Graphene Matrix Research Articles

The Fabrication of Graphene Supported Ni Nanoparticles and Its Doping Influence on The Microstructure and Superconductivity of MgB2

A highly dispersed Ni nanoparticle supported on a graphene matrix (nano-Ni/G) has been successfully synthesized using a novel chemical reduction process to overcome agglomeration in traditional MgB2 preparation methods. The influence of the reduction technique on nanoparticle size and structure was thoroughly investigated using a model system. The resulting nanoparticles were small enough (10 nm) to decorate the 2D graphene layers as sandwich structures. This unique morphology contributes to providing more effective flux pinning centers by forming tiny MgNi2.5B2 and efficiently substituting C for B in MgB2 bulks through the principle of double action. Moreover, the low-melting eutectic liquid formed by Mg-Ni at 506 °C is beneficial for the fast fabrication of well-connected MgB2 at low temperatures. Furthermore, a small enhancement of critical current density (Jc) was observed in the doped sample with respect to the undoped ones. However, the advantages of the as-prepared nanoparticles were greatly suppressed by the large presence of MgO during the deposition process, leading to lower superconducting performance than undoped MgB2 bulks. Based on the analysis, further investigation should focus on inducing more flux pinning centers by controlling impurities during the deposition process for achieving optimal performance.

Laser-Induced Solid-Phase Strategy to Synthesize Single-Atomic Lithiophilic Sites Enabled Dendrite-Free Lithium Deposition on Graphene Matrix.

The introduction of metal Single-atom (SA) to construct lithium-philic active sites shows the ability to guide uniform lithium deposition and improve the stability of lithium hosts. Nevertheless, the development of facile and expedient methods for synthesizing SA remains a considerable challenge. Herein, The SA metal loaded on graphene (Bi@LrGO) is designed by laser-induced solid-phase strategy. The bismuth salts simultaneously decompose under the high local temperature and in the reductive atmosphere induced by laser to form SA metal. Simultaneously, graphene oxide (GO) nanosheets absorb photon energy to be reduced/graphitized into graphene, which serves as anchoring sites for Bismuth Sing-atom (Bi SA) immobilization. The SA metals, supported on the graphene not only provide sufficient lithiophilic sites but also significantly increase the adsorption energy (-2.11eV) with lithium atoms, promote the uniform nucleation and deposition of lithium, and inhibit the growth of lithium dendrites. Additionally, the layered structure of the graphene film adapts to the volume change during the repeated lithium plating/stripping process. Therefore, the symmetrical battery-based Li deposited on Bi@LrGO (Bi@LrGO@Li) achieves an ultra-long stable cycle life of ≈2400h at 1mAcm-2. In particular, a full cell with LiFePO4 cathode provides a good capacity retention of 81.2% at 4C after 600 cycles.

Nitrogen‑sulfur doped graphene-loaded SiO2/Co9S8 composites as anode materials for improved lithium storage

Heteroatom-doped graphene lamellae can effectively modulate the physical and chemical surface activities of Co9S8 materials. The addition of a second dopant atom, such as nitrogen (N) can further improve the composite properties. Herein, novel nitrogen‑sulfur double-doped graphene-loaded SiO2/Co9S8 composites (SiO2/Co9S8@NSG) were prepared by a one-step solvothermal method using polyethylene glycol as the carbon source and cobalt chloride hexahydrate as the cobalt source to yield a Deep Eutectic Solvents (DESs) system. The precursor was then obtained by adding tetraethyl silicate as the silicon source, thiourea as the sulfur source, and urea as the nitrogen source. The uniform distribution of Co9S8 in the N/S-doped graphene matrix formed graphene-coated SiO2 particles SiO2/Co9S8@NSG with high specific surface area, superior ionic conductivity, and elevated theoretical specific capacity. The N/S co-doped graphene matrix not only improved the electrical conductivity and hindered the adhesion of the particles, but also buffered the volume of the Co9S8 change and enhanced the electrochemical performance. The testing of SiO2/Co9S8@NSG composite as an anode for lithium-ion batteries (LIBs) revealed an impressive specific capacity with reversible capacity of 850 mA h/g after 900 cycles at a current density of 0.5 A/g and multiplicative capacity of 730 mA h/g at a current density of 0.1 A/g, confirming excellent cycling stability and a Coulombic efficiency close to 100 %. Overall, the proposed doping strategy looks promising for the development of high-performance LIBs.

A Lennard-Jones potential based cohesive zone model and its application in multiscale damage simulation of graphene reinforced nanocomposites

A new mixed-mode cohesive zone model based on Lennard-Jones potential (LJCZM) is proposed to simulate the interface failure between graphene and epoxy matrix. The values of model parameters are obtained from a large number of molecular dynamics simulations, and a UMAT subroutine is programmed and validated to introduce this model into the ABAQUS platform. This process spans from the nanoscale to the microscale, which provides a new routine for the multiscale damage modeling of the graphene reinforced epoxy nanocomposite at microscale. In addition, the continuous damage phase-field model is used to simulate the matrix damage, and the values of model parameters are determined from the molecular dynamic simulations of the bulk epoxy at nanoscale. At last, the effects of parameters such as volume fraction, aspect ratio, orientation, and curvature of graphene nanoplatelets are investigated. The results indicate that the nanocomposite reinforced with high content and large aspect ratio graphene nanoplatelets presents the lower ultimate stress and fracture strain. In addition, the orientation and waviness of the graphene also significantly affect the mechanical properties of the nanocomposites. The nanocomposite reinforced with graphene platelets with greater waviness has higher stiffness and strength but lower toughness. The rationality and effectiveness of the model are verified through comparison with other existing results.

Confined Mo2C/MoC heterojunction nanocrystals-graphene superstructure anode for enhanced conversion kinetics in sodium-ion batteries

Heterostructure design and integration with conductive materials play a crucial role in enhancing the conversion kinetics of electrode materials for metal-ion batteries. However, integrating nanocrystal heterojunctions into a conductive layer to form a superstructure is a significant challenge, mainly due to the difficulty in maintaining the structural integrity. Here we report a unique glucose-induced heterogeneous nucleation method that enables the independent manipulation of nucleation and growth of Mo2C/MoC heterojunction nanocrystals within 2D layers. Our investigations reveal that the rGO-Mo2C/MoC-rGO superstructure is formed by a topological transformation induced by subsequent heat treatment of the initial hydrothermally prepared rGO-MoO2-rGO precursor. This novel structure embeds Mo2C/MoC heterojunction nanocrystals within a 2D graphene matrix, providing enhanced mechanical stability, accelerated Na+ transport, and improved electron conduction. Ex situ XRD and Raman spectroscopy analyses reveal that the rGO-Mo2C/MoC-rGO superstructure significantly enhances the stability and reversibility of anodes. Leveraging these unique characteristics, the newly developed superstructural anode exhibits remarkable long-term cycling stability and outstanding rate performance. As a result, superstructure anodes demonstrate superior electrochemical capabilities, delivering a specific capacity of 106 mAh/g after enduring 5000 cycles at 1 A/g. Our study underscores the critical importance of superstructure design in propelling the advancement of battery materials.

Influence of Graphene on Sheet Resistivity and Urbach Enery of Nano TiO<sub>2</sub> for DSSC Electrode

Importance of renewable energy cannot be over emphasized. Titanium IV oxide (TiO<sub>2</sub>) is the most suitable semiconductor for dye sensitized solar cell (DSSC) due to its chemical stability, non toxicity and excellent optoelectronic properties. In this research TiO<sub>2</sub> is coated on graphene to enhance its charge transport aiming to reduce recombination which is a main set back in DSSCs. undestanding graphene- TiO<sub>2 </sub>contact is therefore essential for DSSC application. TiO<sub>2</sub> thin films were deposited on single layer graphene (SLG) as well as on flourine tin oxide (FTO) using doctor blading technique. The films were annealed at rates of 2°C /min and 1°C/min up to a temperature of 450°C followed by sintering at this temperature for 30 minutes. Four point probe SRM-232 was used to measure sheet resistance of the samples. The film thickness were obtained from transmittance using pointwise unconstrained minimization approximation (PUMA). UV –VIS spectrophotometer was employed to measure transmittance. Resistivity of TiO<sub>2</sub> on both FTO and Graphene were of order 10<sup>-4</sup> Ωcm. However, TiO<sub>2</sub> annealed on graphene matrix exhibited a slightly lower resistivity 5.6 x10<sup>-4</sup> Ωcm as compared to 6.0x10<sup>-4 </sup>Ωcm on FTO. Optical transmittance on visible region was lower for TiO<sub>2</sub> on FTO than on SLG, 71.48% and 80.11% respectively. Urbach energy (Eu) for weak absorption region decreased with annealing rate. Urbach energies for 1°C/min TiO<sub>2 </sub>on FTO and SLG were 361 meV and 261meV respectively. This was used to account for decrease of disoders of films due to annealing. A striking relation between sheet resistivity and urbach was reported suggesting SLG as a suitable candidate for photoanode of a DSSC.

Enhanced interfacial bonding and mechanical properties of CeO2-coated graphene oxide reinforced 7075 composites

Severe interfacial reactions and interfacial bonding between graphene and Al matrix have been the main challenges to achieve high performance graphene reinforced aluminum matrix composites (AMCs). In this study, a new interfacial structure design was proposed to address the above challenges by coating CeO2 nanoparticles on the surface of graphene oxide (GO). Then, CeO2-coated GO reinforced 7075 (GO/7075) composites were successfully fabricated via ultrasonic assisted casting. It was found that the coated CeO2 on GO could react with Al matrix to form Al11Ce3 and suppress the formation of interfacial product Al4C3. Additionally, the as-formed Al11Ce3 at the interface served as a bridge to tightly bind the GO and Al, thus resulting in forming a strong interfacial bonding, which was favour to the load transfer. Moreover, when adding 1.5 wt% CeO2-coated GO, the average grain size of the composites reduced from 100.8 μm to 38.5 μm. As a result, the composite reinforced with 1.5 wt% CeO2-coated GO demonstrated enhanced mechanical properties with a yield strength of 263.4 MPa and an ultimate tensile strength of 342.8 MPa, 100.8% and 69.4% higher than those of unreinforced 7075 alloy, respectively. Furthermore, the strengthening mechanisms of CeO2-coated GO/7075 composites were discussed in detail.

Rapid Joule heating-induced welding of silicon and graphene for enhanced lithium-ion battery anodes

In the pursuit of enhanced energy storage solutions, the application of silicon-based anode materials faces significant hurdles, primarily stemming from the rapid capacity degradation during battery cycles. This study introduces a novel and efficient method for fabricating Si/graphene composites (F-Si@rGO), enhancing the performance and longevity of silicon-based anodes. Utilizing ultra-high-speed thermal treatment, this technique controls the thermal interaction between carbon and silicon phases, leading to the formation of silicon carbide “riveting points” that firmly anchor silicon nanoparticles within the graphene matrix. This novel method effectively minimizes the problems of phase segregation, which are caused by varying degrees of wettability alteration in the two phases during conventional heat treatments, and guarantees a robust integration of graphene and silicon. This integration results in homogeneous charging and outstanding structural stability of the composites, over extended cycles of use. The resulting Si/graphene composites exhibit exceptional electrochemical performance, achieving a high initial capacity of 1141.3 mAh g−1 at 1C and maintaining a capacity of 894.95 mAh g−1 after 1000 cycles with minimal degradation (0.0216 % per cycle). This synthesis method, notable for its speed and scalability, offers a potential advancement in battery material technology, suggesting a path towards more resilient and efficient energy storage solutions.

Structure engineering and heteroatom doping-enabled high-energy and fast-charging dual-ion batteries

Sodium dual-ion batteries (SDIBs) have attracted extensive attention due to the high working voltage and low cost. Nevertheless, lack of robust anode materials that can achieve highly efficient insertion/extraction of sodium ions still remains a huge challenge to develop the high-performance SDIBs. Herein, we exhibited excellent long-cycling performance (capacity retention of 85 % over 2000 cycles) with large reversible capacity (1788 mA h g−1 under 0.2 A/g) as well as superior rate capability (721 mA h g−1 under 10 A/g) for sodium-ion storage by encapsulating red phosphorus within nitrogen-doped mesoporous graphene particles. And the structural stability of composite during sodiation was directly demonstrated using in-situ transmission electron microscopy. The results of density functional theory reveal that nitrogen doping and formation of PC chemical bonds within graphene matrix may improve the adsorption energy of P atoms and promote the sturdy contact. The adsorption energies of nitrogen-doped graphene for Na+ and PF6− are −2.12 and −3.62 eV, respectively, which shows that the doping of N element is beneficial to the adsorption of Na+ and PF6−. Upon pairing with nitrogen-doped mesoporous graphene particles as cathode, an innovative SDIBs with high energy-power-density of 324 W h kg−1 at 331 W kg−1 and 187 W h kg−1 at 2665 W kg−1 were manufactured. This study opens up an effective strategy towards high-performance SDIBs for electric vehicles and other applications.

A High‐Performance Phosphate Potentiometric Sensor Based on Cobalt Nanoparticles Electroplated on Hierarchically Porous Laser‐Induced Graphene

AbstractPhosphate is an important fertilizer in agriculture and electrochemical sensors based on cobalt (Co) are promising for measurement of phosphate. The deposition of Co onto conductive substrates to form a nano/microstructured Co layer with rich active sites is a typical strategy to improve detection performances. However, the widely used substrates show smooth surfaces, which cannot provide extra active sites. Herein, a high‐performance phosphate sensor is fabricated by generating Co nanoparticles (NPs) on a hierarchically porous laser‐induced graphene (LIG) matrix with a large surface area. Specifically, a Co layer is first electroplated on the LIG matrix. Nevertheless, the pores of LIG will be blocked by the dense Co layer so the performances of the fabricated LIG‐Co sensor exhibit limited enhancements. Therefore, a “nearly all etching (NAE)” technique is developed to transform the dense Co layer to dispersive Co NPs and re‐expose the pores of LIG, both increasing the active sites. Compared to the LIG‐Co sensor, the LIG‐Co NP sensor displays overall superiority. The response time, sensitivity, and linearity are enhanced from ≈60 to ≈10 s, from 0.012 to 0.069 V dec−1, and from 0.973 to 0.998, respectively. The LIG‐Co NP sensor also shows a decent anti‐interference capability.

Activation of peroxymonosulfate by LaCO3OH coupled with N, S co-doped graphene for levofloxacin degradation

There is currently great potential in peroxymonosulfate (PMS) activation by metal-based materials for contaminant treatment. However, secondary environmental damage from common transition metals is often unavoidable. Rare earth metals with high energy level, multi-electron configuration and unique 4f orbital can be used as an electron transfer bridge to reduce interfacial energy loss and promote electron transfer, which were incorporated the catalyst to activate PMS. In this study, calcination and hydrothermal methods were combined to fabricate LaCO3OH in combination with N, S co-doped graphene (LCOH/GNS), which exhibited efficient levofloxacin (LVX) degradation. The results indicated that the LVX removal efficiency reached 89.6 %, and the La3+ leaching was as low as 1.2 mg/L. LaCO3OH (LCOH) was first used for PMS activation and showed excellent degradation properties and reduced ecotoxicity. Doping the graphene matrix with N and S enhances the adsorption of PMS, increases electron transfer and reduces leaching of metal ions, thus promoting the interaction and reaction between LCOH and PMS. As confirmed by radical quenching tests and EPR technique, multiple oxidative pathways may be involved in the degradation process. This paper presented an innovative approach to the rational design of rare earth metal-based carbon catalysts, and it was expected that LCOH/GNS-PMS would prove to be a promising technology for degrading antibiotics in wastewater treatment.

Visible light-assisted S-scheme p- and n-type semiconductors anchored onto graphene for increased photocatalytic H2 production via water splitting

This work reports on photocatalytic hydrogen (H2) production via water splitting by synthesizing CuO and ZnO semiconductors anchored onto graphene by varying the mass ratios of CuO and ZnO into the graphene matrix. The high H2 production performance for binary nanocomposite (CuO/ZnO) compared to its components confirms the synergistic effect between ZnO and CuO nanoparticles. Introducing 10 wt% graphene into CuO and ZnO displayed the highest H2 production reaching to 37.2 mmol/g.h, which was 3.29 times higher than pristine binary nanocomposite (CuO/ZnO). The graphene played a critical role in enhancing the photocatalytic activity of CuO and ZnO towards H2 production, owing to the accelerated transport of photo-excited electrons between the semiconductors. Under the optimum conditions, H2 production by 10 % of graphene into CuO and ZnO reached a maximum value of 48.6 mmol/g.h when Na2S/Na2SO3 was used as a sacrificial agent. The charge transfer carriers were monitored to explain the photocatalytic H2 production mechanism based on the optical property characterizations and S-scheme heterojunction system. An excellent reusability was achieved after five consecutive cycles of H2 production reaction. The outcome of this research introduces a reusable and effective catalyst with a facile and easy configuration for energy production applications and confirms that the decoration of semiconductors on graphene could be a promising strategy for highly-efficient photocatalytic H2production. Furthermore, by offering a clean alternative to fossil fuels and reducing greenhouse gas emissions—especially when produced from renewable sources—hydrogen can significantly contribute to achieving sustainable development goal 7 (SDG 7), thus advancing toward a more sustainable, equitable future.

Titania/graphene nanocomposites from scalable gas-phase synthesis for high-capacity and high-stability sodium-ion battery anodes

In sodium-ion batteries (SIBs), TiO2 or sodium titanates are discussed as cost-effective anode material. The use of ultrafine TiO2 particles overcomes the effect of intrinsically low electronic and ionic conductivity that otherwise limits the electrochemical performance and thus its Na-ion storage capacity. Especially, TiO2 nanoparticles integrated in a highly conductive, large surface-area, and stable graphene matrix can achieve an exceptional electrochemical rate performance, durability, and increase in capacity. We report the direct and scalable gas-phase synthesis of TiO2 and graphene and their subsequent self-assembly to produce TiO2/graphene nanocomposites (TiO2/Gr). Transmission electron microscopy shows that the TiO2 nanoparticles are uniformly distributed on the surface of the graphene nanosheets. TiO2/Gr nanocomposites with graphene loadings of 20 and 30 wt% were tested as anode in SIBs. With the outstanding electronic conductivity enhancement and a synergistic Na-ion storage effect at the interface of TiO2 nanoparticles and graphene, nanocomposites with 30 wt% graphene exhibited particularly good electrochemical performance with a reversible capacity of 281 mAh g−1 at 0.1 C, compared to pristine TiO2 nanoparticles (155 mAh g−1). Moreover, the composite showed excellent high-rate performance of 158 mAh g−1 at 20 C and a reversible capacity of 154 mAh g−1 after 500 cycles at 10 C. Cyclic voltammetry showed that the Na-ion storage is dominated by surface and TiO2/Gr interface processes rather than slow, diffusion-controlled intercalation, explaining its outstanding rate performance. The synthesis route of these high-performing nanocomposites provides a highly promising strategy for the scalable production of advanced nanomaterials for SIBs.

Growth of copper-nickel (Cu-Ni) dual atom catalysts over graphene variants as active anodes for clean oxygen generation: Integrative experimental and computational validation

The development of atomically precise metals on the surface of graphene has led to superior electrocatalytic properties for the clean oxygen production. In this study, Cu single-atom and NiCu dual-atom catalysts supported on different graphene variants were effectively developed as electrocatalysts for the production of clean oxygen. Various techniques, including XRD, SEM, Raman, HR-TEM, EXAFS and XPS, were used to characterize these synthesized electrocatalysts. The extent of reduction in graphene oxide (GO) support was confirmed using Raman analysis which demonstrated a greater ID/IG-apparent intensity ratio, indicating that the GO (ID/IG=0.9) has more sp3-hybridized carbon with respect to the rGO (ID/IG= 0.6). The HR-TEM analysis with EDX and STEM data confirmed the dispersion of Cu and NiCu dimer over the surface of graphene variants. XPS and EXAFS studies revealed predominant metallic nature of Cu and NiCu dimer with the synergistic interplay between the constituent atoms. Copper-nickel dimer catalyst supported on reduced graphene oxide (CuNi/rGO) demonstrated the best electrocatalytic performance, where a lower overpotential of 320 mV was observed to reach a current density of 10 mA cm−2 with lowest Tafel slope of 110 mV/dec for oxygen evolution reaction. Good stability was observed after 1000 CV cycles and 50 h of electrolysis in 1.0 M KOH electrolytic solution at an oxidation potential of 1.62 V (vs RHE). Control experiments were also performed using borosilicate pyrex glass and Teflon made electrochemical cells in order to over rule the probable involvement of leached out impurities in OER reaction under extreme alkaline conditions. The calculations obtained from Density Functional Theory (DFT) suggest that the dual-atom catalysts have lower overpotential (0.33 V at Cu-site) with respect to the single-atom catalysts, which agreed well with the experimental results. Also, the Cu-site OER was found to have lower overpotential (0.33 V) than the Ni-site (0.47 V). Thus, this study can provide valuable insights into developing low-cost dual-atom electrocatalysts, where the synergism between constituent elements in the dimer and their stabilization by graphene matrix can be exploited for various electrochemical reactions.

Architectural engineering of MoSeS material for high-performance aluminum-ion batteries

Architectural engineering emerges as a promising strategy for modulating the energy storage performance of electrode materials. In this study, the incorporation of the S element and a graphene matrix led to the formation of a unique heterojunction structure and defect construction in MoSeS hybrids, resulting in heightened electronic conductivity and increased active sites for aluminum storage. Experimental findings, coupled with density functional theory calculations, indicate that architectural engineering effectively reduces the energy barrier and mitigates structural changes during the diffusion of Al3+. Consequently, MoSeS exhibits an exceptionally high specific capacity of 291.8 mAh/g at a current density of 100 mA g−1, a remarkable rate performance of 106.2 mAh/g at 1000 mA g−1, and outstanding cycling stability with a retained capacity of 158.5 mAh/g over 1000 cycles at 150 mA g−1. The heterojunction structure and defect construction strategy offer an efficient means to tailor electrode materials for high-performance aluminum-ion storage.

Low-temperature compositing of graphene to nanodiamonds by thermal reduction of graphene oxide and photocatalytic properties

Graphene has become a research hotspot in the field of composites due to its special structure and excellent properties The common preparation methods of graphene matrix composites include solvent (hydrothermal) method, sol-gel method, chemical reduction method, electrochemical deposition method, etc. Nanodiamond/reduced graphite oxide (rGO) composites are directly synthesized by low-temperature heat treatment with nanodiamonds and graphite oxide (GO) powders as raw materials with the aid of GO thermal reduction at 195 °C. The degradation ability of samples to methylene blue (MB) under simulated sunlight was tested. Results indicated that GO was thermally reduced to graphene at low temperature, and rGO well combined with diamond. After the introduction of GO, the lattice of nanodiamond underwent distortion. Diamond and graphene formed a quasi-core–shell structure, and the interface between them was well bonded. The composite had a large specific surface area (Brunauer–Emmett–Teller value of 93.13 m2/g). The addition of GO enhanced the absorbance of the samples and reduced the bandgap of nanodiamond. When the ratio of nanodiamond to GO was 6:1, the sample exhibited excellent sunlight photocatalytic activity, and MB degradation rate reached 99.8 % within 40 min. The reduction reaction of GO at low temperature promoted its rapid combination with nanodiamonds. This method had the outstanding advantages of simple process, environment friendliness, and easy mass production.

Time-Efficient Fabrication of Stable Core–Shell Spinel Ferrites on a Self-Assembled Nanoarchitectonic Graphene Matrix as a New-Gen Anode for Li-Ion Batteries

Time-Efficient Fabrication of Stable Core–Shell Spinel Ferrites on a Self-Assembled Nanoarchitectonic Graphene Matrix as a New-Gen Anode for Li-Ion Batteries

The chimera of 2D- and 1D-graphene magnetization by hydrogenation or fluorination: critically revisiting old schemes and proposing new ones by ab initio methods.

Graphene is an ideal candidate material for spintronics due to its layered structure and peculiar electronic structure. However, in its pristine state, the production of magnetic moments is not trivial. A very appealing approach is the chemical modification of pristine graphene. The main obstacle is the control of the geometrical features and the selectivity of functional groups. The lack of a periodic functionalization pattern of the graphene sheet prevents, therefore, the achievement of long-range magnetic order, thus limiting its use in spintronic devices. In such regards, the stability and the magnitude of the instilled magnetic moment depending on the size and shape of in silico designed graphane islands and ribbons embedded in graphene matrix will be computed and analysed. Our findings thus suggest that a novel and magneto-active graphene derivative nanostructure could become achievable more easily than extended graphone or nanoribbons, with a strong potential for future spintronics applications with a variable spin-current density.

Axial heteroatom (P, S and Cl)-decorated Fe single-atom catalyst for the oxygen reduction reaction: a DFT study.

An FeN4 single-atom catalyst (SAC) embedded in a graphene matrix is considered an oxygen reduction reaction (ORR) catalyst for its good activity and durability, and decoration on the Fe active site can further modulate the performance of the FeN4 SAC. In this work, the axial heteroatom (L = P, S and Cl)-decorated FeN4 SAC (FeN4L) and pure FeN4 were comparatively studied using density functional theory (DFT) calculations. It was found that the rate-determining step (RDS) in the ORR on pure FeN4 is the reduction of OH to H2O in the last step with an overpotential of 0.58 V. However, the RDS of the ORR for the axial heteroatom-decorated FeN4L is the reduction of O2 to OOH in the first step. The axial P and S heteroatom-decorated FeN4P and FeN4S exhibit lower activity than pure FeN4 since the overpotentials of the ORR on FeN4P and FeN4S are 1.02 V and 1.09 V, respectively. Meanwhile, FeN4Cl exhibits the best activity towards the ORR since it possesses the lowest overpotential (0.51 V). The main reason is that the axial heteroatom decoration alleviates the adsorption of all the species in the whole ORR, thus modulating the free energy in every elementary reaction step. A volcano relationship between the d band center and the ORR activity can be determined among the axial heteroatom-decorated FeN4L SACs. The d band center of the Fe atom in various FeN4L SACs follows the order of FeN4 > FeN4Cl > FeN4S > FeN4P, whereas the overpotential of the ORR on various catalysts follows the order of FeN4Cl > FeN4 > FeN4S ≈ FeN4P. ΔG(*OH) is a simple descriptor for the prediction of the ORR activity of various axial heteroatom-decorated FeN4L, although the RDS in the ORR is either the first step or the last step. This paper provides a guide to the design and selection of the ORR over SACs with different axial heteroatom decorations, contributing to the rational design of more powerful ORR electrocatalysts and achieving advances in electrochemical conversion and storage devices.

Fabrication and evaluation of a flexible antenna device composed of a compatible iron-oxide clay in a PDMS graphene matrix

We create a flexible and robust conductive polymer composite based on iron oxide and a thin film of clay doped with graphene nanoparticles, and test its application as a wearable device for underground workers.