Molecular Engineering to Regulate the Pseudo-Graphitic Structure of Hard Carbon for Superior Sodium Energy Storage.

Resin-derived hard carbons have shown great advantages in serving as promising anode materials for sodium-ion batteries due to their flexible microstructure tunability. However, it remains a daunting challenge to rationally regulate the pseudo-graphitic crystallite and defect of hard carbon toward advanced sodium storage performance. Herein, a molecular engineering strategy is demonstrated to modulate the cross-linking degree of phenolic resin and thus optimize the microstructure of hard carbon. Remarkably, the resorcinol endows resin with a moderate cross-linking degree, which can finely tune the pseudo-graphitic structure with enlarged interlayer spacing and restricted surface defects. As a consequence, the optimal hard carbon delivers a notable reversible capacity of 334.3 mAh g-1 at 0.02 A g-1, a high initial Coulombic efficiency of 82.1%, superior rate performance of 103.7 mAh g-1 at 2 A g-1, and excellent cycling durability over 5000 cycles. Furthermore, kinetic analysis and in situ Raman spectroscopy are performed to reveal the electrochemical advantage and sodium storage mechanism. This study fundamentally sheds light on the molecular design of resin-based hard carbons to advance sodium energy for scale-up applications.

Achieving high-capacity and durable sodium storage by constructing a binder-free nanotube array architecture of iron phosphide/carbon.

The conversion-type anode material of iron phosphide (FeP) promises enormous prospects for Na-ion battery technology due to its high theoretical capacity and cost-effectiveness. However, the poor reaction kinetics and large volume expansion of FeP significantly degrade the sodium storage, which remains a daunting challenge. Herein, we demonstrate a binder-free nanotube array architecture constructed by FeP@C hybrid on carbon cloth as advanced anodes to achieve fast and stable sodium storage. The nanotubular structure functions in multiple roles of providing short electron/ion transport distances, smooth electrolyte diffusion channels, and abundant active sites. The carbon layer could not only pave high-speed pathways for electron conductance but also cushion the volume change of FeP. Benefiting from these structural virtues, the FeP@C anode receives a high reversible capacity of 881.7 mAh/g at 0.1 A/g, along with a high initial Coulombic efficiency of 90% and excellent rate capability and cyclability in half and full cells. Moreover, the sodium energy reaction kinetics and mechanism of FeP@C are systematically studied. The present work offers a rational design and construction of high-capacity anode materials for high-energy-density Na-ion batteries.

Binder-free barium-implanted MnO2 nanosheets on carbon cloth for flexible zinc-ion batteries.

The intrinsically low electrical conductivity and poor structural fragility of MnO2 have significantly hampered the zinc storage performance. In this work, Ba2+-implanted δ-MnO2 nanosheets have been hydrothermally grown on a carbon cloth (Ba-MnO2@CC) as an extremely stable and efficient cathode material of aqueous zinc-ion batteries. The three-dimensionally porous architecture composed of interwoven thin MnO2 nanosheets effectively shortens the electron/ion transport distances, enlarges the electrode/electrolyte contact area, and increases the active sites for the electrochemical reaction. Meanwhile, Ba2+ could function as an interlayer pillar to stabilize the crystal structure of MnO2. Consequently, the as-optimized Ba-MnO2@CC exhibits remarkable Zn2+ storage capabilities, such as a high capacity (305 mAh g-1 at 0.2 A g-1), prolonged lifespan (95% retention after a 200-cycling test), and superb rate capability. The binder-free cathode is also applicable for flexible energy storage devices with attractive properties. The present investigation provides important insights into designing advanced cathode materials toward wearable electronics.

Manipulating the Host-Guest Chemistry of Cucurbituril to Propel Highly Reversible Zinc Metal Anodes.

Rechargeable aqueous zinc-ion batteries are practically plagued by the short lifespan and low Coulombic efficiency (CE) of Zn anodes resulting from random dendrite deposition and parasitic reactions. Herein, the host-guest chemistry of cucurbituril additive with Zn2+ to achieve longstanding Zn anodes is manipulated. The macrocyclic molecule of cucurbit[5]uril (CB[5]) is delicately designed to reconstruct both the CB[5]-adsorbed electric-double layer (EDL) structure at the Zn interface and the hydrated sheath of Zn2+ ions. Especially benefiting from the desirable carbonyl rims and suitable hydrophobic cavities, the CB[5] has a strong host-guest interaction with Zn2+ ions, which exclusively permits rapid Zn2+ flux across the EDL interface but retards the H2 O radicals and SO4 2- . Accordingly, such a unique particle redistributor warrants long-lasting dendrite-free deposition by homogenizing Zn nucleation/growth and significantly improved CE by inhibiting side reactions. The Zn anode can deliver superior reversibility in CB[5]-containing electrolyte with a ninefold increase of cycle lifetime and an elevated CE of 99.7% under harsh test conditions (10 mA cm-2 /10 mA h cm-2 ). The work opens a new avenue from the perspective of host-guest chemistry to propel the development of rechargeable Zn metal batteries and beyond.

Resolving Deactivation of Low-Spin Fe Sites by Redistributing Electron Density toward High-Energy Sodium Storage.

Prussian blue (PB) has been an emerging class of cathode material for sodium-ion batteries due to its low cost and high theoretical capacity. However, their working voltage and capacity are substantially restricted due to the deactivation of low-spin Fe sites. Herein, we demonstrate a universal strategy to activate the low-spin Fe sites of PB by hybridizing them with the π-π conjugated electronic conductors. The redistribution of electron density between π-π conjugated conductors and PB effectively promotes the participation of low-spin Fe sites in sodium storage. Consequently, the low-spin Fe-induced plateau is greatly aroused, resulting in a high specific capacity of 148.4 mAh g-1 and remarkable energy density of 444.2 Wh kg-1. In addition, the excellent structural stability enables superior cycling stability over 2500 cycles and outstanding rate performance. The work will provide fundamental insight into activating the low-spin Fe sites of PB for advanced battery technologies.

Recycling spent masks to fabricate flexible hard carbon anode toward advanced sodium energy storage.

The massive discard of spent masks during the COVID-19 pandemic imposes great environmental anxiety to the human society, which calls for a reliable and sustainable outlet to mitigate this issue. In this work, we demonstrate a green design strategy of recycling the spent masks to fabricate hard carbon fabrics toward high-efficient sodium energy storage. After a simple carbonization treatment, flexible hard carbon fabrics composed of interwoven microtubular fibers are obtained. When serving as binder-free anodes of sodium-ion batteries, a large Na-ion storage capacity of 280 mAh g-1 is achieved for the optimized sample. More impressively, the flexible anode exhibits an initial coulombic efficiency of as high as 86% and excellent rate/cycling performance. The real-life practice of the flexible hard carbon is realized in the full-cells. The present study affords an enlightening approach for the recycling fabrication of high value-added hard carbon materials from the spent masks for advanced sodium energy storage.

A Seamless Metal-Organic Framework Interphase with Boosted Zn2+ Flux and Deposition Kinetics for Long-Living Rechargeable Zn Batteries.

Zn metal has received immense interest as a promising anode of rechargeable aqueous batteries for grid-scale energy storage. Nevertheless, the uncontrollable dendrite growth and surface parasitic reactions greatly retard its practical implementation. Herein, we demonstrate a seamless and multifunctional metal-organic framework (MOF) interphase for building corrosion-free and dendrite-free Zn anodes. The on-site coordinated MOF interphase with 3D open framework structure could function as a highly zincophilic mediator and ion sifter that synergistically induces fast and uniform Zn nucleation/deposition. In addition, the surface corrosion and hydrogen evolution are significantly suppressed by the interface shielding of the seamless interphase. An ultrastable Zn plating/stripping is achieved with elevated Coulombic efficiency of 99.2% over 1000 cycles and prolonged lifetime of 1100 h at 10 mA cm-2 with a high cumulative plated capacity of 5.5 Ah cm-2. Moreover, the modified Zn anode assures the MnO2-based full cells with superior rate and cycling performance.

Biomass-Derived Hard Carbon with Interlayer Spacing Optimization toward Ultrastable Na-Ion Storage.

Hard carbons as a kind of nongraphitized amorphous carbon have been recognized as potential anode materials for sodium-ion batteries (SIBs) due to its large interlayer spacing. However, the issues in terms of onerous synthetic procedure and elusive working mechanism remains critical bottlenecks for practical implement. Herein, we report a facile production of tubular hard carbon through direct carbonization of platanus flosses (FHC) for the first time. Through optimizing the pyrolysis temperatures, the FHC obtained at 1300 °C possesses a key balance between the interlayer spacing and surface area, which can maintain the substantial active sites as well as reduce the irreversible sodium storage. Accordingly, it can deliver a reversible capacity of 324.6 mAh g-1 with a high initial Coulombic efficiency of 80%, superb rate property of 107.2 mAh g-1 at 2 A g-1, and long operating stability over 1000 cycles. Furthermore, the in situ Raman spectroscopic studies certify that sodium ions are stored in FHC following the "adsorption-insertion" mechanism. Our study could provide a promising route for large-scale development of the biomass-derived carbonaceous anodes for high-performance SIBs.

Boosting large-current-density water oxidation activity and stability by phytic acid-assisted rapid electrochemical corrosion.

Corrosion engineering is an efficient strategy to achieve durable oxygen evolution reaction (OER) catalysts at high current densities beyond 500 mA cm-2. However, the spontaneous electrochemical corrosion has a slow reaction rate, and most of them need to add large amounts of salts (such as NaCl) to accelerate the corrosion process. In this report, a novel and effective phytic acid (PA)-assisted in situ electrochemical corrosion strategy is demonstrated to accelerate the the corrosion process and form bimetallic active catalysts to show excellent OER performance at large current densities. In situ rapid electrochemical corrosion of nickel foam substrate and PA ligands etching realize localized high concentrations of Ni and Fe ions. High concentrations of metal ions will combine with hydroxyl to effectively form defects-enriched NiFe layered double hydroxides porous nanosheets tightly anchoring on the underneath substrate. Remarkably, the activated electrode exhibits excellent OER catalytic activities with ultralow overpotentials of 289 and 315 mV to reach high current densities of 500 and 1000 mA cm-2, respectively. When coupled with Ni-Mo-N hydrogen evolution reaction catalysts, the two-electrode cell merely requires 1.87 V to deliver 1000 mA cm-2. The ligands-assisted rapid electrochemical corrosion strategy provides a fresh perspective for facile, cost-effective, and scale-up production of superior OER catalysts at large current densities.

N -(2-aminoethyl) Acetamide Additive Enables Phase-Pure and Stable α-FAPbI3 for Efficient Self-Powered Photodetectors.

Formamidinium-lead triiodide (FAPbI3 ) perovskite is considered as one of the most promising perovskite materials for high-performance photodetectors because of its narrow bandgap and superior thermal stability. Nevertheless, to realize efficient carrier transport and highly performing photodetectors, it imposes the requirement of fabricating α-FAPbI3 with pure phase, preferred crystal orientation, large grain size, and passivated interface, which still remains challenging. Here, a facile strategy based on additive engineering to obtain pure-phase FAPbI3 perovskite films by introducing N-(2-aminoethyl) acetamide into perovskite precursors is reported. The formation of chemical bond and hydrogen bond between N-(2-aminoethyl) acetamide and perovskite reduces the potential barrier in the phase-transition process from an intermediate yellow phase to a final black phase, passivates the defects of the film, and leads to a high-quality and phase-pure α-FAPbI3 perovskite. A self-powered photodetector based on the as-fabricated FAPbI3 film exhibits a maximum responsivity of 0.48 A W-1 at 700 nm with a peak external quantum efficiency of 95% at 440 nm. Moreover, the optimized device remains 83% of the initial performance after 576 h storage at ambient condition. This work provides a simple and feasible scheme for the preparation of high-quality phase-pure α-FAPbI3 perovskite and associated devices.

Surface-Fe enriched trimetallic (oxy)hydroxide engineered by S-incorporation and ligand anchoring toward efficient water oxidation.

Surface Fe with low-coordination plays a decisive role in the performance of OER catalysts in basic media, however, it is still a huge challenge to construct a Fe-enriched surface. Herein, a novel S-incorporation and ligand anchoring strategy is reported for in-situ synthesis of surface-Fe enriched OER catalysts. During the OER test, the co-etching of S elements and ligands enables the formation of surface-Fe enriched trimetallic (oxy)hydroxide OER catalysts. Benefiting from the high catalytic activity of Fe enriched species on surface, the electrode delivers an ultralow overpotential of 234 mV to reach the current density of 10 mA cm-2 and a superior stability over 50 h. This efficient S-incorporation and ligand anchoring strategy offers a new perspective for in-situ construction of advanced earth-abundant OER catalysts.

Boosting photoelectrochemical activity of bismuth vanadate by implanting oxygen-vacancy-rich cobalt (oxy)hydroxide.

Surface charge recombination is regarded as a detrimental factor that severely downgrades the photoelectrochemical (PEC) performance of bismuth vanadate (BiVO4). In this work, we demonstrate defect-rich cobalt (oxy)hydroxides (Co(O)OH) as an excellent cocatalyst nanolayer sheathed on BiVO4 to substantially improve the PEC water oxidation activity. The self-transformation of metal-organic framework produces an ultrathin Co(O)OH layer rich in oxygen vacancies, which could serve as a powerful hole extraction engine to promote the charge transfer/separation efficiency as well as an excellent oxygen evolution reaction catalyst to accelerate the surface water oxidation kinetics. As a result, the BiVO4/Co(O)OH hybrid photoanode achieves remarkably inhibited surface charge recombination and presents a prominent photocurrent density of 4.2 mA cm-2 at 1.23 V vs. RHE, which is around 2.6-fold higher than that of the pristine BiVO4. Moreover, the Co(O)OH cocatalyst nanolayer significantly reduces the onset potential of BiVO4 photoanodes by 200 mV. This work provides a versatile strategy for rationally preparing oxygen-vacancy-rich cocatalysts on various photoanodes toward high-efficient PEC water oxidation.

Ultrafine MoS2 Nanosheets Vertically Patterned on Graphene for High-Efficient Li-Ion and Na-Ion Storage.

Hierarchically two-dimensional (2D) heteroarchitecture with ultrafine MoS2 nanosheets vertically patterned on graphene is developed by using a facile solvothermal method. It is revealed that the strong interfacial interaction between acidic Mo precursors and graphene oxides allows for uniform and tight alignment of edge-oriented MoS2 nanosheets on planar graphene. The unique sheet-on-sheet architecture is of grand advantage in synergistically utilizing the highly conductive graphene and the electroactive MoS2, thus rendering boosted reaction kinetics and robust structural integrity for energy storage. Consequently, the heterostructured MoS2@graphene exhibits impressive Li/Na-ion storage properties, including high-capacity delivery and superior rate/cycling capability. The present study will provide a positive impetus on rational design of 2D metal sulfide/graphene composites as advanced electrode materials for high-efficient alkali-metal ion storage.

Building Ohmic Contact Interfaces toward Ultrastable Zn Metal Anodes.

Zn metal holds grand promise as the anodes of aqueous batteries for grid-scale energy storage. However, the rampant zinc dendrite growth and severe surface side reactions significantly impede the commercial implementation. Herein, a universal Zn-metal oxide Ohmic contact interface model is demonstrated for effectively improving Zn plating/stripping reversibility. The high work function difference between Zn and metal oxides enables the building of an interfacial anti-blocking layer for dendrite-free Zn deposition. Moreover, the metal oxide layer can function as a physical barrier to suppress the pernicious side reactions. Consequently, the proof-of-concept CeO2 -modified Zn anode delivers ultrastable durability of over 1300 h at 0.5-5 mA cm-2 and improved Coulombic efficiency, the feasibility of which is also evidenced in MoS2 //Zn full cells. This study enriches the fundamental comprehension of Ohmic contact interfaces on the Zn deposition, which may shed light on the development of other metal battery anodes.

Superfine MnO2 Nanowires with Rich Defects Toward Boosted Zinc Ion Storage Performance.

The core challenge of MnO2 as the cathode material of zinc-ion batteries remains to be their poor electrochemical kinetics and stability. Herein, MnO2 superfine nanowires (∼10 nm) with rich crystal defects (oxygen vacancies and cavities) are demonstrated to possess high efficient zinc-ion storage capability. Experimental and theoretical studies demonstrate that the defects facilitate the adsorption and diffusion of hydrogen/zinc for fast ion transportation and the build of a local electric field for improved electron migration. In addition, the superfine nanostructure could provide sufficient active sites and short diffusion pathways for further promotion of capacity and reaction kinetics of MnO2. Remarkably, the defect-enriched MnO2 nanowires manifest an energy density as high as 406 W h kg-1 and an excellent durability over 1000 cycles without noticeable capacity degradation. Mechanistic analysis substantiates a reversible coinsertion/extraction process of H+ and Zn2+ with a simultaneous deposition/dissolution of zinc sulfate hydroxide hydrate nanoflakes. This work could enrich the fundamental understanding of defect engineering and nanostructuring on the development of advanced MnO2 materials toward high-performance zinc-ion batteries.

Mechanistic investigation of silver vanadate as superior cathode for high rate and durable zinc-ion batteries.

Rechargeable aqueous Zn-ion batteries have shown considerable potential for stationary grid-scale energy storage systems owing to their characteristics of low cost and non-pollution. Nevertheless, the development of high-performance cathode materials is still a formidable challenge. In this work, for the first time, we report a superior silver vanadate (ß-AgVO3) cathode for Zn-ion batteries, and demonstrate the fundamental Zn2+ storage mechanism in detail. In sharp contrast to the previously-reported layered vandium-based materials, the ß-AgVO3 cathode experiences an initial phase transition to form a layered Zn3V2O7(OH)2·2H2O through a displacement/reduction reaction of Zn2+/Ag+ in the first discharge process. The in situ generated Ag0 along with the residual Ag+ and structural water within the framework afford high electronic/ionic conductivity, thus enabling enhanced Zn2+ intercalation/deintercalation kinetics in the layered phase. As a consequence, the cathode can deliver remarkable rate performance (103 mAh g-1 at 5000 mA g-1) and long-term cycling stability (95 mAh g-1 after 1000 cycles at 2000 mA g-1). The present study offers a totally new insight into the exploration of non-layered-structured vandium-based cathodes for high performance Zn-ion batteries.

Highly Lithiophilic Cobalt Nitride Nanobrush as a Stable Host for High-Performance Lithium Metal Anodes.

Lithium metal is considered to be a holy grail of the battery anode chemistry due to its large specific capacity. Nevertheless, the uncontrollable formation of lithium dendrites resulting from uneven lithium nucleation/growth and the associated safety risk and short cyclability severely impede the practical use of lithium metal anodes. Herein, we demonstrate a highly lithiophilic cobalt nitride nanobrush on a Ni foam (Co3N/NF) current collector as a stable three-dimensional (3D) framework to inhibit the dendrite formation of lithium. The 3D Co3N/NF nanobrush electrode could enable a low nucleation overpotential for homogeneous deposition of dendrite-free lithium. Compared to the CoO/NF counterpart and the bare Cu foil/Ni foam, the Co3N/NF nanobrush host is of great benefit for enhanced Coulombic efficiencies and longer lifespan at various current densities. The present work will offer a new insight for the exploration of the highly lithiophilic scaffold based on metal nitrides toward high-performance lithium metal anodes.

Flexible Sub-Micro Carbon Fiber@CNTs as Anodes for Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) with potential cost benefits are a promising alternative to lithium-ion batteries (LIBs). However, because of the large radius of K+, current anode materials usually undergo large volumetric expansion and structural collapse during the charge-discharge process. Self-supporting carbon nanotubes encapsulated in sub-micro carbon fiber (SMCF@CNTs) are utilized as the KIB anode in this study. The SMCF@CNT anode exhibits high specific capacity, good rate performance, and cycling stability. The SMCF@CNT electrode has specific capacities of 236 mAh g-1 at 0.1 C and 108 mAh g-1 at 5 C and maintains over 193 mAh g-1 after 300 cycles at 1 C. Furthermore, a combined capacitive and diffusion-controlled K+ storage mechanism is proposed on the basis of the investigation using in situ Raman and quantitative analyses. By coupling the SMCF@CNT anode with the K0.3MnO2 cathode, a pouch cell with good flexibility delivers a capacity of 74.0 mAh g-1 at 20 mA g-1. This work is expected to promote the application of KIBs in wearable electronics.

Structurally Engineered Hyperbranched NiCoP Arrays with Superior Electrocatalytic Activities toward Highly Efficient Overall Water Splitting.

Developing inexpensive transition-metal-based nanomaterials with high electrocatalytic activity is of significant necessity for electrochemical water splitting. In this study, we propose a controllable structural engineering strategy of constructing a hyperbranched architecture for highly efficient hydrogen evolution reaction/oxygen evolution reaction (HER/OER). Hyperbranched NiCoP architecture organized by hierarchical nanorod-on-nanosheet arrays is rationally prepared as a demonstration via a facile solvothermal and phosphorization approach. A strong synergistic benefit from the multiscale building blocks is achieved to enable outstanding electrocatalytic properties in an alkaline electrolyzer, including low HER and OER overpotentials of 71 and 268 mV at 10 mA cm-2, respectively, which significantly outperforms the counterparts of individual nanorods and nanosheets. The bifunctional catalysts also show highly efficient and durable overall water electrocatalysis with a small voltage of 1.57 V to drive a current density of 10 mA cm-2. The present study will open a new window to engineering hyperbranched architectures with exceptional electrocatalytic activities toward overall water splitting.