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Nonmetallic doping and in situ growth techniques for designing electrode materials with excellent electrocatalytic activity are effective strategies to enhance the electrochemical performance. Bifunctional electrode materials for supercapacitors (SCs) and the hydrogen evolution reaction (HER) have attracted great interest due to their potential applications in green energy storage and conversion. Herein, the bimetallic MnCo LDH is anchored on a hollow sulfur (S)-doped MnCo-MOF-74 surface, forming a poplar flower-like 3D composite which is used for SCs and the HER in alkaline media. The fabricated S-MnCo-MOF-74@MnCo LDH/NF electrode exhibits a favorable specific capacitance of 1875.4 F g−1 at 1 A g−1 and steady long-term cycling performance. Moreover, the assembled HSC using S-MnCo-MOF-7@MnCo LDH/NF as the cathode material and active carbon (AC) as the anode material shows 546.4 F g−1 capacitance (1 A g−1) with a maximum energy density of 58 W h kg−1 at 14 000 W kg−1 power density. As an electrocatalyst, S-MnCo-MOF-7@MnCo LDH/NF exhibits excellent HER properties with a small Tafel slope of 128.9 mV dec−1 a low overpotential of 197 mV at 10 mA cm−2 and durable performance for 10 hours in alkaline media. The present work provides insights into understanding and designing active electrode materials for stable hydrogen evolution and high-performing supercapacitors in an alkaline environment. [ABSTRACT FROM AUTHOR]

On account of high energy density and low cost of sulfur, lithium‐sulfur (Li−S) battery has been regarded as an appealing energy storage system to date. Nevertheless, it has faced formidable challenges, mainly pertaining to the fatal shuttle effect and retarded sulfur redox kinetics. Single atom catalysts (SACs) have showcased great promise for addressing these issues owing to their maximum atom utilization efficiency, favorable catalytic activity as well as their good structural tunability at an atomic level, considerably contributing to the recent fruitful advancements in Li−S realm. In this review, we summarize the state‐of‐the‐art strategies in the coordination manipulations of SACs toward highly efficient and durable Li−S batteries. The recent advances, existing issues, and future outlooks are discussed accordingly, aiming to guide the synthetic design of SACs, propel the underlying mechanism understanding and ultimately boost the commercial viability of Li−S batteries. [ABSTRACT FROM AUTHOR]

Lithium‐rich cathodes (LRCs) show great potential to improve the energy density of commercial lithium‐ion batteries owing to their cationic and anionic redox characteristics. Herein, a complete conductive network using carbon nanotubes (CNTs) additives to improve the poor kinetics of LRCs is fabricated. Ex situ X‐ray photoelectron spectroscopy first demonstrates that the slope at a low potential and the following long platform can be assigned to the transition metal and oxygen redox, respectively. The combination of galvanostatic intermittent titration technique and electrochemical impedance spectroscopy further reveal that a battery with CNTs exhibited accelerated kinetics, especially for the O‐redox process. Consequently, LRCs with CNTs exhibit a much better rate and cycling performance (≈89% capacity retention at 2 C for over 200 cycles) than the Super P case. Eventually, TEM results imply that the improved electrochemical performance of the CNTs case also benefits from its more stable bulk and surface structures. Such a facile conductive additive modification strategy also provides a universal approach for the enhancement of the electron diffusion properties of other electrode materials. [ABSTRACT FROM AUTHOR]

Lithium–sulfur batteries (LSBs) are regarded as promising next‐generation energy storage systems owing to their remarkable theoretical energy density (2600 Wh kg‐1) and low cost. However, sluggish electrochemical kinetics, lithium polysulfides (LiPS) shuttling, and uncontrollable Li dendrite growth seriously hamper the commercial application of LSBs. Herein, dual‐functional 3D interconnected free‐standing fibers embedded with TiO2‐TiN heterostructures as an advanced skeleton are designed for concurrently regulating both the sulfur cathode (S/hollow TiO2‐TiN) and Li anode (Li/solid TiO2‐TiN). As a cathode skeleton, the hollow TiO2‐TiN fibers afford synergistic functions of chemical anchoring, physical confinement, and excellent electrocatalysis for LiPS. Meanwhile, the multifunctional skeleton with remarkable lithiophilicity and high conductivity can accomplish uniform Li deposition and homogeneous Li ion flux for inhibiting the growth of dendrites. Benefiting from these advantages, the full battery (S/hollow TiO2‐TiN || Li/solid TiO2‐TiN) exhibits excellent electrochemical performance, including high cycling stability (988.8 mAh g−1 after 200 cycles at 0.5 C) and impressive rate properties (639.3 mAh g−1 at 2 C). This work inaugurates a novel strategy from experimental and theoretical aspects for fabricating LSBs with robust electrochemical performance. [ABSTRACT FROM AUTHOR]

Lithium–sulfur (Li–S) batteries have stimulated a burgeoning scientific and industrial interest owing to high energy density and low materials costs. The favorable reaction kinetics of sulfur species is a key prerequisite for pursuing their commercialization. Recent years have witnessed a wealth of investigations in terms of boosting sulfur redox via rationalizing redox mediators. Defect engineering, which allows for the effective exposure of active sites and optimization of electronic structure, has emerged expeditiously as an essential strategy to enhance polysulfide modulation, and hence expedite Li–S chemistry. Nevertheless, a comprehensive overview of defect engineering in Li–S realm is still lacking. This review emphasizes the recent advances in the rational design and polysulfide modulation strategies of different types of defective mediators. Their unique morphological configuration, superb electrochemical activity, and underlying catalytic mechanism are comprehensively summarized, aiming to deepen the understanding of defect‐mediated Li–S chemistry. Moreover, in situ evolution of defective mediators is discussed to identify the true active sites under aprotic reaction conditions. Opportunities and an outlook of this fast‐developing frontier that may lead to practical implementations of Li–S batteries are proposed. [ABSTRACT FROM AUTHOR]

Functionalizing carbon cathode surfaces with oxygen functional groups is an effective way to simultaneously tailor the fundamental properties and customize the electrochemical properties of aqueous Zn‐ion hybrid capacitors. In this work, the oxygen functional groups of chemically reduced graphene oxide (rGO) are systematically regulated via a series of reductants and varied experimental conductions. Carboxyl and carbonyl have been proven to significantly enhance the aqueous electrolyte wettability, Zn‐ion chemical adsorption, and pseudocapacitive redox activity by experimental study and computational analysis. The rGO cathode produced through hydrogen peroxide assisted hydrothermal reduction exhibits a specific capacitance of 277 F g−1 in 1 m ZnSO4 after optimization of surface oxygen functional groups. In addition, a quasi‐solid‐state flexible Zn‐ion hybrid capacitor (ZHC) with a polyacrylamide gel electrolyte and a high loading mass of 5.1 mg cm−2 are assembled. The as‐prepared quasi‐solid state ZHC can offer a superior areal capacitance of 1257 mF cm−2 and distinguished areal energy density of 342 µW h cm−2. The significant enhancement of redox activity and Zn‐ion storage capability by regulating the oxygen functional groups can shed light on the promotion of electrochemical charge storage properties even beyond protic electrolyte systems. [ABSTRACT FROM AUTHOR]

The lithium–sulfur (Li–S) battery is regarded as a next‐generation energy storage system due to its conspicuous merits in high theoretical capacity (1672 mAh g−1), overwhelming energy density (2600 Wh kg−1), and the cost‐effectiveness of sulfur. However, the practical application of Li–S batteries is still handicapped by a multitude of key challenges, mainly pertaining to fatal lithium polysulfide (LiPS) shuttling and sluggish sulfur redox kinetics. In this respect, rationalizing electrocatalytic processes in Li–S chemistry to synergize the entrapment and conversion of LiPSs is of paramount significance. This review summarizes recent progress and well‐developed strategies of the mediator design toward promoted Li–S chemistry. The current advances, existing challenges, and future directions are accordingly highlighted, aiming at providing in‐depth understanding of the sulfur reaction mechanism and guiding the rational mediator design to realize high‐energy and long‐life Li–S batteries. [ABSTRACT FROM AUTHOR]

Highlights: Utilizing 3D printing allows the fine construction of electrodes with tailorable thickness and precise tuning of mass loading of active materials. 3D-printed NiCoP/MXene//AC asymmetrical supercapacitor full cells harvest a record-high areal/volumetric energy density of 0.89 mWh cm−2/2.2 mWh cm−3.Designing high-performance electrodes via 3D printing for advanced energy storage is appealing but remains challenging. In normal cases, light-weight carbonaceous materials harnessing excellent electrical conductivity have served as electrode candidates. However, they struggle with undermined areal and volumetric energy density of supercapacitor devices, thereby greatly impeding the practical applications. Herein, we demonstrate the in situ coupling of NiCoP bimetallic phosphide and Ti3C2 MXene to build up heavy NCPM electrodes affording tunable mass loading throughout 3D printing technology. The resolution of prints reaches 50 μm and the thickness of device electrodes is ca. 4 mm. Thus-printed electrode possessing robust open framework synergizes favorable capacitance of NiCoP and excellent conductivity of MXene, readily achieving a high areal and volumetric capacitance of 20 F cm−2 and 137 F cm−3 even at a high mass loading of ~ 46.3 mg cm−2. Accordingly, an asymmetric supercapacitor full cell assembled with 3D-printed NCPM as a positive electrode and 3D-printed activated carbon as a negative electrode harvests remarkable areal and volumetric energy density of 0.89 mWh cm−2 and 2.2 mWh cm−3, outperforming the most of state-of-the-art carbon-based supercapacitors. The present work is anticipated to offer a viable solution toward the customized construction of multifunctional architectures via 3D printing for high-energy-density energy storage systems. [ABSTRACT FROM AUTHOR]

Printing is regarded as a revolutionary and feasible technique to guide the fabrication of versatile functional systems with designed architectures. 2D MXenes are nowadays attractive in printed energy storage devices. However, owing to the van der Waals interaction between the MXene layers, the restacking issues within the printed electrodes can significantly impede the ion/electrolyte transport and hence handicap the electrochemical performances. Herein, a melamine formaldehyde templating method is demonstrated to develop crumpled nitrogen‐doped MXene (MXene‐N) nanosheets. The nitrogen doping boosts the electrochemical performances of MXene via enhanced conductivity and redox activity. Accordingly, two types of MXene‐N inks are prepared throughout the optimization of the ink viscosity to fit the 2D screen printing and 3D extrusion printing, respectively. As a result, the screen printed MXene‐N microsupercapacitor delivers an areal capacitance of 70.1 mF cm−2 and outstanding mechanical robustness. Furthermore, the 3D‐printed MXene‐N based supercapacitor manifests an areal capacitance of 8.2 F cm−2 for a three‐layered electrode and readily stores a high areal energy density of 0.42 mWh cm−2. The approach to harnessing such versatile MXene‐N inks offers distinctive insights into the printed energy storage systems with high areal energy density and large scalability. [ABSTRACT FROM AUTHOR]

One-step hydrothermal method is used for the simultaneous construction of three-dimensional self-supported TMA-V 2 CT x /CoV-LDH/NF composites as binder-free electrodes, which demonstrated excellent supercapacitor performance. [Display omitted] Two-dimensional (2D) MXene nanomaterials display great potential for green energy storage. However, as a result of self-stacking of MXene nanosheets and the presence of conventional binders, MXene-based nanomaterials are significantly hindered in their rate capability and cycling stability. We successfully constructed a self-supported stereo-structured composite (TMA-V 2 CT x /CoV-LDH/NF) by in-situ growing 2D cobalt vanadium layered double hydroxide (CoV-LDH) vertically on 2D few-layered V 2 CT x MXene nanosheets and interconnecting it with Ni foam (NF) with a self-supported structure to act as a binder-free electrode. In addition to inhibiting CoV-LDH aggregation, the highly conductive V 2 CT x MXene and CoV-LDH work synergistically to improve charge storage. The specific capacitance of the TMA-V 2 CT x /CoV-LDH/NF electrode is 2374 F/g (1187 C/g) at 1 A/g. At the same time, the TMA-V 2 CT x /CoV-LDH/NF exhibits excellent stability, retaining 85.3 % of its specific capacitance at 20 A/g after 10,000 cycles. In addition, the hybrid supercapacitor (HSC) is assembled based on positive electrode (TMA-V 2 CT x /CoV-LDH/NF) and negative electrode (AC), achieving the maximum energy density of 74.4 Wh kg−1 at 750.3 W kg−1. TMA-V 2 CT x /CoV-LDH/NF has potential as an electrode material for storing green energy. The research strategy provides a development prospect for the construction of novel V 2 CT x MXene-based electrode material with self-supported structures. [ABSTRACT FROM AUTHOR]

• Customizing CoSe 2 @MXene hybrid ink to allow smooth 3D printing. • Revealing structural advances of 3D-printed electrode via theoretical simulation. • Achieving an energy density of 199 Wh kg−1 for 3D-printed potassium-ion hybrid capacitor. Potassium-ion hybrid capacitor (PIHC) has been deemed as an appealing energy storage system thanks to its low cost and reconciled energy/power density. Nevertheless, the rapid capacity deterioration, sluggish anode kinetics and unsatisfied energy output greatly impede its practical implementation. Herein, a fully 3D-printed (3DP) PIHC affording high-energy–density and long-lifetime is conceptually demonstrated based on a 3DP CoSe 2 @Ti 3 C 2 T n MXene anode and a 3DP activated carbon cathode, which can harvest a gravimetric energy density of 199 Wh kg−1 and a 6000-cycled lifespan with a capacity retention of 84.8%. Our 3D-printable CoSe 2 @Ti 3 C 2 T n MXene hybrid ink with desirable rheological property is customized to derive 3DP electrode with facilitated ion diffusion and mass transport, thereby enabling impressive K-ion storage performances. This work would open up a new and facile avenue for the development of stable, safe and credible PIHCs, which could be readily extended to other metal-ion hybrid capacitors. [ABSTRACT FROM AUTHOR]