Controlled electrochemical doping of graphene-based 3D nanoarchitecture electrodes for supercapacitors and capacitive deionisation

Chemically-doped graphenes are promising electrode materials for energy storage and electrosorption applications. Here, an affordable electrochemical green process is introduced to dope graphene with nitrogen. The process is based on reversing the polarity of two identical graphene oxide (GO) electrodes in molten KCl-LiCl-Li 3 N. During the cathodic step, the oxygen functional groups on the GO surface are removed through direct electro-deoxidation reactions or a reaction with the deposited lithium. In the anodic step, nitrogen is adsorbed onto the surface of graphene and subsequently reacts to form nitrogen-doped graphene. The doping process is controllable, and graphene with up to 7.4 at% nitrogen can be produced. The electrochemically treated electrodes show a specific capacitance of 320 F g -1 in an aqueous KOH electrolyte and maintain 96% of this value after 10000 cycles. The electrodes also display excellent electrosorption performance in capacitive deionisation devices with the salt removal efficiency reaching up to 18.6 mg g -1

Ultraflexible and robust graphene supercapacitors printed on textiles for wearable electronics applications

Printed graphene supercapacitors have the potential to empower tomorrow’s wearable electronics. We report a solid-state flexible supercapacitor device printed on textiles using graphene oxide ink and a screen-printing technique. After printing, graphene oxide was reduced in situ via a rapid electrochemical method avoiding the use of any reducing reagents that may damage the textile substrates. The printed electrodes exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate. The unique hierarchical porous structure of the electrodes facilitated ionic diffusion and maximised the surface area available for the electrolyte/ active material interface. The obtained device showed outstanding cyclic stability over 10 000 cycles and maintained excellent mechanical flexibility, which is necessary for wearable applications. The simple printing technique is readily scalable and avoids the problems associated with fabricating supercapacitor devices made of conductive yarn, as previously reported in the literature

Hierarchical NiO/CMK-3 Photocathode for a p-Type Dye-Sensitized Solar Cell with Improved Photoelectrochemical Performance and Fast Hole Transfer.

The sluggish photoelectrochemical performance of p-type dye-sensitized solar cells (p-DSSCs) has hindered its commercial use. In this work, we introduce a novel hierarchical nanocomposite of NiO nanoparticles anchored on highly ordered mesoporous carbons CMK-3 (NiO/CMK-3). Using CMK-3 as a backbone effectively prevented the self-aggregation of NiO nanoparticles and subsequently increased the total specific surface area of the composite for more dye adsorption. The interconnected conductive networks of CMK-3 also served as a split-flow high-speed channel, which was beneficial for hole spin-flow to accelerate hole transfer. The hierarchical NiO/CMK-3 photocathode improved the photovoltaic conversion efficiency to 1.48% in a cell with a Cobalt(II)/(III) electrolyte and a PMI-6T-TPA dye

Self-healing by Diels-Alder cycloaddition in advanced functional polymers: A review

The ability of artificial materials to be healed efficiently, mimicking the living organisms, exhibits a great deal of potential advantages that can revolutionise the operation and maintenance of materials used in various applications. Such self-healable smart materials have been extensively researched in the last few decades, leading to the development of different physical and chemical synthesis approaches. Among these methods, chemical techniques based on reversible cycloadditions or disulfide bonding provide obvious advantages in terms of repeatability, which holds prime importance in determining the commerciality of the healing approach. This review compiles the recent advances in the field of self-healing polymers where the healing ability is introduced by reversible cycloaddition reactions while focusing mainly on the Diels-Alder (DA) reaction. DA is a [4 + 2] cycloaddition reaction where diene and dienophile pairs are used to fabricate thermally reversible crosslinked networks. These covalent bonds provide the necessary reversibility to the healing matrix and impart the desired strength to the polymeric material. There is a considerable body of recent literature where DA bonding has been employed either on its own or along with other healing mechanisms to impart self-healing to polymers. However, lack of a systematic review discussing these works makes it difficult for a beginner to cope with advancements in this field. Most early studies have focused on the healing stimuli and efficiency of healing in polymers but with this review, we would like to explore the healing thermodynamics governing the rupture–repair process in DA polymers along with the use of advanced spectroscopic techniques to study them and their applicability in thermosets, epoxy resins, biopolymers, and polymer nanocomposites. Novel applications for such advanced functional polymers, multifunctional healable polymers, and the outlook for future research, opportunities and challenges in the area are also discussed

Facile mechanochemical synthesis of non-stoichiometric silica-carbon composite for enhanced lithium storage properties

A large number of new electrode materials and novel structural designs are emerging for lithium-ion batteries, yet scalable synthesis and raw material costs still hinder the practical application of such materials. Here, we designed and fabricated a low-cost SiOx/C composite by a facile and scalable mechanofusion route with a ball-milling method. We selected aerosil and graphite precursor-needle coke, which are two widely used materials in industry, as a silicon source and carbon source, respectively. This SiOx/C composite shows a high reversible capacity (ca. 550 mAh g−1) at the 180th cycle and good rate performance. Our scalable synthesis route of electrode materials can stimulate the progress of other energy storage technologies for practical applications

Triple-shell NiO hollow sphere for p-type dye-sensitized solar cell with superior light harvesting

In this article, new p-DSSC electrodes are fabricated using NiO hollow spheres (HSs) prepared through a facial one-step hydrothermal process. The current-voltage (J-V) curve indicates that p-DSSCs fabricated using triple-shell NiO HS have excellent photoelectrochemical performance, with a photoelectrical efficiency of 1.79%. The UV–vis diffused reflectance spectra indicate that the triple-shell NiO HS, with its unique structure, has superior light reflection, scattering ability and large surface area with more inner cavities, which helps harvest more light. Electrochemical impedance spectroscopy (EIS) further confirms that triple-shell NiO HS shows fast dye regeneration, improved hole transport and suppressed recombination. The research work of unique NiO HS is important for the selection of efficient photocathode materials for p-DSSCs

In-situ probing of the thermal treatment of h-BN towards exfoliation

Two-dimensional (2D) hexagonal boron nitride (h-BN) is becoming increasingly interesting for wider engineering applications. Thermal exfoliation is being suggested as a facile technology to produce large quantities of 2D h-BN. Further optimization of the process requires fundamental understanding of the exfoliation mechanism, which is hardly realized by ex-situ techniques. In this study, time resolved in-situ synchrotron X-ray powder diffraction experiments are conducted while heat treating bulk h-BN up to 1273 K. During the heating process, linear expansion of c-axis is observed and the contraction of a-axis up to around 750 K is consistent with previous research. However, a changing behavior from contraction to expansion in a- axis direction is newly observed when heating over 750 K. With the consideration of previous thermally oxidation studies, a hypothesis of thermal assisted exfoliation with oxygen interstitial and substitution of nitrogen at high temperature is proposed

Layer-by-layer electrode fabrication for improved performance of porous polyimide-based supercapacitors

Nanoporous polymers are becoming increasingly interesting materials for electrochemical applications, as their large surface areas with redox-active sites allow efficient adsorption and diffusion of ions. However, their limited electrical conductivity remains a major obstacle in practical applications. The conventional approach that alleviates this problem is the hybridisation of the polymer with carbon-based additives, but this directly prevents the utilisation of the maximum capacity of the polymers. Here, we report a layer-by-layer fabrication technique where we separated the active (porous polymer, top) layer and the conductive (carbon, bottom) layer and used these “layered” electrodes in a supercapacitor (SC). Through this approach, direct contact with the electrolyte and polymer material is greatly enhanced. With extensive electrochemical characterisation techniques, we show that the layered electrodes allowed a significant contribution of fast faradic surface reactions to the overall capacitance. The electrochemical performance of the layered-electrode SC outperformed other reported porous polymer-based devices with a specific gravimetric capacitance of 388 F·g−1 and an outstanding energy density of 65 Wh·kg−1 at a current density of 0.4 A·g−1 . The device also showed outstanding cyclability with 90% of capacitance retention after 5000 cycles at 1.6 A·g−1, comparable to the reported porous polymer-based SCs. Thus, the introduction of a layered electrode structure would pave the way for more effective utilisation of porous organic polymers in future energy storage/harvesting and sensing devices by exploiting their nanoporous architecture and limiting the negative effects of the carbon/binder matrix

Construction of ultrafine ZnSe nanoparticles on/in amorphous carbon hollow nanospheres with high-power-density sodium storage

© 2019 Sodium-ion batteries (SIBs) are considered as a promising candidate to lithium-ion batteries (LIBs) owing to the inexpensive and abundant sodium reserves. However, the application of anode materials for SIBs still confront rapid capacity fading and undesirable rate capability. Here we simultaneously grow ultrafine ZnSe nanoparticles on the inner walls and the outer surface of hollow carbon nanospheres (ZnSe@HCNs), giving a unique hierarchical hybrid nanostructure that can sustain a capacity of 361.9 mAh g −1 at 1 A g −1 over 1000 cycles and 266.5 mAh g −1 at 20 A g −1 . Our investigations indicate that the sodium storage mechanism of ZnSe@HCNs electrodes is a mixture of alloying and conversion reactions, where ZnSe converts to Na 2 Se and NaZn 13 through a series of intermediate compounds. Also, a full cell is constructed from our designed ZnSe@HCNs anode and Na 3 V 2 (PO 4 ) 3 cathode. It delivers a reversible discharge capacity of about 313.1 mAh g −1 after 100 cycles at 0.5 A g −1 with high Columbic efficiency over 98.2%. The outstanding sodium storage of as-prepared ZnSe@HCNs is attributed to the confinement of ZnSe structural changes both inside/outside of hollow nanospheres during the sodiation/desodiation processes. Our work offers a promising design to enable high-power-density electrodes for the various battery systems

Electrochemically exfoliated graphene and molybdenum disulfide nanoplatelets as lubricant additives

In this work, two different 2D materials, molybdenum disulfide nanoplatelets (MSNP) and graphene nanoplatelets (GNP), prepared by electrochemical exfoliation, were used as additives to prepare nanolubricants. The tribological behaviour of the nanolubricants was evaluated under two configurations (pure sliding and rolling/sliding) using two different tribometers: an Universal Macro Materials Tester (UMT-3) and a Mini Traction Machine (MTM2). Wear volume was determined, after the sliding tests, in a confocal microscope (Leica DCM 3D) and the worn surface was analyzed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Raman microscopy. Lubrication mechanisms of GNP and MSNP dispersed in an engine oil for improving its antifriction and antiwear capabilities are proposed. The traction coefficient determination was performed at a 50% of slide-to-roll ratio and at different temperatures. The results showed that the nanolubricants formulated with both types of additives, in their lowest concentration, improved friction and wear in sliding tests, compared to neat engine oil. In addition, only the nanolubricants with the MSNP nano additive at loadings of 0.05 and 0.2 wt% showed friction reductions compared to the commercial engine oil under the rolling/sliding tests