While solar cell technology is booming, intermittent availability of sunlight motivates new vistas for multifunctional devices capable of energy capture and storage on the same material, i.e., direct or two‐electrode bifunctional solar batteries. Herein, simulations and experiments are utilized to take a closer look at efficiency limitations and design considerations, and guidelines are proposed to operate a solar battery comprised of the 2D carbon nitride potassium poly(heptazine imide), K‐PHI, as a bifunctional solar battery photoanode in conjunction with the separator poly(N‐vinylcarbazole) and cathode poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate. An optical design of this device is developed by proposing light absorption in a charge collection layer within the photoanode and calculating photocharging current and charging time as figures of merit. The much larger efficiency of operation via rear illumination for K‐PHI layer thicknesses >200 nm is highlighted and enhancement strategies without modifying the photoactive layer are proposed. Finally, adapted Ragone plots are introduced and it is shown how the solar batteries are capable of improving energy and charge output solely via illumination (for the design under 1 sun, the energy and charge output increase by 60% and 63%, respectively) without modifying the device.

Solar batteries capable of harvesting sunlight and storing solar energy present an attractive vista to transition our energy infrastructure into a sustainable future. Here we present an integrated, fully earth-abundant solar battery based on a bifunctional (light absorbing and charge storing) carbon nitride (K-PHI) photoanode, combined with organic hole transfer and storage materials. An internal ladder-type hole transfer cascade via a transport layer is used to selectively shuttle the photogenerated holes to the PEDOT:PSS cathode. This concept differs from previous designs such as light-assisted battery schemes or photocapacitors and allows charging with light during both electrical charge and discharge, thus substantially increasing the energy output of the cell. Compared to battery operation in the dark, light-assisted (dis)charging increases charge output by 243%, thereby increasing the electric coulombic efficiency from 68.3% in the dark to 231%, leading to energy improvements of 94.1% under illumination. This concept opens new vistas towards compact, highly integrated devices based on multifunctional, carbon-based electrodes and separators, and paves the way to a new generation of earth-abundant solar batteries.

Fast charging is one of the key requirements for next-generation lithium-ion batteries, however, lithium-ion diffusion rates of typical electrode materials are limited. Nanosizing of active electrode material is a common strategy to increase the effective lithium-ion diffusion transport rate, but it also decreases the volumetric energy/power density and stability of the battery. In this work, nickel niobate NiNb2O6 is demonstrated for the first time as a new intrinsic high-rate anode material for lithium-ion batteries without the requirement of realizing nano-architectures. The NiNb2O6 host crystal structure exhibits only a single type of channel for lithium-ion intercalation and can be fully lithiated with a capacity of about 244 mAh g(-1) at low current densities. Interestingly, a high diffusion coefficient of 10(-12) cm(2) s(-1) at 300 K enables fast (dis)charging at high current densities resulting in high capacities of 140 and 50 mAh g(-1) for 10 and 100C respectively. The minimal volume change during lithiation is the origin of the stable reversible lithiation process in NiNb2O6 and leads to 81% capacity retention after 20 000 cycles at 100C. Finally, full cell systems against LiFePO4 and Li[Ni0.8Co0.1Mn0.1]O-2 (NCM811) cathodes demonstrate the promising energy storage performance of nickel niobate anodes in practical battery devices.

The exfoliation mechanism of high charge density 2D tantalum oxide nanosheets was optimized. Single monolayers and thicker thin films were realized and the bandgap of single nanosheets was measured electrically.

Mixed titanium-niobium oxides are considered to be promising anode candidates due to the high theoretical capacity based on the presence of multiple redox couples (Nb5+/Nb4+, Nb4+/Nb3+ and Ti4+/Ti3+). Among them, layered titanoniobates with a two-dimensional (2D) nanosheet structure are expected to expose most surface and near-surface active sites and a minimal Li+ diffusion pathway, and thus could exhibit ultrafast pseudocapacitive dominated lithium storage performance. This work presents the synthesis of 2D HTiNbO5/H-Ti3C2Tx nanohybrid anodes via a combined exfoliation and co-flocculation strategy taking advantage of the ultrathin 2D structure of HTiNbO5 nanosheets and the high electronic conductivity of H-Ti3C2Tx nanosheets. This leads to the random restacking of these two nanosheets and the formation of plane-to-plane contact, insuring excellent transfer kinetics of electrons as well as Li+ ions. Benefitting from such unique 2D lamellar structure, the HTiNbO5/HTi3C2Tx nanohybrid anode with an optimized (3:1) mass ratio is able to exhibit fast lithium storage process by delivering a high capacity of 111.5 mAh.g (-1) at a current density of 5 A g(-1) (similar to 20.6C). Our results demonstrate the feasibility of such co-flocculation strategy for designing new high-rate anode material, which outperforms the original bulk HTiNbO5 compound, making it a promising candidate for application in ultrafast lithium-ion batteries.

Heterostructures constructed from two-dimensional (2D) building blocks have shown promise for field-effect transistors, memory devices, photosensors and other electronic applications. 2D nanosheet crystals are typically constructed into multilayer heterostructures using layer-by-layer methods, which cannot be used to fabricate large-scale and thick heterostructures, due to the time-consuming nature and low efficiency of the process. An alternative approach to deposit different 2D materials in the controllable fashion is by inkjet printing. Here we show the fabrication of supercapacitors based on 2D heterostructures by inkjet printing Ti3C2Tx MXene nanosheets as electrodes, followed by inkjet printing graphene oxide nanosheets as solid-state electrolyte. The free water molecules trapped between graphene oxide sheets facilitate proton movement through the layered solid electrolyte. The as-made heterostructures show high areal capacitance, good cycling stability and high areal energy and power densities comparable with existing printed supercapacitors. Moreover, the specific capacitance can be increased further by addition of liquid electrolytes.

Lithium ion batteries are essential for energy storage in many applications, such as portable electronic devices and electric vehicles. However, charge-discharge rates and cycle life of the current batteries are insufficient to fulfill the targeted requirements of projected future devices, due to the severe limitations of conventional graphite anodes. Niobium tungsten oxides have recently been attracting attention as a new anode material for fast (dis)charging, owing to their stable host structure for lithium intercalation. It was originally believed that nanoscaling and nanostructuring would have a negligible effect on its electrochemical performance. However, the influence of the particle and grain size of niobium tungsten oxide electrodes on its electrochemical behavior is still an open question. This work reports on an investigation of the dependence of the lithiation process on the grain size of Nb18W16O93 anodes down to 60 nm. The results demonstrate that downscaling below 100 nm significantly enhances the lithiation dynamics of niobium tungsten oxide. Furthermore, it suggests that the grain boundaries of Nb18W16O93 have significant influence to the fast lithiation process. It provides a new perspective on the impact of downscaling grains to improve the electrochemical performance of Nb18W16O93 anodes for realizing fast (dis)charging in future energy storage devices.

Two-dimensional nanosheets show promise as electrode materials for high electrochemical performance lithium-ion batteries owing to their unique properties. However, individual nanosheets cannot meet all the required properties for batteries in one material to achieve optimal performance. Here, we demonstrate a new type of two-dimensional heterostructure cathode material for lithium-ion batteries by inkjet printing a composite ink based on high capacity V 2 O 5 nanosheets and high electronic conductivity Ti 3 C 2 T x nanosheets. The excellent electronic conductivity of Ti 3 C 2 T x nanosheets and layer-by-layer heterostructure design enable fast electron transport and minimization of detrimental volume changes during the electrochemical process, respectively. The printed cathodes exhibit a high capacity of 321 mAh g − 1 at 1C, high-rate capability of 112 mAh g − 1 at 10.5C and good cycling stability after 680 cycles with 91.8% capacity retention, indicating high electrochemical performance of the printed heterostructure cathode. This work opens new opportunities of two-dimensional heterostructures for high performance energy storage applications. © 2021 The

Research into 2-dimensional materials has soared during the last couple of years. Next to van der Waals type 2D materials such as graphene and h-BN, less well-known oxidic 2D equivalents also exist. Most 2D oxide nanosheets are derived from layered metal oxide phases, although few 2D oxide phases can be also made by bottom-up solution syntheses. Owing to the strong electrostatic interactions within layered metal oxide crystals, a chemical process is usually needed to delaminate them into their 2D constituents. This Review article provides an overview of the synthesis of oxide nanosheets, and methods to assemble them into nanocomposites, mono- or multilayer films. In particular, the use of Langmuir-Blodgett methods to form monolayer films over large surface areas, and the emerging use of ink jet printing to form patterned functional films is emphasized. The utilization of nanosheets in various areas of technology, for example, electronics, energy storage and tribology, is illustrated, with special focus on their use as seed layers for epitaxial growth of thin films, and as electrochemically active electrodes for supercapacitors and Li ion batteries.

As a thriving member of the 2D nanomaterials family, MXenes, i.e., transition metal carbides, nitrides, and carbonitrides, exhibit outstanding electrochemical, electronic, optical, and mechanical properties. They have been exploited in many applications including energy storage, electronics, optoelectronics, biomedicine, sensors, and catalysis. Compared to other 2D materials, MXenes possess a unique set of properties such as high metallic conductivity, excellent dispersion quality, negative surface charge, and hydrophilicity, making them particularly suitable as inks for printing applications. Printing and pre/post-patterned coating methods represent a whole range of simple, economically efficient, versatile, and eco-friendly manufacturing techniques for devices based on MXenes. Moreover, printing can allow for complex 3D architectures and multifunctionality that are highly required in various applications. By means of printing and patterned coating, the performance and application range of MXenes can be dramatically increased through careful patterning in three dimensions; thus, printing/coating is not only a device fabrication tool but also an enabling tool for new applications as well as for industrialization.

Printed flexible energy storage devices such as micro-supercapacitors require high electrochemical performance for practical applications. Here, we report a high volumetric energy density of up to 1.13 x 10(-3) Wh cm(-3) at a power density of 0.11 W cm(-3) by inkjet printing of Fe-doped MnO2 nanosheets inks as active materials on polyimide substrates. The enhancement results from atomic-level substitutional doping of 3d metal ions (Co, Fe, Ni) in sub-nanometer thick 2D MnO2 nanosheets. Substitutional doping introduces new electronic states near the Fermi level, thereby enhancing the electronic conductivity and contributing to the formation of redox-active 3d surface states. Fe-doped MnO2 showed the best performance in terms of specific areal and volumetric capacitance. Our finding suggests that the rational doping at atomic scale shows great promise for achieving high energy and power density flexible energy storage devices.

Inkjet printing is considered as a promising technique for flexible electronics fabrication owing to its simple, versatile, environmental-friendly and low-cost features. The key to inkjet printing is ink formulation. In this work a highly concentrated ink containing two-dimensional delta-MnO2 nanosheets with an average lateral size of 89 nm and around 1 nm thickness was used. By engineering the formulation of the delta-MnO2 ink, it could be inkjet printed on O-2 plasma treated glass and polyimide film substrates to form delta-MnO2 patterns without undesired "coffee-ring" effect. As a proof-of-concept application, all-solid-state symmetrical micro-supercapacitors (MSCs) based on delta-MnO2 nanosheet ink were fabricated. The fabricated MSCs showed excellent mechanical flexibility and good cycling stability with a capacitance retention of 88% after 3600 charge-discharge cycles. The MSCs attained the highest volumetric capacitance of 2.4 F cm(-3), and an energy density of 1.8.10(-4) Wh cm(-3) at a power density of 0.018 W cm(-3), which is comparable with other similar devices and show great potential as energy storage units for low-cost flexible and wearable electronics applications.

[C16MIM]CF3COO and GO were used as template and 2D planar substrate for in situ growth of Co3O4 NR-P/GO.

An overview of recent progress in the development of 2D manganese oxide nanosheet‐based pseudocapacitors is provided, with emphasis on underlying methods and strategies. 2D manganese oxide nanosheets are sheet‐like monocrystallites of ≈0.5 nm thickness and lateral dimensions of 50–5000 nm. MnO2 nanosheets are synthesized in the form of colloids, which can be readily utilized in wet‐chemical processes like ink‐jet printing. The synthetic strategies to make 2D δ‐MnO2 nanosheets by bottom‐up and top‐down approaches are discussed, and the relationship between the ionic defect structure of δ‐MnO2 nanosheets and their pseudocapacitance is explained. The basic principles and experimental challenges of ink‐jet printing of 2D materials at high resolution, and the development of 2D nanosheet‐based inks are discussed, with emphasis on δ‐MnO2, graphene, and graphene oxide. The fabrication and performance of δ‐MnO2 nanosheet derived pseudocapacitors, including ink‐jet printed flexible microsupercapacitors, is described. The relationship between the electrode thickness and layer architecture and the specific capacitance is explained.

Paper-based microfluidics combined with printed electronics has the potential to yield exceptionally powerful point-of-care diagnostic devices at extremely low cost. To achieve such devices, new manufacturing methodologies must be developed to allow scalable, low-cost production whilst maintaining good reproducibility and performance. In this paper, we discuss the use of high-resolution inkjet printing of various advanced materials as a means to achieve the production of such devices. We present preliminary examples of printing techniques to produce both paper-based microfluidic devices and printed electronic components, which could be further developed into highly integrated, powerful, yet single-use, diagnostic devices. High-resolution inkjet printing of PDMS hydrophobic barriers on nitrocellulose membranes is demonstrated as a means to generate precise (~60-μm-wide) microfluidic circuits allowing low sample volume consumption. To our knowledge, these are the narrowest features produced in paper-based analytical devices via non-lithographic methods. In addition, a novel printing technique based upon agarose gel is demonstrated as a means to directly print microfluidic circuits in paper that may reduce fabrication time and costs as well allow deposition of agarose gel for electrophoresis applications. Printing methods are also used to deposit silver nanoparticle ink electrodes on nitrocellulose with good conductivity, and an all-printed, organic field-effect transistor on a silicon substrate is further presented. These examples serve to highlight the potential application of advanced printing techniques to the production of low-cost, highly functional diagnostic devices.

Porous hollow Co₃O₄ with rhombic dodecahedral structures were prepared by the calcination of ZIF-67 ([Co(mim)2; mim = 2-methylimidazolate]) rhombic dodecahedral microcrystals. A supercapacitor was successfully constructed by adopting the resulting porous hollow Co₃O₄ rhombic dodecahedral structure as the electrode material, which showed a large specific capacitance of 1100 F g(-1) and retained more than 95.1% of the specific capacitance after 6000 continuous charge-discharge cycles. The excellent capacitive properties and stability mark the porous hollow Co₃O₄ with the rhombic dodecahedral structure as one of the most promising electrode materials for high-performance supercapacitors.