Activated carbon fibers with manganese dioxide coating for flexible fiber supercapacitors with high capacitive performance

Fiber supercapacitor(FSC)is a promising power source for wearable/stretchable electronics and high capacitive performance of FSCs is highly desirable for practice flexible applications.Here,we report a composite of manganese dioxide(Mn O_2)and activated carbon fibers(ACFs)with high MnO_2mass loading and microporous structure(abbreviated as Mn O_2@ACF),which is used as a fiber electrode to produce a FSC with a high capacitive performance and a good flexibility.The MnO_2@ACF composite electrode in FSCs delivers an ultrahigh specific capacitance of 410 mF/cm^2at 0.1 mA/cm^2,corresponding to a high energy density of 36μWh/cm^2and high power density of 726μW/cm^2.Such high capacitive performance and simple fabrication method indicates that the Mn O_2@ACF composite is a very promising electrode material for flexible fiber supercapacitors.

Facile synthesis of free-standing nickel chalcogenide electrodes for overall water splitting

Developing high-performance noble metal-free and free-standing catalytic electrodes are crucial for overall water splitting. Here, nickel sulfide（NiS） and nickel selenide（Ni Se） are synthesized on nickel foam（NF） with a one-pot solvothermal method and directly used as free-standing electrodes for efficiently catalyzing hydrogen evolution reaction（HER） and oxygen evolution reaction（OER） in alkaline solution.In virtue of abundant active sites, the NiS/NF and the NiS e/NF electrodes can deliver a current density of 10 m A cmat only 123 m V, 137 m V for HER and 222 m V, 271 m V for OER. Both of the hierarchical NiS/NF and Ni Se/NF electrodes can serve as anodes and cathodes in electrocatalytic overall watersplitting and can achieve a current density of 10 m A cmwith an applied voltage of.59 V and 1.69 V,respectively. The performance of as-obtained NiS/NF||NiS/NF is even close to that of the noble metalbased Pt/C/NF||IrO/NF system.

Dual-ion hybrid supercapacitor:Integration of Li-ion hybrid supercapacitor and dual-ion battery realized by porous graphitic carbon

Lithium-ion hybrid supercapacitors(Li-HSCs) and dual-ion batteries(DIBs) are two types of energy storage devices that have attracted extensive research interest in recent years. Li-HSCs and DIBs have similarities in device structure, tendency for ion migration, and energy storage mechanisms at the negative electrode. However, these devices have differences in energy storage mechanisms and working potentials at the positive electrode. Here, we first realize the integration of a Li-HSC and a DIB to form a dual-ion hybrid supercapacitor(DIHSC), by employing mesocarbon microbead(MCMB)-based porous graphitic carbon(PGC) with a partially graphitized structure and porous structure as a positive electrode material. The MCMB-PGC-based DIHSC exhibits a novel dual-ion battery-capacitor hybrid mechanism: it exhibits excellent electronic double-layer capacitor(EDLC) behavior like a Li-HSC in the low-middle wide potential range and anion intercalation/de-intercalation behavior like a DIB in the high-potential range. Two types of mechanisms are observed in the electrochemical characterization process, and the energy density of the new DIHSC is significantly increased.

ZnS-assisted evolution of N,S-doped hierarchical porous carbon nanofiber membrane with highly exposed Fe-N_(4)/C_(x) sites for rechargeable Zn-air battery

Binder-free bifunctional electrocatalysts are attractive for rechargeable Zn-air batteries(ZABs)in gridscale energy storage and flexible electronics,but suffering from the sluggish mass transport and inadequate catalytic capability.Herein,we propose a scalable approach of in-situ engineering highly exposed Fe-N_(4)/Cxsites on the N,S-doped porous carbon nanofiber membrane as a binder-free air electrode catalyst for ZABs.ZnS nanospheres are firstly used as integrated structure-directing agents to facilitate the electronic modulation of Fe-N_(4)/Cxsites by S doping and construct the hierarchical macro/meso/micropores at high temperature.Neither additional step for removal of ZnS nanospheres nor doping process is required,significantly simplifying the pore formation process and improving the S doping efficiency.Benefiting from the enhanced intrinsic activity of high-density Fe-N_(4)/Cxsites(23.53μmol g^(-1))and the optimized mass transport of carbon nanofibers,as-synthesized electrocatalyst shows a positive half-wave potential of 0.89 V for oxygen reduction reaction and a small overpotential of 0.47 V at 10 m A cm^(-2)for oxygen evolution reaction.When used as the air cathode catalyst for ZABs,it delivers a high specific capacity of 699 m Ah g^(-1)at 5 m A cm^(-2),a large peak power density of 228 m W cm^(-2)and a prolonged cycling over 1000 h.At 10 m A cm^(-2),a robust structure with atomically dispersed Fe is also remained after cycling for 420 h.Due to the flexible properties of the electrocatalyst,as-assembled quasi-solid-state ZAB shows stable cycling over 90 h at alternately flat/bent states,demonstrating great prospects in flexible electronic device applications.

Efficient electrocatalytic overall water splitting and structural evolution of cobalt iron selenide by one-step electrodeposition

Developing bifunctional electrocatalysts with both high catalytic activity and high stability is crucial for efficient water splitting in alkaline media.Herein,a Fe-incorporated dual-metal selenide on nickel foam(Co_(0.9)Fe_(0.1)-Se/NF) is synthesized via a facile one-step electrodeposition method.As-synthesized materials could serve as self-supported bifunctional electrocatalysts with excellent catalytic activity towards oxygen evolution reaction(OER) and hydrogen evolution reaction(HER) in alkaline media.Experimental results show that delivering a 10 mA cm^(-2) water splitting current density only requires a cell voltage of 1.55 V.In addition,a very stable performance could be kept for about 36 hours,indicating their excellent working stability.Moreover,by means of phase analysis,we have identified that the evolution of the synthesized Co_(0.9)Fe_(0.1)-Se/NF experiences two entirely different processes in HER and OER,which hydroxide and oxyhydroxide are regarded as the real active sites,respectively.This work may pave the way to further understanding the relationships between the reactivity and stability of chalcogenide-based electrocatalysts and facilitating the rational design of efficient electrocatalysts for future renewable energy system applications.

Photoluminescence manipulation in two-dimensional transition metal dichalcogenides

Two-dimensional transition metal dichalcogenides(TMDCs)have been regarded as an intriguing platform for exploring novel physical phenomena and optoelectronic devices due to their excitonic emission characteristics derived from the atomic thin thickness and reduced dielectric screening effect.Notably,monolayer TMDCs with a direct bandgap exhibiting strong photoluminescence(PL)are promising candidates for the light-emitting devices,while the interlayer excitons in heterostructures hold great potential for the photonic chips and optical communication applications.However,the non-ideal photoluminescent intensity and quality due to the ultrathin thickness and high defect density of experimentally obtained monolayer TMDCs limit the further development for the light-emission applications.Here,we summarize the research progress on the PL manipulation of the excitonic emission in TMDCs,where the PL intensity enhancement and emission wavelength regulation are included.The concept and characteristics of excitons are overviewed firstly,followed by the discussion on the evaluation and characterization of excitonic emission.The state-of-the-art progress on the manipulation of the neutral excitons and interlayer excitons PL are then summarized.Finally,the challenges and prospects are proposed.

Facile synthesis of bimodal macroporous g-C_3N_4/SnO_2 nanohybrids with enhanced photocatalytic activity

It is of vital importance to construct highly interconnected,macroporous photocatalyst to improve its efficiency and applicability in solar energy conversion and environment remediation.Graphitic-like C_3N_4(g-C_3N_4),as an analogy to two-dimensional(2D)graphene,is highly identified as a visible-lightresponsive polymeric semiconductor.Moreover,the feasibility of g-C_3N_4 in making porous structures has been well established.However,the preparation of macroporous g-C_3N_4 with abundant porous networks and exposure surface,still constitutes a difficulty.To solve it,we report a first facile preparation of bimodal macroporous g-C_3N_4 hybrids with abundant in-plane holes,which is simply enabled by in-situ modification through thermally treating the mixture of thiourea and SnCl_4(pore modifier)after rotary evaporation.For one hand,the formed in-plane macropores endow the g-C_3N_4 system with plentiful active sites and short,cross-plane diffusion channels that can greatly speed up mass transport and transfer.For another,the heterojunctions founded between g-C_3N_4 and SnO_2 consolidate the electron transfer reaction to greatly reduce the recombination probability.As a consequence,the resulted macroporous gC_3N_4/SnO_2 nanohybrid had a high specific surface area(SSA)of 44.3 m^2/g that was quite comparable to most nano/mesoporous g-C_3N_4 reported.The interconnected porous network also rendered a highly intensified light absorption by strengthening the light penetration.Together with the improved mass transport and electron transfer,the macroporous g-C_3N_4/SnO_2 hybrid exhibited about 2.4-fold increment in the photoactivity compared with pure g-C_3N_4.Additionally,the recyclability of such hybrid could be guaranteed after eight successive uses.

Facile fabrication of three-dimensional interconnected nanoporous N-TiO_2 for efficient photoelectrochemical water splitting

Three-dimensional （3D） interconnected porous architectures are expected to perform well in photoelectrochemical （PEC） water splitting due to their high specific surface area as well as favourable porous properties and interconnections. In this work, we demonstrated the facile fabrication of 3D interconnected nanoporous N-doped TiO2 （N-TiO2 network） by annealing the anodized 3D interconnected nanoporous TiO2 （TiO2 network） in ammonia atmosphere. The obtained N-TiO2 network exhibited broadened light absorption, and abundant, interconnected pores for improving charge separation, which was supported by the reduced charge transfer resistance. With these merits, a remarkably high photocurrent density at 1.23 V vs. reversible hydrogen electrode （RHE） was realized for the N-TiO2 network without any co-catalysts or sacrificial reagents, and the photostability can be assured after long term illumination. In view of its simplicity and efficiency, this structure promises for perspective PEC applications.

g-C_(3)N_(4) templated mesoporous carbon with abundant heteroatoms as high-rate anode material for dual-carbon sodium ion hybrid capacitors

Sodium ion hybrid capacitors(SIHCs)are regarded as advanced power supply systems.Nevertheless,the kinetics imbalance of cathode and anode suppresses the further performance improvement of SIHCs.The carbonaceous anode materials are promising and many strategies have been utilized to increase the capacity of sloping region or accelerate the reaction rate of plateau region.However,it is still challenging to simultaneously realize high mesopore/micropore volume ratio,large interlayer distance(>0.37 nm),and abundant and favorable heteroatoms-doping by a simple method.Herein,we report N,P,O ternarydoped mesoporous carbon(PNPOC-T,T=700,800 or 900)with large interlayer distance(~0.4 nm)as anode materials.The PNPOC-T were prepared by a simple in-situ polymerization of aniline and phytic acid on the exfoliated graphitic nitrogen carbide(g-C3N4)and subsequent carbonization.The obtained PNPOC-800 exhibits an excellent rate performance(101.5 mA·h·g^(-1) at 20 A·g^(-1)),which can be attributed to the high surface-controlled capacitive behavior ratio and rapid ion diffusion.The optimum SIHCs display a high energy density of 105.48 W·h·kg^(-1) and a high power density of 13.59 kW$kg1.Furthermore,the capacitance retention rate of SIHCs can reach 87.43%after 9000 cycles at 1 A·g^(-1).

Inorganic Nanotube/Organic Nanoparticle Hybrids for Enhanced Photoelectrochemical Properties

Inorganic/organic nanohybrids composed of arrayed TiO_2 nanotubes（Ti NTs）/porphyrin nanoparticles（NPs） have been fabricated via a wet chemical approach. The inorganic component, particularly the arrayed one-dimensional（1D） nanostructures, provides high charge-carrier mobility and rapid charge transport. The organic component exhibits extensive visible light absorption and good solution processability. Additionally, the geometric restraint by supramolecular assembly renders an improved photostability. A combination of these two components could thus allow for an efficient solar energy conversion. In this work, a colloid of porphyrin NPs prepared by a solvent exchange method is coated on anodic Ti NTs by means of a dip-coating treatment to form inorganic/organic hybrids. The hybrids exhibit an improvement on solar absorption and a significant enhancement on photocurrent generation at a small bias compared with individual component. Herein, the inorganic/organic nanohybrids are proved to be excellent photoanodes highly responsive to visible light and thus pave a way to discover new inorganic/organic assemblies for high-performance optoelectronic applications, as well as for device integration.

Organic semiconductor nanostructures:optoelectronic properties,modification strategies,and photocatalytic applications

Organic semiconductors(OSCs)possess diverse chemical structures and tailored optoelectronic properties via simple chemical modifications,so increasing use of them are found in efficient visible-light photo-catalysis.However,the weak chemical bonds and the poor charge behavior(e.g.,low concentration of free charge carriers,low carrier mobility)intrinsic in them,always incur quite limited stability and efficiency.Therefore,the assembly of them into refined nanostructures or nanocomposites is usually proposed to enhance their optoelectronic properties,as well as the photocatalytic efficiency and reliability.Zero-dimensional(0D)nanoparticles are low in size and hence high specific surface area(SSA);One-dimensional(1D)nanostructures are usually arranged in an orderly long range thus leading to low surface defect density and increased carrier mobility;Two-dimensional(2D)nanostructures are particularly capa-ble of enhancing the photogenerated charge utilization because of their large reaction sites and shortened charge transport length.Furthermore,the building of heterogeneous interfaces in the nanocomposites can effectively facilitate the special charge separation.All these highlight the importance of organic nanos-tructures in improving the photocatalytic activity and stability.Therefore,organic semiconductor nanostructures(OSNs)have been increasingly used in the photocatalytic water splitting into H_(2) and O_(2),CO_(2) reduction,pollutant decomposition,disinfection,etc.In this review,we first examine the important optoelectronic properties of OSNs that govern the photocatalytic processes;we then analyze different classes of OSNs and their mechanistic pathways,with an emphasis on the structure-property relationships;we also introduced various photocatalytic applications of OSNs;we lastly propose the challenges and future outlook in real use.

Environment-friendly preparation of exfoliated graphite and functional graphite sheets

Exfoliated graphite(EG)is promising oil sorbent as well as an intermediate product for the preparation of flexible graphite films(FGFs).It has been a critical challenge to energy conservation and pollution abatement for the traditional EG production technique.Here,we propose a simple and effective preparation method to acquire EG in which flake graphite is intercalated and exfoliated at room temperature,not involving any pollutant emission.The influence factors in the preparation process were explored,such as the amount of H_(2)SO_(4)and H_(2)O_(2),the temperature for the preparation of room temperature exfoliated graphite(RTEG).In contrast to the EG by high temperature exfoliation(HTEG),RTEG exhibits a homogeneous structure and a significantly increased volume and surface area.Moreover,EG blocks with high oil sorption capacity and excellent reuse performance can be obtained by RTEG method.Especially,FGFs fabricated by RTEG has high flexibility,thermal conductivity and electrical conductivity.It suggests that this environment-friendly technology is suitable for large-scale industrial implementation of graphite-based oil sorbents and flexible materials.