Eco-Friendly, Direct Deposition of Metal Nanoparticles on Graphite for Electrochemical Energy Conversion and Storage

Flexible Linker-Based Triazine-Functionalized 2D Covalent Organic Frameworks for Supercapacitor and Gas Sorption Applications

Covalent organic frameworks (COFs) having a large surface area, porosity, and substantial amounts of heteroatom content are recognized as the ideal class of materials for energy storage and gas sorption applications. In this work, we have synthesized four different porous COF materials by the polycondensation of a heteroatom-rich flexible triazine-based trialdehyde linker, namely 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (TPT-CHO), with four different triamine linkers. Triamine linkers were chosen based on differences in size, symmetry, planarity, and heteroatom content, leading to the synthesis of four different COF materials named IITR-COF-1, IITR-COF-2, IITR-COF-3, and IITR-COF-4. IITR-COF-1, synthesized within 24 h from the most planar and largest amine monomer, exhibited the largest Brunauer-Emmett-Teller (BET) surface area of 2830 m2 g-1, superior crystallinity, and remarkable reproducibility compared to the other COFs. All of the synthesized COFs were explored for energy and gas storage applications. It is shown that the surface area and redox-active triazene rings in the materials have a profound effect on energy and gas storage enhancement. In a three-electrode setup, IITR-COF-1 achieved an electrochemical stability potential window (ESPW) of 2.0 V, demonstrating a high specific capacitance of 182.6 F g-1 with energy and power densities of 101.5 Wh kg-1 and 298.3 W kg-1, respectively, at a current density of 0.3 A g-1 in 0.5 M K2SO4 (aq) with long-term durability. The symmetric supercapacitor of IITR-COF-1//IITR-COF-1 exhibited a notable specific capacitance of 30.5 F g-1 and an energy density of 17.0 Wh kg-1 at a current density of 0.12 A g-1. At the same time, it demonstrated 111.3% retention of its initial specific capacitance after 10k charge-discharge cycles. Moreover, it exhibited exceptional CO2 capture capacity of 25.90 and 10.10 wt % at 273 and 298 K, respectively, with 2.1 wt % of H2 storage capacity at 77 K and 1 bar.

Research progress of MOFs/carbon nanocomposites on promoting ORR in microbial fuel cell cathodes

With the rapid development of the economy, energy demand is more urgent. Microbial fuel cells (MFCs) have the advantages of non-toxic, safety, and environmental protection, and are considered the ideal choice for the next generation of energy storage equipment. However, the slow kinetics of oxygen reduction reaction (ORR) on MFC air cathodes and the high cost of traditional platinum (Pt) catalysts hinder their practical application, so there is a need to develop efficient, low-cost, and stable electrocatalysts as alternatives. Recently, metal-organic framework (MOFs) has attracted wide attention in electrocatalysis. Electrocatalysts prepared by the nanocomposite of MOFs and carbon nanomaterials have multiple advantages, such as adjustable chemical properties, high specific surface area, and good electrical conductivity, which have been proven to be a promising electrocatalytic material. In this paper, the latest research progress of metal-organic frames (MOFs) and carbon nanocomposites is reviewed, and the preparation methods and modification of MOFs and carbon nanofibers, carbon nanotubes, and graphene composites are introduced, respectively, as well as their applications in MFC cathode. Finally, the main prospects of MOFs/carbon nanocomposite catalysts are put forward.

Chemical Influence of Carbon Interface Layers in Metal/Oxide Resistive Switches

Thin layers introduced between a metal electrode and a solid electrolyte can significantly alter the transport of mass and charge at the interfaces and influence the rate of electrode reactions. C films embedded in functional materials can change the chemical properties of the host, thereby altering the functionality of the whole device. Using X-ray spectroscopies, here we demonstrate that the chemical and electronic structures in a representative redox-based resistive switching (RS) system, Ta₂O₅/Ta, can be tuned by inserting a graphene or ultrathin amorphous C layer. The results of the orbitalwise analyses of synchrotron Ta L₃-edge, C K-edge, and O K-edge X-ray absorption spectroscopy showed that the C layers between Ta₂O₅ and Ta are significantly oxidized to form CO_x and, at the same time, oxidize the Ta layers with different degrees of oxidation depending on the distance: full oxidation at the nearest 5 nm Ta and partial oxidation in the next 15 nm Ta. The depth-resolved information on the electronic structure for each layer further revealed a significant modification of the band alignments due to C insertion. Full oxidation of the Ta metal near the C interlayer suggests that the oxygen-vacancy-related valence change memory mechanism for the RS can be suppressed, thereby changing the RS functionalities fundamentally. The knowledge on the origin of C-enhanced surfaces can be applied to other metal/oxide interfaces and used for the advanced design of memristive devices.

Deep neural network analysis of nanoparticle ordering to identify defects in layered carbon materials

Smoothness/defectiveness of the carbon material surface is a key issue for many applications, spanning from electronics to reinforced materials, adsorbents and catalysis. Several surface defects cannot be observed with conventional analytic techniques, thus requiring the development of a new imaging approach. Here, we evaluate a convenient method for mapping such "hidden" defects on the surface of carbon materials using 1-5 nm metal nanoparticles as markers. A direct relationship between the presence of defects and the ordering of nanoparticles was studied experimentally and modeled using quantum chemistry calculations and Monte Carlo simulations. An automated pipeline for analyzing microscopic images is described: the degree of smoothness of experimental images was determined by a classification neural network, and then the images were searched for specific types of defects using a segmentation neural network. An informative set of features was generated from both networks: high-dimensional embeddings of image patches and statics of defect distribution.

Oxygenated functional group-driven spontaneous fabrication of Pd nanoparticles decorated porous carbon nanosheets for electrocatalytic hydrodechlorination of 4-chlorophenol

Researchers have been committed to reducing the hazardous pollutants by developing efficient catalysts while ignoring the pollution caused by the use of toxic surface capping agents, reductants and/or organic solvents in the catalyst preparation process. To alleviate such problems, we here report a novel one-step oxygenated functional group-driven electroless deposition strategy to synthesize clean and uniformly distributed Pd nanoparticles (NPs) using porous carbon nanosheets (PCN) as both substrates and reducing agents. It is observed that the oxygenated functional groups enriched PCN possesses a low work function and allows the spontaneous reduction of PdCl₄^2- ions to Pd NPs deposited on the PCN support (Pd/PCN). The particle size of Pd NPs can be flexibly modulated by simply controlling the immersing time and thereby their maximum catalytic performances can be achieved. Specifically, the optimal Pd/PCN-08 with a Pd loading of 3.0 wt% shows an excellent activity with a turnover frequency of 0.38 min^-1 for electrocatalytic hydrodechlorination (ECH) of 4-chlorophenol (4-CP), superior to the previously reported materials. The stability of Pd/PCN-08 for 4-CP ECH is impressive in repetitive cycles. This work proposes a facile and efficient strategy to synthesize high-performance catalysts for detoxifying the hazardous organic pollutants.