Carbon-based asymmetric capacitor for high-performance energy storage devices

Carbon-based materials are widely used in energy storage research, as attractive materials with high conductivity, low cost, and high availability. However, a relatively low performance (e.g., energy and power densities) compared with metal oxides is an obstacle to use for commercial applications. Herein, we report on high-performance metal oxide-free asymmetric capacitors (ASCs) using n-type and p-type graphene films which are doped by nitrogen and boron atoms, respectively, exhibiting high energy and power densities with excellent stability. The enhanced performances of the ASCs arises from the synergistic effect of the non-faradaic capacitance and pseudocapacitance, which are confirmed with new analysis using cyclic voltammetry and electrochemical impedance spectroscopy for a pseudocapacitance effect of intercalation/deintercalation and galvanostatic charge-discharge profiles for and non-faradaic capacitance. The new ASC in an ionic liquid electrolyte (e.g., pure EMIMBF4) shows the high energy density of 77.41 Wh kg−1 in 3.0 V of the operating potential window with the excellent retention stability of ∼87% after 10,000 cycles. The carbon-based asymmetric capacitor of semiconducting graphene electrodes can offer the promise of exploiting both non-faradaic capacitance and intercalation/deintercalation pseudocapacitance to obtain a high-performance energy storage device. © 2019 Elsevier Lt

Highly transparent and flexible supercapacitors using graphene-graphene quantum dots chelate

Nowadays, transparent and flexible energy storage devices are attracting a great deal of research interest due to their great potential as integrated power sources. In order to take full advantage of transparent and flexible devices, however, their power sources also need to be transparent and flexible. In the present work we fabricated new transparent and flexible micro-supercapacitors using chelated graphene and graphene quantum dots (GQDs) by a simple electrophoretic deposition (EPD) method. Through a chelate formation between graphene and GQDs with metal ions, the GQD materials were strongly adhered on an interdigitated pattern of graphene (ipG-GQDs) and its resulting porous ipG-GQDs film was used as the active material in the micro-supercapacitors. Amazingly, these supercapacitor devices showed high transparency (92.97% at 550 nm), high energy storage (9.09 μF cm-2), short relaxation time (8.55 ms), stable cycle retention (around 100% for 10,000 cycles), and high stability even under severe bending angle 45° with 10,000 cycles. © 2016 Elsevier Ltd126301sciescopu

A molecular approach to an electrocatalytic hydrogen evolution reaction on single-layer graphene

A major challenge in the development of electrocatalysts is to determine a detailed catalysis mechanism on a molecular level for enhancing catalytic activity. Here, we present bottom-up studies for an electrocatalytic hydrogen evolution reaction (HER) process through molecular activation to systematically control surface catalytic activity corresponding to an interfacial charge transfer in a porphyrin monolayer on inactive graphene. The two-dimensional (2D) assembly of porphyrins that create homogeneous active sites (e.g., electronegative tetrapyrroles (N4)) on graphene showed structural stability against electrocatalytic reactions and enhanced charge transfer at the graphene-liquid interface. Performance operations of the graphene field effect transistor (FET) were an effective method to analyse the interfacial charge transfer process associated with information about the chemical nature of the catalytic components. Electronegative pristine porphyrin or Pt-porphyrin networks, where intermolecular hydrogen bonding functioned, showed larger interfacial charge transfers and higher HER performance than Ni-, or Zn-porphyrin. A process to create surface electronegativity by either central N-4 or metal (M)-N-4 played an important role in the electrocatalytic reaction. These findings will contribute to an in-depth understanding at the molecular level for the synergetic effects of molecular structures on the active sites of electrocatalysts toward HER1441sciescopu

Tunable Sub-nanopores of Graphene Flake Interlayers with Conductive Molecular Linkers for Supercapacitors

Although there are numerous reports of high performance supercapacitors with porous graphene, there are few reports to control the interlayer gap between graphene sheets with conductive molecular linkers (or molecular pillars) through a π-conjugated chemical carbon-carbon bond that can maintain high conductivity, which can explain the enhanced capacitive effect of supercapacitor mechanism about accessibility of electrolyte ions. For this, we designed molecularly gap-controlled reduced graphene oxides (rGOs) via diazotization of three different phenyl, biphenyl, and para-terphenyl bis-diazonium salts (BD1-3). The graphene interlayer sub-nanopores of rGO-BD1-3 are 0.49, 0.7, and 0.96 nm, respectively. Surprisingly, the rGO-BD2 0.7 nm gap shows the highest capacitance in 1 M TEABF4 having 0.68 nm size of cation and 6 M KOH having 0.6 nm size of hydrated cation. The maximum energy density and power density of the rGO-BD2 were 129.67 W h kg-1 and 30.3 kW kg-1, respectively, demonstrating clearly that the optimized sub-nanopore of the rGO-BDs corresponding to the electrolyte ion size resulted in the best capacitive performance. © 2016 American Chemical Society117191sciescopu

Highly Stretchable and Conductive Silver Nanoparticle Embedded Graphene Flake Electrode Prepared by In situ Dual Reduction Reaction

The emergence of stretchable devices that combine with conductive properties offers new exciting opportunities for wearable applications. Here, a novel, convenient and inexpensive solution process was demonstrated to prepare in situ silver (Ag) or platinum (Pt) nanoparticles (NPs)-embedded rGO hybrid materials using formic acid duality in the presence of AgNO3 or H2 PtCl6 at low temperature. The reduction duality of the formic acid can convert graphene oxide (GO) to rGO and simultaneously deposit the positively charged metal ion to metal NP on rGO while the formic acid itself is converted to a CO2 evolving gas that is eco-friendly. The AgNP-embedded rGO hybrid electrode on an elastomeric substrate exhibited superior stretchable properties including a maximum conductivity of 3012S cm-1 (at 0 % strain) and 322.8S cm-1 (at 35 % strain). Its fabrication process using a printing method is scalable. Surprisingly, the electrode can survive even in continuous stretching cycles. © 2015, Nature Publishing Group. All rights reserved113141sciescopu

Highly stable multi-layered silicon-intercalated graphene anodes for lithium-ion batteries

© 2020 Cambridge University Press. All rights reserved.To avoid degradation of silicon anodes in lithium-ion batteries (LIBs), the authors report a new two-dimensional multi-layered Si-intercalated rGO (rGO/Si) anode prepared by direct growth of Si into a porous multi-layered reduced graphene oxide (rGO) film. Direct Si deposition onto the porous rGO film allows the Si layers to be intercalated into the film via in situ replacement of the oxygen groups of the multi-layered graphene oxide (GO) with Si through thermal reduction of the GO film. The porous rGO acts as a cushion against the expansion of the Si layer during lithiation, preventing the Si from being pulverized and producing highly stable LIBs11Nsciescopu

Fast diffusion supercapacitors via an ultra-high pore volume of crumpled 3D structure reduced graphene oxide activation

In order to obtain a high performance supercapacitor, there are several factors that must be achieved including a high specific surface area (SSA), high electrical conductivity, and a high diffusion rate of the electrolyte due to an appropriate pore volume. Herein, we report a high performance supercapacitor using activated non-stacked reduced graphene oxide (a-NSrGO) that has a high SSA (up to 999.75 m2 g-1) with intrinsic high graphene conductivity (1202 S m-1) and fast diffusion of the electrolyte. Due to a high total pore volume (5.03 cm3 g-1) and a wide pore size distribution from macro- to micropores (main pore width: 0.61 - 0.71 nm) in the a-NSrGO sheets, the as-prepared a-NSrGO electrode shows high specific capacitance (105.26 F g-1) and a short relaxation time (τ0 = 1.5 s) in a propylene carbonate (PC)-based organic electrolyte. A maximum energy density of 91.13 W h kg-1 and a power density of 66 684.73 W kg-1 were estimated in a fully packaged coin cell. The high performance of the a-NSrGO supercapacitors is attributed to their specific appearance and enlarged pore distribution with high SSA. © The Royal Society of Chemistry 2015113141sciescopu

Highly Bendable, Conductive, and Transparent Film by an Enhanced Adhesion of Silver Nanowires

Recently, silver nanowires (AgNWs) have attracted considerable interest for their potential application in flexible transparent conductive films (TCFs). One challenge for the commercialization of AgNW-based TCFs is the low conductivity and stability caused by the weak adhesion forces between the AgNWs and the substrate. Here, we report a highly bendable, conductive, and transparent AgNW film, which consists of an underlying poly­(diallyldimethyl-ammonium chloride) (PDDA) and AgNW composite bottom layer and a top layer-by-layer (LbL) assembled graphene oxide (GO) and PDDA overcoating layer (OCL). We demonstrated that PDDA could increase the adhesion between the AgNW and the substrate to form a uniform AgNW network and could also serve to improve the stability of the GO OCL. Hence, a highly bendable, conductive, and transparent AgNW–PDDA–GO composite TCF on a poly­(ethylene terephthalate) (PET) substrate with Rs ≈ 10 Ω/sq and <i>T</i> ≈ 91% could be made by an all-solution processable method at room temperature. In addition, our AgNW–PDDA–GO composite TCF is stable without degradation after exposure to H₂S gas or sonication

Highly Bendable, Conductive, and Transparent Film by an Enhanced Adhesion of Silver Nanowires

Recently, silver nanowires (AgNWs) have attracted considerable interest for their potential application in flexible transparent conductive films (TCFs). One challenge for the commercialization of AgNW-based TCFs is the low conductivity and stability caused by the weak adhesion forces between the AgNWs and the substrate. Here, we report a highly bendable, conductive, and transparent AgNW film, which consists of an underlying poly­(diallyldimethyl-ammonium chloride) (PDDA) and AgNW composite bottom layer and a top layer-by-layer (LbL) assembled graphene oxide (GO) and PDDA overcoating layer (OCL). We demonstrated that PDDA could increase the adhesion between the AgNW and the substrate to form a uniform AgNW network and could also serve to improve the stability of the GO OCL. Hence, a highly bendable, conductive, and transparent AgNW–PDDA–GO composite TCF on a poly­(ethylene terephthalate) (PET) substrate with Rs ≈ 10 Ω/sq and <i>T</i> ≈ 91% could be made by an all-solution processable method at room temperature. In addition, our AgNW–PDDA–GO composite TCF is stable without degradation after exposure to H₂S gas or sonication

Development of a SnS Film Process for Energy Device Applications

Tin monosulfide (SnS) is a promising p-type semiconductor material for energy devices. To realize the device application of SnS, studies on process improvement and film characteristics of SnS is needed. Thus, we developed a new film process using atomic layer deposition (ALD) to produce SnS films with high quality and various film characteristics. First, a process for obtaining a thick SnS film was studied. An amorphous SnS2 (a-SnS2) film with a high growth rate was deposited by ALD, and a thick SnS film was obtained using phase transition of a-SnS2 film by vacuum annealing. Subsequently, we investigated the effect of seed layer on formation of SnS film to verify the applicability of SnS to various devices. Separately deposited crystalline SnS and SnS2 thin films were used as seed layer. The SnS film with a SnS seed showed small grain size and high film density from the low surface energy of the SnS seed. In the case of the SnS film using a SnS2 seed, volume expansion occurred by vertically grown SnS grains due to a lattice mismatch with the SnS2 seed. The obtained SnS film using the SnS2 seed exhibited a large reactive site suitable for ion exchange