Continuous Electron Transport Pathway Research Articles

Platinum Cluster Decoration on Hollow Carbon Spheres for High-Efficiency Hydrogen Evolution Reaction.

Currently, platinum (Pt)/carbon support composite materials have tremendous application prospects in the hydrogen evolution reaction (HER). However, one of the primary challenges for boosting their performance is designing a substrate with the desired microstructure. Herein, the intact hollow carbon spheres (HCSs) were prepared via template method. Based on the morphology variation of the as-prepared HCSs-x, we conjectured that the polydopamine (PDA) core was generated first and then slowly grew into a complete overburden (SiO2@PDA). Afterward, Pt atomic clusters were anchored on the outer shells of HCSs-4 to construct composite electrocatalysts (Pty/HCSs-4) by a chemical reduction method. Due to the low charge-transfer resistance, the HCSs have a large electrochemical surface area and provide a continuous electron transport pathway, boosting the atom utilization efficiency during hydrogen production and release. The synthesized Pt2.5/HCSs-4 electrocatalysts exhibit excellent HER activity in acidic media, which can be ascribed to the compositional modulation and delicate structural design. Specifically, when the overpotential is 10 A g-1, the overpotential can achieve 92 mV. This work opens a new route to fabricate Pt-based electrocatalysts and brings a new understanding of the formation mechanism of HCSs.

Hydrothermal synthesis of high-performance cobalt phosphate nanorod architecture as bifunctional electrocatalysts for rechargeable Zn-air batteries and supercapatteries

Transition metal phosphate bifunctional electrocatalysts demonstrate superior oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and capacitive properties owing to their high electrocatalytic and conductive activities. In this report, cobalt phosphate (Co3P2O8) nanorod (NR) electrocatalytic materials were developed via a facile one-step hydrothermal synthesis, followed by an annealing process. The unique NR structures offer superior electrocatalytic activities, continuous and quick electron transport pathways, short ion diffusion lengths, and rich active sites toward rechargeable zinc-air batteries (ZABs) and supercapatteries (SCs). The self-assembled Co3P2O8 NR electrocatalyst revealed higher current density values during the OER and ORR measurements than the commercially available Pt/C and IrO2 materials. The Co3P2O8 NR electrocatalyst exhibited an excellent OER overpotential of 180 mV. The electocatalyst also showed superior onset and half-wave potentials of 0.92 V and 0.80 V, respectively. Moreover, the fabricated Co3P2O8 NRs-based ZAB exhibited better durability than the Pt/C-based ZAB. Significantly, the Co3P2O8 NR electrode demonstrated an excellent specific capacity of 373 mAh g−1 with outstanding cycling stability of 99% after 5000 cycles. Additionally, the fabricated Co3P2O8 NRs//activated carbon SC demonstrated high specific energy and power densities of 25.62 Wh kg−1 and 2953.12 W kg−1, respectively with remarkable cycling stability of 89% after 7000 cycles. Specifically, the practical applicability of the fabricated Co3P2O8 NRs-based ZAB and SC was tested using a blue light-emitting diode nameplate energized by two devices in series. Overall, the catalytic and energy-storage properties of the Co3P2O8 NR material can provide a new pathway for high-energy electrochemical applications.

Gradient H-Bonding Supports Highly Adaptable and Rapidly Self-Healing Composite Binders with High Ionic Conductivity for Silicon Anodes in Lithium-Ion Batteries.

An ideal binder for high-energy-density lithium-ion batteries (LIBs) should effectively inhibit volume effects, exhibit specific functional properties (e.g., self-repair capabilities and high ionic conductivity), and require low-cost, environmentally friendly mass production processes. This study adopts a synergistic strategy involving gradient (strong-weak) hydrogen bonding to construct a hard/soft polymer composite binder with self-healing abilities and high battery cell environments adaptability in LIBs. The meticulously designed 3D network structure comprising continuous electron transport pathways buffers the mechanical stresses caused by changes in silicon volume and improves the overall stability of the solid electrolyte interphase film. The Si-based anode with a polymer composite binder poly(acrylic acid-g-ureido pyrimidinone5% )/polyethylene oxide (Si/PAA-UPy5% /PEO) achieves a reversible capacity of 1245 mAh g-1 after 200 cycles at 0.5 C, which is 6.6 times higher than that of the Si/PAA anode. After 200 cycles at 0.2 A g-1 , a half-cell comprising Si/C anode with a polymer composite binder (Si/C/PAA-UPy5% /PEO) has a remaining specific capacity of 420 mAh g-1 and a capacity retention rate of 79%. The corresponding full cell with a Li-based cathode (LiFePO4 /Si/C/PAA-UPy5% /PEO) has an initial area capacity of 0.96 mAh cm-2 and retains an area capacity of 0.90 mAh cm-2 (capacity retention rate = 93%) after 100 cycles at 0.2 A g-1 .

An advanced 3D gel cathode with continuous ion and electron transport pathway for solid-state lithium batteries

Ta-doped Li7La3Zr2O12 (LLZTO) is known as a garnet-type solid-state electrolyte with high ionic conductivity and good stability against lithium metal anode, which is regarded as one of the most promising electrolytes for the commercialization of solid-state batteries (SSBs). However, the poor electron and ion transport among cathode active material particles, as well as the large interfacial impedance between LLZTO ceramic pellet and cathode, remain major issues for SSBs. In this work, we proposed a novel 3D gel cathode based on the “cation-π” interaction between the organic cations in ionic liquid (IL) and the large electron-rich π-system in single-walled carbon nanotubes (SWNTs). The designed gel cathode, which is composed of SWNTs, IL and LiFePO4 (LFP) without binder, possesses a good wettability with the LLZTO ceramic pellet and affords highly efficient conductive pathways for electrons and ions through the interface and entire cathode. As a consequence, the assembled SSBs with the gel cathode exhibit excellent long-term cycling stability with a high capacity retention of 91.74% after 700 cycles at 0.5C, and a high coulombic efficiency close to 100% can be achieved over the course of cycling at 25 °C.

In-situ growth of TiO2 film on carbonized eggshell membrane as 3D electrode for high-performance lithium storage

3D electrodes have shown extraordinary promise for electrochemical energy storage devices in wearable electronics. However, it is still a significant challenge to rationally design 3D electrode that has the characteristics of lightweight, flexibility, low cost, high performance and miniaturization. In this work, we present a novel design of 3D electrode by directly growing the nanocrystalline TiO2 film on carbonized eggshell membrane. The unique architecture can supply not only a continuous electron transport pathway through an interconnected carbon fibrous network but also an efficient electrolyte flux via an interpenetrating porous network. Besides, nanocrystalline TiO2 film on carbonized eggshell membrane offers a short ion diffusion path in the solid-phase, leading to a rapid kinetic of electrochemical reaction. When tested as an anode for Li-ion battery, TiO2 film in 3D electrode demonstrated excellent electrochemical performance with a large reversible capacity, excellent rate capacity and long life cycling property.

Electrochemically Induced Metal-Organic-Framework-Derived Amorphous V2 O5 for Superior Rate Aqueous Zinc-Ion Batteries.

The electrochemical performance of vanadium-oxide-based cathodes in aqueous zinc-ion batteries (ZIBs) depends on their degree of crystallinity and composite state with carbon materials. An in situ electrochemical induction strategy was developed to fabricate a metal-organic-framework-derived composite of amorphous V2 O5 and carbon materials (a-V2 O5 @C) for the first time, where V2 O5 is in an amorphous state and uniformly distributed in the carbon framework. The amorphous structure endows V2 O5 with more isotropic Zn2+ diffusion routes and active sites, resulting in fast Zn2+ transport and high specific capacity. The porous carbon framework provides a continuous electron transport pathway and ion diffusion channels. As a result, the a-V2 O5 @C composites display extraordinary electrochemical performance. This work will pave the way toward design of ZIB cathodes with superior rate performance.

Electrochemically Induced Metal–Organic‐Framework‐Derived Amorphous V2O5 for Superior Rate Aqueous Zinc‐Ion Batteries

AbstractThe electrochemical performance of vanadium‐oxide‐based cathodes in aqueous zinc‐ion batteries (ZIBs) depends on their degree of crystallinity and composite state with carbon materials. An in situ electrochemical induction strategy was developed to fabricate a metal–organic‐framework‐derived composite of amorphous V2O5 and carbon materials (a‐V2O5@C) for the first time, where V2O5 is in an amorphous state and uniformly distributed in the carbon framework. The amorphous structure endows V2O5 with more isotropic Zn2+ diffusion routes and active sites, resulting in fast Zn2+ transport and high specific capacity. The porous carbon framework provides a continuous electron transport pathway and ion diffusion channels. As a result, the a‐V2O5@C composites display extraordinary electrochemical performance. This work will pave the way toward design of ZIB cathodes with superior rate performance.

Thread like structured VO2 microspheres for improved lithium-ion storage kinetics and stability

Abstract Among vanadium-based materials, VO2(B), sharing octahedral VO6 structure with cavities, are considered as cathode materials due to their high capacity and multiple oxidation state. However, it has its own limitations such as low cyclic stability and sluggish charge storage kinetics arising from large structural deformation and poor electrical conductivity. In order to resolve these problems, we report a microsphere of thread like structured VO2(B) consisting of interconnected particles each other, providing continuous and facile electron and ion transport pathway. The robust internetworked microspherical structure leads to prevent the drastic volume variation during Li insertion/de-insertion process. More specifically, the as-synthesized VO2(B) displays high capacity of 225.6 mAh g−1 at 50 mA g−1 with a Columbic efficiency of 98%, high rate retention of 70% at 300 mA g−1, and good cycle stability of 72% after 350 cycles at 300 mA g−1. In addition, their structural and phase reversibility are confirmed by the in-situ XRD of VO2(B), where position of crystalline (002) peak after several electrochemical processes nearly returns on the origin position during Li insertion/de-insertion.

Molten-salt/oxalate mediating Fe and N-doped mesoporous carbon sheet nanostructures towards highly efficient and durable oxygen reduction electrocatalysis

Abstract Designer Fe-N/C-type oxygen reduction electrocatalysts with ultrahigh active-sites density and distinctive physical properties are recently considered to be a new frontier in energy technology. In this work, we creatively propose a new strategy for the controllable synthesis of iron and nitrogen co-doped mesoporous Fe-N/C-type graphene-like carbon nanosheet structures via NaCl template-assisted two-step calcination of iron coordinated with triazine compounds using potassium oxalate as a pore-activator. The synthesized Fe-N/C electrocatalyst exhibits unexpectedly ORR catalytic performance with a half-wave potential of ca. 0.846 V and an onset potential of ca. 1.02 V that compare favourably with the best Pt/C catalyst, but its electrochemical stability and methanol-tolerant property are more excellent. It is found that the unique mesoporous structure, the excellent electro-conductivity and the full exposure of N-doped catalytic sites (e.g., pyridinic-N, graphitic-N and Fe-Nx) of the gained Fe-N/C catalyst can facilitate the transport of electrolyte ions, reaction intermediates and products, maintain continuous electron-transport pathways, and minimize the agglomeration of catalytic sites to further boost the reaction rate and ORR activity. This study provides a new avenue to design high-performance and low-cost nanocarbon-based catalytic materials with dense active sites for some important reactions in new energy devices.

Self-assembled NaV6O15 flower-like microstructures for high-capacity and long-life sodium-ion battery cathode

Na-ion batteries are one of the promising alternative energy storage devices for current Li-ion batteries due to the low cost and similar electrochemistry. The most critical challenge for Na-ion batteries is to develop high-capacity and long-lifespan electrode materials which are comparable to Li-ion batteries. Herein, we use a simple method to prepare nanoflake-constructed microflowers layered sodium vanadium oxide (NaV6O15) via self-assembled process. As cathode material of sodium ion battery, the prepared NaV6O15 microflowers deliver a capacity of 126 mAh g−1 at 100 mA g−1. Significantly, the capacity can remain 87% after 2000 cycles at a current density of 5 A g−1. This superior performance can be attributed to the continuous electron transport pathway, improved electrical conductivity, and excellent stress relaxation, which are revealed by the electrochemical kinetics and structure evolution studies of the material in the cell.

A conductive self-healing hydrogel binder for high-performance silicon anodes in lithium-ion batteries

Although silicon has been viewed as the ideal anode material due to its superior specific capacity, silicon materials easily break down because of its large volume changes during frequent charge-discharge cycles. Polymeric binders play key roles on maintaining the mechanical integrity of electrodes and contributing substantially to improving cycle lives. Here, we design and prepare that a novel conductive self-healing hydrogel (ESVCA) binder with 3D conductive network, excellent stretchablity and fast self-healing ability coating on the surface the Si particle by in-situ polymerization method. The stretchable 3D self-healable network structure could effectively restrain the huge volume change of Si particles during lithiation and delithiation cycles to maintain mechanical integrity of the Si electrodes while 3D continuous electron transport pathways insuring the high conductivities and better electric contacts among active Si particles. The Si-ESVCA electrode not only exhibits a reversible capacity of 1786 mA h g−1 at 500 mA g−1 with a capacity retention of 71.3% after 200 cycles at ambient temperature, but also maintains superior cycling stability with a capacity retention of 74.1% and remains a high reversible capacity of 1743 mA h g−1 after 200 cycles at current density of 2000 mA g−1 at elevated temperature.

3D self-branched zinc-cobalt Oxide@N-doped carbon hollow nanowall arrays for high-performance asymmetric supercapacitors and oxygen electrocatalysis

This study reports the design and fabrication of ultrathin zinc-cobalt oxide nanoflakes@N-doped carbon hollow nanowall arrays (ZnCo2O4@NC NWAs) from vertically aligned 2D Co-MOF solid nanowall arrays by controllable cation ion-exchange and post annealing strategies. The unique 3D self-branched nanostructure anchored on flexible carbon textiles (CTs) can offer short ion diffusion length, fast and continuous electron transport pathway, and abundant reaction active sites. More importantly, the rational incorporation of Zn2+ generates hollow structure as well as reduces the intrinsic band gap, which further enhance the ion transportation efficiency and electronic conductivity. The above superiorities endow the 3D self-branched ZnCo2O4@NC/CTs electrodes with remarkable performances in terms of flexible asymmetric supercapacitor and oxygen electrocatalysis. When evaluated as a flexible cathode for asymmetric supercapacitor, the as-fabricated ZnCo2O4@NC/CTs electrode exhibits outstanding electrochemical performance with a wide work voltage up to 2.0 V, high areal energy density of 0.278 mWh cm−2 (or volumetric energy density of 2.32 mWh cm−3) and long-term cycling stability (∼85.89% capacitance retention over 6000 cycles). Additionally, the ZnCo2O4@NC/CTs electrode shows excellent oxygen evolution reaction (OER) performance with a small overpotential of 196.4 mV at 10 mA cm−2 and long-term durability (over 45 h). This work provides a rational design strategy for controllable synthesis of 3D self-branched hollow nanostructure on flexible substrate for energy storage and conversion applications.

In situ construction of nitrogen-doped graphene with surface-grown carbon nanotubes as a multifactorial synergistic catalyst for oxygen reduction

Two-dimensional graphene-based materials attract much attention in catalysis due to their high specific surface area and continuous electron transport pathways. However, this material is suffering layer stacking, resulting the masked of most surface active sites, and also being detrimental to mass transfer. Based on the amine-aldehyde resin polymerization method, we constructed a multifactorial synergistic catalyst of nitrogen-doped graphene with surface in situ grown carbon nanotubes (CNTs, Co@NGC). This construction involving two to three-dimensional structural transformation not only avoids layer stacking, but further facilitates the formation of more well-dispersed Co and N species embedded into carbon networks of graphene and CNTs (to form CoN and CN active sites) and increases the accessibility of active sites. After evaluating the test results of comparative experiments, we elucidated the formation process and the activity source of the catalyst. The prepared optimal Co@NGC-800 realized praiseworthy oxygen reduction activity in alkaline media, showing an onset potential of 1.00 V (vs RHE) and a half-wave potential of 0.86 V (vs RHE). Enhanced stability attained comparing with NG (nitrogen doped graphene without the growth of CNTs), the half-wave potential of Co@NGC-800 lost only 8 mV after 40 000 s chronoamperometry.

Boosting the Deep Discharging/Charging Lithium Storage Performances of Li3VO4 through Double-Carbon Decoration.

With high theoretical capacity, good ionic conductivity, and suitable working plateaus, Li3VO4 has emerged as an eye-catching intercalation anode material for lithium storage. However, Li3VO4 suffers from poor electrical conductivity and 20% volume variation under deep discharging/charging conditions. Herein, we present a "double-carbon decoration" strategy to tackle both issues. Deflated balloon-like Li3VO4/C/reduced graphene oxide (LVO/C/rGO) microspheres with continuous electron transport pathways and sufficient free space for volume change accommodation are fabricated through a facile spray-drying method. Under deep discharging/charging conditions (0.02-3.0 V), LVO/C/rGO achieves a high intercalation capacity of 591 mA h g-1. With high capacity and outstanding stability, LVO/C/rGO outperforms other intercalation anode materials (such as graphite, Li4Ti5O12, and TiO2). In situ X-ray diffraction measurement reveals that the lithium storage is realized through both solid-solution reaction and two-phase reaction mechanisms. A LVO/C/rGO//LiNi0.8Co0.15Al0.05O2 lithium-ion full cell is also assembled. In such full cell, LVO/C/rGO also demonstrates high specific capacity and excellent cycling stability. The above results manifest that the LVO/C/rGO anode has the potential to be applied in the next-generation high-performance lithium-ion batteries.

ZnSe Microsphere/Multiwalled Carbon Nanotube Composites as High-Rate and Long-Life Anodes for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are considered as one of the most favorable alternative devices for sustainable development of modern society. However, it is still a big challenge to search for proper anode materials which have excellent cycling and rate performance. Here, zinc selenide microsphere and multiwalled carbon nanotube (ZnSe/MWCNT) composites are prepared via hydrothermal reaction and following grinding process. The performance of ZnSe/MWCNT composites as a SIB anode is studied for the first time. As a result, ZnSe/MWCNTs exhibit excellent rate capacity and superior cycling life. The capacity retains as high as 382 mA h g-1 after 180 cycles even at a current density of 0.5 A g-1. The initial Coulombic efficiency of ZnSe/MWCNTs can reach 88% and nearby 100% in the following cycles. The superior electrochemical properties are attributed to continuous electron transport pathway, improved electrical conductivity, and excellent stress relaxation.

Dual or multi carbonaceous coating strategies for next-generation batteries

Dual or multi carbonaceous coatings construct continuous electron-transport pathways within the entire electrodes together with conformal surface protection.

Pyrolyzed bacterial cellulose/graphene oxide sandwich interlayer for lithium–sulfur batteries

Herein, a facile strategy for the synthesis of sandwich pyrolyzed bacterial cellulose (PBC)/graphene oxide (GO) composite was reported simply by utilizing the large-scale regenerated biomass bacterial cellulose as precursor. The unique and delicate structure where three-dimensional interconnected bacterial cellulose (BC) network embedded in two-dimensional GO skeleton could not only work as an effective barrier to retard polysulfide diffusion during the charge/discharge process to enhance the cyclic stability of the Li–S battery, but also offer a continuous electron transport pathway for the improved rate capability. As a result, by utilizing pure sulfur as cathodes, the Li–S batteries assembled with PBC/GO interlayer can still exhibit a capacity of nearly 600 mAh·g−1 at 3C and only 0.055% capacity decay per cycle can be observed over 200 cycles. Additionally, the cost-efficient and environment-friendly raw materials may enable the PBC/GO sandwich interlayer to be an advanced configuration for Li–S batteries.

Polyimide-Wrapped Carbon Nanotube As High Capacity and Rate Anode for Aqueous Rechargeable Na-Ion Batteries

Rechargeable lithium-ion batteries (LIBs) are rapidly extended from portable device to electric vehicle and smart grids owing to their high energy density and long cycling life. However, its potential for large-scale applications in electric vehicles and energy storage is hampered by the high production costs and finite supply of lithium. With this background, an attractive approach to circumvent this problem is to use an aqueous electrolyte for Na-ion batteries (NIBs). Researchers hope to overcome this problem by replacing it with sodium, which is cheaper, nontoxic, and easier to process and almost infinitely abundant. In this study, pyromellitic dianhydride (PMDA)-derived polyimide deposited on the carbon nanotubes were used as anode of aqueous electrolyte battery. That is, polyimide was directly polymerized on the surface of CNT. SEM and TEM revealed that the polyimide was homogeneously wrapped the surface of the CNTs and formed a uniform shell. This suggests that the interactions between polyimide molecules and CNTs overcame the Van der Waals interaction between CNTs, which generally otherwise would result in separate growth or aggregates of polyimide. The charge-discharge characteristics were investigated by using 3-electrode beaker cell with 2M Na2SO4 solution. The reduction and oxidation of polyimide are accompanied by the association and disassociation of Na+ ions with oxygen as described in Fig. 1. Each formula unit is able to transfer four electrons through two steps, which may allow a high theoretical specific capacity, 280.4 mAh g-1. The polyimide-wrapped carbon nanotube exhibited much superior high-rate and long cycling performance to conventional inorganic anode. The calculation of diffusion coefficient and impedance study revealed that these high performances were attributed to the advantages of hierarchical core-shell structure. The conductive CNT core offered continuous electron transport pathways and thin polyimide shell provides rapid Na+ ion diffusion pathways. Thus, the bicontinuous electron/ion transport channel greatly facilitate the ion diffusion kinetics and reduce the charge transport resistance, resulting in the excellent rate capability. Figure 1

FeS2@C nanowires derived from organic-inorganic hybrid nanowires for high-rate and long-life lithium-ion batteries

Abstract One-dimensional (1D) porous FeS2@C nanowires as a high cathode material for lithium-ion batteries (LIBs) are synthesized on a large-scale from an organic-inorganic hybrid nanowire precursor. The FeS2@C nanowires not only provide a continuous and fast electron transport pathway, favorable diffusion kinetics, but also provide the protection buffer the volume expansion and effectively prevent the polysulfides from dissolving in the electrolyte during cycling. Attributing to the synergistic advantages of both 1D porous nanostructure and the encapsulation of thin amorphous carbon layers, the FeS2@C nanowires exhibit remarkable lithium storage performance with a high specific capacity of 889 mA h g−1 at 0.1 A g−1 and 521 mA h g−1 at 10 A g−1. Moreover, a discharge energy density of 1225 Wh kg−1 is obtained at 2 A g−1 and remains as high as 637 Wh kg−1 after 1000 cycles, which is even higher than the LiCoO2 cathode. The results demonstrate that the potential for applications in LIBs with high power density and long cycling life.

Growth of three dimensional flower-like molybdenum disulfide hierarchical structures on graphene/carbon nanotube network: An advanced heterostructure for energy storage devices

We report the design and synthesis of three dimensional flower-like molybdenum disulphide (f-MoS2) hierarchical structures, on reduced graphene oxide (RGO)/oxidized multi-walled carbon nanotube (o-MWCNT) backbone (f-MoS2/RGO/o-MWCNT), through one-pot hydrothermal method. Control experiments reveal that the homogenously distributed o-MWCNTs on RGO play an essential role for the formation of such morphology. As an anode for lithium ion batteries, the f-MoS2/RGO/o-MWCNT hybrid delivers a high reversible capacity of 1275 mAh g−1 at the current density of 100 mA g−1, superior rate capability and excellent long cycle life, with capacity retention of 93% after 100 cycles. The outstanding electrochemical performance can be attributed to the large surface area, short diffusion length and continuous electron transport pathway, as a consequence of the intimate contact between f-MoS2, graphene, and o-MWCNTs.