Ion Transport Channels Research Articles

Multiple Surface Optimizations for a Highly Durable LiCoO2 beyond 4.6 V

AbstractRecently, lots of researches have focused on enhancing the structure stability of LiCoO2 (LCO) at a cutoff voltage of 4.6 V (vs Li/Li+) at room temperature. However, the high temperature (≥45 °C) performances are more significant for practical applications. Herein, the mechanism of unsatisfactory structure stability of LCO at 45 °C via comparing a commercial LCO (C‐LCO) and a surface optimized LCO (O‐LCO) is revealed first. The deteriorated structure stability of LCO at 45 °C is mainly due to two aspects: i) the promoted bulk Li+ ion diffusion kinetics at 45 °C leads to a higher state of charge for the charged LCO, which triggers more side reactions; ii) the more prominent surface structure collapse at 45 °C blocks the Li+ ion transport channels. Surface optimizations, including the anions (F− and PO43−) and cations (Al3+) surface modulation and a subsurface spinel reinforcement, are comprehensively applied to alleviate the side reaction and structure collapse issues of O‐LCO, leading to a high reversible discharge capacity of 238 mAh g−1, as well as an obviously enhanced cycle and floating stability at 45 °C and beyond 4.6 V. A new insight is provided here for developing more advanced and practical high‐voltage LCO.

Hydration characteristics, structure evolution of marine cement composites with high durability modified by colloidal nano-silica for low carbon footprints

The porous structure of cement composites provides channels for the invasion of chloride ions in marine environment, which limits their service life and low carbon footprints. Colloidal nano-silica (CNS) with the particle size of 10–30 nm theoretically can refine the pore structure, block the chloride ion transport channel. Thus, it is beneficial to improve the service life of cement composites and reduce the consumption of cement and carbon dioxide emission. In this paper, the CNS was introduced to partially replace high sulfate resistance Portland cement (HSRPC) preparing HSRPC-CNS composite. The hydration characteristics, strength property, porous structure and chloride ion resistance were investigated. The results revealed that the addition of CNS was effective in improving the properties of HSRPC-CNS composite, and the most suitable content of CNS was 3 wt%. In this case, the hydration process of HSRPC-CNS composite was accelerated, and the 28-days compressive strength increased by 12.26%. Additionally, as the CNS content increases to 3 wt%, the porosity and chloride diffusion coefficient decreased by 32.39% and 41.99%, respectively. Therefore, CNS can be used as a sustainable nano additive that improved compactness, alleviated chloride ion permeability and reduced carbon dioxide emissions in HSRPC-based composites.

Composite Solid Electrolyte Composed of 3D Ceramic Ion Transport Channel and in-Situ Formed Polymer Matrix

Rechargeable lithium-ion batteries (LIBs) with high energy density and excellent cycling performance have been widely used as portable power supplies for consumer electronics. In recent years, LIBs have expanded their applications to electric vehicles (EVs) and large energy storage systems (ESSs). Existing LIBs use liquid electrolytes, which have safety issues such as inflammability, leakage, and explosion. All-solid-state lithium-ion batteries (ASSLIBs) using various solid electrolytes, such as inorganic electrolytes and polymer electrolytes, have been extensively studied to alleviate safety issues and improve energy density. In addition, composite solid electrolytes (CSEs), which combine the advantages of ceramic and polymer electrolytes, are of particular interest. However, CSE based on a polymer matrix has low ionic conductivity at room temperature, making it difficult to use as an electrolyte for high-performance ASSLIB. In this study, we designed a highly efficient 3D LAGP framework for lithium ion transport that enhances the overall conductivity of CSE. This stiffer 3D LAGP structure also inhibits the growth of Li dendrites. The polymer component of CSE is manufactured using thermal polymerization of vinyl ethylene carbonate (VEC). In addition, excellent electrode-electrolyte interface properties were achieved using in-situ thermal polymerization technology. The optimized CSE exhibited high ionic conductivity of 0.79 mS cm-1 and excellent potential stability up to 5.09 V vs. Li/Li+ at 30 °C. The Li/CSE/NCM811 cells showed excellent rate performance and cycling potential. Therefore, a CSE composed of a 3D LAGP framework and a VEC-based polymer can be used as a potential electrolyte for ASSLIBs.

From Li to Na: Exploratory Analysis of Fe-Based Phosphates Polyanion-Type Cathode Materials by Mn Substitution.

Both LiFePO4 (LFP) and NaFePO4 (NFP) are phosphate polyanion-type cathode materials, which have received much attention due to their low cost and high theoretical capacity. Substitution of manganese (Mn) elements for LFP/NFP materials can improve the electrochemical properties, but the connection between local structural changes and electrochemical behaviors after Mn substitution is still not clear. This study not only achieves improvements in energy density of LFP and cyclic stability of NFP through Mn substitution, but also provides an in-depth analysis of the structural evolutions induced by the substitution. Among them, the substitution of Mn enables LiFe0.5 Mn0.5 PO4 to achieve a high energy density of 535.3 Wh kg-1 , while NaFe0.7 Mn0.3 PO4 exhibits outstanding cyclability with 89.6% capacity retention after 250 cycles. Specifically, Mn substitution broadens the ion-transport channels, improving the ion diffusion coefficient. Moreover, LiFe0.5 Mn0.5 PO4 maintains a more stable single-phase transition during the charge/discharge process. The transition of NaFe0.7 Mn0.3 PO4 to the amorphous phase is avoided, which can maintain structural stability and achieve better electrochemical performance. With systematic analysis, this research provides valuable guidance for the subsequent design of high-performance polyanion-type cathodes.

Nickel-iron sulfide nanoparticles supported on biomass-derived N-doped hierarchical porous carbon as a robust electrode for supercapacitors

Biomass-based carbon electrode material with hierarchical porous structure is considered as a promising candidate for supercapacitor applications, which could enhance the electron transfer and shorten the ion diffusion pathways. However, the low energy density of carbon-based materials seriously affects their wide applications. Herein, 3D N-doped hierarchical porous carbon coupled with nickel-iron sulfide nanoparticles (Fe5Ni4S8/FeS@N-HPC) is fabricated by a simple pyrolysis process. The 3D N-doped interconnected porous structure with large specific surface area provides more channels for ion transport and electron transfer. The nickel-iron sulfide nanoparticles in the porous carbon offer numerous sites for reduction and oxidation occurring to improve the charge storage for supercapacitors. Consequently, the synthesized Fe5Ni4S8/FeS@N-HPC electrode exhibits excellent electrochemical properties. The optimized Fe5Ni4S8/FeS@N-HPC composite fabricated under 800 °C displays an excellent capacitance of 2812.4 F g−1 (734.56 C g−1) at a current density of 0.5 A g−1. Beside, the Fe5Ni4S8/FeS@N-HPC-800//active carbon asymmetric supercapacitor shows an energy density of 76.8 W h kg−1 at a power density of 395.03 W kg−1 and superior cycling stability of 93.24% over 10,000 charge-discharge cycles. Our work presents a novel approach to the construction of high-performance electrode materials for supercapacitors.

Electrophoretic deposition and hydroplastic foaming synthesis of three-dimensional graphene-based supercapacitor electrodes with high performance and stability

Supercapacitors (SC) are electrochemical devices that can store and deliver high power quickly and without degradation after a large number of cycles. Graphene has a wide range of applications in supercapacitors. However, its excellent performance is limited by the stacking of graphene, which reduces the electron/ion transport rate and electrochemical active sites. Three-dimensional graphene can reduce graphene stacking, which not only has more electron/ion transport channels but also increases the specific surface area and provides more electrochemically active sites. Graphene-based supercapacitor electrodes are prepared by a two-step process and do not use any conductive agents or polymeric binders. The first step is to deposit graphene oxide (GO) onto the skeleton of nickel foam (NF) using electrophoretic deposition (EPD) to obtain the precursor GO-NF. The second step is to use the hydroplastic foaming (HPF) method to stretch the graphene sheets to prepare HRGO-NF electrodes. NF provides a stable three-dimensional skeleton and GO can be stabilized on the skeleton by EPD, which improves the stability and structure of the electrode. GO is reduced to RGO by HPF and porous structures are generated between the layers. The layered porous structure effectively provides abundant ion transport channels and considerable electrochemically active sites. The capacitance value is 195 F g− 1 when the current density is 0.5 A/g. When the scan rate is 100 mv/s have 10,000 cycles, the specific capacitance value is maintained at about 98% compared with the initial capacitance, which has good cycling stability. In this work, the simple preparation process of the 3D graphene material constructed has high specific capacitance and high stability, which provides a new idea for the design and preparation of carbon electrode materials for high-performance supercapacitors.

NiCo2S4 nanocone arrays on three-dimensional graphene with small hole diameters for asymmetric supercapacitor

Chemical vapor deposition (CVD) is utilized to fabricate 3D graphene (3D Gr) with small hole diameters using nickel nanoparticles sintered at high temperatures as the sacrificial template. NiCo2S4 nanocone arrays (NiCo2S4 NCAs) are vertically grown in situ on the 3D Gr by a seeding layer and hydrothermal synthesis process. The results show the hole diameters of 3D Gr are ∼ 3 µm. The small hole diameters of 3D Gr not only enhances the high electrical conductivity but also increases the contact area to the solution. Moreover, NiCo2S4 NCAs on the 3D Gr can provide more electrochemical redox activities and shorter channels for ion transport. NiCo2S4 NCAs/3D Gr is applied as a supercapacitor electrode, showing a specific capacitance of 948.9 F/g at 1 A/g. In addition, an asymmetric supercapacitor is assembled with the NiCo2S4 NCAs/3D Gr as the cathode material and the activated carbon as the anode material. The supercapacitor has an energy density of 64.1 Wh/kg at the power density of 1153.8 W/kg. It exhibits 90 % capacitance retention under 10, 000 charge and discharge cycles at 10 A/g.

Nitrogen-doped Ti3C2Tx/TiO2-graphene hybrid materials with 3D interconnected structure compatible with ionic liquid-based electrolyte for high performance supercapacitors

Ti3C2Tx, a typical MXene, bears tremendous attention as a type of potential electrode materials for supercapacitors. Regrettably, though Ti3C2Tx electrode has excellent capacitance in aqueous electrolytes, it cannot achieve high energy density due to a narrow operating potential window of the aqueous electrolytes. Herein, we demonstrate a well-designed hybrid material: nitrogen-doped Ti3C2Tx-reduced graphene oxide with in situ formed TiO2 nanopaticles bridged by -NH- (N-Ti3C2Tx/TiO2-RGO), and meanwhile formulate a ternary mixed electrolyte of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EmimTFSI), acetonitrile (ACN), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to match the hybrid material. The N-Ti3C2Tx/TiO2-RGO hybrid possesses a 3D cross-linked porous structure with rapid transport channels for the electrolyte ions. The formulated ionic liquid-based electrolyte has a wide electrochemical stability window and free lithium ions are able to conduct Faradaic redox reactions. Benefiting from its unique architectural structure, the N-Ti3C2Tx/TiO2-RGO material delivers an enhanced specific capacitance (specific capacity) of 188 F g−1 (338 C g−1) at 1 A g−1 and exhibits a high rate capability. Furthermore, the assembled asymmetrical supercapacitor with the N-Ti3C2Tx/TiO2-RGO-5 anode and the self-synthesized p-phenylenediamine functionalized reduced graphene oxide (PPD-RGO) cathode delivers a high energy density of 46 Wh kg−1 at a high-power density of 1550 W kg−1. This work develops a simple strategy to assemble 2D MXene sheets into 3D porous electrode materials compatible to the ionic liquid-based electrolyte for high performance supercapacitors.

Construction of efficient ion transport channels in MOFs-blended poly (ether ether ketone) containing multiple ion transport sites

In this paper, trimethyl poly (ether ether ketone) (T-PEEK) containing multiple sites was prepared by a polycondensation reaction, and afterwards, brominated T-PEEK (Br-T-PEEK) and imidazole functionalized T-PEEK (Im-T-PEEK) were prepared by substitution reaction. And cationic metal organic frameworks UiO-66-NH2 (C-MOF) was synthesized as fillers. Composite membranes were fabricated by incorporating cationic UiO-66-NH2 into imidazole functionalized Im-T-PEEK. Im-T-PEEK/C-MOF-5% (the weight percentage of C-MOF was 5%) composite membranes exhibit good mechanical properties, such as Young's modulus of 2319.06 MPa and tensile strength of 38.34 MPa. The ionic conductivity of the composite membrane, Im-T-PEEK/C-MOF-5%, achieved a remarkable value of 106.4 mS cm−1 at a temperature of 80 °C. All the membranes exhibited good alkaline stability. After immersing the prepared membranes in a solution of 1 M NaOH at a temperature of 60°C for a duration of 360 h, it was observed that the ionic conductivity of the membranes retained more than 70% of their initial ionic conductivity. Furthermore, the open-circuit voltage and peak power density of Im-T-PEEK/C-MOF-5% reached 0.904 V and 154.26 mW cm−2, respectively. In a word, this study presents a promising strategy for the preparation of advanced anion exchange membranes (AEMs) with good properties for energy conversion and storage applications.

S/N co-doped graphene porous skeleton loaded with Ni-Co active material for lithium storage

The flexible porous skeleton of S/N co-doped graphene aerogel (SNGA) can not only provide abundant ion transport channels but also improve the rate capability of graphene. Herein, taking the advantage of SNGA structure, NiCoO2 and NiCo2S4 were loaded onto the surface of SNGA (denoted as NiCoO2/SNGA-X and NiCo2S4/SNGA-X) via two-step hydrothermal and one-step hydrothermal method, respectively. The results show that NiCoO2 and NiCo2S4 particle agglomeration can be successfully mitigated since the Ni-Co binding process is influenced by the high specific surface area carbon source of SNGA. In addition, the NiCo2S4 prepared by one-step hydrothermal process plays the role of intercalation support during the formation of SNGA, which makes the porous structure of NiCo2S4/SNGA-X more compact and coherent. Benefiting from adequate active sites and porous structure, NiCoO2/SNGA-X and NiCo2S4/SNGA-X show high reversible capacity as anode materials for lithium energy storage. NiCoO2/SNGA-0.4 exhibits superior stability of 356.3 mA h g−1 at the current density of 1 A g−1 after 300 cycles, NiCo2S4/SNGA-0.3 exhibits excellent rate capability of 259.7 mA h g−1 at the current density of 5 A g−1. Lithium ion battery anode materials with high reversible specific capacity under high current density were successfully prepared. The research would provide a theoretical guidance for further application of SNGA skeletons.

Li iontronics in single-crystalline T-Nb2O5 thin films with vertical ionic transport channels.

The niobium oxide polymorph T-Nb2O5 has been extensively investigated in its bulk form especially for applications in fast-charging batteries and electrochemical (pseudo)capacitors. Its crystal structure, which has two-dimensional (2D) layers with very low steric hindrance, allows for fast Li-ion migration. However, since its discovery in 1941, the growth of single-crystalline thin films and its electronic applications have not yet been realized, probably due to its large orthorhombic unit cell along with the existence of many polymorphs. Here we demonstrate the epitaxial growth of single-crystalline T-Nb2O5 thin films, critically with the ionic transport channels oriented perpendicular to the film's surface. These vertical 2D channels enable fast Li-ion migration, which we show gives rise to a colossal insulator-metal transition, where the resistivity drops by 11 orders of magnitude due to the population of the initially empty Nb 4d0 states by electrons. Moreover, we reveal multiple unexplored phase transitions with distinct crystal and electronic structures over a wide range of Li-ion concentrations by comprehensive in situ experiments and theoretical calculations, which allow for the reversible and repeatable manipulation of these phases and their distinct electronic properties. This work paves the way for the exploration of novel thin films with ionic channels and their potential applications.

Stabilize Sodium Metal Anode by Integrated Patterning of Laser-Induced Graphene with Regulated Na Deposition Behavior.

Metallic sodium is regarded as the most potential anode for sodium-ion batteries due to its high capacity and earth-abundancy. Nevertheless, uncontrolled Na dendrite growth and infinite volume change remain great challenges for developing high-performance sodium metal batteries. This work provides a simple and general approach to stabilize sodium metal anode (SMA) by constructing Sn nanoparticles-anchored laser-induced graphene on copper foil (Sn@LIG@Cu) consisting of Sn@LIG composite, polyimide (PI) columns, and Cu current collector. The Sn-based sodiophilic species effectively reduce the Na nucleation overpotential and regulate the dendrite Na-free deposition. While the flexible PI columns act as binder and buffer the volume variation of Na during cycling. Besides, the unique patterned structure provides continuous and rapid channels for ion transportation, promoting the Na+ transport kinetics. Therefore, the as-fabricated Sn@LIG@Cu electrode exhibits outstanding rate performance to 40mA cm-2 and excellent cycling stability without dendrite growth, which is confirmed by in-situ optical microscopy observation. Moreover, the practical full cell based on such an anode displays a favorable rate capability of up to 10 C and cycling performance at 5 C for 600 cycles. This work thus demonstrates a facile, highly-efficient, and scalable approach to stabilize SMAs and can be extended to other battery systems.

Preparation of proton exchange membrane with intrinsic micropores constructing efficient ion transport channels based on segmented copolymer (sulfonated polyimide)

The development of high conductivity proton exchange membranes (PEM) with efficient ion channels is a focus of fuel cell research. In this work, PEMs based on sulfonated polyimide are prepared by a simple synthesis route. The conformational change of the polymer depends on the type of polymeric chemical structure, leading to the formation of nanoscale cavities and ion channels for rapid proton transport, as evidenced by micropore porosities tests and proton conductivity tests. CO2 adsorption and desorption curves determined that the pore distribution of the polymer is 0.3–1.5 nm, and the specific surface area is up to 106.644 m3g−1, and the microphase separation channels are measured by X-ray diffraction. The introduction of microporous structures and microphase separation channels work together to make excellent electrochemical performance. The proton conductivity of SPI-B40 with the ion-exchange capacity (IEC) of 1.76 mmol g−1 is up to 0.146 S cm−1 at 80 °C, and the power density can reach 869 mW cm−2.

Bi Nanosheets on Porous Carbon Cloth Composites for Ultrastable Flexible Nickel-Bismuth Batteries.

The use of bismuth (Bi) as an anode material in nickel-metal batteries has gained significant attention due to its highly reversible redox reaction and suitable operating conditions. However, the cycling stability and flexibility of nickel-bismuth (Ni//Bi) batteries need to be further improved. This paper employs a facile electrodeposition technique to prepare Bi nanosheets uniformly grown on a porous carbon cloth (PCC), denoted as Bi-PCC electrodes. The Bi-PCC electrode portrays a specific surface area and good wettability that enable fast charge transfer and ion transport channels. Consequently, the Bi-PCC electrode demonstrates a high specific capacity of up to 297.1 mAh g-1 at 2 A g-1, with a capacity retention of up to 71.5% at 2-40 A g-1 and an impressive capacity retention of 79.9% after 1000 cycles at 2-40 A g-1. More importantly, the flexible rechargeable Ni//Bi battery (denoted as Ni(OH)2-PCC//Bi-PCC) with Bi-PCC as the anode and Ni(OH)2-PCC as the cathode has excellent electrochemical performance. The Ni(OH)2-PCC//Bi-PCC battery boasts a remarkable capacity retention of 93.6% after 3000 cycles at 10 A g-1. Further, the cell presents a maximum energy density of 73.1 Wh kg-1 and an impressive power density of 11.9 kW kg-1.

Correlation between the morphology of carbon nanofibers and the transport characteristics of Li-ions in a battery anode under fast charging conditions

Energy storage materials for electric vehicles and energy storage systems must be able to supply high capacity quickly, which requires efficient Li-ion transport within the anode active material. The transport of Li ions through a battery system can lead to concentration polarization and subsequent overpotential, which can limit the electrochemical performance, especially under fast charging conditions. To overcome these limitations, it is important to control solvated Li-ion transport and design an anode material with a rational approach. One way to achieve this is by controlling the morphology of carbon nanofibers (CNFs) to create ion transport channels. A facile method for this was investigated using an immiscible polymer blend electrospinning system and interpreting a ternary phase diagram. The effects of the morphology and space characteristics of each CNF on the electrochemical performance were studied, particularly the rate capability and cycle stability under fast charging conditions. These characteristics were analyzed in terms of the transport properties of the electrochemical species in different types of ion channels.

Relationship between chloride ion permeation resistance of ultra-high performance concrete and lightweight aggregate ratio

This paper investigates the effects of different substitution rates of lightweight aggregate (LWA) on the workability, mechanical properties, and chloride ion permeability of ultra-high performance concrete (UHPC). A two-dimensional model based on the random distribution of irregular LWA particles was established to simulate chloride diffusion. Based on experimental and simulation results, the influencing mechanism of LWA substitution rate on the chloride ion penetration resistance of UHPC was further explored. The results indicate that during the LWA mixing process, its porous structure causes premature release of water involved in internal curing, leading to degradation of the pore structure and interfacial transition zone. Therefore, with the increase of LWA substitution rate, not only does the working and mechanical properties of UHPC decrease, but also the chloride ion transport channels increase, leading to an accelerated migration rate of chloride ions in UHPC.

Combination of porous structure and MnO2 modification for improving capacitance of planar BDD electrode

Wearable electronic devices have become a preferred choice for health monitoring, but suffer from low capacitance of planar electrodes. This work aims to improve the capacitive performance through the combination of porous boron-doped diamond (BDD) and MnO2 modification. BDD film was deposited on the substrate of titanium foam using hot-filament chemical vapor deposition (HFCVD). Constant-voltage deposition was then employed to deposit MnO2 on the BDD, and the deposition time was adjusted to evaluate the influence of MnO2 modification on the electrode capacitance. Porous structure formed by titanium foam enables BDD electrode to exhibit larger specific surface area, and reach a capacitance of 67.9 mF/cm2. Porous BDD/MnO2 film (MnO2 deposited for 1500 s) shows pea-like morphology and has optimal capacitive performance. BDD/MnO2-1500 s electrode displays a maximum capacitance of 1383.6 mF/cm2 at a current density of 2 mA/cm2, which is about 195 times that of the planar BDD electrode (7.1 mF/cm2 at a current density of 2 mA/cm2) along with a minimum Rct value of 2 Ω. This allows us to see the fact that improvement mechanism of combining porous structure and MnO2 modification may result from common effect of three following aspects: (1) Porous structure gives BDD superior specific surface area and favorable ion transport channels than planar electrode; (2) Pseudocapacitance effect of MnO2 increases the capacitance density; (3) Pea structure of MnO2 may markedly increase the specific surface area of the film and shorten ion/electronic diffusion distances.

Multiblock copolymers with disulfonated bis(phenylsulfonylphenyl) sulfone group for polymer electrolyte membrane water electrolysis

Hydrogen, a zero-emissions fuel, is increasingly being targeted as a source of renewable energy. However, hydrogen production by electrolysis is limited by the characteristics of the hydrogen-separating membrane. Here, a series of multiblock copolymers composed of a hydrophilic block based on disulfonated bis(phenyulfonylphenyl) sulfone groups, and a hydrophobic block based on bis(p-phenoxyphenyl) ether groups is developed for application as a proton exchange membrane for water electrolysis. The multiblock copolymers combining stiff hydrophilic block and flexible hydrophobic block are expected to have reduced water swelling and low hydrogen permeability even under full-wet and high-temperature conditions in water electrolysis. Microscopy and X-ray scattering analyses of the multiblock copolymer-based membranes reveal strong nanophase separation and well-developed ion transport channels. The as-synthesized membranes exhibit advantages including low swelling, high proton conductivity, good mechanical and thermal properties, high oxidative stability, and reduced hydrogen permeability. A membrane electrode assembly employing the multiblock copolymer membrane achieved a current density above 3 A cm−2 at 1.8 V, far surpassing that of Nafion 212, and a long-term operating stability exceeding 500 h, demonstrating the suitability of the membrane for practical water electrolysis.

Fabrication of hierarchical porous carbon for oxygen reduction reaction by selective hydrolysis of hemicelluloses and lignin from eucalyptus wood

As a wood containing many ordered cell cavities and blood vessels, eucalyptus is an ideal precursor material in preparing hierarchical porous carbon electrodes for Zn-air batteries. However, insufficient micro-mesoporous and minor active sites inhibit the application of wood-directly derived carbon materials in Zn-air batteries. Hence, a simple and cost-effective formic acid pretreatment method was proposed to prepare nitrogen-doped bulk phase catalysts with abundant micro-mesoporous and enough high active sites from eucalyptus. Formic acid pretreatment selectively removed part of lignin and hemicelluloses, thus generating abundant nanopores and contributing to the introduction of more nitrogen active sites. Moreover, the obtained bulk carbon had high mechanical strength and wonderful electrical conductivity, containing cross-linked networks and natural ion transport channels. Benefiting from the above advantages, the bulk carbon catalyst could be directly used as self-supported cathode, and the resulting Zn-air batteries achieved a long cycle life of more than 300 h. This work provides a simple and feasible method for the development of biomass-derived hierarchical bulk-phase porous carbons for energy-related applications.

Robust selective swelling-induced pyridine-containing membranes with advanced conductivity for vanadium redox flow batteries

Various electrochemical energy conversion and storage devices, such as membrane-based fuel cells and redox flow batteries, are in high demand for low-cost, easy-to-fabricate membranes with high conductivity, selectivity, and robust stability. In this work, unique pyridine-containing membranes (PyEPEK) are prepared for vanadium redox flow batteries (VRFBs), one of the most promising large-scale energy storage technologies. Selective swelling-induced PyEPEK membranes are facilely prepared, in which the basic pyridine-containing segments are selectively swelled with hot H3PO4 (50 wt%) to generate wider ion transport channels for enhanced conductivity, and the hydrophobic trifluoromethyl-containing segments provide a rigid backbone and endow the membrane with high selectivity. Compared to the benchmark Nafion212 membrane (area resistance 0.14 Ωcm2, mechanical strength 17.0 MPa), the resulting PyEPEK membrane exhibits better conductivity (area resistance, 0.13 Ωcm2) and about 2.8 times higher mechanical strength (>49.0 MPa). The PyEPEK-80 membrane exhibits impressive VRFB performance (coulombic efficiency = 99.56%, voltage efficiency = 93.40%, and energy efficiency = 92.98%) at 80 mA cm−2, which is the highest energy efficiency reported so far using dense ion exchange membranes. This work provides a strategy for designing and fabricating easy-to-prepare, low-cost, high-performance membranes for electrochemical energy conversion and storage devices.