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The creation of ultrafine alloy nanoparticles (5 nm) that can maintain surface activity and avoid aggregation for heterogeneous catalysis has received much attention and is extremely challenging. Here, ultrafine PtRh alloy nanoparticles imprisoned by the cavities of reduced chiral covalent imine cage (PtRh@RCC3) are prepared successfully by an organic molecular cage (OMC) confinement strategy, while the soluble RCC3 can act as a homogenizer to homogenize the heterogeneous PtRh alloy in solution. Moreover, the X-ray absorption near-edge structure (XANES) results show that the RCC3 can act as an electron-acceptor to withdraw electrons from Pt, leading to the formation of higher valence Pt atoms, which is beneficial to improving the catalytic activity for the reduction of 4-nitrophenol. Attributed to the synergistic effect of Pt/Rh atoms and the unique function of the RCC3, the reaction rate constants of Pt

3D-printed micro-supercapacitors (MSCs) have emerged as the ideal candidates for energy storage devices owing to their unique characteristics of miniaturization, structural diversity, and integration. Exploring the 3D printing technology for various materials and architectures of MSCs is key to realizing customization and optimizing the performance of 3D-printed MSCs. In this review, we summarize the latest progress in 3D-printed MSCs with regards to general printing approaches, printable materials, and rational design considerations. Specifically, several general types of 3D printing techniques (their working principles, available materials, resolutions, advantages, and disadvantages) and their applications to fabricate electrodes with different energy storage mechanisms, and various electrolytes, are summarized. We further discuss research directions in terms of integrated systems with other electronics. Finally, future perspectives on the research and development directions in this important field are further discussed.

A bi-phase ionic conductive polyether-based composite electrolyte was obtained by in situ polymerization, which synergistically achieves high ion-conduction (6.6 × 10−4 S cm−1, 25 °C), and a chemically stable solid electrolyte interphase.

Lithium-sulfur (Li-S) batteries with high theoretical energy densities have long been identified a promising energy storage system. Nonetheless, it is not trivial to simultaneously achieve dendrite-free lithium metal anode and stable sulfur cathode for practical applications. To tackle this issue, we herein design an oxygen-functionalized mesoporous carbon nanofiber framework decorated with well-distributed nickel nanoparticles as bifunctional hosts for both electrodes. The combined theoretical and experimental results reveal that the regulated electric field stemming from the oxygenated and mesoporous structure can effectively facilitate the uniform nucleation and growth of dendrite-free Li metal in local nanofiber and whole electrode levels. Meanwhile, the strong affiliation of oxygenated groups to lithium polysulfides greatly alleviate the shuttle effect, leading to impressive cyclic stability. When coupling above optimal electrodes into a flexible Li-S full battery with an ultralow negative to positive capacity ratio of 2.0, the new battery presents remarkable electrochemical performance with a high rate capability of 882 mAh g−1 at 2.0 C and an extremely low capacity decay rate of 0.005% per cycle over 300 cycles. The stable electrochemical performance exhibited by a flexible Li-S battery under different mechanical deformations paves the way for future practical applications in flexible energy storage devices based on the bifunctional hosts.

Sodium (Na) metal is considered a promising anode material for high-energy Na batteries due to its high theoretical capacity and abundant resources. However, uncontrollable dendrite growth during the repeated Na plating/stripping process leads to the issues of low Coulombic efficiency and short circuits, impeding the practical applications of Na metal anodes. Herein, we propose a silver-modified carbon nanofiber (CNF@Ag) host with asymmetric sodiophilic features to effectively improve the deposition behavior of Na metal. Both density functional theory (DFT) calculations and experiment results demonstrate that Na metal can preferentially nucleate on the sodiophilic surface with Ag nanoparticles and uniformly deposit on the whole CNF@Ag host with a "bottom-up growth" mode, thus preventing unsafe dendrite growth at the anode/separator interface. The optimized CNF@Ag framework exhibits an excellent average Coulombic efficiency of 99.9% for 500 cycles during Na plating/stripping at 1 mA cm-2 for 1 mAh cm-2. Moreover, the CNF@Ag-Na symmetric cell displays stable cycling for 500 h with a low voltage hysteresis at 2 mA cm-2. The CNF@Ag-Na//Na3V2(PO4)3 full cell also presents a high reversible specific capacity of 102.7 mAh g-1 for over 200 cycles at 1 C. Therefore, asymmetric sodiophilic engineering presents a facile and efficient approach for developing high-performance Na batteries with high safety and stable cycling performance.

Owing to the excellent redox reversibility and structural diversity, polytriphenylamine (PTPAn) has been regarded as one of the promising cathode candidates for sodium-ion batteries. However, it still suffers from the bulk aggregation and low operating capacity in practical applications. Assisted by the in-situ polymerization, leaf-like PTPAn nanosheets are uniformly introduced on the surface of carbon nanofibers (CNFs) to form the free-standing CNF@PTPAn composite electrodes. Interestingly, the formation mechanism of the leaf-on-branch structure of CNF@PTPAn composites is systematically explored, confirming that the controlling of oxidation rate and growth degree plays crucial roles in tuning the morphology and active material content of the composite electrodes. Supported by the capacity-cutting analysis, the effective coupling between the active PTPAn and conductive CNFs can provide fast electron/ion-shuttling channels and deepen the electrochemical reaction process. At 50 mA g−1, the capacity of the optimized CNF@PTPAn composite can reach 105 mA h g−1, with a stable rate capability of 78 mA h g−1 even at 400 mA g−1 after 500 cycles in a half cell. The detailed kinetic analysis confirms that the ion-storage behaviors in the low-voltage region can be tailored for the improved capacitive contribution and diffusion coefficients. Meanwhile, the flexible CNF-based full cell with CNF@PTPAn as the cathode and CNFs as the anode exhibits a high energy density of 60 W h kg−1 at 938 W kg−1. Based on this, the rational design is expected to provide more possibilities to obtain advanced freestanding electrode systems.

Separators are indispensable components of modern electrochemical energy storage devices such as lithium-ion batteries (LIBs). They perform the critical function of physically separating the electrodes to prevent short-circuits while permitting the ions to pass through. While conventional separators using polypropylene (PP) and polyethylene (PE) are prone to shrinkage and melting at relatively high temperatures (150 °C or above) causing short circuits and thermal runaway, separators made of thermally stable polyimides (PIs) are electrochemically stable and resistant to high temperatures, and possess good mechanical strength—making them a promising solution to the safety concerns of LIBs. In this review, the research progress on PI separators for use in LIBs is summarized with a special focus on molecular design and microstructural control. In view of the significant progress in advanced chemistries beyond LIBs, recent advances in PI-based membranes for applications in lithium-sulfur, lithium-metal, and solid-state batteries are also reviewed. Finally, practical issues are also discussed along with their prospects.

Green and environmentally friendly electrocatalytic nitrogen (N2) fixation to synthesize ammonia (NH3) is recognized as an effective method to replace the traditional Haber–Bosch process. However, the difficulties in N2 adsorption and fracture of hard N≡N bond still remain major challenges in electrocatalytic N2 reduction reactions (NRR). From the perspectives of enhancing N2 adsorption and providing more catalytic sites, two-dimensional (2D) FeS2 nanosheets and three-dimensional (3D) metal organic framework-derived ZnS embedded within N-doped carbon polyhedras are grown on the carbon cloth (CC) template in this work. Thus, a composite NRR catalyst with multi-dimensional structures, which is signed as FeS2/ZnS-NC@CC, is obtained for using over a wide pH range. The uniform distribution of hollow ZnS-NC frameworks and FeS2 nanosheets on the surface of CC largely increase the N2 enrichment efficiency and offer more active sites, while the CC skeleton acts as an independent conductive substrate and S-doping helps promote the fracture of N≡N bond during the NRR reaction. As a result, the FeS2/ZnS-NC@CC electrode achieves a high Faraday efficiency of 46.84% and NH3 yield of 58.52 μg h−1 mg−1 at -0.5 V vs. Ag/AgCl in 0.1 M KOH. Furthermore, the FeS2/ZnS-NC@CC electrode displays excellent NRR catalytic activity in acidic and neutral electrolytes as well, which outperforms most previously reported electrocatalysts including noble metals. Therefore, this work provides a new way for the design of multi-dimensional electrocatalysts with excellent electrocatalytic efficiency and stability for NRR applications.

Despite the high theoretical specific capacity, the main challenges of rechargeable lithium-sulfur (Li-S) batteries, including the unceasing shuttle of soluble lithium polysulfides (LiPSs) and severe Li corrosion, seriously hinder their commercial and practical applications. Herein, a bifunctional polyvinyl alcohol/poly(lithium acrylate) (C-PVA/PAA-Li) composite nanofiber separator is developed to address the main challenges in Li-S batteries by simultaneously allowing rapid lithium ion transport and ionic shielding of polysulfides. The C-PVA/PAA-Li composite nanofiber membrane is prepared via the facile electrospinning strategy, followed by thermal crosslinking and in-situ lithiation processes. Differing from the conventional Celgard-based coating methods accompanied by impaired lithium ion transport efficiency, the C-PVA/PAA-Li composite nanofiber membrane possesses well-developed porous structures and high ionic conductivity, thus synergistically reducing the charge transfer resistance and inhibiting the growth of lithium dendrites. The resulting Li-S batteries exhibit an ultra-low fading rate of 0.08% per cycle after 400 cycles at 0.2 C, and a capacity of 633 mAhg−1 at a high current density of 3 C. This study presents an inspiring and promising strategy to fabricate emerging dual-functional separators, which paves the pathway for the practical implementation of ultra-stable and reliable Li-S battery systems.

Desirable areal and volumetric capacitances of electrodes with high mass loading are of great significance for compact energy storage in practical applications. The key challenge remains in the structural design of electrodes with interconnected micro-/macro-networks for unimpeded electron and ion transport. Herein, three-dimensional (3D) printed carbon aerogel (CA) microlattices are designed with tunable thickness to realize high areal capacitance. By using polyamic acid (PAA) as a crosslinker, graphene oxide/polyamic acid (GP) ink exhibits ideal printability and formability to ensure the continuous printing of self-supported and programmable 3D structures. After subsequent freeze-drying and thermal treatment, the as-obtained CA exhibits not only a well-maintained macrostructure of the extruded shape but also a porous microstructure from the interconnected GP gel. As a result, the 3D printed CA microlattice presents a quasi-proportional increase in areal capacitance with thickness, achieving a desirable areal/volumetric capacitance (870.3 mF cm−2/1.7 F cm−3) under high mass loading (15.3 mg cm−2) and large thickness (4.9 mm). This work offers a promising strategy to construct a customizable structure of a supercapacitor and provides new insights to dramatically improve the energy storage properties of microdevices with limited area.

A better solid-liquid-gas three-phase boundary is vital for low energy cost oxygen evolution reaction (OER), making the designed regulation of interfacial atmosphere necessary. Herein, we find that the OER electrocatalysis can be dramatically improved by synergistically forming disordered electronic structures and superficial amorphous layers, as superficial oxyhydroxide, phosphorus-doped NiFe2O4 nanoarrays on nitrogen-doped carbon nanofibers (OP-NiFe2O4/NCNFs). Unveiled by the depth-profiling analysis from the X-ray photoelectron spectroscopy, the contents of phosphorous doping in the OP-NiFe2O4 nanoarrays change dynamically from outside to inside due to its in situ superficial reconstruction into the oxyhydroxide layer, thereby accelerating electron transfer between heterogeneous phases. As revealed by density functional theory calculations, this amorphous oxyhydroxide layer and dynamically varied phosphorous content would positively shift the d-band center of the NiFe2O4-related compounds, leading to lower adsorption energy towards water molecule. Thus, the OP-NiFe2O4/NCNF electrocatalyst displays a low overpotential of 260 mV at a current density of 10 mA cm-2 and a small Tafel slope of 44.8 mV dec-1 in an alkaline medium.

Lithium (Li) metal is considered as the best anode candidate for next-generation high-energy batteries due to its ultralow electrochemical potential and extremely high theoretical capacity. However, issues arising from the undesired growth of lithium dendrites and infinite volumetric change have seriously hindered the practical application of lithium metal batteries (LMBs). Here, we designed a super-lithiophilic amorphous zinc oxide-doped carbon nanofiber framework with uniformly-distributed and parallel multichannels (MCCNF@ZnO) to achieve the homogeneous distribution of electric field and Li

Stand-off Raman spectroscopy combines the advantages of both Raman spectroscopy and remote detection to retrieve molecular vibrational fingerprints of chemicals at inaccessible sites. However, it is currently restricted to the detection of pure solids and liquids and not widely applicable for dispersed molecules in air. Herein, we realize real-time stand-off SERS spectroscopy for remote and multiplex detection of atmospheric airborne species by integrating a long-range optic system with a 3D analyte-sorbing metal–organic framework (MOF)-integrated SERS platform. Formed via the self-assembly of Ag@MOF core–shell nanoparticles, our 3D plasmonic architecture exhibits micrometer thick SERS hotspot to allow active sorption and rapid detection of aerosols, gas, and volatile organic compounds down to parts-per-billion levels, notably at a distance up to 10 m apart. The platform is highly sensitive to changes in atmospheric content, as demonstrated in the temporal monitoring of gaseous CO2 in several cycles. Importantly, we demonstrate the remote and multiplex quantification of polycyclic aromatic hydrocarbon mixtures in real time under outdoor daylight. By overcoming core challenges in current remote Raman spectroscopy, our strategy creates an opportunity in the long-distance and sensitive monitoring of air/gaseous environment at the molecular level, which is especially important in environmental conservation, disaster prevention, and homeland defense. Ministry of Education (MOE) Nanyang Technological University Accepted version X.Y.L. thanks the Singapore Ministry of Education Tier 1 (RG11/18) and Tier 2 (MOE2016-T2-1-043) grants. G.C.P.-Q. and C.S.L.K. are thankful for Nanyang President’s Graduate Scholarships. N.Y. is thankful for the CN Yang scholarship. T.L. acknowledges the funding support from the National Natural Science Foundation of China (51433001).

Silicon (Si)/carbon nanocomposites have attracted extensive interests as emerging electrode materials in lithium-ion batteries (LIBs) due to their numerous premium features of high capacity, good conductivity, excellent ductility and long cycle life. Herein, we introduce a novel nitrogen-doped porous carbon fiber framework entrapped with Si nanoparticles (Si@NPCNF) by an improved electrospinning strategy with an in-situ reaction bath of pyrrole as the special collector. It is interesting that the in-situ collected polypyrrole (PPy) coated Si/PMMA precursor fibers show uniform diameter around 1.2–1.5 μm with three-dimensional (3D) interconnected porous structures. After heat treatment at 850 °C, the resulted Si@NPCNF nanocomposite with high porosity and large surface area, can effectively relieve the severe volume expansion of silicon to reduce the pulverization of Si anode during the discharge/charge processes. Furthermore, the thin N-doped carbon layer derived from PPy can largely improve the conductivity of Si anode and shorten the Li+ diffusion distance. Meanwhile, the 3D porous structure can efficiently prevent Si from directly contacting with electrolyte to improve the cycling stability of LIBs. Therefore, the Si@NPCNF nanocomposite exhibits outstanding electrochemical performance which delivers a high initial capacity of 1521 mA h g−1 at 0.1 A g−1, a good rate capability of 648 mA h g−1 at 2 A g−1 and excellent cycle stability of 515.5 mA h g−1 after 200 cycles at 1 A g−1, being promising as a high-performance anode material for lithium-ion batteries.

Lithium–sulfur (Li–S) batteries are extremely attractive for next-generation energy storage technologies owing to their high energy density, low cost and environmental friendliness. Nevertheless, the severe shuttle effect of soluble lithium polysulfides (LiPS) has been one of the major technical challenges causing the rapid capacity fading of Li–S batteries. Herein, we prepare a uniquely designed polyacrylonitrile/poly(acrylic acid) composite nanofiber separator with controllable pore structures and abundant electronegative groups, which is denoted as E-PAN/PAA, to effectively suppress the shuttling effect of LiPS. By a facile electrospinning strategy combined with ethanol steaming treatment, poly(acrylic acid) can be in situ extracted out from the inside of PAN/PAA composite nanofibers to precisely tune the pore structure of the nanofiber separator. As a result, the optimized E-PAN/PAA separator can act as an ionic sieve to allow fast Li+ transport while effectively inhibiting LiPS migration as well, leading to a high initial capacity of 1232 mA h g−1 at 0.1C and a remarkable cycling stability with an ultra-low fading rate of 0.03% per cycle over 500 cycles at 1C. Moreover, the E-PAN/PAA separator presents a remarkable combination of excellent electrolyte wettability, thermal stability and mechanical properties, providing a valuable strategy for the design and manufacture of advanced Li–S battery separators.

Unraveling the role of transition-metal doping in affecting the native spinel-structured nanosheets' water splitting remains a grand challenge. In this work, a series of spinel-structured nanosheets wrapped hollow nitrogen-doped carbon polyhedrons were constructed, and doped transition-metal domains were deliberately introduced on the surface. Theoretical investigations show that their energy level can be finely tuned via direct transition-metal doping engineering. As a prototype, an Fe-doped NiCo₂O₄ nanosheets wrapped hollow nitrogen-doped carbon polyhedron (Fe–NiCo₂O₄@HNCP) exhibits outstanding bifunctional electrocatalytic performances with low overpotentials (η = 270 mV for OER, η = 84 mV for HER), low Tafel slopes (b = 42 mV dec⁻¹ for OER, b = 47 mV dec⁻¹ for HER), and high durability. The enhanced performance is attributed to the synergistic effects of energy level matching for electron transfer, and partial charge delocalization-induced rich active sites for reactant adsorption via thermodynamic and kinetic acceleration. This work may open a new pathway to design highly active and stable transition-metal doped electrocatalysts by manipulated energy levels for efficient overall water splitting. We are really grateful for the financial support from the National Natural Science Foundation of China (51433001, 21674019, 21604010), the Science and Technology Commission of Shanghai Municipality (16520722100), the Program of Shanghai Academic Research Leader (17XD1400100), the “Chenguang Program” supported by the Shanghai Education Development Foundation and Shanghai Municipal Education Commission (16CG39) and the Engineering and Physical Sciences Research Council (EPSRC, EP/L015862/1). The computational center of USTC is acknowledged for computational support.

Faradaic efficiency for the nitrogen reduction reaction (NRR) is often limited by low N

Hydrogen evolution reaction (HER) has been severely suppressed by the first proton adsorption step, due to the “shackles” of the surrounding water in the form of hydronium ions (H13O6+). Here, it has been found anionic vacancies in NiCo2A4 (A = O, S, Se) can weaken the shackles of surrounding water in H13O6+, resulting into efficient capture of H+ to form a H+-enriched field. Taking selenium vacancy-rich NiCo2Se4 nanowires on nitrogen-doped carbon nanofibers as an example, it displays higher electrocatalytic activities with low overpotential of 168 mV at 10 mA cm−2 and a Tafel slope of 49.8 mV dec−1. The HER performance is strongly related to the anionic vacancy size, the larger the anionic vacancy size is (VSe > VS > VO), the higher the HER activity does. Guided by density functional theory calculations, it is found that the point defect structures can not only strengthen its interfacial linkage force with H+ by weakening the hydration force of contiguous hydronium ion, but also increase its charge density for efficient electron transfer to adsorbed H+. Therefore, this work creates a useful strategy to optimize the HER performance of traditional bimetallic compounds by engineering the solid-liquid-gas three-phase interfacial interaction.

Electrochemical nitrogen-to-ammonia conversion by the nitrogen reduction reaction (NRR) under ambient conditions is regarded as a potential approach to tackle the energy-intensive Haber–Bosch process with excessive CO2 emission. However, the NRR is still restricted by low faradaic efficiency and NH3 yield, which is due to the chemical inertness of N-related groups for efficient adsorption/activation on the electrocatalysts. Here, a series of spinel-structured nanosheet wrapped hollow nitrogen-doped carbon polyhedra with abundant oxygen vacancies are constructed successfully. From theoretical aspects, these materials show increased charge density on their surface for enhanced capture and activation of N2 molecules. As a result, oxygen vacancy-rich NiCo2O4 on hollow N-carbon polyhedra (Vo-rich NiCo2O4@HNCP) shows outstanding electrocatalytic NRR performance with high production yield (NH3: 4.1 μg h−1 cm−2/17.8 μg h−1 mg−1; faradaic efficiency: 5.3%) and high stability under ambient conditions and is superior to the counterpart oxygen vacancy-poor electrocatalysts. Oxygen vacancy engineering introduces a new concept for rational design of advanced NRR catalysts for energy conversion systems.

The bio-inspired hierarchical “grape cluster” superstructure provides an effective integration of one-dimensional carbon nanofibers (CNF) with isolated carbonaceous nanoparticles into three-dimensional (3D) conductive frameworks for efficient electron and mass transfer. Herein, a 3D N-doped porous carbon electrocatalyst consisting of carbon nanofibers with grape-like N-doped hollow carbon particles (CNF@NC) has been prepared through a simple electrospinning strategy combined with in-situ growth and carbonization processes. Such a bio-inspired hierarchically organized conductive network largely facilitates both the mass diffusion and electron transfer during the oxygen reduction reactions (ORR). Therefore, the metal-free CNF@NC catalyst demonstrates superior catalytic activity with an absolute four-electron transfer mechanism, strong methanol tolerance and good long-term stability towards ORR in alkaline media.

Larger interlayer distance and higher doping efficiency of heteroatoms are considered to be the two most effective solutions to modulate the electronic structure of carbon materials to achieve improved electrochemical storage performances. Here, an innovative popping process is applied to puff biomaterials, i.e., the Chinese “five grains” of round-grained rice and wheat, into aerogels using the traditional Chinese popcorn machine. Thus, well-defined and interconnected three-dimensional pores are constructed within the biomaterial-derived carbon aerogels after a one-step pyrolysis process. As a result, the interlayer distance of the carbon nanosheets is slightly expanded from ∼3.6 to ∼3.7 A, providing more expanded channels for rapid diffusion and adsorption of heteroatom precursors on the surface of the carbon layers. Therefore, a high amount of nitrogen and sulfur incorporation has been realized in the pyrolyzed carbon nanosheets, which further expand the interlayer distance between the carbon layers fro...

Nanoporous gold (NPG) promises efficient light-to-heat transformation, yet suffers limited photothermal conversion efficiency owing to the difficulty in controlling their morphology for direct modulation of thermo-plasmonic properties. Herein, we showcase a series of shape-controlled NPG nanoparticles with distinct bowl- (NPG-B), tube- (NPG-T) and plate-like (NPG-P) structures for quantitative temperature regulation up to 140 oC in < 1 s using laser irradiation. Notably, NPG-B exhibits a highest photothermal efficiency of 68% which is >12 and 39 percentage points better than other NPG shapes (NPG-T, 56%; NPG-P, 49%) and Au nanoparticles (29%), respectively. We attribute NPG-B’s superior photothermal performance to its >13% enhanced light absorption cross section compared to other Au nanostructures. We further realize an ultrasensitive heat-mediated light-to-mechanical “kill switch” by integrating NPG-B with a heat-responsive shape-memory polymer (SMP/NPG-B). This SMP/NPG-B hybrid is analogous to a photo-triggered mechanical arm, and can be activated swiftly in

As one of the typical organic cathode materials for sodium ion batteries (SIBs), 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) is formidably challenged in practical applications because of its low electrical conductivity, sluggish reaction kinetics, inferior rate capability and cycle life. Inspired by the ultra-strong capillarity of wood’s aligned hierarchical microchannels toward ions and water during metabolism, we have designed a novel composite nanofibrous organic cathode consisting of PTCDA/nitrogen-doped carbon/carbon nanotubes (PTCDA/NC/CNT) for SIBs. The PTCDA/NC/CNT cathode exhibits rapid ionic/electronic transport properties and ultrafast reaction kinetics owing to the synergistic effects of the interconnected conductive frameworks and ultra-strong capillarity deriving from the hierarchical micro/nanotunnels. As a result, a highly reversible capacity of 135.6 mA h g−1 at 50 mA g−1, excellent rate performance and ultra-long cyclic stability with over 95% capacity retention after 500 cycles at 1000 mA g−1 are achieved for the PTCDA/NC/CNT cathode in SIBs. Remarkably, an all-organic battery using the PTCDA/NC/CNT cathode and conjugated sodium carboxylate/CNT anode also delivers a high energy density of 85 W h kg−1 at a power density of 665 W kg−1. This bio-inspired design provides a promising strategy for the development of next-generation all-organic sodium-ion full batteries.

To pursue high-performance energy storage devices with both high energy density and power density, nitrogen-doped carbon nanofibers (CBC-N) derived from bacterial cellulose are used both as a three-dimensional template for space-confined hydrothermal growth of NiCo 2 S 4 , and as the highly conductive negative electrode material for asymmetric supercapacitor assembly. Notably, uniformly dispersed NiCo 2 S 4 nanoparticles with only 3–5 nm are successfully immobilized on the surface of CBC-N fibers to form the CBC-N@NiCo 2 S 4 composite, which effectively prevents the severe aggregation of NiCo 2 S 4 nanoparticles and fully utilizes the outstanding electrochemical activity and capacity of NiCo 2 S 4 as the pseudocapacitive electrode material. Benefiting from the conductive CBC-N fiber template with hierarchical architectures and its coupling with uniformly dispersed NiCo 2 S 4 nanoparticles, the CBC-N@NiCo 2 S 4 composite exhibits high capacitance of 1078 F g −1 at 1 A g −1 and excellent capacity retention of 94.6% (918.5 F g −1 at 5 A g −1 ). Furthermore, the asymmetric supercapacitor demonstrates high energy density of 42.6 Wh kg −1 at power density of 1500 W kg −1 , and long-term cycling stability of 96.8% retention after 5000 cycles. Therefore, this work provides a new strategy to develop biomass-derived high-performance electrode materials for potential applications in supercapacitors.

Tailoring the size and controlling the morphology of particular nano-architectures are considered as two promising strategies to improve the catalytic performance of metal nanocrystals towards hydrogen evolution reactions (HERs). Herein, mesoporous cobalt phosphide nanotubes (CoP-NTs) with a three-dimensional network structure have been obtained through a facile and efficient electrospinning technique combined with thermal stabilization and phosphorization treatments. The thermal stabilization process has been demonstrated to play a key role in the morphological tailoring of Co3O4 nanotubes (Co3O4-NTs). As a result, the CoP-NTs show one-dimensional hollow tubular architecture instead of forming a worm-like tubular CoP structure (W-CoP-NTs) or severely aggregated CoP powder (CoP-NPs) which originate from the Co3O4 nanotubes without thermal stabilization treatment and Co3O4 nanoparticles, respectively. Satisfyingly, under an optimized phosphorization degree, the CoP-NT electrode exhibits a low onset overpotential of 53 mV with a low Tafel slope of 50 mV dec−1 during the HER process. Furthermore, the CoP-NT electrode is capable of driving a large cathodic current density of 10 mA cm−2 at an overpotential of 152 mV, which is much lower than those of its contrast samples, i.e. CoP-NPs (211 mV) and W-CoP-NTs (230 mV). Therefore, this work provides a feasible and general strategy for constructing three-dimensionally organized mesoporous non-noble metal phosphide nanotubes as promising alternative high-performance electrocatalysts for the commercial platinum ones.

Electrospinning is a simple and highly versatile method to produce one-dimensional polymeric, inorganic, and hybrid nanomaterials with controllable diameters, morphologies, and compositions. Due to their high aspect ratios, large surface areas, high porosities, and tunable compositions, electrospun nanofiber electrodes are considered ideal candidates for applications in a variety of high-performance electrochemical energy storage devices. This chapter discusses recent research on electrospun nanomaterials for supercapacitor (SC) applications, including the architecture designs and their electrochemical performance. According to the charge storage mechanisms of SC electrodes, electrospun nanomaterials can be mainly classified into three kinds: electrochemical double-layer capacitive carbon nanofiber-based materials, pseudocapacitive conducting polymers, and metal oxide nanofiber materials and their hybrid materials. For each material class, the emphasis is directed at addressing the relationship between the compositions, nanostructures, and electrochemical properties of the electrospun nanomaterials. This chapter highlights the recent advances of electrospun nanomaterials for SCs, suggests new strategies to improve their electrochemical performance further, and pushes forward the future prospects of these promising materials for energy storage applications.

Lithium-sulfur (Li–S) batteries have been regarded as one kind of the most attractive candidates for next-generation energy storage devices for their high theoretical energy density and fairly low cost. However, the “shuttle effect” caused by diffusion of soluble polysulfides and uncontrollable growth of lithium dendrite seriously deteriorate the long-term cycle stability and safety of Li–S batteries in practical applications. Herein, a highly porous polyvinyl alcohol (PVA)/sodium carboxylmethyl cellulose (CMC) composite separator with three-dimensional ion-selective nanochannels has been successfully fabricated via a facile non-solvent induced separation method. The abundant negative –COO- groups inside the nanochannels can hinder the undesired polysulfides penetrating through the separator, but allow Li+ transporting rapidly and induce uniform lithium stripping/plating. As a result, the Li–S battery using the porous PVA/CMC composite separator realizes stable cycling with a low decay rate of 0.045% per cycle over 500 cycles at 1 C. This work offers a feasible strategy to design advanced multifunctional Li–S battery separators.

High-performance electrocatalysts with excellent catalytic activity and long durability competitive to Pt are urgently necessary for fuel cell development. Here, a novel self-standing membrane of nitrogen-doped carbon nanofibers (NCNF) has been developed, acting as a three-dimensionally networked and conductive template for immobilization of electrochemically active Co 3 O 4 particles. Thus, nanocubic-Co 3 O 4 coated NCNF (NCNF@Co 3 O 4 ) composite fiber membrane with hierarchical structures is obtained, which subtly combines the synergistic effects between the electroactive nanocubic-Co 3 O 4 , efficient surface nitrogen doping and highly conductive NCNF network. Therefore, the NCNF@Co 3 O 4 composite exhibits excellent catalytic activity toward oxygen reduction reactions with positive E peak potential, high current density and superior durability over the commercial Pt/C catalyst, being a promising noble metal-free catalyst for practical fuel cell applications.

Hierarchically structured carbon aerogels consisting of one-dimensional carbon nanofibers and a three-dimensional carbon skeleton are prepared by sequential imidization and carbonization of bacterial cellulose/poly(amic acid) composite aerogels. The as-obtained carbon aerogels show excellent compressive properties, and can be directly used as versatile adsorbents for various liquids with superior sorption capacity and extraordinary recycling performance. Interestingly, the recycled carbon aerogels can still be used as electrode materials for supercapacitors with a high specific capacitance of 194.7 Fg¢1 and excellent stability, which is attributed to the interconnected pores for fast ion diffusion, the maximized active site exposure for efficient charge adsorptions, and crosslinked carbon nanofibers for rapid electron transport. Therefore, this work provides a new strategy to develop multidimensional carbonaceous materials for both environmental and energy applications.

As a novel kind of carbon-based material, carbon aerogels have attracted widespread attention owing to their integrated properties of a large internal surface area, small pore size, and outstanding mechanical strength. In this study, a fascinating carbon aerogel has been rationally designed with a unique cellular structure, consisting of one-dimensional carbon nanofibers derived from oxidized polyacrylonitrile (o-PAN) and two-dimensional carbon sheets originating from polyimide (PI). The interconnected o-PAN/PI (oPP) carbon aerogel exhibits low density but increased mechanical strength and can not only act as a versatile adsorbent but also as an ideal template for the in situ growth of MnO2 nanosheets to obtain oPP@MnO2 hybrid carbon aerogel. The oPP@MnO2 composite aerogel exhibits extraordinary electrochemical characteristics with a maximum specific capacitance of 1066 F g−1, approaching the theoretical value (1370 F g−1) of MnO2. Moreover, an assembled oPP@MnO2//activated oPP (A-oPP) asymmetric supercapacitor delivers a considerably high energy density of up to 30.3 W h kg−1, highlighting the advantages of the unique cellular structure of the oPP carbon aerogel and oPP@MnO2 hybrid carbon aerogel. Therefore, the successful fabrication of the oPP carbon aerogel widens the scope of traditional electrospun lamellar membranes to multi-dimensional aerogels, providing a new strategy for the construction of nanofiber-based materials for energy storage and environmental protection applications.

A flexible composite nanofibrous organic cathode, consisting of naphthalene-based polyimide/nitrogen-doped carbon/carbon nanotubes (NPI/NC/CNT) with hierarchical micro/nanoporous structure, is designed for sodium-ion batteries (SIBs). The in-situ formed three-dimensional conductive network can achieve a uniform distribution and increased interfacial contact between electroactive NPI and electrolyte, thereby leading to high utilization of NPI. As a result, the free-standing NPI/NC/CNT cathode delivers high reversible capacity, superior rate capability, and excellent cycling stability for SIBs.