AgxZny Protective Coatings with Selective Zn2+/H+ Binding Enable Reversible Zn Anodes.

Zinc (Zn) metal anodes suffer from the dendrite growth and hydrogen evolution reaction (HER) in classical aqueous electrolytes, which severely limit their lifespan. We propose a rational design of AgxZny protective coatings with selective binding to Zn2+ against H+ to simultaneously regulate the Zn growth pattern and the HER kinetics. We further demonstrate that by tuning the composition of the AgxZny coating the Zn deposition behavior can be readily tuned from the conventional plating/stripping (on Zn-AgZn3 coating) to alloying/dealloying (on Ag-AgZn coating), resulting in precise control of the Zn growth pattern. Moreover, the synergy of Ag and Zn further suppresses the competitive HER. As a result, the modified Zn anodes possess a significantly enhanced lifespan. This work provides a new strategy for enhancing the stability of Zn and potentially other metal anodes by precisely manipulating the binding strength of protons and metal charge carriers in aqueous batteries.

Direct Dioxygen Radical Coupling Driven by Octahedral Ruthenium-Oxygen-Cobalt Collaborative Coordination for Acidic Oxygen Evolution Reaction.

The acidic oxygen evolution reaction (OER) has long been the bottleneck of proton exchange membrane water electrolyzers given its harsh oxidative and corrosive environments. Herein, we suggest an effective strategy to greatly enhance both the acidic OER activity and stability of Co3O4 spinel by atomic Ru selective substitution on the octahedral Co sites. The resulting highly symmetrical octahedral Ru-O-Co collaborative coordination with strong electron coupling effect enables the direct dioxygen radical coupling OER pathway. Indeed, both experiments and theoretical calculations reveal a thermodynamically breakthrough heterogeneous diatomic oxygen mechanism. Additionally, the active Ru-O-Co units are well-maintained upon the acidic OER thanks to the electron transfer from surrounding electron-enriched tetrahedral Co atoms via bridging oxygen bonds that suppresses the overoxidation and thus dissolution of active Ru and Co species. Consequently, the prepared catalyst, even with a low Ru mass loading of ca. 42.8 µg cm-2, exhibits an attractive acidic OER performance with a low overpotential of 200 mV and a low potential decay rate of 0.45 mV h-1 at 10 mA cm-2. Our work suggests an effective strategy to significantly enhance both the acidic OER activity and stability of low-cost electrocatalysts.

Electrostatic Shielding Regulation of Magnetron Sputtered Al-Based Alloy Protective Coatings Enables Highly Reversible Zinc Anodes.

The uncontrolled zinc dendrite growth during plating leads to quick battery failure, which hinders the widespread applications of aqueous zinc-ion batteries. The growth of Zn dendrites is often promoted by the "tip effect". In this work, we propose a generate strategy to eliminate the "tip effect" by utilizing the electrostatic shielding effect, which is achieved by coating Zn anodes with magnetron sputtered Al-based alloy protective layers. The Al can form a surface insulating Al2O3 layer and by manipulating the Al content of Zn-Al alloy films, we are able to control the strength of the electrostatic shield, therefore realizing a long lifespan of Zn anodes up to 3000 h at a practical operating condition of 1.0 mA cm-2 and 1.0 mAh cm-2. In addition, the concept can be extended to other Al-based systems such as Ti-Al alloy and achieve enhanced stability of Zn anodes, demonstrating the generality and efficacy of our strategy.

A Hydrazine-Nitrate Flow Battery Catalyzed by a Bimetallic RuCo Precatalyst for Wastewater Purification along with Simultaneous Generation of Ammonia and Electricity.

The traditional technologies for industrial and agricultural effluent treatment are often energy-intensive. Herein, we suggest an electrochemical redox strategy for spontaneous and simultaneous decontamination of wastewater and generation of both fuels and electricity at low cost. Using hydrazine and nitrate effluents as a demonstration, we propose a hydrazine-nitrate flow battery (HNFB) that can efficiently purify the wastewater and meanwhile generate both ammonia fuel and electricity with the assistance of our developed bimetallic RuCo precatalyst. Specifically, the battery delivers a peak power density of 12 mW cm-2 and continuously operates for 20 h with an ammonia yield rate of ca. 0.38 mmol h-1 cm-2 under 100 mA cm-2 . The generated electricity can further drive a hydrazine electrolyzer to produce hydrogen fuel. Our work provides an alternative pathway to purify wastewater and generate high value-added fuels at low cost.

Co-Solvent Electrolyte Engineering for Stable Anode-Free Zinc Metal Batteries.

Anode-free metal batteries can in principle offer higher energy density, but this requires them to have extraordinary Coulombic efficiency (>99.7%). Although Zn-based metal batteries are promising for stationary storage, the parasitic side reactions make anode-free batteries difficult to achieve in practice. In this work, a salting-in-effect-induced hybrid electrolyte is proposed as an effective strategy that enables both a highly reversible Zn anode and good stability and compatibility toward various cathodes. The as-prepared electrolyte can also work well under a wide temperature range (i.e., from -20 to 50 °C). It is demonstrated that in the presence of propylene carbonate, triflate anions are involved in the Zn2+ solvation sheath structure, even at a low salt concentration (2.14 M). The unique solvation structure results in the reduction of anions, thus forming a hydrophobic solid electrolyte interphase. The waterproof interphase along with the decreased water activity in the hybrid electrolyte effectively prevents side reactions, thus ensuring a stable Zn anode with an unprecedented Coulombic efficiency (99.93% over 500 cycles at 1 mA cm-2). More importantly, we design an anode-free Zn metal battery that exhibits excellent cycling stability (80% capacity retention after 275 cycles at 0.5 mA cm-2). This work provides a universal strategy to design co-solvent electrolytes for anode-free Zn metal batteries.

Surface and Interface Engineering of Zn Anodes in Aqueous Rechargeable Zn-Ion Batteries.

Rechargeable zinc-ion batteries (ZIBs) have shown great potential as an alternative to lithium-ion batteries. The ZIBs utilize Zn metal as the anode, which possesses many advantages such as low cost, high safety, eco-friendliness, and high capacity. However, on the other hand, the Zn anode also suffers from many issues, including dendritic growth, corrosion, and passivation. These issues are largely related to the surface and interface properties of the Zn anode. Many efforts have therefore been devoted to the modification of the Zn anode, aiming to eliminate the above-mentioned problems. This review gives a comprehensive summary on the mechanism behind these issues as well as the recent progress on Zn anode modification with focus on the strategies of surface and interface engineering, covering the design and application of both the Zn anode supports and surface protective layers, along with abundant examples. In addition, the promising research directions and perspective on these strategies are also presented.

MXene hydrogels: fundamentals and applications.

Hydrogels have recently garnered tremendous interest due to their potential application in soft electronics, human-machine interfaces, sensors, actuators, and flexible energy storage. Benefiting from their impressive combination of hydrophilicity, metallic conductivity, high aspect ratio morphology, and widely tuneable properties, when two-dimensional (2D) transition metal carbides/nitrides (MXenes) are incorporated into hydrogel systems, they offer exciting and versatile platforms for the design of MXene-based soft materials with tunable application-specific properties. The intriguing and, in some cases, unique properties of MXene hydrogels are governed by complex gel structures and gelation mechanisms, which require in-depth investigation and engineering at the nanoscale. On the other hand, the formulation of MXenes into hydrogels can significantly increase the stability of MXenes, which is often the limiting factor for many MXene-based applications. Moreover, through simple treatments, derivatives of MXene hydrogels, such as aerogels, can be obtained, further expanding their versatility. This tutorial review intends to show the enormous potential of MXene hydrogels in expanding the application range of both hydrogels and MXenes, as well as increasing the performance of MXene-based devices. We elucidate the existing structures of various MXene-containing hydrogel systems along with their gelation mechanisms and the interconnecting driving forces. We then discuss their distinctive properties stemming from the integration of MXenes into hydrogels, which have revealed an enhanced performance, compared to either MXenes or hydrogels alone, in many applications (energy storage/harvesting, biomedicine, catalysis, electromagnetic interference shielding, and sensing).

Aqueous Zinc-Ion Storage in MoS2 by Tuning the Intercalation Energy.

Aqueous Zn-ion batteries present low-cost, safe, and high-energy battery technology but suffer from the lack of suitable cathode materials because of the sluggish intercalation kinetics associated with the large size of hydrated zinc ions. Herein we report an effective and general strategy to transform inactive intercalation hosts into efficient Zn2+ storage materials through intercalation energy tuning. Using MoS2 as a model system, we show both experimentally and theoretically that even hosts with an originally poor Zn2+ diffusivity can allow fast Zn2+ diffusion. Through simple interlayer spacing and hydrophilicity engineering that can be experimentally achieved by oxygen incorporation, the Zn2+ diffusivity is boosted by 3 orders of magnitude, effectively enabling the otherwise barely active MoS2 to achieve a high capacity of 232 mAh g-1, which is 10 times that of its pristine form. The strategy developed in our work can be generally applied for enhancing the ion storage capacity of metal chalcogenides and other layered materials, making them promising cathodes for challenging multivalent ion batteries.

Plasma-Assisted Synthesis of NiCoP for Efficient Overall Water Splitting.

Efficient water splitting requires highly active, earth-abundant, and robust catalysts. Monometallic phosphides such as Ni2P have been shown to be active toward water splitting. Our theoretical analysis has suggested that their performance can be further enhanced by substitution with extrinsic metals, though very little work has been conducted in this area. Here we present for the first time a novel PH3 plasma-assisted approach to convert NiCo hydroxides into ternary NiCoP. The obtained NiCoP nanostructure supported on Ni foam shows superior catalytic activity toward the hydrogen evolution reaction (HER) with a low overpotential of 32 mV at -10 mA cm-2 in alkaline media. Moreover, it is also capable of catalyzing the oxygen evolution reaction (OER) with high efficiency though the real active sites are surface oxides in situ formed during the catalysis. Specifically, a current density of 10 mA cm-2 is achieved at overpotential of 280 mV. These overpotentials are among the best reported values for non-noble metal catalysts. Most importantly, when used as both the cathode and anode for overall water splitting, a current density of 10 mA cm-2 is achieved at a cell voltage as low as 1.58 V, making NiCoP among the most efficient earth-abundant catalysts for water splitting. Moreover, our new synthetic approach can serve as a versatile route to synthesize various bimetallic or even more complex phosphides for various applications.

Efficient Overall Water-Splitting Electrocatalysis Using Lepidocrocite VOOH Hollow Nanospheres.

Herein we report the control synthesis of lepidocrocite VOOH hollow nanospheres and further their applications in electrocatalytic water splitting for the first time. By tuning the surface area of the nanospheres, the optimal performance can be achieved with low overpotentials of 270 mV for the oxygen evolution reaction (OER) and 164 mV for the hydrogen evolution reaction (HER) at 10 mA cm-2 in 1 m KOH, respectively. Furthermore, when used as both the anode and cathode for overall water splitting, a low cell voltage of 1.62 V is required to reach the current density of 10 mA cm-2 , making the VOOH hollow nanospheres an efficient alternative to water splitting.

Controlled synthesis of layered double hydroxide nanoplates driven by screw dislocations.

Layered double hydroxides (LDHs) are a family of two-dimensional (2D) materials with layered crystal structures that have found many applications. Common strategies to synthesize LDHs lead to a wide variety of morphologies, from discrete 2D nanosheets to nanoflowers. Here, we report a study of carefully controlled LDH nanoplate syntheses using zinc aluminum (ZnAl) and cobalt aluminum (CoAl) LDHs as examples and reveal their crystal growth to be driven by screw dislocations. By controlling and maintaining a low precursor supersaturation using a continuous flow reactor, individual LDH nanoplates with well-defined morphologies were synthesized on alumina-coated substrates, instead of the nanoflowers that result from uncontrolled overgrowth. The dislocation-driven growth was further established for LDH nanoplates directly synthesized using the respective metal salt precursors. Atomic force microscopy revealed screw dislocation growth spirals, and under transmission electron microscopy, thin CoAl LDH nanoplates displayed complex contrast contours indicative of strong lattice strain caused by dislocations. These results suggest the dislocation-driven mechanism is generally responsible for the growth of 2D LDH nanostructures, and likely other materials with layered crystal structures, which could help the rational synthesis of well-defined 2D nanomaterials with improved properties.

Hydrothermal continuous flow synthesis and exfoliation of NiCo layered double hydroxide nanosheets for enhanced oxygen evolution catalysis.

We report the controlled synthesis of NiCo layered double hydroxide (LDH) nanoplates using a newly developed high temperature high pressure hydrothermal continuous flow reactor (HCFR), which enables direct growth onto conductive substrates in high yield and, most importantly, better control of the precursor supersaturation and, thus, nanostructure morphology and size. The solution coordination chemistry of metal-ammonia complexes was utilized to synthesize well-defined NiCo LDH nanoplates directly in a single step without topochemical oxidation. The as-grown NiCo LDH nanoplates exhibit a high catalytic activity toward the oxygen evolution reaction (OER). By chemically exfoliating LDH nanoplates to thinner nanosheets, the catalytic activity can be further enhanced to yield an electrocatalytic current density of 10 mA cm(-2) at an overpotential of 367 mV and a Tafel slope of 40 mV dec(-1). Such enhancement could be due to the increased surface area and more exposed active sites. X-ray photoelectron spectroscopy (XPS) suggests the exfoliation also caused some changes in electronic structure. This work presents general strategies to controllably grow nanostructures of LDH and ternary oxide/hydroxides in general and to enhance the electrocatalytic performance of layered nanostructures by exfoliation.

Operando Analysis of NiFe and Fe Oxyhydroxide Electrocatalysts for Water Oxidation: Detection of Fe4⁺ by Mössbauer Spectroscopy.

Nickel-iron oxides/hydroxides are among the most active electrocatalysts for the oxygen evolution reaction. In an effort to gain insight into the role of Fe in these catalysts, we have performed operando Mössbauer spectroscopic studies of a 3:1 Ni:Fe layered hydroxide and a hydrous Fe oxide electrocatalyst. The catalysts were prepared by a hydrothermal precipitation method that enabled catalyst growth directly on carbon paper electrodes. Fe(4+) species were detected in the NiFe hydroxide catalyst during steady-state water oxidation, accounting for up to 21% of the total Fe. In contrast, no Fe(4+) was detected in the Fe oxide catalyst. The observed Fe(4+) species are not kinetically competent to serve as the active site in water oxidation; however, their presence has important implications for the role of Fe in NiFe oxide electrocatalysts.

Regulating the Electrode-Electrolyte Interfaces of Lithium-High Nickel Batteries via a Multifunctional Additive.

Lithium metal batteries with high nickel ternary (LiNixCoyMn1-x-yO2, x ≥ 0.8) as the cathode hold the promise to meet the demand of next-generation high energy density batteries. However, the unsatisfactory stability of electrode-electrolyte interfaces limits their practical applications. In this work, N-methyl-N-trimethylsilyltrifluoroacetamide (NMTFA) is suggested as a new functional electrolyte additive to stabilize the Li∥LiNi0.9Co0.05Mn0.05O2 chemistry by forming robust and effective electrode-electrolyte interphases, namely the anode-electrolyte interphase (AEI, or conventionally called SEI) and cathode-electrolyte interphase (CEI). The NMTFA-derived SEI/CEI greatly enhances the battery performance that a capacity retention of 82.1% after 200 cycles at 1C charge/discharge is achieved, significantly higher than that without NMTFA addition (52.5%). Moreover, the NMTFA also improves the thermal stability of the electrolyte and inhibits the hydrolysis of LiPF6. This work provides new clues for the optimization of electrolyte formulation for lithium-high nickel batteries through modulating interfaces.

An acid-alkaline furfural hybrid battery for furoate and bipolar hydrogen production.

We propose an acid-alkaline furfural hybrid battery that can achieve a discharging power density of 47 mW cm-2 under 100 mA cm-2 energy output with a H2 faradaic efficiency (FE) up to ca. 200% and a furoate FE of around 97% with the aid of our developed Pt-Cu electrocatalyst.

Status and Opportunities of Zinc Ion Hybrid Capacitors: Focus on Carbon Materials, Current Collectors, and Separators.

Zinc ion hybrid capacitors (ZIHCs), which integrate the features of the high power of supercapacitors and the high energy of zinc ion batteries, are promising competitors in future electrochemical energy storage applications. Carbon-based materials are deemed the competitive candidates for cathodes of ZIHC due to their cost-effectiveness, high electronic conductivity, chemical inertness, controllable surface states, and tunable pore architectures. In recent years, great research efforts have been devoted to further improving the energy density and cycling stability of ZIHCs. Reasonable modification and optimization of carbon-based materials offer a remedy for these challenges. In this review, the structural design, and electrochemical properties of carbon-based cathode materials with different dimensions, as well as the selection of compatible, robust current collectors and separators for ZIHCs are discussed. The challenges and prospects of ZIHCs are showcased to guide the innovative development of carbon-based cathode materials and the development of novel ZIHCs.

Sputtered binder-free Cu3N electrode materials for high-performance quasi-solid-state asymmetric supercapacitors.

Developing high-efficiency electrode materials is of great importance in manufacturing supercapacitor devices with superior electrochemical performance. Herein, we for the first time report a binder-free method for controllable growth of Cu3N electrode materials via magnetron sputtering for supercapacitor applications. Benefiting from their unique polyhedral structure and good electrical conductivity, Cu3N electrodes can achieve an areal capacity of 90.7 mC cm-2 at 1 mA cm-2 and outstanding cycling stability with a capacity retention of 97.4% after 20 000 cycles. In particular, the assembled Cu3N//active carbon quasi-solid-state asymmetric supercapacitor can exhibit a maximum energy density of 13.2 µW h cm-2 and a power density of 4.8 mW cm-2 with an operating voltage of 1.6 V. These remarkable performances demonstrate the great potential of sputtered Cu3N electrode materials for future energy storage applications.

In Situ Alloying Sites Anchored on an Amorphous Aluminum Nitride Matrix for Crystallographic Reorientation of Zinc Deposits.

Secondary aqueous zinc-ion batteries (ZIBs) are considered as one of the promising energy storage devices, but their widespread application is limited by the Zn dendrite issues. In this work, we propose a rational design of surface protective coatings to solve this problem. Specifically, a silver (Ag) nanoparticle embedded amorphous AlN matrix (AlN/Ag) protective layer is developed. The former would alloy in situ with Zn to form AgZn3 alloy sites, which subsequently induce the Zn deposition with preferred (002) facets. The latter can effectively alleviate the structural expansion during repeated Zn plating/stripping. Consequently, the delicately designed AlN/Ag@Zn anode delivers an enhanced stability with a long lifespan of more than 2600 h at 1 mA cm-2 and 1 mAh cm-2. Moreover, the AlN/Ag@Zn||Mn1.4V10O24·nH2O full batteries can be operated for over 8000 cycles under 5 A g-1. Our work not only suggests a promising Zn anode protective coating but also provides a general strategy for the rational design of surface protective layers for metal anodes.

Synergy of VN and Fe2O3 Enables High Performance Anodes for Asymmetric Supercapacitors.

Fe2O3 is one of the most common anode materials beyond carbons but suffers from unsatisfactory capacity and poor stability, which are associated with the insufficient utilization of active material and the structural instability caused by the phase transformation. In this work, we report an effective strategy to overcome the above issues through electronic structure optimization by constructing delicately designed Fe2O3@VN core-shell structure. The Fe2O3@VN/CC exhibits a much higher areal capacity of 254.8 mC cm-2 at 5 mA cm-2 (corresponding to 318.5 mF cm-2, or 265.4 F g-1) than the individual VN (48 mC cm-2, or 60 mF cm-2) or Fe2O3/CC (93.36 mC cm-2, or 116.7 mF cm-2), along with enhanced stability. Moreover, the assembled asymmetric supercapacitor devices based on Fe2O3@VN/CC anode and RuO2/CC cathode show a high stack energy density of 0.5 mWh cm-3 at a power density of 12.28 mW cm-3 along with good stability (80% capacitance retention after 14000 cycles at 10 mA cm-2). This work not only establishes the Fe2O3@VN as a high-performance anode material but also suggests a general strategy to enhance the electrochemical performance of traditional anodes that suffer from low capacity (capacitance) and poor stability.

Recent Advances in Copper-Doped Titanium Implants.

Titanium (Ti) and its alloys have been extensively used as implant materials in clinical practice due to their high corrosion resistance, light weight and excellent biocompatibility. However, the insufficient intrinsic osteogenic capacity of Ti and its alloys impedes bone repair and regeneration, and implant-related infection or inflammation remains the leading cause of implant failure. Bacterial infections or inflammatory diseases constitute severe threats to human health. The physicochemical properties of the material are critical to the success of clinical procedures, and the doping of Cu into Ti implants has been confirmed to be capable of enhancing the bone repair/regeneration, angiogenesis and antibacterial capability. This review outlines the recent advances in the design and preparation of Cu-doped Ti and Ti alloy implants, with a special focus on various methods, including plasma immersion implantation, magnetron sputtering, galvanic deposition, microarc oxidation and sol-gel synthesis. More importantly, the antibacterial and mechanical properties as well as the corrosion resistance and biocompatibility of Cu-doped Ti implants from different methods are systematically reviewed, and their prospects and limitations are also discussed.