Binder Free Hierarchical Mesoporous Carbon Foam for High Performance Lithium Ion Battery

Constructing of CoP-Nb2O5 p-n heterojunction with built-in electric field to accelerate the charge migration in electrocatalytic hydrogen evolution

Studying interfacial charge transfer is of great significance for the preparation of electrocatalysts with high activity for the hydrogen evolution reaction (HER). Particularly, exploring the in-depth catalytic mechanisms and facile fabrication methods of narrow bandgap metal phosphides remains worthwhile. This work successfully combined catalytically inert n-type Nb2O5 with p-type CoP to prepare a p-n heterojunction (CoP-Nb2O5). The self-supporting heterojunction was fabricated by gas-phase phosphorization of the Co(OH)2-Nb2O5 precursor obtained through hydrothermal-electrodeposition strategy. By analyzing the electronic and band structures of CoP and Nb2O5, it was found that there exists a built-in electric field (BEF) in the heterojunction. This BEF can modulate the electronic structure of CoP at the interface, enhance its intrinsic activity and accelerate charge migration. The subsequent experimental results also demonstrate that Nb2O5 can significantly enhance the activity and stability of CoP. Our findings can serve as a novel perspective on the application of p-n heterojunction in the field of energy storage and conversion.

Palladium Decorated N-Doped Carbon Foam as a Highly Active and Selective Catalyst for Nitrobenzene Hydrogenation

Carbon foam was synthesized by the carbonization of 4-nitroaniline. The reaction is an alternative of the well-known "carbon snake" (or sugar snake) demonstration experiment, which leads to the formation of nitrogen-doped carbon foils due to its nitrogen content. The synthesized carbon foils were grinded to achieve an efficient catalyst support. Palladium nanoparticles were deposited onto the surface of the support, which showed continuous distribution. The prepared Pd nanoparticle decorated carbon foils showed high catalytic activity in nitrobenzene hydrogenation. By applying the designed catalyst, total nitrobenzene conversion, a 99.1 n/n% aniline yield, and an exceptionally high selectivity (99.8 n/n%) were reached. Furthermore, the catalyst remained active during the reuse tests (four cycles) even without regeneration.

Heterostructure Fe2O3 nanorods@imine-based covalent organic framework for long cycling and high-rate lithium storage

Fe₂O₃ as an anode for lithium-ion batteries has attracted intense attention because of its high theoretical capacity, natural abundance, and good safety. However, the inferior cycling stability, low-rate performance, and limited composite varieties hinder the application of Fe₂O₃-based materials. In this work, an Fe₂O₃@COF-LZU1 (FO@LZU1) anode was prepared via an imine-based covalent organic framework (COF-LZU1) covering on the exterior surface of Fe₂O₃ after rational optimization. With its unique heterostructure, the COF-LZU1 layer not only effectively alleviated the volume expansion during cycling but also improved the charge-transfer capability because of the π-conjugated system. Moreover, the organic functional group (CN, benzene ring) for COF-LZU1 provided more redox-active sites for Li⁺ storage. Under the contributions of both Fe₂O₃ nanorods and COF-LZU1, the FO@LZU1_50% exhibited an ultrahigh initial capacity and long-term cycling performance with initial discharge capacities of 2143 and 2171 mA h g^-1 after 300 cycles under 0.1 A g^-1, and rate performance of 1310 and 501 mA h g^-1 at 0.3 and 3 A g^-1, respectively. In addition, a high retention capacity of 1185 mA h g^-1 was achieved at 1 A g^-1 after 500 cycles. Furthermore, a full-cell with the FO@LZU1_50% anode and LiCoO₂ cathode exhibited superior cycling and rate performance, which still maintained a reversible capacity of 260 mA h g^-1 after 200 cycles even at a current density of 1 A g^-1. The proposed strategy offers a new perspective for exploring the high-rate capability and designability of Fe₂O₃-based electrode materials.

Composite Carbon Foams as an Alternative to the Conventional Biomass-Derived Activated Carbon in Catalytic Application

The suitability of a new type of polyurethane-based composite carbon foam for several possible usages is evaluated and reported. A comparison of the properties of the as-prepared carbon foams was performed with widely available commercial biomass-derived activated carbon. Carbon foams were synthesized from polyurethane foams with different graphite contents through one-step activation using CO₂. In this work, a carbon catalyst was synthesized with a moderately active surface (S_BET = 554 m²/g), a thermal conductivity of 0.09 W/mK, and a minimum metal ion content of 0.2 wt%, which can be recommended for phosgene production. The composite carbon foams exhibited better thermal stability, as there is a very little weight loss at temperatures below 500 °C, and weight loss is slower at temperatures above 500 °C (phosgene synthesis: 550–700 °C). Owing to the good surface and thermal properties and the negligible metallic impurities, composite carbon foam produced from polyurethane foams are the best alternative to the conventional coconut-based activated carbon catalyst used in phosgene gas production.

Cobalt ferrite nanoparticle-loaded nitrogen-doped carbon sponge as a magnetic 3D heterogeneous catalyst for monopersulfate-based oxidation of salicylic acid

As salicylic acid (SAL) is increasingly consumed as a pharmaceutical product, release of SAL into the environment poses threats to ecology because of its low bio-degradability. Thus, SO₄^•--based chemical oxidation processes have been proposed for degrading SAL. Since monopersulfate (MPS) represents a primary reagent for generating SO₄^•-, and Co is the most capable metal for activating MPS to generate SO₄^•-, C₃O₄ NPs are frequently proposed for activating MPS but they are difficult to recover from water. Thus CoFe₂O₄ is considered as a magnetic alternative to Co₃O₄, and loading of CoFe₂O₄ NPs on substrates could further improve dispersion and avoid aggregation of NPs. Therefore, this study proposes a 3-Dimensional (3D) hierarchical catalyst which is fabricated by loading CoFe₂O₄ NPs on nitrogen-doped carbon sponge (NCS). The NCS is not only adopted as a support for CoFe₂O₄ NPs but also provides additional catalytic sites and enhances catalytic activities of CoFe₂O₄ NPs for MPS activation. As a result, CoFe₂O₄ NPs loaded on NCS (CFNCS) exhibits substantially higher catalytic activities than CoFe₂O₄ NPs and NCS individually with 100% of SAL could be afforded within 30 min. E_a of SAL degradation of 47.4 kJ/mol by CFNCS-activated MPS is also lower than those by other reported catalysts, whereas the RSE was 11.1%, which was also much higher than most of reported values. These features demonstrate that CFNCS is a promising 3D catalyst for enhancing MPS activation to degrade SAL. The findings obtained here are also insightful to develop efficient MPS-activating catalysts for eliminating contaminants.

Unified Description of the Specific Heat of Ionic Bulk Materials Containing Nanoparticles

The specific heat behavior in bulk nanomaterials (NMs) obtained by adding nanoparticles to pure suspending media has attracted a lot interest in recent years. Controversial results about NMs specific heat (c_p) have been reported in the literature, where nanoparticles (NPs) of different sizes and materials were suspended in solid and liquid salts at different concentrations and temperatures. However, a unified picture explaining the c_p enhancements and diminutions by adding NPs to pure salts is still missing. In this work, we present a general theoretical thermostatic model aimed at describing the c_p behavior in two-component ionic bulk nanomaterials containing NPs. The model, designed to work in the dilute regime, divides the NM in three regions: bulk suspending medium (SM), nanoparticles, and interface regions. It includes the effects of temperature, NP size, and NP concentration (mass fraction), allowing us to calculate c_p variations with respect to the pure SM and the ideal NM (where NP and SM are assumed to not interact). We then use the model to interpret results of our classical molecular dynamics simulations, which we perform in the solid and liquid phases of NMs representative of three different classes, defined according to the atomic interactions at the interface. The analysis reveals nontrivial and competing effects influencing c_p, such as system-dependent atomic rearrangements at the interface, vibrations of the NP as a whole and c_p variations coming from the individual NP and SM specific heats. Our study contributes to the interpretation of past controversial results and helps in designing NMs with improved thermal properties, which is highly relevant for industrial applications in thermal energy storage and renewable energy production.

Co3O4 nanocube-decorated nitrogen-doped carbon foam as an enhanced 3-dimensional hierarchical catalyst for activating Oxone to degrade sulfosalicylic acid

As sulfosalicylic acid (SUA) is extensively used as a pharmaceutical product, discharge of SUA into the environment becomes an emerging environmental issue because of its low bio-degradability. Thus, SO₄^--based advanced oxidation processes have been proposed for degrading SUA because of many advantages of SO₄^-. As Oxone represents a dominant reagent for producing SO₄^-, and Co is the most capable metal for activating Oxone to generate SO₄^-, it is critical to develop an effective but easy-to-use Co-based catalysts for Oxone activation to degrade SUA. Herein, a 3D hierarchical catalyst is specially created by decorating Co₃O₄ nanocubes (NCs) on macroscale nitrogen-doped carbon form (NCF). This Co₃O₄-decorated NCF (CONCF) is free-standing, macroscale and even squeezable to exhibit interesting and versatile features. More importantly, CONCF consists of Co₃O₄ NCs evenly distributed on NCF without aggregation. The NCF not only serves as a support for Co₃O₄ NCs but also offers additional active sites to synergistically enhance catalytic activities towards Oxone activation. Therefore, CONCF exhibits a higher catalytic activity than the conventional Co₃O₄ nanoparticles for activating Oxone to fully eliminate SUA in 30 min with a rate constant of 0.142 min^-1. CONCF exhibits a much lower Ea value of SUA degradation (35.2 kJ/mol) than reported values, and stable catalytic activities over multi-cyclic degradation of SUA. The mechanism of SUA degradation is also explored, and degradation intermediates of SUA degradation are identified to provide a possible pathway of SUA degradation. These features validate that CONCF is certainly a promising 3D hierarchical catalyst for enhanced Oxone activation to degrade SUA. The findings obtained here are also insightful to develop efficient heterogeneous Oxone-activating catalysts for eliminating emerging contaminants.

Eggshell-Membrane-Derived Carbon Coated on Li2FeSiO4 Cathode Material for Li-Ion Batteries

Lithium iron orthosilicate (LFS) cathode can be prepared via the polyol-assisted ball milling method with the incorporation of carbon derived from eggshell membrane (ESM) for improving inherent poor electronic conduction. The powder X-ray diffraction (XRD) pattern confirmed the diffraction peaks without any presence of further impure phase. Overall, 9 wt.% of carbon was loaded on the LFS, which was identified using thermogravimetric analysis. The nature of carbon was described using parameters such as monolayer, and average surface area was 53.5 and 24 m2 g−1 with the aid of Langmuir and Brunauer–Emmett–Teller (BET) surface area respectively. The binding energy was observed at 285.66 eV for C–N owing to the nitrogen content in eggshell membrane, which provides more charge carriers for conduction. Transmission electron microscopy (TEM) images clearly show the carbon coating on the LFS, the porous nature of carbon, and the atom arrangements. From the cyclic voltammetry (CV) curve, the ratio of the anodic to the cathodic peak current was calculated as 1.03, which reveals that the materials possess good reversibility. Due to the reversibility of the redox mechanism, the material exhibits discharge specific capacity of 194 mAh g−1 for the first cycle, with capacity retention and an average coulombic efficiency of 94.7% and 98.5% up to 50 cycles.

Fluorinated hybrid solid-electrolyte-interphase for dendrite-free lithium deposition

Lithium metal anodes have attracted extensive attention owing to their high theoretical specific capacity. However, the notorious reactivity of lithium prevents their practical applications, as evidenced by the undesired lithium dendrite growth and unstable solid electrolyte interphase formation. Here, we develop a facile, cost-effective and one-step approach to create an artificial lithium metal/electrolyte interphase by treating the lithium anode with a tin-containing electrolyte. As a result, an artificial solid electrolyte interphase composed of lithium fluoride, tin, and the tin-lithium alloy is formed, which not only ensures fast lithium-ion diffusion and suppresses lithium dendrite growth but also brings a synergistic effect of storing lithium via a reversible tin-lithium alloy formation and enabling lithium plating underneath it. With such an artificial solid electrolyte interphase, lithium symmetrical cells show outstanding plating/stripping cycles, and the full cell exhibits remarkably better cycling stability and capacity retention as well as capacity utilization at high rates compared to bare lithium.

Here the authors report a simple method to create a solid electrolyte interphase that is tightly anchored onto the surface of lithium metal anode. This artificial structure suppresses dead and dendrite Li and stores Li via formation of alloys, enabling impressive battery performance.

Investigating the Effect of Reaction Time on Carbon Dot Formation, Structure, and Optical Properties

Carbon dots, a young member of the carbon nanomaterial family, are quasi-spherical nanoparticles, which have fluorescent properties as their key characteristic. A wide range of starting materials and synthetic routes have been reported in the literature, divided into two main categories: a top-down and bottom-up approach. Moreover, a series of different parameters that affect the properties of carbon dots have been investigated, including temperature, starting pH, as well as precursor concentration. However, the effect of reaction time has not been extensively monitored. In our study, a biomass derivative was treated hydrothermally with varying reaction times to draw a solid formation mechanism. In addition, we monitored the effect of reaction time on optical and structural characteristics, as well as the chemical composition of our materials. Our key findings include a four-stage formation mechanism, a higher level of crystallinity, and an increasing brightness over reaction time.

Utilizing the Space-Charge Region of the FeNi-LDH/CoP p-n Junction to Promote Performance in Oxygen Evolution Electrocatalysis

The modulation of electron density is an effective option for efficient alternative electrocatalysts. Here, p-n junctions are constructed in 3D free-standing FeNi-LDH/CoP/carbon cloth (CC) electrode (LDH=layered double hydroxide). The positively charged FeNi-LDH in the space-charge region can significantly boost oxygen evolution reaction. Therefore, the j at 1.485 V (vs. RHE) of FeNi-LDH/CoP/CC achieves ca. 10-fold and ca. 100-fold increases compared to those of FeNi-LDH/CC and CoP/CC, respectively. Density functional theory calculation reveals OH^- has a stronger trend to adsorb on the surface of FeNi-LDH side in the p-n junction compared to individual FeNi-LDH further verifying the synergistic effect in the p-n junction. Additionally, it represents excellent activity toward water splitting. The utilization of heterojunctions would open up an entirely new possibility to purposefully regulate the electronic structure of active sites and promote their catalytic activities.

Lightweight Hierarchical Carbon Nanocomposites with Highly Efficient and Tunable Electromagnetic Interference Shielding Properties

High-performance electromagnetic interference shielding is becoming vital for the next generation of telecommunication and sensor devices among which portable and wearable applications require highly flexible and lightweight materials having efficient absorption-dominant shielding. Herein, we report on lightweight carbon foam-carbon nanotube/carbon nanofiber nanocomposites that are synthesized in a two-step robust process including a simple carbonization of open-pore structure melamine foams and subsequent growth of carbon nanotubes/nanofibers by chemical vapor deposition. The microstructure of the nanocomposites resembles a 3-dimensional hierarchical network of carbonaceous skeleton surrounded with a tangled web of bamboo-shaped carbon nanotubes and layered graphitic carbon nanofibers. The microstructure of the porous composite enables absorption-dominant (absorbance ∼0.9) electromagnetic interference shielding with an effectiveness of ∼20-30 dB and with an equivalent mass density normalized shielding effectiveness of ∼800-1700 dB cm³ g^-1 at the K-band frequency (18-26.5 GHz). Moreover, the hydrophobic nature of the materials grants water-repellency and stability in humid conditions important for reliable operation in outdoor use, whereas the mechanical flexibility and durability with excellent piezoresistive behavior enable strain-responsive tuning of electrical conductivity and electromagnetic interference shielding, adding on further functionalities. The demonstrated nanocomposites are versatile and will contribute to the development of reliable devices not only in telecommunication but also in wearable electronics, aerospace engineering, and robotics among others.

Nitrogen-doped graphene fiber webs for multi-battery energy storage

Freestanding carbon-based electrodes with large surface areas and pore volumes are essential to fast ion transport and long-term energy storage. Many of the current porous carbon substrates are composed of particulates, making it difficult to form a self-supported structure. Herein, novel highly porous nitrogen-doped graphene fiber webs (N-GFWs) are prepared using a facile wet-spinning method. The wet chemical process facilitates simultaneous N-doping and surface wrinkling of graphene fibers in a one-pot process. The atomic structure and electrical conductivity of N-GFWs are tailored by tuning the degree of N-doping and thermal reduction for multi-battery charge storage in both lithium-oxygen batteries (LOBs) and lithium-sulfur batteries (LSBs). The N-GFW900 electrode presents an excellent electrocatalytic activity and the cathode with a high areal loading of 7.5 mg cm-2 delivers a remarkable areal capacity of 2 mA h cm-2 at 0.2 mA cm-2 for LOBs. The N-GFW700 interlayer with abundant oxygenated and nitrogen functional groups demonstrates effective entrapment of polysulfides in LSBs, delivering a much improved specific capacity after 200 cycles at 0.5C with a remarkable decay rate of 0.04%. The current approach paves the way for rational design of porous graphene-based electrodes, satisfying multifunctional requirements for high-energy storage applications.

Ruthenium atomically dispersed in carbon outperforms platinum toward hydrogen evolution in alkaline media

Hydrogen evolution reaction is an important process in electrochemical energy technologies. Herein, ruthenium and nitrogen codoped carbon nanowires are prepared as effective hydrogen evolution catalysts. The catalytic performance is markedly better than that of commercial platinum catalyst, with an overpotential of only -12 mV to reach the current density of 10 mV cm-2 in 1 M KOH and -47 mV in 0.1 M KOH. Comparisons with control experiments suggest that the remarkable activity is mainly ascribed to individual ruthenium atoms embedded within the carbon matrix, with minimal contributions from ruthenium nanoparticles. Consistent results are obtained in first-principles calculations, where RuCxNy moieties are found to show a much lower hydrogen binding energy than ruthenium nanoparticles, and a lower kinetic barrier for water dissociation than platinum. Among these, RuC2N2 stands out as the most active catalytic center, where both ruthenium and adjacent carbon atoms are the possible active sites.

Self-recovery in Li-metal hybrid lithium-ion batteries via WO3 reduction

It has been a challenge to use transition metal oxides as anode materials in Li-ion batteries due to their low electronic conductivity, poor rate capability and large volume change during charge/discharge processes. Here, we present the first demonstration of a unique self-recovery of capacity in transition metal oxide anodes. This was achieved by reducing tungsten trioxide (WO3) via the incorporation of urea, followed by annealing in a nitrogen environment. The reduced WO3 successfully self-retained the Li-ion cell capacity after undergoing a sharp decrease upon cycling. Significantly, the reduced WO3 also exhibited excellent rate capability. The reduced WO3 exhibited an interesting cycling phenomenon where the capacity was significantly self-recovered after an initial sharp decrease. The quick self-recoveries of 193.21%, 179.19% and 166.38% for the reduced WO3 were observed at the 15th (521.59/457.41 mA h g-1), 36th (538.49/536.61 mA h g-1) and 45th (555.39/555.39 mA h g-1) cycles respectively compared to their respective preceding discharge capacity. This unique self-recovery phenomenon can be attributed to the lithium plating and conversion reaction which might be due to the activation of oxygen vacancies that act as defects which make the WO3 electrode more electrochemically reactive with cycling. The reduced WO3 exhibited a superior electrochemical performance with 959.1/638.9 mA h g-1 (1st cycle) and 558.68/550.23 mA h g-1 (100th cycle) vs. pristine WO3 with 670.16/403.79 mA h g-1 (1st cycle) and 236.53/234.39 mA h g-1 (100th cycle) at a current density of 100 mA g-1.

From Checkerboard-Like Sand Barriers to 3D Cu@CNF Composite Current Collectors for High-Performance Batteries

While the architecture, surface morphology, and electrical conductivity of current collectors may significantly affect the performance of electrochemical cells, many challenges still remain in design and cost-effective fabrication of highly efficient current collectors for a new generation of energy storage and conversion devices. Here the findings in design and fabrication of a 3D checkerboard-like Cu@CNF composite current collector for lithium-ion batteries are reported. The surface of the current collector is modified with patterned grooves and amorphous carbon nanofibers, imitating the checkerboard-like sand barriers in desert regions. Due to a combined effect of the grooves and the carbon nanofibers, a battery based on this current collector retains a reversible capacity of 410.1 mAh g-1 (beyond the theoretical capacity of carbonaceous materials of 372 mAh g-1) with good capacity retention (greater than 84.9% of the initial capacity after 50 cycles), resulting in 66.2% and 42.6% improvement in reversible capacity and capacity retention, respectively, compared to the batteries using traditional Cu current collectors. Based on the excellent electrochemical performance, this composite current collector is believed to be an attractive alternative to the traditional commercially used current collectors for the anode of high-power energy storage systems.