In situ coupling of lignin-derived carbon-encapsulated CoFe-CoxN heterojunction for oxygen evolution reaction

Exploring highly active and stable electrocatalysts for oxygen evolution reaction (OER) is crucial for developing water splitting and rechargeable metal-air batteries. In this study, a hybrid electrocatalyst of CoFe alloy and Co_xN heterojunction encapsulated and anchored in N-doped carbon support (CoFe-Co_xN@NC) was in situ coupled via the pyrolysis of a novel coordination polymer derived from lignin biomacromolecule. CoFe-Co_xN@NC exhibited outstanding OER activity with a low overpotential of 270 mV at 10 mA cm⁻² and stability with an increment of 20 mV, comparable to commercial Ir/C. DFT calculations showed that Co_xN and N-doped graphitic encapsulation can reduce the binding strength between *O and CoFe alloy, limit metal leaching and agglomeration, and improve electron transfer efficiency, considerably enhancing the OER activity and stability. In situ coupling approach for preparing alloy and nitride heterojunctions on N-doped lignin-derived carbon offers a promising and universal catalyst design for developing renewable energy conversion technologies.     

Ba0.95La0.05FeO3−δ–multi-layer graphene as a low-cost and synergistic catalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) is critical to many important energy conversion and storage processes. However, the kinetics of OER is typically sluggish, and conventional OER catalysts are scarce and expensive. Hence, inexpensive and effective catalysts that accelerate the OER kinetics and reduce the overpotential are urgently needed. In this paper, we reported multi-layer graphene-supported perovskite Ba_0.95La_0.05FeO_3−δ (BLF–MLG) as a highly active OER catalyst. Electrochemical results showed that the BLF–MLG hybrid exhibited a high current density (∼23 mA/cm² at 0.60 V vs. mercury/mercury oxide electrode (MMO)) and a more negative onset potential (∼0.43 V vs. MMO). Furthermore, the hybrid showed a smaller Tafel slope (77 mV/decade) and improved long-term stability. The remarkable OER performance is mainly attributed to the synergistic effect between BLF and graphene.     

MOF nanosheet array-derived NiS with Co,N-doped carbon layer: A highly efficient oxygen evolution electrocatalyst

The development of the hydrogen industry from electrolytic water is confined in great measure to the slow kinetics of oxygen evolution reaction (OER), which means the rational design of a stabilized and efficient OER electrode is the key. The construction of easily accessible hydroxide ion (OH^?) adsorption sites can effectively accelerate the kinetics of the OER. Herein, the NiS/CoNC electrocatalysts, which can effectively adsorb OH^? and exhibited excellent OER performance in an alkaline environment, were obtained by pyrolysis and sulfidation of NiCo-MOF nanosheets on nickel foam (NF). In particular, the optimized NiS/CoNC electrocatalyst achieved an overpotential of 46/106 mV at 10/100 mA cm^?2 and Tafel slope of 57.41 mV dec^?1, which is superior to most reported materials. The outstanding function of OER results from the NiOOH/CoOOH active component generated by surface reconstruction after activation of the NiS/CoNC catalyst and the excellent charge transfer capability of the NiS component. This work offers a scheme to construct the electrocatalysts derived from MOF with excellent OER performance.     

Enhanced irradiation-resistance of polymer-derived SiC by incorporation of multiwalled carbon nanotubes

In this work, multiwalled carbon nanotubes were introduced into polycarbosilane to fabricate carbon nanotubes reinforced nano-SiC composites (MWCNTs/ PCS-nano-SiC). Radiation effects on MWCNTs/ PCS-nano-SiC were studied by irradiation with 2 MeV Au²⁺ ions at room temperature and doses ranging from 2 × 10¹⁴ to 8 × 10¹⁴ ions/cm². The sample pyrolyzed at 1400 °C and containing 3 wt% carbon nanotubes exhibited excellent overall performances. The multiple graphite layers in the MWCNTs provided "absorption traps" for defects, improving the efficiency of defect recombination. Tightly combined MWCNTs/ PDC interface is required to enable the two phases to protect each other during irradiation. The critical amorphization dose was increased upon structural optimization, and the hardness degradation was significantly reduced. The rise of Young's modulus at a high damage dose was discovered because of the "interface-driven shrinkage" of nano-SiC. The present study provides insight into SiC_f/ SiC design for an advanced nuclear system.     

The Heterojunction of Ni and Co9S8 was Synthesized and Anchored on Carbon Nanotubes to Improve the Performance of Water Electrolysis

Developing durable, low-cost water electrolysis catalysts plays a critical role in solving clean energy problems. Herein, we synthesized Ni/Co₉S₈@CNT micro flower comprising Ni/Co₉S₈ mesoporous nanosheets and carbon nanotubes (CNT). HRTEM images indicate that the Ni/Co₉S₈@CNT micro flower contains abundant Ni/Co₉S₈ heterojunctions. The band structure and coupling effect of the Ni/Co₉S₈ heterostructure optimizes the transfer of electrons, thus the synergistic hybrid effectively improves conductivity and electrocatalytic performance. Therefore, Ni/Co₉S₈@CNT shows good evolution reaction (OER) and hydrogen evolution reaction (HER) performance in an alkaline environment. Specifically, at a current density of 10 mA cm^?2, the overpotential of OER is 289 mV, and the overpotential of HER is 228 mV. The Tafel slope is 69 mV dec^?1. In addition, Ni/Co₉S₈@CNT in alkaline electrolyte only loses 10% of its activity after working for 10 h at a current density of 10 mA cm^?2. These results indicate that composite materials composed of transition metal sulfides and highly conductive carbon materials are a good choice for low-cost electrocatalysts.

Graphic abstract

Synthesize the heterojunction of metal Ni and Co9S8 and anchor it on the CNT to improve the performance of OER and HER.

     

Study of structural and electrochemical characteristics of Co-based hypo-hyper d-electrocatalysts for hydrogen evolution

Structural and electrochemical characteristics of hypo-hyper d-electrocatalytic materials aimed for preparation of electrodes for hydrogen evolution were studied. The basic catalytic material was prepared of 10% amorphous Co (grain size <2 nm), 18% amorphous TiO₂ and Vulcan XC-72, by sol-gel procedure. A number of modifications were applied aimed at improving the materials performances: (i) TiO₂ was transformed into anatase by heating at 480 °C for 1 h, (ii) multiwalled carbon nanotubes (MWCNT) were used as a catalyst support instead of Vulcan XC-72 and (iii) Mo was added to Co phase in a quantity of 25 at.% (Mo:Co = 1:3).Both, material's intrinsic catalytic activity and surface area were affected by these modifications. As a result, the electrocatalytic activity for hydrogen evolution was improved, e.g. transformation of TiO₂ into anatase form lowers the HER overpotential (η) for 15 mV at 60 mA cm⁻². Introduction of MWCNTs lowered η for 30 mV, while addition of Mo to metallic phase for 40 mV.The complete modification of all three catalyst's components (10% MoCo₃ + 18% anatase + MWCNTs) was the most effective with 60 mV decrease of overpotential.Characterization was made by XRD, SEM, IR and XPS methods. Surface area was measured by means of cyclic voltammetry.     

Effects of adding different morphological carbon nanomaterials on supercapacitive performance of sol–gel manganese oxide films

In this study, the supercapacitive performances of manganese oxide films were investigated by adding different carbon nanomaterials, including carbon nanocapsules (CNC), multiwalled carbon nanotubes (MWCNTs) and multi-layered graphene. The manganese oxide films were prepared with manganese acetate precursor by sol–gel method, and the post-treatment effects were also examined. With a heat-treatment above 300 °C, the as-prepared amorphous films transformed to a compound of Mn₃O₄ and Mn₂O₃ phases, and the smooth surface became rough as well. Cyclic voltammogram (CV) tests showed that the manganese oxide film, which was mixed with 0.05 wt% MWCNTs and annealed at 350 °C for 1 h, exhibited the optimized specific capacitance, 339.1 F/g. During 1000CV cycles, the specific capacitances of original manganese oxide film decreased gradually from 198.7 to 149.1 (75%) F/g. After same number of cycle tests, the modified films containing 0.025 wt% CNC, 0.05 wt% MWCNTs and 0.1 wt% graphene retained 201.8 (64.2%), 267.4 (78.9%) and 193.1 (57.4%) F/g respectively. The results indicates that the supercapacitive performance of manganese oxide films were significantly modified by carbon nanomaterials; in addition, the MWCNTs additive could also reduce the decay rate.     

Bomb calorimetry as a bulk characterization tool for carbon nanostructures

Multiwalled carbon nanotubes (MWCNTs) consisting of coaxial graphene cylinders (cylindrical MWCNTs), cones (herringbone MWCNTs) or carbon fibers were combusted in an isothermal bomb calorimeter. Their standard enthalpies of formation were determined to be 16.56 ± 2.76 kJ mol⁻¹(C – per carbon mol) for carbon fibers, 21.70 ± 1.32 kJ mol⁻¹(C) for herringbone MWCNTs and 8.60 ± 0.52 kJ mol⁻¹(C) for cylindrical ones. All materials were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, thermogravimetry, and elemental analysis. A linear correlation between the standard enthalpies of formation and D/G and G′/G Raman bands ratio (D – band is centered at 1350 cm⁻¹, G – 1585 cm⁻¹, G′ – 2700 cm⁻¹) demonstrates the applicability of bomb calorimetry for characterization of the “defectiveness” of the bulk carbon material in the sense Raman spectroscopy is widely used nowadays. Also, we show that the calorimetry may be used to estimate the oxygen content in the bulk carbon nanomaterials, as there is a linear correlation between the oxygen content (both total content and in carboxyl groups separately) and the standard enthalpies of formation for herringbone nanotubes oxidized by nitric acid.     

High-capacity graphene oxide/graphite/carbon nanotube composites for use in Li-ion battery anodes

A composite of graphene oxide sheets, carbon nanotubes (CNTs), and commercial graphite particles was prepared. The composite’s use as a high-capacity and binder-free anode material for Li-ion batteries was examined. Results showed that this novel composite had a very high reversible Li-storage capacity of 1172.5 mA h g⁻¹ at 0.5C (1C = 372 mA g⁻¹), which is thrice that of commercial graphite anode. The composite also exceeded the theoretical sum of capacities of the three ingredients. More importantly, its reversible capacity below 0.25 V can reach up to 600 mA h g⁻¹. In summary, the graphene oxide/graphite/CNT composite had higher reversible capacity, better cycling performance, and similar rate capability compared with the graphene oxide/graphite composite.     

The preparation of cation-functionalized multi-wall carbon nanotube/sulfonated polyurethane composites

Covalent functionalization of multi-wall carbon nanotubes (MWCNTs) with minimal alteration to the MWCNT surface is important to achieve homogenously dispersed carbon nanotubes while maintaining their unique mechanical and electrical properties. Carboxylic acid derivatized MWCNTs (MWCNT-COOH) were covalently functionalized with 3,3′-iminobis(N,N-dimethylpropylamine) (DMPA). Upon subsequent quaternization of DMPA, dendritic ammonium cation-functionalized MWCNTs (MWCNT-DMPA⁺) were formed, where two ammonium cations were incorporated per amide site. Thermogravimetric analysis and X-ray photoelectron spectroscopy demonstrated successful covalent functionalization and formation of the surface-bound ammonium salt. Raman spectroscopy and atomic force microscopy indicated the absence of an appreciable decrease in the MWCNT aspect ratio. Compared with pristine MWCNTs and MWCNT-COOH, MWCNT-DMPA⁺ exhibited enhanced dispersibility in N,N-dimethylformamide (DMF) as observed with UV–Visible spectroscopy and transmission electron microscopy (TEM). In addition, blending the cation-bound MWCNT-DMPA⁺ with anion-bound sulfonated polyurethane in DMF generated novel composites with a nanotube content ranging from 0.5 to 5 wt.%. Characterization of the composite films using both field emission scanning electron microscopy and TEM revealed that MWCNT-DMPA⁺ exhibited uniform dispersion in sulfonated polyurethane matrices even at 5 wt.%. Tensile analysis showed that the modulus of the sulfonated polyurethane matrix linearly increased with MWCNT-DMPA⁺ content.     

Enhanced electrochemical activity of rechargeable carbon fluorides–sodium battery with catalysts

In order to improve the electrochemical performance of Na/CF_x cell, fluorinated multi-walled carbon nanotubes (F-MWCNTs) and a new composite consisting of CF_x, graphene nanosheets (GNS) and FeF₃ (labeled as CGF for short) were employed as cathode materials in rechargeable room-temperature sodium batteries for the first time. The polarizations of Na/F-MWCNTs and Na/CGF cell were found to be 1600 and 800 mV, respectively. These values were much lower than that of Na/CF_x cell (2000 mV). MWCNTs formed after the discharge process with intrinsic high surface area, high catalytic activity and “cage” type structure enhance charge reaction activity. Analogically, the combination of GNS and FeF₃ with CF_x provides more active sites to facilitate the decomposition of NaF during charge process. Moreover, the CGF electrode may have specific channels to avoid the dissolution of fluorine into the electrolyte similarly as the structure function of the F-MWCNTs electrode, leading to much better cycling performance. Overall, our results have demonstrated that the electrochemical performance of Na/CF_x cell can be greatly improved by using MWCNTs and FeF₃–GNS as catalysts.     

Towards high purity graphene/single-walled carbon nanotube hybrids with improved electrochemical capacitive performance

CoMgAl layered double hydroxides were prepared as catalysts for the in situ synchronous growth of graphene and single-walled carbon nanotubes (SWCNTs) from methane by chemical vapor deposition. The as-calcined CoMgAl layered double oxide (LDO) flakes served as the template for the deposition of graphene, and Co nanoparticles (NPs) embedded on the LDOs catalyzed the growth of SWCNTs. After the removal of CoMgAl LDO flakes, graphene (G)/SWCNT/Co₃O₄ hybrids with SWCNTs directly grown on the surface of graphene and 27.3 wt.% Co₃O₄ NPs encapsulated in graphene layers were available. Further removal of the Co₃O₄ NPs by a CO₂-oxidation assistant purification method induced the formation of G/SWCNT hybrids with a high carbon purity of 98.4 wt.% and a high specific surface area of 807.0 m²/g. The G/SWCNT/Co₃O₄ hybrids exhibited good electrochemical performance for pseudo-capacitors due to their high Co₃O₄ concentration and the high electrical conductivity of SWCNTs and graphene. In another aspect, the G/SWCNT hybrids can be used as excellent electrode materials for double-layer capacitors. A high capacity of 98.5 F/g_electrode was obtained at a scan rate of 10 mV/s, 78.2% of which was retained even when the scan rate increased to 500 mV/s.     

Influence of a cyclic butylene terephthalate oligomer on the processability and thermoelectric properties of polycarbonate/MWCNT nanocomposites

The thermoelectric properties of melt-processed nanocomposites consisting of a polycarbonate (PC) thermoplastic matrix filled with commercially available carboxyl (–COOH) functionalized multi-walled carbon nanotubes (MWCNTs) were evaluated. MWCNTs carrying carboxylic acid moieties (MWCNT-COOH) were used due the p-doping that the carboxyl groups facilitate, via electron withdrawing from the electron-rich π-conjugated system. Preliminary thermogravimetric analysis (TGA) of MWCNT-COOH revealed that the melt-mixing was limited at low temperatures due to thermal decomposition of the MWCNT functional groups. Therefore, PC was mixed with 2.5 wt% MWCNT-COOH (PC/MWCNT-COOH) at 240 °C and 270 °C. In order to reduce the polymer melt viscosity, a cyclic butylene terephthalate (CBT) oligomer was utilized as an additive, improving additionally the electrical conductivity of the nanocomposites. The melt rheological characterization of neat PC and PC/CBT blends demonstrated a significant decrease of the complex viscosity by the addition of CBT (10 wt%). Optical and transmission electron microscopy (OM, TEM) depicted an improved MWCNT dispersion in the PC/CBT polymer blend. The electrical conductivity was remarkably higher for the PC/MWCNT-COOH/CBT composites compared to the PC/MWCNT-COOH ones. Namely, the PC/MWCNT-COOH/CBT processed at 270 °C exhibited the best values with electrical conductivity; σ = 0.05 S/m, Seebeck coefficient; S = 13.55 μV/K, power factor; PF = 7.60 × 10⁻⁶μW/m K⁻², and thermoelectric figure of merit; ZT = 7.94 × 10⁻⁹. The PC/MWCNT-COOH/CBT nanocomposites could be ideal candidates for large-scale thermal energy harvesting, even though the presently obtained ZT values are still too low for commercial applications.     

Controllable preparation of Ti/TiO2-NTs/PbO2–CNTs–MnO2 layered composite materials with excellent electrocatalytic activity for the OER in acidic media

High oxygen evolution overpotential and low corrosion resistance are the main challenges for oxygen evolution materials in acidic media. In this study, a novel composite material, Ti/TiO₂-NTs/PbO₂–CNTs–MnO₂, with high oxygen evolution electrocatalytic activity was successfully prepared. First, TiO₂ nanotubes (TiO₂-NTs) were synthesized in situ on a Ti sheet via anodization and used as an intermediate layer. Subsequently, the adhesion and conductivity of the TiO₂-NTs layer were increased through additional anodization, annealing, and electrochemical reduction. Finally, PbO₂ was electrodeposited with a constant current in a lead acetate medium and doped with carbon nanotubes (CNTs) and MnO₂. The surface morphology, phase composition, and electrochemical performance of the composite materials were investigated. Notably, in an acidic electrolyte (150 g/L H₂SO₄), Ti/TiO₂-NTs/PbO₂–CNTs–MnO₂ exhibited good stability (30 h) and a low oxygen evolution overpotential of 410 mV at 50 mA/cm², which is almost equivalent to that of precious metals (RuO₂ and IrO₂) and 499 mV lower than that of the industrial Pb–0.76 wt% Ag alloy. The outstanding performance is mainly attributed to the high aspect ratio of the TiO₂-NT structure, synergistic effects of the active particles, and inherently good electrochemical properties of the active particles. Therefore, this study provides a new synthetic route for oxygen evolution materials in acidic media.     

Metal oxide/carbon nanosheet arrays derivative of stacked metal organic frameworks for triggering oxygen evolution reaction

Numerous clean energy systems rely on the oxygen evolution process (OER), which takes place during water splitting reaction. For this purpose, transition-metal oxides have garnered considerable attentions as a prominent OER electrocatalysts. In present study, we fabricate the nanosheet arrays of metal oxide/carbon (MOx/C; M = Fe, Ag, and Mn) fabricated via hydrothermal route. As templates, this approach employs the covered 2-dimensional (2D) metal-organic frameworks (2D-MOFs), and these MOx/C arrays made from 2D MOFs exhibit significant electrocatalytic activity and durability. Among all, Ag₂O/C showed the overpotentials of 270 mV at a current density (j) of 10 mA cm^?2, while the tafel slope is 45 mV dec^?1, that is lower than other metal oxide-based catalysts like MnO/C, and Fe₂O₃/C. It also shows 48 h high stability due to the conductive nature, larger surface area and the presence of carbon cage for easy transfer of electrons. The conceptual framework and synthetic strategy employed in this study can be applied to create more multi-metal oxide anchoring Ag₂O carbon matrix-based electrocatalysts that are extremely efficient, affordable, and perform significantly better in OER and other future applications.     

A novel hydrazine electrochemical sensor based on a carbon nanotube-wired ZnO nanoflower-modified electrode

ZnO nanoflowers were synthesized by a simple process (ammonia-evaporation-induced synthetic method) and were applied to the hydrazine electrochemical sensor. The prepared material was characterized by means of scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) and was then immobilized onto the surface of a glassy carbon electrode (GCE) via multi-walled carbon nanotubes (MWCNTs) to obtain ZnO/MWCNTs/GCE. The potential utility of the constructed electrodes was demonstrated by applying them to the analytical determination of hydrazine concentration. An optimized limit of detection of 0.18 μM was obtained at a signal-to-noise ratio of 3 and with a fast response time (within 3 s). Additionally, the ZnO/MWCNTs/GCE exhibited a wide linear range from 0.6 to 250 μM and higher sensitivity for hydrazine than did the ZnO modified electrode without immobilization of MWCNTs.     

Au@Pt core-shell nanoparticles supported on multiwalled carbon nanotubes for methanol oxidation

Au@Pt core-shell nanoparticles were synthesized by a simple one-step ultraviolet irradiation method and were then assembled on functionalized multiwalled carbon nanotubes (MWCNTs) surface. This new type of Au@Pt/MWCNTs composite catalysts was characterized by UV–vis spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning TEM, HRTEM, and electrochemical techniques. The results revealed that the Au@Pt nanoparticles with an average diameter less than 5 nm were well coated on the MWCNTs surface. As compared with commercial Pt/C catalysts, the Au@Pt/MWCNTs prepared using Au/Pt atomic ratio of 1:1 exhibited distinctly higher activity and better stability toward methanol oxidation in alkaline media.     

Application of nitrogen-doped graphene nanosheets in electrically conductive adhesives

Nitrogen-doped graphene nanosheets (N-GNSs) were used as a conductive filler for a polymer resin adhesive and as a performance improver for a silver-filled electrically conductive adhesive (ECA). The N-GNS samples were prepared by the chemical-intercalation/thermal-exfoliation of graphite followed by a thermal treatment in NH₃. Only 1 wt.% of N-GNSs was required for the adhesive to reach a percolation threshold, and the performance using N-GNSs was much better than that obtained using carbon black or multi-walled carbon nanotubes (MWCNTs). The effect of N-GNS or MWCNT additives on reducing the electrical resistivity of Ag-particle filled ECAs at low Ag loading ratios was also investigated. With 30 wt.% of Ag filler, the polymer resin was still non-conducting, while a resistivity of 4.4 × 10⁻² Ω-cm was obtained using an Ag/N-GNS hybrid filler fortified with only 1 wt.% of N-GNSs due to large specific surface area, high aspect ratio, and good electrical conductivity of the doped graphene.     

Electrodeposition of catalytically active nickel for the oxygen evolution reaction — effects of anionic composition

Nickel electrodes were prepared by electrodeposition in electrolytes of various anionic compositions. The deposition conditions and bath types were evaluated with special emphasis on the electrocatalytic properties for the oxygen evolution reaction (OER). Electrochemical characterizations in a 5 mol/L KOH solution at 25°C showed that the electrode deposited from the chloride bath, having a low Tafel slope of 50 mV/dec and an overpotential of 396 mV at 100 mA/cm², is the most catalytically active among electrodes prepared in electrolytes of various anionic compositions. The electrode activity for the OER is related to the real surface areas, which depend on the anion compositions in the deposition bath and the deposition conditions.     

Cationic photocured epoxy nanocomposites filled with different carbon fillers

In this work, the effect of several carbon fillers, exfoliated graphite (EG), functionalized graphene sheets (FGS), multi-walled carbon nanotubes (MWCNTs), and oxidized multi-walled carbon nanotubes (f-MWCNTs), were compared on the curing process and physical properties of a cationically photocurable epoxy resin. The extent of the photopolymerization was monitored by Real-Time FTIR spectroscopy. It was found that all the nanofillers delayed the curing reaction probably due to a shielding effect as well as to an increase of the resin viscosity. All the systems showed an electrical percolation threshold, but with MWCNTs was attained at a lower concentration (<0.1 wt.%). In addition, FGS showed the best response in terms of the dynamic mechanical and microindentation performances. An increase of more than 20 °C in the glass transition temperature was observed with the addition of 1 wt.% of FGS.