Search

The capacitance and rate performance of Ti3CNTx-based films can be significantly improved by interlayer intercalation and surface modification.

A multilayer fabric consisting of PAN fibers with MXene coating prepared by time-difference blow-spinning exhibits remarkable EMI shielding due to synergistic effects of surface reflection, internal multiple scattering and multiple reflections.

Stacking different two-dimensional (2D) nanomaterials into composite structures opens an opportunity to fabricate electrodes combining the advantages of the individual nanomaterials. Here, different types of MXene nanosheets are combined to create flexible all-MXene hybrid films with high gravimetric capacitance and excellent rate performance for flexible supercapacitors. Ti3C2Tx nanosheets are introduced in between Nb2CTx layers, leading to a significantly increased interlayer spacing. The self-restacking of both types of MXene nanosheets is effectively impeded, accelerating the diffusion of electrolyte ions and enabling more accessible 2D nanochannels. The freestanding Ti3C2Tx/Nb2CTx films deliver a high gravimetric capacitance of 370 F g−1 at a scan rate of 2 mV s−1, good rate performance with 56.1% capacitance retention at 200 mV s−1 and a long cycle life. Furthermore, the energy density of the assembled all-solid-state symmetric supercapacitor can reach up to 5.5 mW h g−1 at a power density of 141.4 mW g−1. Serving as a stable power source unit, the all-solid-state supercapacitor was also integrated with a flex sensor to fabricate a self-powered device. The route to fabricate Ti3C2Tx/Nb2CTx hybrid films with enhanced electrochemical performance is also applicable for other MXenes, promoting the application of MXenes in flexible supercapacitors and integrated electronic devices.

Interfacial engineering is highly promising in the research field of flexible energy storage devices. Massive efforts have confirmed the beneficial effects of controlled interfaces in enhancing energy storage. Despite the extensive studies on constructing multilevel interfaces in the fabrication of flexible electrodes, a deep understanding of the role of interfaces from the electrochemical perspective is lacking, particularly the operational feasibility in extreme conditions. Herein, we designed a carbon cloth (CC) based double-interface CC@Ni(OH)Cl@NiO by a solvothermal, chemical bath, and subsequent annealing method. We obtained both remarkable areal capacitance (8290 mF cm−2 at 30 mA cm−2) and excellent cycling stability (73.9% capacitance retention after 1000 cycles), approximately double than those for the single-interface CC@Ni(OH)Cl. Correspondingly, ultrahigh current tolerance was endowed with a stable charge–discharge capacitance of 3580 mF cm−2 at 120 mA cm−2. A flexible quasi-solid-state asymmetric supercapacitor device, CC@Ni(OH)Cl@NiO//graphene, was assembled, which achieved favorable capacitive ability and splendid flexibility as well as mechanical stability. Through the synchrotron radiation technique, we demonstrated that synergistic double interfaces afford the benefits of stable Ni–O covalency during the electrochemical cycles, and meanwhile bring about more structural distortion and active electronic behavior on the surface state, which simultaneously stimulated capacitive ability and stability. Importantly, our study reveals a positive role of double interfaces from the electrochemical perspective of flexible electrodes for widespread energy storage in the future.

Herein, this work demonstrates the design and synthesis of multicomponent hybrid material NiSχ@MnCoOχ/NF core–shell nanoarrays with high charge storage performance for supercapacitors. The needle-like MnCoOχ nanoarrays as the skeleton of the core layer are grown vertically on the Ni foam via a hydrothermal method, while the NiSχ nanosheets are engineered to anchor onto the surface to form the shell via an electrodeposition method. The unique core–shell architecture provides a large number of reactive sites for MnCoOχ and NiSχ, enhances the number of ion diffusion channels and fast electron transfer pathway. As advanced electrode, NiSχ@MnCoOχ/NF delivers a high specific capacity of 1358 C g−1 (4.84 C cm−2) at 0.5 A g−1, which is 2.05 times that of MnCoOχ/NF (661 C g−1 or 1.35 C cm−2). Furthermore, the hybrid supercapacitor device (NiSχ@MnCoOχ/NF//rGO/NF) exhibits a high specific capacitance of 181.71 F g−1 (2.26 F cm−2), a long cycle life, and a maximum specific energy of 64.61 Wh kg−1, suggesting a great potential for practical application. Therefore, an ingeniously designed core–shell array structure can effectively realize the charge storage potential of the Mn–Co oxides and Ni sulfides, and this work presents an alternative method for constructing hybrid architectures for advanced electrochemical energy storage materials.

Coplanar energy storage devices with interdigitated electrodes have attracted a significant amount of attention as micropower units for portable and flexible electronics, and self-powered systems. Herein, we propose a simple, cost-effective, and scalable two-step screen-printing process to fabricate flexible coplanar asymmetric microscale hybrid device (MHD) with a higher energy density compared to carbon-based microsupercapacitors. 2D titanium carbide MXene (Ti3C2Tx) with a large inlayer spacing is selected as negative electrode, and Co-Al layered double hydroxide (LDH) nanosheets are selected as positive electrode. The assembled coplanar, all-solid-state, asymmetric MHD possesses a higher energy density (8.84 μWh cm−2) compared to the MXene-based, coplanar, symmetric microsupercapacitors (3.38 μWh cm−2), and exhibit excellent flexibility and reliability, as well as cycling stability (92% retention of the initial capacitance after 10,000 cycles). Moreover, we integrate the coplanar asymmetric MHDs with the force sensing resistors as portable power source units to fabricate lightweight and inexpensive integrated force sensors, which can be used to detect applied pressure variation. The two-step screen-printing method can also be extended to other MXenes and various positive electrode materials for fabrication of coplanar asymmetric MHDs on flexible substrates. Therefore, we believe that the two-step screen-printing method opens up new avenues toward developing flexible coplanar asymmetric MHDs, thus promoting the application of MHDs based on MXenes for flexible integrated electronic devices.

Herein, Ni-Co oxide nanowire arrays on graphene supported by Ni foam are fabricated by a simple strategy. In this strategy, the Ni-Co oxide nanosheets are induced to evolve into ultra-fine nanowires with high length/diameter ratio through two-step hydrothermal process, which can effectively increase the surface area, enhance electrochemical activity and improve electron/charge transfer efficiency, thereby resulting in enhanced charge storage performance. It is worth noting that the graphene as a support help to optimize capacitive performance of Ni-Co oxides nanowires. As expected, Ni-Co oxide nanowires anchored on graphene show enhanced specific capacitance of 2619.4 F g−1, due to high-efficient synergistic effect of graphene. However, Ni-Co oxides nanowires directly anchored on Ni foam without graphene have a relatively low specific capacitance of 1950.7 F g−1 at 1 A g−1, but still higher that that of Ni-Co oxides nanosheets arrays (1632.4 F g−1). Furthermore, the hybrid supercapacitor assembled by the Ni-Co oxides nanowires anchored on graphene and nitrogen doped graphene materials shows a specific energy of 24.8 Wh kg−1 and great cycle stability of 90.3% retention after 8000 cycles. This work also provides a strategy to construct novel Ni-Co oxides materials with high charge storage performance for supercapacitor.

Binder-free electrodes employed in supercapacitor devices can exhibit excellent electrochemical performances due to the improvement of electronic conductivity and the utilization rate of electrode materials. However, a simple, efficient and tunable strategy for preparation of binder-free MXene-based electrodes, especially for developing a general method for fabricating the MXene-based wearable flexible supercapacitors, still remains a challenge to meet the requirements of practical applications. In this study, we fabricated binder-free MXene-based films with adjustable mass loading and reduced agglomeration on the nickel foam and wearable flexible fabric substrates by the modified electrophoretic deposition method using organic colloid containing few-layers Ti 3 C 2 T x nanoflakes. Their electrochemical performances are studied by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy, respectively. The binder-free electrodes can deliver high capacitance (∼140 F g −1 in alkaline electrolyte), stable cycling performance with no capacitance loss after 10,000 cycles and good rate performance, which can be attributed to the reduced agglomeration of Ti 3 C 2 T x films with a layer-by-layer self-assembled stackable structure, optimized pore-size distribution (∼4 nm) and excellent electronic conductivity, enhancing the accessibility to electrolyte ions and enabling full utilization of the MXene nanoflake surfaces.

Developing low-cost and high-capacity anode materials is one of the momentous issues in lithium-ion batteries (LIBs). In this study, we propose a facile one-pot hydrothermal strategy to synthesize silicon-doped FeOOH@reduced graphene oxide (Si-FeOOH@rGO) composites, which integrate the advantages of hybridization and doping engineering as novel anodes for LIBs. The Si-FeOOH nanorods are uniformly grown on the conductive rGO sheets with the formation of Fe−O−C bonding at interfaces. Results demonstrate that the doping of Si can effectively suppress the aggregation of active nanoparticles, facilitate Li+ diffusion, and promote the conversion reaction of FeOOH. As a result, the optimized Si-FeOOH@rGO composite manifests high reversibility (1370.5 mAh g−1 at 0.1 A g−1 over 200 cycles), outstanding rate capability (690.4 mAh g−1 at 1 A g−1, 599.2 mAh g−1 at 2 A g−1) and excellent long-term cyclability (920.1 mAh g−1 at 0.5 A g−1 and 612.7 mAh g−1 at 1 A g−1 after 380 cycles). The simple fabrication strategy and superior electrochemical performance indicate that this novel Si-FeOOH@rGO composite shows a great application prospect as anode material for advanced LIBs.

The successful synthesis of a self-supported 3D hetero-structured Co3O4 array on Ni foam under hydrothermal conditions is described herein. In this unique nanoarray structure, the Co3O4 nanowires are anchored onto the surface of Co3O4 nanoflakes, which effectively enlarge the surface area, provide rich active states for the Faraday redox reaction and promote the diffusion rate of the electrolyte ions. The super-capacitive performance of the hetero-structured Co3O4 array is shown to be easily optimized by altering the hydrothermal reaction time to control the integration of the Co3O4 nanowires onto the surface of the nanoflakes. As expected, the hetero-structured Co3O4 array synthesized using a hydrothermal time of 8 h exhibits remarkable super-capacitive performance, such as a high specific capacitance of 2053.1 F g−1 and a high rate capability. Further, the hybrid supercapacitor device assembled using the hetero-structured Co3O4 array and graphene has an energy density of 22.2 Wh kg−1 and outstanding cycle stability. The capacitance retention is up to 93.3% after 10,000 cycles, demonstrating the great potential of the Co3O4 array for supercapacitor application. This work also provides a better strategy for enhancing the charge storage capacity of the metal oxides.

Developing self-powered integrated energy conversion and storage devices (ECSDs) is regarded as a promising approach to meet the quickly increasing demand for portable and wearable electronics. In this work, we describe a concept of using reduced graphene oxide (rGO) as a binder bridging electrochemically active conducting particles and enabling the manufacturing of flexible all-solid-state rGO/Ti3C2Tx (MXene) film-based supercapacitors. These supercapacitors were integrated with flexible thin-film solar cells by the co-cathode method to fabricate ECSDs. The porous rGO/Ti3C2Tx films were produced by vacuum-assisted filtration of the GO/Ti3C2Tx dispersion, followed by reduction at 300 °C under vacuum. This approach eliminated the need for the delamination of MXenes and allowed for the manufacturing of thick electrodes with good electrolyte accessibility. The volumetric and gravimetric capacitance of the rGO/Ti3C2Tx film in 6 M KOH reached 370 F cm−3 and 405 F g−1, respectively, which can be related to the synergistic effect of rGO and Ti3C2Tx. The assembled all-solid-state supercapacitors (SCs) using the polyvinyl alcohol (PVA)/KOH gel electrolyte exhibited a high energy density of 63 mW h cm−3 at a power density of 0.06 W cm−3. Their capacitance did not change after 10 000 charge/discharge cycles at the current density of 5 A g−1, ensuring stable performance of the ECSDs.

Two-dimensional transition-metal carbides called MXenes are emerging electrode materials for energy storage due to their metallic electrical conductivity and low ion diffusion barrier. In this work, we combined Ti2 CTx MXene with graphene oxide (GO) followed by a thermal treatment to fabricate flexible rGO/Ti2 CTr film, in which electrochemically active rGO and Ti2 CTr nanosheets impede the stacking of layers and synergistically interact producing ionically and electronically conducting electrodes. The effect of the thermal treatment on the electrochemical performance of Ti2 CTx is evaluated. As anode for Li-ion storage, the thermally treated Ti2 CTr possesses a higher capacity in comparison to as-prepared Ti2 CTx . The freestanding hybrid rGO/Ti2 CTr films exhibit excellent reversible capacity (700 mAh g-1 at 0.1 Ag-1 ), cycling stability and rate performance. Additionally, flexible rGO/Ti3 C2 Tr films are made using the same method and also present improved capacity. Therefore, this study provides a simple, yet effective, approach to combine rGO with different MXenes, which can enhance their electrochemical properties for Li-ion batteries.