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Developing new optimized bifunctional photocatalyst is of great significant for achieving the high-performance photo-assisted Li-O2 batteries. Herein, a novel bifunctional photo-assisted Li-O2 system is constructed by using siloxene nanosheets with ultra-large size and few-layers due to its superior light harvesting, semiconductor characteristic, and low recombination rate. An ultra-low charge potential of 1.90 V and ultra-high discharge of 3.51 V have been obtained due to the introduction of this bifunctional photocatalyst into Li-O2 batteries, and these results have realized the round-trip efficiency up to 185 %. In addition, this photo-assisted Li-O2 batteries exhibits a high rate (129 % round-trip efficiency at 1 mA cm-2 ), a prolonged cycling life with 92 % efficiency retention after 100 cycles, and the highly reversible capacity of 1170 mAh g-1 at 0.75 mA cm-2 . This work will open the vigorous opportunity for high-efficiency utilization of solar energy into electric system.

As a conductive polymer with great potential, poly(3,4-ethylenedioxythiophene) (PEDOT) has been developed as a high-rate supercapacitor electrode but stores less energy due to its limited theoretic...

By using Ti3C2Tx quantum dots as interlayer spacers, Ti3C2Tx nanosheets/Ti3C2Tx quantum dots/RGO (reduced graphene oxide) fiber (M6M3RG1) is prepared by a wet-spinning method; it shows good capacit...

Lithium sulfur batteries are expected to be one of the most promising energy storage systems due to their high energy density, low cost and environmental friendliness. However, the shuttle effect of lithium polysulfides severely hampers their practical application. The design of the sulfur cathode is one of the most important approaches to overcome the problem. In this work, MoS2 nanosheets have been successfully grown on the surface of hollow carbon spheres (HCS) to obtain MoS2@HCS nanocomposites with uniform morphology. The growth behavior of MoS2 nanosheets was also proved by adjusting the pore structure of HCS. With a sulfur loading of 74%, the MoS2@HCS/S cathode exhibits a high initial reversible capacity of 1419 mA h g-1 at a current density of 0.1 C and remains at 1010 mA h g-1 after 100 cycles. Even at 0.5 C, a capacity of 795 mA h g-1 can be retained after 600 cycles, corresponding to a capacity retention rate of 63.1%. By adjusting the concentration of the sulfur source, the relationship between different growth quantities of MoS2 and the cycling performance of the battery was also investigated. The excellent electrochemical performance of the MoS2@HCS/S cathode can be fully attributed to its physical and chemical double adsorption effect on lithium polysulfides, which has been confirmed through the visible adsorption and X-ray Photoelectron Spectroscopy (XPS) experiments. This work provides a simple design concept and method to synthesize a nanocomposite-based sulfur host for high performance lithium sulfur batteries.

The preparation of two-dimensional boron (B) nanosheets, especially for borophene, is still a challenge because of its unique structure and complex B–B bonds in bulk boron. In the present work, a novel preparation technology for borophene with only a few layers and large flake sizes is developed by a solvothermal-assisted liquid phase exfoliation process, consisting of ball milling-thinning, solvothermal swelling, and probe ultrasonic delamination. The exfoliation effect of the bulk B precursors is related to the surface tension and Hildebrand parameter of the selected solvents such as acetone, N,N-dimethyl formamide (DMF), acetonitrile, ethanol, and N-methyl pyrrolidone (NMP), and a relative small surface tension when using solvents is favorable for the exfoliation of bulk B. Four-layer thick borophene and an average lateral size of 5.05 μm can be obtained in acetone as the exfoliating solvent. The surface composition of the exfoliated few-layer borophene with large flake size hardly changes, while the chemical state of B changes to some extent because they are partly oxidized on the surface by contaminates before and after exfoliation. This acetone solvothermal-assisted liquid phase exfoliation technique can be used to prepare high quality borophene with large horizontal sizes, and it will provide the basis to study few-layer borophene with large sizes further.

Sodium-ion capacitors (SICs) have gained great interest for mid- to large-scale energy storage applications because of their high energy and high power densities as well as long cycle life and low cost. Herein, a T-Nb2O5 nanoparticles/N-doped graphene hybrid anode (T-Nb2O5/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl5 at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-Nb2O5 nanoparticles with average size of 17 nm were uniformly anchored on the surface of the nitrogen-doped reduced GO because their growth and aggregation were hindered, and also, the electronic conductivity and the active sites of T-Nb2O5/NG were improved by doping nitrogen. The T-Nb2O5/NG anode showed superior rate capability (68 mA h g–1 even at 2 A g–1) and good cycling life (106 mA h g–1 at 0.2 A g–1 for 200 cycles and 83 mA h g–1 at 1 A g–1 for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-Nb2O5/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg–1 at a power density of 100 W kg–1 and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g–1) and showed a promising application for highly efficient energy storage systems.

Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible hybrid film with outstanding flexibility and electrochemical performance is prepared via a vacuum filtration method. The three-dimensional interconnect structure is constructed by reduced graphene oxide and single-walled carbon nanotube, and Mn3O4 nanoplates with pesudocapacitance are embedded into the interconnect structure. The regular interconnect structure and a synergetic effect between graphene oxide/single-walled carbon nanotube and Mn3O4 make the Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible film electrode exhibit a large areal capacitance of 796 mF cm−2. All-solid-state Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible supercapacitor is prepared by using the hybrid film as electrodes and sandwiching the PVA–KOH gel electrolyte, it exhibits a large area specific capacitance of 360 mF cm−2 and the capacitance maintains 95% after 5000 charge/discharge cycles. The assembled supercapacitor exhibits both outstanding mechanical performance and a high areal energy density of 32 μW h cm−2 at an areal power density of 0.392 mW cm−2. The Mn3O4/reduced graphene oxide/single-walled carbon nanotube flexible supercapacitors exhibit significant potentiality in flexible and wearable electronics owing to their excellent flexibility, high energy density and long cycle life.

Two-dimensional (2D) materials have gained significant attention owing to their unique physical and chemical properties, which arise mainly from their high surface–bulk ratios and topological effects. Since the discovery of graphene in 2004, the family of 2D materials has expanded rapidly. Thus far, several single-element 2D materials (graphene, phosphorene, etc.) have been reported; the majority of them contain two (MoS2, WSe2, etc.) or more elements (Mo2CTx, CrPS4, Bi2Sr2CaCu2Ox, etc.). Of these, three-element 2D materials, also called ternary 2D materials, represent a rather attractive direction of recent years. Typical ternary 2D materials include metal phosphorous trichalcogenides (MPTs), ternary transition metal chalcogenides (TMDs), transition metal carbides and nitrides (MXenes) and 2D ternary oxides. Ternary 2D systems result in multiple degrees of freedom to tailor their physical properties via stoichiometric variation. Moreover, they exhibit some properties not characteristic of binary 2D systems, such as band gap tuning. In this paper, we have reviewed the recent progress in various ternary 2D materials on the basis of their classification (MPTs, ternary 2D MXenes, ternary TMDs, BCN and other ternary 2D materials). The synthesis methods, structures, key properties (such as band gap tuning, phase transition and topological phase), and their applications, are summarized. In addition, the strategies to tackle challenges, as well as the outlooks of this field, are presented. Ministry of Education (MOE) Accepted version

Ti3C2Tx nanosheets/reduced graphene oxide (Ti3C2Tx/RGO-0.9) fiber with superior flexibility and high volumetric capacitance is prepared by spinning the suspension of Ti3C2Tx nanosheets and graphene oxide (GO) nanosheets and followed by treating in HI solution at 80 °C. The oxidation of Ti3C2Tx nanosheets can be effectively protected in N2 atmosphere at 5 °C, and the as-prepared Ti3C2Tx/RGO-0.9 fiber electrode shows a specific volume capacitance of 415 F cm−3 at a current density of 1 A cm−3 in 1 M H2SO4 electrolyte and superior flexibility. Ti3C2Tx/RGO//PANI (polyaniline)/RGO all-solid-state asymmetrical fiber supercapacitor (AFSC) is assembled by using Ti3C2Tx/RGO-0.9 fiber as negative electrode and PANI/RGO-0.4 fiber as positive electrode in PVA-H2SO4 gel electrolyte, it exhibits not only excellent volumetric capacitance of 25 F cm−3 at a current density of 20 mA cm−3, but also high energy density of up to 3.4 mWh cm−3 at a power density of 10.2 mW cm−3. Moreover, the assembled AFSC shows outstanding flexibility and mechanical property, its volumetric capacitance has no obvious change after bending 500 times. The high energy density and superior mechanical flexibility make it can be used as a promising flexible power source in the fields of portable wearable electronic devices.

Ti2Nb2O9/reduced graphene oxide (Ti2Nb2O9/RGO) hybrid anode is fabricated by flocculation of HTiNbO5 nanosheets and graphene oxide (GO) nanosheets, followed by annealing HTiNbO5/GO composite at 500 °C in Ar for 1 h, in which HTiNbO5 nanosheets are prepared by ion-exchange and followed by exfoliating process using KTiNbO5 as precursor. HTiNbO5 nanosheets are topotactically transformed into Ti2Nb2O9 nanosheets and GO is reduced into RGO by calcining the HTiNbO5/GO composite, causing enhanced Na+-intercalation pseudocapacitive behavior and significantly improved conductivity for Ti2Nb2O9/RGO hybrid anode. Ti2Nb2O9/RGO hybrid anode delivers superior rate capability (206 mAh g−1 at 4 A g−1) and excellent cycling performance with 95% capacity retention at 1 A g−1 over 1000 cycles. A hybrid device is assembled using Ti2Nb2O9/RGO as the anode and activated carbon (AC) as the cathode, it shows a maximum high energy density of 96 Wh kg−1 at a power density of 75 W kg−1, and the energy density still maintains 39 Wh kg−1 when the power density achieves as high as 10029 W kg−1. Moreover, the assembled device displays good cycling stability with a capacity retention of 79% after 10,000 cycles. This work can provide new insights on fabrication of Ti-Nb oxides-graphene based composite anode for sodium ion capacitors.

Electrocatalysts play an important role in oxygen reduction reaction (ORR) in promoting the reaction process. Although commercial Pt/C exhibits excellent performance in ORR, the low duration, high cost, and poor methanol tolerance seriously restrict its sustainable development and application. TinO2n&minus, 1 (3 &le, n &le, 10) is a series of titanium sub-oxide materials with excellent electrical conductivity, electrochemical activity, and stability, which have been widely applied in the field of energy storage and catalysis. Herein, we design and synthesize Ti4O7/Ti3O5 (T4/T3) dual-phase nanofibers with excellent ORR catalytic performance through hydrothermal growth, which is followed by a precisely controlled calcination process. The H2Ti3O7 precursor with uniform size can be first obtained by optimizing the hydrothermal growth parameters. By precisely controlling the amount of reducing agent, calcination temperature, and holding time, the T4/T3 dual-phase nanofibers with uniform morphology and coherent interfaces can be obtained. The orientation relationships between T4 and T3 are confirmed to be [ 001 ] T 3 / / [ 031 ] T 4 , ( 100 ) T 3 / / ( 92 6 &macr, ) T 4 , and ( 010 ) T 3 / / ( 1 2 &macr, 6 ) T 4 , respectively, based on comprehensive transmission electron microscopy (TEM) investigations. Furthermore, such dual-phase nanofibers exhibit the onset potential and half-wave potential of 0.90 V and 0.75 V as the ORR electrocatalysts in alkaline media, respectively, which illustrates the excellent ORR catalytic performance. The rotating ring-disk electrode (RRDE) experiment confirmed the electron transfer number of 3.0 for such catalysts, which indicates a mixture of two electron and four electron transfer reaction pathways. Moreover, the methanol tolerance and cycling stability of the catalysts are also investigated accordingly.

As a green pollution-free reaction, oxygen reduction reaction (ORR) plays a significant role in many energy storage and conversion devices. Although commercial Pt/C possesses the highest ORR activity (especially in acidic medium), the high cost, low stability and poor methanol tolerance making the development of non-platinum electrocatalysts with high performance especially important. Herein, we design and synthesize a carbon nanofiber decorated by Ti4O7/Ti3O5 dual-phase nanoparticles (CNF/T4/T3) as ORR catalysts with excellent activity. With the employment of electrospinning followed by precisely controlled calcination process, the composite catalysts with uniform fibrous morphology can be obtained. Such CNF/T4/T3 composite catalysts exhibited an improved electrochemical performance with onset and half-wave potential of 0.91 V and 0.78 V respectively in alkaline solution. By comparing the catalytic performance with the pure T4 or T3 phase decorated on the same carbon nanofiber, it is found that the mixture of the two titanium sub-oxide phases can optimize the onset potential and limited current density at the same time. Density functional theory calculations suggest that different steps of ORR take place on T3 and T4 successively, which is the main reason of the excellent ORR performance for the dual-phase structure. This work provided a novel designing concept for the functional electrocatalysts using electrospinning technique for the application of energy storage and conversion.

The development of compressible supercapacitor highly relies on the innovative design of electrode materials with both superior compression property and high capacitive performance. This work reports a highly compressible supercapacitor electrode which is prepared by growing electroactive NiCo2S4 (NCS) nanosheets on the compressible carbon sponge (CS). The strong adhesion of the metallic conductive NCS nanosheets to the highly porous carbon scaffolds enable the CS–NCS composite electrode to exhibit an enhanced conductivity and ideal structural integrity during repeated compression–release cycles. Accordingly, the CS–NCS composite electrode delivers a specific capacitance of 1093 F g–1 at 0.5 A g–1 and remarkable rate performance with 91% capacitance retention in the range of 0.5–20 A g–1. Capacitance performance under the strain of 60% shows that the incorporation of NCS nanosheets in CS scaffolds leads to over five times enhancement in gravimetric capacitance and 17 times enhancement in volumetric capaci...

Organic–inorganic heterostructures are an emerging topic that is very interesting for optoelectronics. Here, non-conventional p–n junctions are investigated using organic rubrene single crystal and 2D MoS2 as the p- and n-type semiconducting materials, respectively. The current-rectifying behavior is clearly observed in the junction device. The rectification ratio can be electrically tuned by the gate voltage due to the 2D nature of the heterostructure. The devices also show good photoresponse properties with a photoresponsivity of ≈500 mA W−1 and a fast response time. These findings suggest a new route to facilitate the design of nanoelectronic and optoelectronic devices based on layered inorganics and organics.

The characteristics of field-effect transistors (FETs) fabricated from thin films and single crystals of phenacene molecules are fully reported in this review together with the electronic and crystal structures of phenacenes. Phenacene molecules possess a low HOMO level and a wide band gap. The highest mobility observed in the phenacene thin-film FETs is 7.4 cm2 V–1 s–1 for [6]phenacene, and in single-crystal FETs the highest value is 6.3 cm2 V–1 s–1 for [7]phenacene. The phenacene thin-film FETs show O2-sensing properties unlike their single-crystal FETs. The bias-stress effect is fully investigated for phenacene single-crystal FETs. Furthermore, the low-voltage operation of phenacene single-crystal FETs with electric-double-layer (EDL) capacitors is reported. The temperature dependence of phenacene single-crystal FETs is reported to clarify the transport mechanism, which is suggestive of band-like transport.

The interface between the single crystal and the Au source/drain electrodes in [7]phenacene single-crystal field-effect transistors (FETs) was modified using 14 electron acceptors with different redox potentials. The effective hole-injection barrier heights (ϕheffs) for [7]phenacene single-crystal FETs have been plotted as a function of the redox potential (Eredox) of the inserted electron acceptors, showing that the ϕheff decreases with increasing Eredox. The highest ϕheff occurs without inserted material (electron acceptors), and this deviates from the otherwise linear relationship between ϕheff and Eredox. We have investigated the temperature dependence of ϕheff in an attempt to determine why the ϕheff value without inserted material is so high, which suggests that no additional barrier, such as a tunneling barrier, is formed in the device. We conclude that the pure Schottky barrier in this FET is lowered very significantly by the insertion of an electron acceptor. The gate-voltage dependence of ϕheff ...

Ni 2+ –Fe 3+ layered double hydroxide material with large size up to 4 μm and regular morphology was prepared via a topochemical approach by using urea as a hydrolysis agent and mannitol as a stabilizer. α-type Ni 2+ –Fe 2+ hydroxide with micrometer size and hexagonal shape was firstly prepared, and the effect of the reaction time, total metal ion concentration and the concentration of urea on the particle size and morphology of the α-type Ni 2+ –Fe 2+ hydroxide was investigated. α-type Ni 2+ –Fe 2+ hydroxide material was then oxidized by iodine in chloroform, and hydrotalcite-like Ni 2+ –Fe 3+ LDH material with large size and regular hexagonal morphology was obtained. The obtained Ni 2+ –Fe 3+ LDH material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and FT-IR spectrum (IR), respectively.

The assembling behavior between graphite oxide (GO) nanosheets and polydiallyldimethylammonium (PDDA) polycations was investigated by both layer-by-layer method and flocculated technology, and the capacitive performance of the assembled hybrid composite was also studied. Sequential alternate adsorption of GO nanosheets and PDDA polycations yielded multilayer films while their simple mixing produced lamellar materials. X-ray diffraction (XRD) indicated that the combination of the multilayer film produced XRD Bragg peak having basal spacing of 1.09 nm, which was compatible with the sum of one layer GO nanosheets and one layer of PDDA polycations. A different assembling process took place for the flocculated material; its XRD Bragg peaks had multilayer spacing of 1.49 nm, which was compatible with the sum of one layer GO nanosheets and two layers of PDDA polycations. UV–visible absorption spectra exhibited progressive enhancement of optical density due to GO, providing strong evidence for regular growth of multilayer films. Scanning electron microscopy images of the multilayer film and flocculated material displayed lamellar features. The flocculated material showed good capacitive behavior and cycling stability, and the specific capacitance value was 176 F g−1.

Field-effect transistors (FETs) based on [6]phenacene thin films were fabricated with SiO2 and parylene gate dielectrics. These FET devices exhibit field-effect mobility in the saturation regime as high as 7.4 cm(2) V(-1) s(-1), which is one of the highest reported values for organic thin-film FETs. The two- and four-probe mobilities in the linear regime display nearly similar values, suggesting negligible contact resistance at 300 K. FET characteristics were investigated using two-probe and four-probe measurement modes at 50-300 K. The two-probe mobility of the saturation regime can be explained by the multiple shallow trap and release model, while the intrinsic mobility obtained by the four-probe measurement in the linear regime is better explained by the phenomenon of transport with charge carrier scattering at low temperatures. The FET device fabricated with a parylene gate dielectric on polyethylene terephthalate possesses both transparency and flexibility, implying feasibility of practical application of [6]phenacene FETs in flexible/transparent electronics. N-channel FET characteristics were also achieved in the [6]phenacene thin-film FETs using metals that possess a small work function for use as source/drain electrodes.

We report the observation of zero resistivity (\ensuremath{\rho}) in a hydrocarbon superconductor, and describe the temperature dependence of \ensuremath{\rho} in metal-doped hydrocarbons. The resistivity of K-doped picene (K${}_{x}$picene) has been recorded from pellet samples in a four-terminal measurement mode. A drop in $\ensuremath{\rho}$ is observed below 7 K for K${}_{3.1}$picene and below 11 K for K${}_{3.5}$picene, which clearly displays zero resistivity. The resistivity drop at 7 K is consistent with the superconducting critical temperature (${T}_{\mathrm{c}}$) obtained from the magnetic susceptibility of the 7 K phase of K${}_{3}$picene, while the drop at 11 K is inconsistent with the ${T}_{\mathrm{c}}$'s of both the 7 and 18 K phases of K${}_{3}$picene reported previously. The temperature dependence of \ensuremath{\rho} for both samples exhibits granular-metal-like behavior in the normal state.

2D transition metal dichalcogenides are promising channel materials for the next-generation electronic device. Here, vertically 2D heterostructures, so called van der Waals solids, are constructed using inorganic molybdenum sulfide (MoS2 ) few layers and organic crystal - 5,6,11,12-tetraphenylnaphthacene (rubrene). In this work, ambipolar field-effect transistors are successfully achieved based on MoS2 and rubrene crystals with the well balanced electron and hole mobilities of 1.27 and 0.36 cm2 V-1 s-1 , respectively. The ambipolar behavior is explained based on the band alignment of MoS2 and rubrene. Furthermore, being a building block, the MoS2 /rubrene ambipolar transistors are used to fabricate CMOS (complementary metal oxide semiconductor) inverters that show good performance with a gain of 2.3 at a switching threshold voltage of -26 V. This work paves a way to the novel organic/inorganic ultrathin heterostructure based flexible electronics and optoelectronic devices.

We report electronic structure and physical properties of metal doped picene as well as selective synthesis of the phase exhibiting 18 K superconducting transition. First, Raman scattering is used to characterize the number of electrons transferred from the dopants to picene molecules. The charge transfer leads to a softening of Raman scattering peaks, which enables us to determine the number of transferred electrons. From this we have identified that three electrons are transferred to each picene molecule in the superconducting doped-picene solids. Second, we report the pressure dependence of Tc in 7 and 18 K phases of K3picene. The 7 K phase shows a negative pressure-dependence, while the 18 K phase exhibits a positive pressure-dependence which cannot be understood with a simple phonon mechanism of BCS superconductivity. Third, we report a new synthesis method for superconducting K3picene by a solution process with monomethylamine, CH3NH2. This method enables one to prepare selectively the K3picene sample exhibiting 18 K superconducting transition. The discovery of suitable way for preparing K3picene with Tc = 18 K may facilitate clarification of the mechanism of superconductivity.

Transistor characteristics are studied for field-effect transistors (FETs) with thin films of [6]phenacene, which has six benzene rings and W-shape structure. The molecular alignment preferable for FET transport is found to be formed in [6]phenacene thin films. The transistor shows clear p-channel FET characteristics with field-effect mobility μ as high as 3.7 cm2 V−1 s−1. The similar O2 sensing properties to picene FET are observed in [6]phenacene thin film FET. The bias stress properties are observed in [6]phenacene thin film FET. The pulse-voltage application suppresses the bias-stress effect and it enables a continuous O2 sensing in [6]phenacene FET.

New carbon-based superconductors are synthesized by intercalating metal atoms into the solid-phase hydrocarbons picene and coronene. The highest reported superconducting transition temperature, T(c), of a hydrocarbon superconductor is 18 K for K(3)picene. The physics and chemistry of the hydrocarbon superconductors are extensively described for A(x)picene (A: alkali and alkali earth-metal atoms) for x = 0-5. The theoretical picture of their electronic structure is also reviewed. Future prospects for hydrocarbon superconductors are discussed from the viewpoint of combining electronics with condensed-matter physics: modification of the physical properties of hydrocarbon solids is explored by building them into a field-effect transistor. The features of other carbon-based superconductors are compared to clarify the nature of hydrocarbon superconductors.