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Fundamental understanding of ion electroadsorption processes in porous electrodes on a molecular level provides important guidelines for next-generation energy storage devices like electric double layer capacitors (EDLCs). Porous carbons functionalized by heteroatoms show enhanced capacitive performance, but the underlying mechanism is still elusive, due to the lack of reliable tools to precisely identify multiple N species and establish clear structure property relations. Here, we use advanced analytical techniques such as low-temperature solid-state NMR (ssNMR) and electrochemical quartz crystal microbalance (EQCM) to relate the complex nitrogen functionalities to the charging mechanisms and capacitive performance. For the first time, it is demonstrated at a molecular level that N-doping strongly influences the electroadsorption mechanism in EDLCs. Without N-doping, anion (SO 4 2- ) adsorption-desorption dominates the charging mechanism, whereas after doping, Li + electroadsorption plays a key role. With the help of EQCM, it is demonstrated that SO 4 2- is strongly immobilized on the N-doped surface, leaving Li + as the main charge carrier. The smaller size and higher concentration of Li + compared to SO 4 2- benefit a higher capacitance. Amine/amide N is responsible for high capacitance, but surprisingly the pyridinic, pyrrolic, and graphitic N groups have no significant influence. 2D 1 H- 15 N NMR spectroscopy indicates that the conversion from pyridinium to pyrrolic N gives rise to a slightly decreased capacitance. This work not only demonstrates ssNMR as a powerful tool for surface chemistry characterization of electrode materials but also uncovers the related charging mechanism by EQCM, paving the way toward a comprehensive picture of EDLC chemistry.

Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer π-stacking of the COF to form undulated layers caused by bending along the C-S-C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity. Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium-sulfur (Li-S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge-discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li-S batteries on a molecular level.

In this study, a simple one-pot method was used to prepare a multifunctional platform for synergistic chemo- and photothermal therapy,, which is composed of zeolitic imidazolate framework-8 (ZIF-8) as drug nanocarriers and the embedded graphene quantum dots (GQDs) as local photothermal seeds. The structure, drug release behavior, photothermal effect, and synergistic therapeutic efficiency of the ZIF-8/GQD nanoparticles were systematically investigated. Using doxorubicin (DOX) as a model anticancer drug, the results showed that monodisperse ZIF-8/GQD nanoparticles with a particle size of 50-100 nm could encapsulate DOX during the synthesis procedure and trigger DOX release under acidic conditions. The DOX-loaded ZIF-8/GQD nanoparticles could efficiently convert near-infrared (NIR) irradiation into heat and thereby increase the temperature. More importantly, with breast cancer 4T1 cells as a model cellular system, the results indicated that the combined chemo- and photothermal therapy with DOX-ZIF-8/GQD nanoparticles exhibited a significant synergistic effect, resulting in a higher efficacy to kill cancer cells compared with chemotherapy and photothermal therapy alone. Hence, ZIF-8/GQD nanoparticles would be promising as versatile nanocarriers for synergistic cancer therapy., Competing Interests: The authors declare no competing financial interest.

In this work a simple and scalable approach to coat nonmagnetic nanoparticles with few-layer graphene is presented. In addition, the easy processing of such nanoparticles to remove their core, leaving only the 3D graphene nanoshell, is demonstrated. The samples are comprehensively characterized, as are their versatility in terms of functionalization and as a material for electrochemical storage. Indeed, these 3D graphene nanostructures are easily functionalized much as is found with carbon nanotubes and planar graphene. Electrochemical investigations indicate these nanostructures are promising for stable long-life battery applications. Finally, initial toxicological investigations suggest no acute health risk from these 3D graphene nanostructures.