Tunable Fe/N co-doped 3D porous graphene with high density Fe-Nx sites as the efficient bifunctional oxygen electrocatalyst for Zn-air batteries

Nitrogen-doped transition metal materials display promising potential as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Fe/N co-doped three-dimensional (3D) porous graphene (FeN-3D-PG) is prepared via a template method using sodium alginate as the carbon source and low polymerization degree melamine resin as the nitrogen source. The low polymerization degree melamine resin can form complexes with Fe³⁺ in the aqueous solution and further forms high density Fe-N_x active sites during pyrolysis. Meanwhile, the formed 3D porous structure efficiently promotes the uniform distribution of Fe-N_x active sites. The FeN-3D-PG catalyst exhibits pH-independent ORR activity. For OER, the catalyst possesses a low over potential (370 mV at 10 mA cm⁻²) in alkaline electrolyte. The Zn-air batteries (ZABs) using FeN-3D-PG as cathode exhibits a power density up to 212 mW cm⁻², a high specific capacity of 651 mAh g⁻¹, and the charge-discharge stability of 80 h. This work provides new sight to transition metal materials based ZABs with excellent performance.     

Reduced graphene oxide-ZnO hybrid composites as photocatalysts: The role of nature of the molecular target in catalytic performance

Spurred by controversial literature findings, we enwrapped reduced graphene oxide (rGO) in ZnO hierarchical microstructures (rGO loadings spanning from 0.01 to 2 wt%) using an in situ synthetic procedure. The obtained hybrid composites were carefully characterized, aiming at shining light on the possible role of rGO on the claimed increased performance as photocatalysts. Several characterization tools were exploited to unveil the effect exerted by rGO, including steady state and time resolved photoluminescence, electron microscopies and electrochemical techniques, in order to evaluate the physical, optical and electrical features involved in determining the catalytic degradation of rhodamine B and phenol in water.Several properties of native ZnO structures were found changed upon the rGO enwrapping (including optical absorbance, concentration of native defects in the ZnO matrix and double-layer capacitance), which are all involved in determining the photocatalytic performance of the hybrid composites. The findings discussed in the present work highlight the high complexity of the field of application of graphene-derivatives as supporters of semiconducting metal oxides functionality, which has to be analyzed through a multi-parametric approach.     

Ultra-Robust Flexible Electronics by Laser-Driven Polymer-Nanomaterials Integration

Polyethylene terephthalate (PET) is the most widely used polymer in the world. For the first time, the laser-driven integration of aluminum nanoparticles (Al NPs) into PET to realize a laser-induced graphene/Al NPs/polymer composite, which demonstrates excellent toughness and high electrical conductivity with the formation of aluminum carbide into the polymer is shown. The conductive structures show an impressive mechanical resistance against >10000 bending cycles, projectile impact, hammering, abrasion, and structural and chemical stability when in contact with different solvents (ethanol, water, and aqueous electrolytes). Devices including thermal heaters, carbon electrodes for energy storage, electrochemical and bending sensors show this technology's practical application for ultra-robust polymer electronics. This laser-based technology can be extended to integrating other nanomaterials and create hybrid graphene-based structures with excellent properties in a wide range of flexible electronics’ applications.     

Improving through-thickness conductivity of carbon fiber reinforced polymer using carbon nanotube/polyethylenimine at the interlaminar region

The through-thickness conductivity of carbon fiber reinforced polymer (CFRP) composite was increased by incorporating multiwalled carbon nanotubes in the interlaminar region. Carbon nanotubes (CNTs) were dispersed in a polyethylenimine (PEI) binder, which was then coated onto the carbon fiber fabric. Standard vacuum-assisted resin infusion process was applied to fabricate the composite laminates. This modification technique aims to enhance the electrical conductivity in through-thickness direction for the purpose of nondestructive testing, damage detection, and electromagnetic interference shielding. CNT concentrations ranging from 0 to 0.75 wt% were used and compared to pristine CFRP samples (reference). The through-thickness conductivity of the CFRP exhibited an improvement of up to 781% by adopting this technique. However, the dispersion of CNT in PEI led to a viscosity increase and poor wetting properties which resulted in the formation of voids/defects, poor adhesion (as shown in scanning electron micrographs) and the deterioration of the mechanical properties as manifested by interlaminar shear strength and dynamic mechanical analysis measurements.     

Constructing 3D honeycomb-like CoMn2O4 nanoarchitecture on nitrogen-doped graphene coating Ni foam as flexible battery-type electrodes for advanced supercapattery

Reasonable structural design is significant to enable the performance in advanced energy storage devices. Herein, a 3D honeycomb-like CoMn₂O₄ nanoarchitecture (CMO) on nitrogen-doped graphene (NG) coating Ni foam (denoted as Ni/NG/CMO) flexible battery-type electrode was prepared by a facile two-step hydrothermal strategy. The honeycomb-like CoMn₂O₄ arrays not only provide abundant active sites but can also be closely combined with the Ni foam/NG substrate, which enables high reversible capacity and good cycle stability during the long cycles. Benefiting from the compositional features and 3D honeycomb-like nanoarchitecture, the Ni/NG/CMO composite electrode displays improved electrochemical performance with remarkable specific capacity of 527.0C g⁻¹ at a current density of 1 A g⁻¹, outstanding rate capability (338.6C g⁻¹ even at 20 A g⁻¹). In addition, a flexible binder-free supercapattery device has been assembled with Ni/NG/CMO as positive electrode and 3D Ni/NG as negative electrode. Such a supercapattery delivers a high energy density of 44.1 Wh·kg⁻¹ at 992.6 W kg⁻¹, 20.3 Wh·kg⁻¹ at 12430.0 W kg⁻¹ as well as excellent cycling durability. The 3D honeycomb-like Ni/NG/CMO could be considered as an advanced flexible battery-type material for high capacity and energy density fields.     

Highly dispersed MnO nanoparticles supported on N-doped rGO as an efficient oxygen reduction electrocatalyst via high-temperature pyrolysis

Transition metal-based compounds, due to their excellent ORR catalytic performance under alkaline condition, have recently emerged as one of the most promising alternatives to noble metal-based ORR catalysts. It is worth noting that manganese oxide can take an unique advantage for decomposition of intermediate adsorption products H₂O₂ and can effectively reduce O₂ to OH⁻. However, most research has focused on MnO₂, while attention has rarely been paid to MnO catalysts. In addition, under high-temperature pyrolysis condition, MnO is the most stable manganese oxide but MnO nanoparticles easily agglomerate. Hence, it is very difficult to obtain well-dispersed and small-sized MnO nanoparticles. Herein, on the basis of pre-synthesizing uniformly distributed manganese complexes on the reduced graphene oxide (rGO), we innovatively prepare highly dispersed and small-sized MnO nanoparticles (~3.94 nm) via high-temperature pyrolysis, which are uniformly anchored on N-doped reduced graphene oxide (NrGO) as an efficient oxygen reduction electrocatalyst. The as-obtained MnO/NrGO (1050 °C) electrocatalyst achieves satisfactory onset potential (0.942 V) and half-wave potential (0.820 V) under alkaline condition. And the limiting current density is 4.17 mA cm⁻², which is very close to that of Pt/C (20 wt%, JM). Meanwhile, MnO/NrGO (1050 °C) catalyst presents superior longstanding durability and methanol resistance than Pt/C (JM). This work indicates that high-temperature pyrolysis can improve the purity of manganese oxide, simultaneously the defects of NrGO can reduce particle size of MnO nanoparticles, which are greatly beneficial to improve ORR performance. This work provides a new idea for research of MnO catalysts for ORR in the future.     

H2 production from the hydrolytic dehydrogenation of methylamine-borane catalyzed by sulfonated reduced graphene oxide-aided synthesis of ruthenium nanoparticles

A new catalyst was prepared using sulfonated reduced graphene oxide support with a large surface area containing ruthenium nanoparticles (Ru@rGO-SO₃H). The developed Ru@rGO-SO₃H catalyst was used in the hydrogen production process from the hydrolytic dehydrogenation of methylamine-borane (MeAB). Sulfonated reduced graphene oxide and the developed catalyst were characterized by Raman and FT-IR spectroscopies, ICP-OES, XRD, XPS, TEM, TEM-EDX, SEM and SEM-EDX techniques. The average particle size of Ru nanoparticles, which were homogeneously distributed on the sulfonated reduced graphene oxide surface, was found as 2.2 ± 0.2 nm. After analyzing the effect of nanocatalyst and substrate concentrations on the catalytic reaction, reactions were realized at different temperatures, the efficiency of the Ru@rGO-SO₃H nanocatalyst in initial turnover frequency (TOF_initial) and the activation parameters (E_a, ΔH^# and ΔS^#) were calculated. According to the data obtained, the TOF_initial value was calculated as 5300.86 h^{− 1} (88.35 min^{− 1}). E_a, ΔH^# and ΔS^# values were also calculated as 53.83 kJ/mol, 50.73 kJ/mol and −51.55 J/mol.K, respectively. Finally, when the reusability performance results of the catalyst are evaluated, it is found that the catalyst is very stable and retains its initial effectiveness to a great extent (>95%) after the 5th reuse.     

A DFT study on enhanced adsorption of H2 on Be-decorated porous graphene nanosheet and the effects of applied electrical fields

The adsorption of the hydrogen molecule on the pure porous graphene nanosheet (P-G) or the one decorated with Be atom (Be-G) was investigated by the first-principle DFT calculations. The Be atom was adsorbed on the P-G with a binding energy of ?1.287 eV to successfully establish the reasonable Be-G. The P-G was a poor substrate to interact weakly with the H₂, whereas the Be-G showed a high affinity to the adsorbed H₂ with an enhanced adsorption energy and transferred electrons of ?0.741 eV and 0.11 e, respectively. A molecular dynamics simulation showed that the H₂ could also be adsorbed on the Be-G at room temperature with a reasonable adsorption energy of ?0.707 eV. The interaction between the adsorbed H₂ and the Be-G was further enhanced with the external electrical fields. The applied electrical field of ?0.4 V/Å was found to be the most effective to enhance the adsorption of H₂ on the Be-G with the modified adsorption energy and the improved transferred electrons being ?0.708 eV and 0.17 e, respectively. Our study shows that the Be-G is a promising substrate to interact strongly with the H₂ and could be applied as a high-performance hydrogen gas sensor, especially under the external electrical field.     

Electrophoretic deposition of graphene oxide on carbon brush as bioanode for microbial fuel cell operated with real wastewater

Microbial fuel cell (MFC) is a promising technology for simultaneous wastewater treatment and energy harvesting. The properties of the anode material play a critical role in the performance of the MFC. In this study, graphene oxide was prepared by a modified hummer's method. A thin layer of graphene oxide was incorporated on the carbon brush using an electrophoretic technique. The deoxygenated graphene oxide formed on the surface of the carbon brush (RGO-CB) was investigated as a bio-anode in MFC operated with real wastewater. The performance of the MFC using the RGO-CB was compared with that using plain carbon brush anode (PCB). Results showed that electrophoretic deposition of graphene oxide on the surface of carbon brush significantly enhanced the performance of the MFC, where the power density increased more than 10 times (from 33 mWm^?2 to 381 mWm^?2). Although the COD removal was nearly similar for the two MFCs, i.e., with PCB and RGO-CB; the columbic efficiency significantly increased in the case of RGO-CB anode. The improved performance in the case of the modified electrode was related to the role of the graphene in improving the electron transfer from the microorganism to the anode surface, as confirmed from the electrochemical impedance spectroscopy measurements.     

Li0.95Na0.05MnPO4/C nanoparticles compounded with reduced graphene oxide sheets for superior lithium ion battery cathode performance

Sodium-substituted LiMnPO₄/C/reduced graphene oxide (LNMP@rGO) was synthesized in this study via freeze drying and carbon thermal reduction method with graphene oxide as carbon source. Sodium ion doping is optimized and rGO effects are evaluated by XRD, SEM, TEM, BET, Raman, and electrochemical performance measurements. Well-distributed nanoparticles with average size of ~50?nm are evenly distributed on the surface or intercalation between rGO layers, resulting in a porous ion/electronic conductive network. Compared to 122.3?mA?h?g^?1 in unmodified LNMP, the best LNMP@rGO (20?mg rGO) exhibits an excellent initial discharge capacity of 150.4?mA?h?g^?1 at 0.05?C at 122.9% of the initial capacity. The capacity retention rate is 95.8% of the initial capacity after 100 cycles at 1?C. Capacity of 101.2?mA?h?g^?1 is preserved even at rates as high as 10?C.