hence, synthetic control of GNRs with enhanced solution dispersibility is also our consideration.
Novel Curved Nanographenes
Curved nanographenes have grown to become an important field of research due to their fascinating intermolecular packing, extraordinary chiroptical properties and dynamic behavior resulting from their contorted conformation, which are not shared by the traditional “flatland”. To date, two distinct strategies have been established for the synthesis of curved polycyclic aromatic hydrocarbons (PAHs), including the imposition of non-hexagonal rings and the introduction of steric strain in the molecular skeleton. The increased solubility, novel aromaticity, helicity, chirality, and curvature-dependent opto-electronic properties are key features of this class of PAHs. We are particularly interested in controlling the geometry and the aromaticity of curved π-conjugated systems with the aim of the development of novel functional materials for organic electronics and spintronics.
Heteroatom-doping (isoelectronic) Carbon Nanostructures
Replacing single or multiple carbon atoms in the sp2-carbon framework by heteroatoms such as nitrogen, boron, oxygen, phosphorous or a combination of them, is an efficient and unique pathway to tune their optoelectronic properties without changing the structural skeleton. Additionally, the stability and aromaticity of the resulting carbon nanostructures can be strongly influenced. We are particularly interested in developing new methodologies to synthesize the isoelectronic carbon nanostructures and explore their new functions for electronics and energy-related fields. The fundamental aspects of chemistry and physics of the heteroatom-doped carbon nanostructures are the core of our interests.
Following on the decades of investigation on the synthetic linear conjugated polymers with notable application potential in organic electronics such as organic field-effect transistors, organic solar cells and organic light-emitting diodes, two-dimensional conjugated polymers (2D CPs) have recently attracted growing research interest as a new generation of organic semiconducting materials. 2D CPs, as represented by graphene and 2D p-conjugated covalent-organic frameworks, are characterized by multi-strands of linear conjugated polymers with in-plane π-conjugation and regular 2D framework structures. The 2D CP subgroup of the Chair of Molecular Functional Materials is geared towards the synthesis of unprecedented 2D conjugated polymers with tailored opto-electronic properties by organic and polymer chemistry. We are focused to establish the rational synthetic methodologies for the solution synthesis of crystalline vinylene- and aryl-linked 2D CPs under controlled reaction conditions, among others. Furthermore, we aim to explore the unprecedented structure-property relationships of 2D CPs based on a variety of characterization methods. We also target at the implementation of these innovative materials into a variety of applications, such as organic electronics, spintronics, energy storage and conversion.
Vinylene-linked 2D CPs have attracted increasing attention in terms of their intrinsic chemical stability and enhanced delocalized electronic structures. However, the synthesis of crystalline vinylene-linked 2D CPs remains challenging, because the C=C bond formation suffers from lower reversibility resulting in kinetically controlled amorphous porous polymers. The crystallinity of the obtained vinylene-linked 2D CP is not high yet, and the size of crystallites is limited to tens of nanometers. To achieve highly crystalline vinylene-linked 2D CPs, we like to gain deep understanding and controlling of the reaction kinetics to facilitate the reversibility, which is essential for achieving highly crystalline vinylene-linked 2D CPs. Other synthetic strategies for the novel 2D conjugated polymers including 2D polythiophene, 2D polypyrrole, etc, are also explored in our group.
Unprecedented 2D CPs
2D CPs have the advantage that the structures or topologies can be easily tailored by the implementation of different building blocks. In particular, the design of the monomers with different sizes, symmetries, substituents and reactive sites dramatically influence the structure and topology of 2D CPs. We are interested in the synthesis of unprecedented 2D CPs with attractive building blocks, topologies or functionalities.
Unique Properties of 2D CPs
Linear conjugated polymers have been well explored for electronic and optoelectronic devices. However, they provide a low charge carrier mobility due to the intermolecular hop of charges. To overcome these limitations, the extension of the π-conjugation into a second dimension provides a plausible solution to increase their mobility. For instance, graphene, which is a prototype 2D CP, demonstrates a high charge mobility of up to 200 0000 cm2V-1s-1. Although graphene has attractive electronic properties, it remains useless as a semiconducting material and thus for possible applications in digital electronics, because of the missing energy gap. In contrast, synthetic 2D CPs with a fully π-conjugated structure provide a well-defined energy-gap, which can be tailored by the organic synthesis. We are interested in the synthesis of highly conjugated 2D CPs with tailored redox- and/or (opto)electronic properties, which can be implemented into a variety of applications, such as electronics, optoelectronics, spintronics, energy storage, etc.
So far, solution synthesis of 2D materials met with limited success due to the decreasing solubility of the synthesized compound with the increase of each single repeating unit, which leads to its precipitation and limits its lateral size to several nanometers. Moreover, in solution there is no driving force enabling the synthesized compounds to grow into a 2D geometry. To overcome this disadvantage, we use interfaces as reaction places where the ordering of monomers and the polymerization into large-area 2D materials occurs simultaneously.
HETEROSTRUCTURES FOR OPTOELECTRONICS
The success of graphene has triggered the birth of other two-dimensional sheets with a thickness of one atom or molecule. Reassembly of these sheets with graphene into three-dimensional stacks with one atom-/molecule-layer precision has led to the emergence of graphene van-der-Waals heterostructures as a new class of materials. The structures provide enormous opportunities to combine the properties of all individual components, to explore their synergic effects, and thus to tailor them for a specific application. We focus on the generation of graphene heterostructures with conjugated 2D materials for flexible optoelectronics.
NOVEL POROUS POLYMERS
Porous polymers with controllable porosity at the atomic scale have attracted tremendous attention due to their easy-controlled porous channels, availability of various building blocks, light weight, prominent physicochemical properties and numerous potential applications in sensing, gas storage and separation, energy storage and conversion, etc. We are focusing on the design and synthesis of novel porous polymers with dimensionality control (including conjugated microporous polymers, hyper-cross-linked porous polymers, covalent triazine-based frameworks), which will open a new door to emerging applications.
POROUS CARBON MATERIALS
Porous carbons possess controllable and hierarchical pore sizes (micropore, mesopore, and macropore) with different pore structures (order and disorder) showing a variety of applications for energy storage and conversion. Novel controlled synthetic protocols and new functions as well as the understanding of mechanisms become essential for porous carbon materials.
POROUS CARBON-HYBRID SYSTEMS
Due to the high surface area and good conductivity of porous carbons, integration of porous carbons with functional inorganic nanomaterials becomes one promising approach to build up new hybrid materials for energy applications with enhanced performance.
The assembly of graphene and its derivatives with inorganic species opens up an exciting new field in design and construction of composites with hierarchical superstructures. Until now, diverse synthetic protocols have been developed for hybridization of graphene with a series of different inorganic substances including transition metal nanoparticles/nanosheets, transition metal oxides/sulfides/phosphides. Our focus is the development of 2D hybrid materials with sandwich-like morphology and hierarchical macroporous structures for applications in energy storage and conversion.
Next-generation Energy Materials
- Novel Carbon Nanostructures
Novel carbon materials with tailor-made structures (e.g., topological defect, porosity, dopant, morphology) are of significant interest for a variety of energy-related applications. We are seeking for the development of novel structurally well-defined carbon nanostructures. The fundamental understanding of carbon growth mechanism, and new physical/chemical/electrochemical properties will be explored in the context of our research.
- 2D Redox-Active Carbon-Rich Frameworks
2D carbon-rich frameworks (including carbon-conjugated metal-organic frameworks (MOFs) and covalent organic frameworks (COFs)) have emerged as a group of intelligent multi-functional materials, owing to the designable topologies at the molecular level, regular porosities, and large specific surface areas. These materials offer great opportunities to design and synthesize new energy storage electrodes by organizing redox-active monomers into the periodic framework structures. We are highly interested in the design and synthesis of new framework molecules, as well as the investigation of these molecules for the next-generation energy storage technologies.
- 2D Materials & Van der Waals Heterostructures
The large family of atomically thin 2D materials (e.g., Graphene, Phosphorene, MXenes, TMDs, 2D organic materials) collectively covers a very broad range of chemical and physical properties. Van der Waals interaction between distinct 2D materials shows considerable compatibility, allowing the flexible assembly of 2D heterostructures that can synergize each building block's desirable properties. We are particularly interested in developing controllable synthetic routes, surface/defect chemistry control, unique/exceptional physicochemical properties, and energy applications of novel 2D materials and their heterostructures.
- Supercapacitors and Hybrid-Ion Capacitors
Supercapacitors, which are power-featured energy storage devices, deliver a power density that is one order of magnitude larger than that of lithium-ion batteries. Hybrid-ion capacitors represent one type of emerging energy storage devices, which are made up of a battery-type electrode and a capacitor-type electrode. To achieve high-performance supercapacitor/hybrid-ion capacitor devices, we aim at fabricating thin-film electrodes with large accessible electrochemically activated surfaces, high electrical conductivity, and an elaborate device structure with efficient ion diffusion pathways.
- Dual-Ion Batteries
Anion-storage chemistry provides the possibility to enable battery cathodes with high potential windows (e.g., anion-intercalation graphite with an average discharge potential of > 4.5 V vs. Li+/Li). It opens up new application opportunities for constructing plenty of dual-ion batteries (DIBs), which significantly contrast with the conventional ‘rocking-chair’ Li-ion batteries. We are interested in the development of new anion-storage materials, rational electrolyte preparation, and novel dual-ion battery configuration design.
- Multi-Valent Metal-Ion Batteries
Multivalent metal-ion chemistry offers feasible pathways to develop next-generation energy storage technologies with higher energy density, better safety, and lower cost, as the corresponding metals (e.g., Zn, Mg, Al) can be directly used as ideal multielectron-redox anodes. The main challenge of multivalent metal-ion batteries lies in the large difficulty of multivalent metal ions to be stored in convention battery materials, due to the large ionic size and strong repulsive intercalation with host materials. Our research efforts focus on developing high-performance cathode materials for accommodating multivalent metal ions, innovative approaches to alleviate the sluggish ion-storage kinetics, and construction of high-performance battery devices.
- Functional Devices & Smart Integration
The development of many cutting-edge technologies (e.g., wearable/implantable healthcare devices, environmental monitoring, internet of things) triggers the development of modern electronics towards miniaturized, portable, multi-functional, and highly integrated device systems. High demand for power sources with the same features is imposed, as traditional energy storage devices (e.g., supercapacitors and batteries) may not be of suitable choices. In this regard, we are highly interested in developing miniaturized energy storage devices (micro-supercapacitors and micro-batteries), introducing multi-functionalities into energy storage devices (e.g., mechanically flexibility/stretchability, sensing functions, stimulus-responsive functions), and constructing highly integrated self-powered energy systems.
- Electrocatalytic Oxygen Reactions (Metal-Air Batteries, Fuel Cells)
The increasing energy crisis and environmental pollution require innovative solutions for the use of renewable energies. Electrocatalytic oxygen reactions (OER, ORR) are the vital process for next-generation electrochemical energy storage and conversion technologies, e.g., metal-air batteries and fuel cells. Due to their earth-abundance and unique physicochemical properties, carbon-rich nanomaterials can serve as novel materials and electrodes for catalyzing the sluggish oxygen reaction kinetics. In order to achieve high catalytic performance in energy storage and conversion systems, we primarily focus on synthesizing novel carbon-based catalysts with improved intrinsic activity and favorable porous structures for mass transport.
- Photoelectrochemical Water Splitting
Due to the high energy density and clean combustion product, hydrogen (H2) has been universally proposed as a promising energy carrier for future energy conversion and storage devices. Conjugated polymers, featuring tunable band gaps/positions and tailored active centers at the molecular level, are attractive photoelectrode materials for energy conversion. Developing conjugated polymers with small bandgaps, high separation capability of photoinduced holes and electrons, and highly active catalytic centers, provides a promising pathway for photoelectrochemical hydrogen/oxygen evolution reactions.
- Nanofluidic Osmotic Power Generation
The osmotic energy between river water and seawater, also known as salinity gradient energy or blue energy, has been identified as promising clean, renewable, and non-intermittent sources of energy. Currently, the industrial utilization of such worldwide energy is mainly limited by the low performance of the commercial ion-exchange membrane. The unique electrolyte transport phenomena in the 2D nanofluidic channel system open a new avenue to harvest osmotic energy. We primarily focus on the design and construction of novel nanofluidic membranes based on synthetic 2D materials, investigation of the ion transport behaviour, and exploration of their application in osmotic power generation.