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In this work, zeolitic imidazolate frameworks (ZIF‐8@ZIF‐67)‐based core–shell structure as a supercapacitor electrode is synthesized. The core–shell structure is designed with a ZIF‐8 core, onto which a ZIF‐67 shell is grown. This unique architecture aims to expedite the diffusion of electrolyte ions, facilitate inner–outer metal ion electron transfer, and consequently enhance electrochemical performance. When used as an active electrode material, the material delivers 263.43 F g−1 of capacitance at 0.5 A g−1 of discharge rate. The core–shell structure exhibits 68% of surface contribution toward the total capacitance. At the scan rate of 50 mV s−1, the sample almost exhibits equal contribution of diffusion and surface charge contribution. Further an asymmetric supercapacitor (ASC) device is assembled, featuring a ZIF‐8@ZIF‐67 core–shell metal‐organic framework (MOF) as a positive electrode and waste‐tissue‐paper‐derived activated carbon as negative electrode using 1 m H2SO4 aqueous electrolyte. The ASC device delivers an energy density of 38.4 Wh kg−1 at the power density of 0.8 kW kg−1, along with long cycle life of 95.2% after an extensive 10 000 cycles. In this work, the significance of the ZIF‐based core–shell structure in advancing supercapacitor technology, which further can be extended to multiple core–shell structure and other MOF combination, is highlighted. [ABSTRACT FROM AUTHOR]

In this study, nanosized zeolitic imidazolate framework‐8 (ZIF‐8) crystal has been produced on the universitetet i oslo‐66 (UiO‐66) metal–organic framework (MOF) to make core–shell structure using a layer‐by‐layer deposition method. In comparison to the pristine UiO‐66 and ZIF‐8, the core–shell MOF exhibits superior performance in terms of specific capacitance. This enhanced performance is attributed to its remarkable ability to facilitate the rapid diffusion of electrolyte ions through nanosized ZIF‐8 and enhance the electron transfer process involving the inner and outer metal ions within the UiO‐66@ZIF‐8 structure. Remarkably, the core–shell structure achieves an impressive specific capacitance of 588.8 F g−1 at a current density of 0.5 A g−1 using 1 m sulfuric acid (H2SO4) aqueous electrolyte. Additionally, the UiO‐66@ZIF‐8 core–shell material is demonstrated as a positive electrode, coupled with activated carbon (AC) derived from waste tissue paper serving as the negative electrode, in the fabrication of an asymmetric supercapacitor (ASC) device. At a power density of 400 W kg−1, this assembled asymmetric device delivers a notably high energy density of 53 Wh kg−1 along with a cyclic stability of 94.8% after 10 000 cycles. This study substantiates the superior performance of the UiO‐66@ZIF‐8 core–shell MOF structure as a highly effective supercapacitor electrode material, surpassing the performance of its pristine MOF counterparts. [ABSTRACT FROM AUTHOR]

In the context of emerging electric devices, the demand for advanced energy storage materials has intensified. These materials must encompass both surface and diffusion-driven charge storage mechanisms. While diffusion-driven reactions offer high capacitance by utilizing the bulk of the material, their effectiveness diminishes at higher discharge rates. Conversely, surface-controlled reactions provide rapid charge/discharge rates and high power density. To strike a balance between these attributes, we devised a tri-composite material, TiO2/Carbon/MoS2 (T10/MoS2). This innovative design features a highly porous carbon core for efficient diffusion and redox-active MoS2 nanosheets on the surface. Leveraging these characteristics, the T10/MoS2 composite exhibited impressive specific capacitance (436 F/g at 5 mV/s), with a significant contribution from the diffusion-controlled process (82%). Furthermore, our symmetrical device achieved a notable energy density of ~ 50 Wh/kg at a power density of 1.3 kW/kg. This concept holds promise for extending the approach to other Metal–Organic Framework (MOF) structures, enabling enhanced diffusion-controlled processes in energy storage applications. [ABSTRACT FROM AUTHOR]

This work shows the possibility of using plasma nitriding under ultra-high-vacuum conditions to introduce nitrogen into a titanium dioxide structure in the form of nanotubes with a diameter of about 110 nm. Nanotubes were produced by the anodic oxidation of Ti foil in a solution based on glycerine and water with the addition of ammonium fluoride at a voltage of 25 V. Based on experimental evidence obtained by X-ray photoelectron spectroscopy (XPS, in situ), it has been shown that alternating nitriding and annealing processes at 450 °C leads to formation of Ti-N-O, Ti-N, and Ti-O-N chemical bonds in the TiO2 crystal structure (anatase). The observed changes were identified as interstitial or substitutional admixtures or variations of these. The spectrophotometric and spectrophotoelectrochemical tests performed showed that the photoactivity of the photoanodes doped with nitrogen and annealed at 450 °C in the UV–vis range was significantly greater than that of the photoanodes without nitrogen. The highest maximum photocurrent density, of about 30.0 μA·cm–2 at a wavelength of λ = 350 nm, was obtained for the double-nitrided and once-annealed sample, where nitrogen was mainly incorporated in the interstitial positions in the TiO2 lattice. For the materials not nitrided as well as annealed only at 450 °C and pristine, the worse photoresponse was received at the levels of ∼16 and ∼0.2 μA·cm–2, respectively. The thermo-chemical treatment applied also effectively extended the operational range of the photoanodes toward visible light, where a wide maximum of light absorption was observed from ∼400 to ∼700 nm, with a maximum wavelength of 550 nm and an estimated bandgap energy of 2.5 eV. Our investigations confirmed that photoelectrochemical (PEC) performance for TiO2 NT-based photoanodes was achieved by the optimum annealing condition and concentration of nitrogen, where the narrowed bandgap was observed by generating a new N 2p energy level above the O 2p valence band. The following research techniques were used to identify the changes taking place in the materials produced: XPS spectroscopy, UV–vis spectroscopy, PEC measurements, X-ray diffraction structural measurements, and scanning electron microscopic observations. [ABSTRACT FROM AUTHOR]

The structural and chemical modification of TiO 2 nanotubes (NTs) by the deposition of a well-controlled Au deposit was investigated using a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), Raman measurements, UV-Vis spectroscopy and photoelectrochemical investigations. The fabrication of the materials focused on two important factors: the deposition of Au nanoparticles (NPs) in UHV (ultra high vacuum) conditions (1-2 × 10 -8 mbar) on TiO 2 nanotubes (NTs) having a diameter of ∼110 nm, and modifying the electronic interaction between the TiO 2 NTs and Au nanoparticles (NPs) with an average diameter of about 5 nm through the synergistic effects of SMSI (Strong Metal Support Interaction) and LSPR (Local Surface Plasmon Resonance). Due to the formation of unique places in the form of "hot spots", the proposed nanostructures proved to be photoactive in the UV-Vis range, where a characteristic gold plasmonic peak was observed at a wavelength of 580 nm. The photocurrent density of Au deposited TiO 2 NTs annealed at 650 °C was found to be much greater (14.7 μA cm -2 ) than the corresponding value (∼0.2 μA cm -2 ) for nanotubes in the as-received state. The IPCE (incident photon current efficiency) spectral evidence also indicates an enhancement of the photoconversion of TiO 2 NTs due to Au NP deposition without any significant change in the band gap energy of the titanium dioxide ( E g ∼3.0 eV). This suggests that a plasmon-induced resonant energy transfer (PRET) was the dominant effect responsible for the photoactivity of the obtained materials., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The nitrogen doping of titanium dioxide nanotubes (TiO 2 NTs) was investigated as a result of well-controlled plasma nitriding of TiO 2 NTs at a low temperature. This way of nitrogen doping is proposed as an alternative to chemical/electrochemical methods. The plasma nitriding process was performed in a preparation chamber connected to an X-ray photoelectron spectroscopy (XPS) spectrometer, and the nitrogen-doped TiO 2 NTs were next investigated in situ by XPS in the same ultrahigh vacuum (UHV) system. The collected high-resolution (HR) XPS spectra of N 1s, Ti 2p, O 1s, C 1s, and valence band (VB) revealed the formation of chemical bonds between titanium, nitrogen, and oxygen atoms as substitutional or interstitial species. Moreover, the results provided a characterization of the electronic states of N-TiO 2 NTs generated by various plasma nitriding and annealing treatments. The VB XPS spectrum showed a reduction in the TiO 2 band gap of about 0.6 eV for optimal nitriding and heat-treated conditions. The TiO 2 NTs annealed at 450 or 650 °C in air (ex situ) and nitrided under UHV conditions were used as reference materials to check the formation of Ti-N bonds in the TiO 2 lattice with a well-defined structure (anatase or a mixture of anatase and rutile). Scanning electron microscopy microscopic observations of the received materials were used to evaluate the morphology of the TiO 2 NTs after each step of the nitriding and annealing treatments., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)