Abstract2D material hydrogels have recently sparked tremendous interest owing to their potential in diverse applications. However, research on the emerging 2D MXene hydrogels is still in its infancy. Herein, we show a universal 4D printing technology for manufacturing MXene hydrogels with customizable geometries, which suits a family of MXenes such as Nb2CTx, Ti3C2Tx, and Mo2Ti2C3Tx. The obtained MXene hydrogels offer 3D porous architectures, large specific surface areas, high electrical conductivities, and satisfying mechanical properties. Consequently, ultrahigh capacitance (3.32 F cm−2 (10 mV s−1) and 233 F g−1 (10 V s−1)) and mass loading/thickness-independent rate capabilities are achieved. The further 4D-printed Ti3C2Tx hydrogel micro-supercapacitors showcase great low-temperature tolerance (down to –20 °C) and deliver high energy and power densities up to 93 μWh cm−2 and 7 mW cm−2, respectively, surpassing most state-of-the-art devices. This work brings new insights into MXene hydrogel manufacturing and expands the range of their potential applications.

The development of new and more accurate fabrication technologies has, in the past few years, boosted interest in advanced device manufacturing. 2D materials, thanks to their diverse properties and dispersibility in liquid carriers, constitute a rich toolbox for ink-based applications. However, the lack of standardized production methods offering a good compromise between performance and affordability has so far been a limiting factor for the application of 2D inks. In this Review, we provide a comprehensive description of the steps involved in device fabrication for different applications, from material selection and ink formulation to printing strategies and device assembly. We conclude with a critical overview of the main scientific and technical limitations currently faced by 2D inks and the related printing technologies and discuss their market penetration and implementation stage. TOC: Two-dimensional materials are some of the best candidates for printed technologies. This review provides an insightful overview on inks formulation processes, from materials selection and deposition techniques to applications. Future commercialization of printed devices is also thoroughly discussed. [H1] IntroductionLayered materials are a diverse group of materials exhibiting a broad spectrum of electronic, electrochemical and photonic properties 1-3 . Despite the interest of these bulk properties, the true potential of layered materials is unlocked when they are exfoliated to 2D layers 4 .

Polymer cathode materials are promising alternatives to inorganic counterparts for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) due to their high theoretical capacity, adjustable molecular structure, and strong adaptability to different counterions in batteries, etc. However, they suffer from poor practical capacity and low rate capability because of their intrinsically poor conductivity. Herein, we report the synthesis of self-assembled graphene/poly(anthraquinonyl sufide) (PAQS) composite aerogel (GPA) with efficient integration of a three-dimensional (3D) graphene framework with electroactive PAQS particles via a novel dispersion-assembly strategy which can be used as a free-standing flexible cathode upon mechanical pressing. The entire GPA cathode can deliver the highest capacity of 156 mAh g at 0.1 C (1 C = 225 mAh g) with an ultrahigh utilization (94.9%) of PAQS and exhibits an excellent rate performance with 102 mAh g at 20 C in LIBs. Furthermore, the flexible GPA film was also tested as cathode for SIBs and demonstrated a high-rate capability with 72 mAh g at 5 C and an ultralong cycling stability (71.4% capacity retention after 1000 cycles at 0.5 C) which has rarely been achieved before. Such excellent electrochemical performance of GPA as cathode for both LIBs and SIBs could be ascribed to the fast redox kinetics and electron transportation within GPA, resulting from the interconnected conductive framework of graphene and the intimate interaction between graphene and PAQS through an efficient wrapping structure. This approach opens a universal way to develop cathode materials for powerful batteries with different metal-based counter electrodes.

The designable structure with 3D structure, ultrathin 2D nanosheets, and heteroatom doping are considered as highly promising routes to improve the electrochemical performance of carbon materials as anodes for lithium-ion batteries. However, it remains a significant challenge to efficiently integrate 3D interconnected porous frameworks with 2D tunable heteroatom-doped ultrathin carbon layers to further boost the performance. Herein, a novel nanostructure consisting of a uniform ultrathin N-doped carbon layer in situ coated on a 3D graphene framework (NC@GF) through solvothermal self-assembly/polymerization and pyrolysis is reported. The NC@GF with the nanosheets thickness of 4.0 nm and N content of 4.13 at% exhibits an ultrahigh reversible capacity of 2018 mA h g at 0.5 A g and an ultrafast charge-discharge feature with a remarkable capacity of 340 mA h g at an ultrahigh current density of 40 A g and a superlong cycle life with a capacity retention of 93% after 10 000 cycles at 40 A g . More importantly, when coupled with LiFePO cathode, the fabricated lithium-ion full cells also exhibit high capacity and excellent rate and cycling performances, highlighting the practicability of this NC@GF.

Potassium ion hybrid capacitors (KICs) have drawn tremendous attention for large-scale energy storage applications because of their high energy and power densities and the abundance of potassium sources. However, achieving KICs with high capacity and long lifespan remains challenging because the large size of potassium ions causes sluggish kinetics and fast structural pulverization of electrodes. Here, we report a composite anode of VO2–V2O5 nanoheterostructures captured by a 3D N-doped carbon network (VO2–V2O5/NC) that exhibits a reversible capacity of 252 mAh g–1 at 1 A g–1 over 1600 cycles and a rate performance with 108 mAh g–1 at 10 A g–1. Quantitative kinetics analyses demonstrate that such great rate capability and cyclability are enabled by the capacitive-dominated potassium storage mechanism in the interfacial engineered VO2–V2O5 nanoheterostructures. The further fabricated full KIC cell consisting of a VO2–V2O5/NC anode and an active carbon cathode delivers a high operating voltage window of 4.0 V and energy and power densities up to 154 Wh kg–1 and 10 000 W kg–1, respectively, surpassing most state-of-the-art KICs.

Low-temperature thermocatalytic degradation of LDPE is successfully achieved by NiCoMnO4 powders.

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Inevitable dissolution in aqueous electrolytes, intrinsically low electrical conductivity, and sluggish reaction kinetics have significantly hampered the zinc storage performance of vanadium oxide‐based cathode materials. Herein, core–shell N‐doped carbon‐encapsulated amorphous vanadium oxide arrays, prepared via a one‐step nitridation process followed by in situ electrochemical induction, as a highly stable and efficient cathode material for aqueous zinc‐ion batteries (AZIBs) are reported. In this design, the amorphous vanadium oxide core provides unobstructed ions diffusion routes and abundant active sites, while the N‐doped carbon shell can ensure efficient electron transfer and greatly stabilize the vanadium oxide core. The assembled AZIBs exhibit remarkable discharge capacity (0.92 mAh cm−2 at 0.5 mA cm−2), superior rate capability (0.51 mAh cm−2 at 20 mA cm−2), and ultra‐long cycling stability (≈100% capacity retention after 500 cycles at 0.5 mA cm−2 and 97% capacity retention after 10 000 cycles at 20 mA cm−2). The working mechanism is further validated by in situ X‐ray diffraction combined with ex situ tests. Moreover, the fabricated cathode is highly flexible, and the assembled quasi‐solid‐state AZIBs present stable electrochemical performance under large deformations. This work offers insights into the development of high‐performance amorphous vanadium oxide‐based cathodes for AZIBs.