An Innovative Concept of Membrane-Free Redox Flow Batteries with Near-Zero Contact Distance Between Electrodes.

Given that the ion-exchange membrane takes up more than 30% of redox flow battery (RFB) cost, considerable cost reduction is anticipated with the membrane-free design. However, eliminating the membrane/separator would expose the membrane-free RFBs to a higher risk of short-circuits, and the dendrite growth may aggravate this issue. The current strategy based on expanding distances between electrodes is proposed to address short-circuit issues. Nevertheless, this approach would decrease the energy efficiency (EE) and could not restrain dendrite growth fundamentally. Herein, an inexpensive and electron-insulating boron nitride nanosheets (BNNSs)-Nylon hybrid interlayer (BN/Nylon) is developed for general membrane-free RFBs to achieve "near-zero distance" contact between electrodes. And the Lewis acid sites (B atoms) in BNNS can interact with the Lewis base anions in electrolytes, enabling a reduced Pb2+concentration gradient. Additionally, the ultrahigh thermal conductivity and mechanical strength of BNNSs promote the uniform plating/stripping process of Pb and PbO2. Compared with conventional soluble lead RFBs, introducing BN/Nylon interlayers boosts EE by ≈38.2% at 25 mA cm-2, and extends the cycle life to 100 cycles. This innovative strategy premieres the application of the BN/Nylon interlayer concept, offering a novel perspective for the development of general membrane-free RFBs.

Silver Nanowires-Based Flexible Gold Electrode Overcoming Interior Impedance of Nanomaterial Electrodes.

In the development of nanomaterial electrodes for improved electrocatalytic activity, much attention is paid to the compositions, lattice, and surface morphologies. In this study, a new concept to enhance electrocatalytic activity is proposed by reducing impedance inside nanomaterial electrodes. Gold nanodendrites (AuNDs) are grown along silver nanowires (AgNWs) on flexible polydimethylsiloxane (PDMS) support. The AuNDs/AgNWs/PDMS electrode affords an oxidative peak current density of 50 mA cm-2 for ethanol electrooxidation, a value ≈20 times higher than those in the literature do. Electrochemical impedance spectroscopy (EIS) demonstrates the significant contribution of the AgNWs to reduce impedance. The peak current densities for ethanol electrooxidation are decreased 7.5-fold when the AgNWs are electrolytically corroded. By in situ surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT) simulation, it is validated that the ethanol electrooxidation favors the production of acetic acid with undetectable CO, resulting in a more complete oxidation and long-term stability, while the AgNWs corrosion greatly decreases acetic acid production. This novel strategy for fabricating nanomaterial electrodes using AgNWs as a charge transfer conduit may stimulate insights into the design of nanomaterial electrodes.

Semi-Embedded Structured Bi Nanospheres for Boosted Self-Heating-Induced Healing of Li-Dendrites.

It is reported that self-heating-induced healing on lithium metal anodes (LMAs) provides a mitigation strategy for suppressing Li dendrites. However, how to boost the self-heating-induced healing of Li-dendrites and incorporate it into Li-host design remains an imminent problem that needs to be solved. Herein, a new bismuth nanosphere semi-buried carbon cloth (Bi-NS-CC) material with a 3D flexible host structure is proposed. The ultrasmall Bi nanospheres are uniformly and densely distributed on carbon fiber, providing active sites to form uniform Li3 Bi alloy with molten lithium, thereby guiding the injection of molten metallic lithium into the 3D structure to form a self-supporting composite LMAs. The ingenious semi-embedded structure with strong interfacial C─Bi ensures superior mechanical properties. Interestingly, when the current density reaches up to 10 mA cm-2 , the lithium dendrites undergo self-heating. Carbon cloth as a host can quickly and uniformly transfer heat, which induces the uniform migration of Li on anodes. The semi-embedded structure with strong C─Bi ensures Bi nanospheres guide the formation of smooth morphology even under these harsh conditions (high-temperature, high-rate, etc.). Consequently, at 10 mA cm-2 /10 mAh cm-2 , the Li/Li3 Bi-NS-CC realizes ultra-long cycles of 1500 h and ultra-low overpotential of 15 mV in a symmetric cell.

Mesoporous Gold Film with Surface Sulfur Modification to Enable Dendrite-Free Lithium Plating/Stripping for Long-Life Lithium Metal Anodes.

The formation of a lithiophilic phase is an effective method to inhibit the growth of lithium dendrites and obtain high-performance Li metal anodes (LMAs). Nonetheless, previous studies have overlooked the underlying mechanistic studies that modulate the structure of the lithiophilic phase as well as lithiophilicity. A self-supporting sulfur-modified mesoporous gold film on nickel foam (SMGF@NF) for LMAs is created with mesoporous structure, which can provide sufficient active sites for uniform lithium deposition. The synergistic promotion of lithiophilic gold and sulfur leads to uniform lithium nucleation and induces consistent lithium removal during lithium stripping. The doping of S promotes the decomposition of bistrifluoromethanesulfonimide lithium salt to generate lithium fluorde, thus forming a more stable solid electrolyte interface. Combining the multifaceted advantages of SMGF@NF, its lithium-plated electrode can achieve ultralong cycle life in symmetrical batteries (over 1000 h at 0.5 mA cm-2 and 1 mAh cm-2 ) and ultralow overpotential (≈10 mV). Meanwhile, the Li-SMGF@NF||LiFePO4 full cell achieves a high cycling performance and rate capability (92.4% capacity retention after 1000 cycles at 5 C). The study probes into the composite electrode surface composition and structure, revealing the mechanism of high-performance LMAs.

Novel Flexible Ag/AgCl Quasi-Reference Electrode with Fishbone Nanowire Structure for Remarkable Potential Stability, Long-Term Reliability, and Noninvasive Electrocardiography.

The roadblocks for the planar silver/silver chloride (Ag/AgCl) quasi-reference electrode (qRE) development are the potential stability and long-term reliability as potentiometric sensors. Although there is a significant amount of work on potentiometric screen-printed and inkjet-printed sensors, none of the REs has comparable performance to that of the conventional glass RE and knowledge on reliable planar Ag/AgCl qREs is still limited. Here, a novel fishbone-structured flexible Ag/AgCl qRE (Fishbone-Ag/AgCl qRE) was developed and its stability and long-term reliability were significantly improved. The stability of the Fishbone-Ag/AgCl qRE was comparable to that of a commercial glass Ag/AgCl RE. In a long-term stability test, the Fishbone-Ag/AgCl qRE could continuously and stably operate for more than 4 h. Shelf-life testing revealed a 6 month life span. The conductivity and diameter of the nanowires in the fishbone structure of the Ag/AgCl qRE had important influences on electrochemical properties. The conductivity of the qRE influenced the charge-transfer rate in the electrode so that it affected the potential stability. Thicker diameter and slight chlorination on the surface of the AgNWs resulted in enhanced long-term reliability of the qRE. The capabilities of this new nanostructured material were applied in vivo for noninvasive monitoring of electrocardiogram. The discovery is elementary and substantially informs improved nanostructure RE design for testing and commercial medical device applications.

Conductive Iodine-Doped Red Phosphorus Enabled Dendrite-Free Lithium Deposition on MXene Matrix.

The highest theoretical capacity and lowest redox potential of lithium metal make lithium-based batteries the "holy grail" of the next-generation batteries. However, the uncontrollable dendrite growth and infinite volume change of lithium seriously hinder the real-world implementation of lithium-based batteries. Herein, a flexible MXene@iodine-doped red phosphorus (MXene@RP) paper with iodine-doped red phosphorous particles evenly distributed on the surface and interlayer of MXene matrix is designed by a simple vapor condensation reduction approach. The MXene@RP paper can be used as an efficient matrix to enable dendrite-free lithium deposition. On the one hand, the iodine doping alleviates the low conductivity shortcoming of red phosphorus, making it facilitate homogeneous lithium nucleation, thus promoting uniform lithium deposition and suppressing dendrite growth. On the other hand, the unique layered structure of conductive MXene paper provides ion transport channels and free spaces for lithium loading, alleviating the volume change induced structural damage. As a result, the MXene@RP paper with preloaded lithium exhibits long-term cycling stability. Particularly, a full cell based on Li-MXene@RP anode can maintain 81.4% of the initial capacity after 600 cycles at 4 C. The MXene@RP-based anode increases the potential applications of MXene and provides a guide for the design of dendrite-free lithium hosts.

General Growth of Carbon Nanotubes for Cerium Redox Reactions in High-Efficiency Redox Flow Batteries.

Carbon nanotubes (CNTs) possess remarkable mechanical, electrical, thermal, and optical properties that predestine them for numerous potential applications. The conventional chemical vapor deposition (CVD) route for the production of CNTs, however, suffers from costly and complex issues. Herein, we demonstrate a general and high-yield strategy to grow nitrogen-doped CNTs (NCNTs) on three-dimensional (3D) graphite felt (GF) substrates, through a direct thermal pyrolysis process simply using a common tube furnace, instead of the costly and complex CVD method. Specifically, the NCNTs-decorated GF (NCNT-GF) electrode possesses enhanced electrocatalytic performance towards cerium redox reactions, mainly due to the catalytic effect of N atoms doped into NCNTs, and ingenious and hierarchical 3D architecture of the NCNT-GF. As a result, the cell with the NCNT-GF serving as a positive electrode shows the improved energy efficiency with increases of about 53.4% and 43.8% over the pristine GF and the acidly treated GF at a high charge/discharge rate of 30 mA cm-2, respectively. Moreover, the as-prepared NCNT catalyst-enhanced electrode is found to be highly robust and should enable a long-term cycle without detectable efficiency loss after 500 cycles. The viable synthetic strategy reported in this study will contribute to the further development of more active heteroatom-doped CNTs for redox flow batteries.

Phytic Acid-Assisted Formation of Hierarchical Porous CoP/C Nanoboxes for Enhanced Lithium Storage and Hydrogen Generation.

Application of transition metal phosphides (TMPs) for electrochemical energy conversion and storage has great potential to alleviate the energy crisis. Although there are many methods to get TMPs, it is still immensely challenging to fabricate hierarchical porous TMPs with superior electrochemical performances by a simple, green, and secure approach. Herein, we report a facile method to synthesize the CoP/C nanoboxes by pyrolysis of phytic acid (PA) cross-linked Co complexes that are acquired from reaction of PA and ZIF-67. The PA can not only slowly etch ZIF-67 and gain a hollow structure but also act as a source of phosphorus to prepare CoP/C nanoboxes. The CoP/C nanoboxes deliver an ultrahigh specific capacity (868 mA h g-1 at 100 mA g-1) and excellent cycle stability (523 mA h g-1 after 1000 cycles at 500 mA h g-1) when used as anode materials for lithium-ion batteries. Moreover, when used as an electrocatalyst for hydrogen evolution reaction, the CoP/C nanoboxes exhibit ultralow overpotential, small Tafel slope, and excellent durability in acidic media. The method to produce CoP/C nanoboxes is easy and environmentally friendly and can be readily extended to design other TMPs/C nanocomposites.

Graphite felts modified by vertical two-dimensional WO3 nanowall arrays: high-performance electrode materials for cerium-based redox flow batteries.

Cerium-based redox flow batteries (RFBs) are very attractive for highly efficient energy storage applications with industrial-scale storage capacity. However, the development of active, stable, and earth-abundant catalysts for cerium redox reactions with sluggish kinetics remains a major challenge. Herein, for the first time, two-dimensional (2D) nanostructured architectures were used to design and fabricate efficient and stable electrocatalysts from earth-abundant components toward the Ce(iv)/Ce(iii) redox reaction. A novel WO3/GF hybrid architecture (WGF) built from WO3 nanowall arrays (NWAs) anchored on graphite felt (GF) surfaces was prepared for cerium-based RFBs. This unique hybrid exhibits superior electrocatalytic performance since the vertical nanowall arrays display open and ordered structures that ensure full exposure of the active sites toward electrolytes, which allows direct and full contact of every nanowall with the electrolyte. As an electrode for cerium redox reactions, this WGF electrode exhibits a 42.1% and 32.0% increase in energy efficiency as compared with that of pristine GF and acid-treated GF at a high charge/discharge rate of 30 mA cm-2. Moreover, the long-term cycling performance confirms the superior durability of the as-prepared WGF. This study suggests that the use of 2D nanostructures combined with vertical array microstructures is a promising strategy for efficient electrocatalysts toward cerium redox reactions with scale-up potential.

A Core-Shell Fe/Fe2 O3 Nanowire as a High-Performance Anode Material for Lithium-Ion Batteries.

The preparation of novel one-dimensional core-shell Fe/Fe2 O3 nanowires as anodes for high-performance lithium-ion batteries (LIBs) is reported. The nanowires are prepared in a facile synthetic process in aqueous solution under ambient conditions with subsequent annealing treatment that could tune the capacity for lithium storage. When this hybrid is used as an anode material for LIBs, the outer Fe2 O3 shell can act as an electrochemically active material to store and release lithium ions, whereas the highly conductive and inactive Fe core functions as nothing more than an efficient electrical conducting pathway and a remarkable buffer to tolerate volume changes of the electrode materials during the insertion and extraction of lithium ions. The core-shell Fe/Fe2 O3 nanowire maintains an excellent reversible capacity of over 767 mA h g(-1) at 500 mA g(-1) after 200 cycles with a high average Coulombic efficiency of 98.6 %. Even at 2000 mA g(-1) , a stable capacity as high as 538 mA h g(-1) could be obtained. The unique composition and nanostructure of this electrode material contribute to this enhanced electrochemical performance. Due to the ease of large-scale fabrication and superior electrochemical performance, these hybrid nanowires are promising anode materials for the next generation of high-performance LIBs.

Coated/Sandwiched rGO/CoSx Composites Derived from Metal-Organic Frameworks/GO as Advanced Anode Materials for Lithium-Ion Batteries.

Rational composite materials made from transition metal sulfides and reduced graphene oxide (rGO) are highly desirable for designing high-performance lithium-ion batteries (LIBs). Here, rGO-coated or sandwiched CoSx composites are fabricated through facile thermal sulfurization of metal-organic framework/GO precursors. By scrupulously changing the proportion of Co(2+) and organic ligands and the solvent of the reaction system, we can tune the forms of GO as either a coating or a supporting layer. Upon testing as anode materials for LIBs, the as-prepared CoSx -rGO-CoSx and rGO@CoSx composites demonstrate brilliant electrochemical performances such as high initial specific capacities of 1248 and 1320 mA h g(-1) , respectively, at a current density of 100 mA g(-1) , and stable cycling abilities of 670 and 613 mA h g(-1) , respectively, after 100 charge/discharge cycles, as well as superior rate capabilities. The excellent electrical conductivity and porous structure of the CoSx /rGO composites can promote Li(+) transfer and mitigate internal stress during the charge/discharge process, thus significantly improving the electrochemical performance of electrode materials.