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Transition metal phosphides (TMPs) are battery-typed materials with superior conductivity and redox activity, thereby making them promising in fiber-shaped hybrid capacitors (FSHCs). Yet designed synthesis of nanostructured TMPs on conductive fiber substrate as binder-free electrode is essential to improve their electrochemical performance. This work proposes an efficient strategy to directly grow hierarchical NiCoP nanosheet arrays (NSAs) on carbon nanotube fibers (CNTFs) by using a hydrothermal process and subsequent gas-solid phosphorization. Benefiting from the ordered nanosheet structure, the NiCoP/CNTF electrode exhibits a specific capacity of 0.711 mAh cm−2 at a current density of 1 mA cm−2. Matching this electrode with a negative electrode of CNTF supported vanadium nitride (VN) NSAs, we fabricated a high-performance twisted FSHC with a maximum operating voltage of 1.6 V. Owing to the ultrahigh electrochemical performance of the hybrid fiber electrodes, the FSHC device delivers a high specific capacitance of 325.6 mF cm−2 (108.53 F cm−3) at the current density of 1 mA cm−2, and achieves an energy density of 115.78 μWh cm−2. Moreover, it displays excellent flexibility with negligible capacitance loss after 5000 bending cycles. Thus, this work elucidates a feasible route to construct NiCoP-based fiber electrodes for wearable energy storage devices.

Flexible fiber-shaped supercapacitors hold promising potential in the area of portable and wearable electronics. Unfortunately, their general application is hindered by the restricted energy densities due to low operating voltage and small specific surface area. Herein, an all-solid-state fiber-shaped asymmetric supercapacitor (FASC) possessing ultrahigh energy density is reported, in which the positive electrode was designed as Na-doped MnO2 nanosheets on carbon nanotube fibers (CNTFs) and the negative electrode as MoS2 nanosheet-coated CNTFs. Owing to the excellent properties of the designed electrodes, our FASCs exhibit a large operating potential window (0-2.2 V), a remarkable specific capacitance (265.4 mF/cm2), as well as an ultrahigh energy density (178.4 μWh/cm2). Moreover, the devices are of outstanding mechanical flexibility.

With the increasing requirement of the hydrogen energy storage and chemical reactant, it gets to be emergent to exploit room-temperature high-performance hydrogen sensors. By designing a gasochromic-Pd-WO3/graphene/Si tandem structure, here we report an optoelectronic hydrogen sensor, which is working at the room temperature. In this device architecture, the graphene/Si acts as a photodetector layer by using its photovoltaic property and the tandem Pd-WO3 film serves as a hydrogen gas sensing layer by using its gasochromic behavior. While the device is exposed to the hydrogen gas, the transmittance of the Pd-WO3 can be tuned, which is synchronously sensed by the graphene/Si photodetector. With this principle, the device can detect the hydrogen gas with the concentration down to 0.05 vol% and the response time less than 13 s and the recovery time less than 43 s. This indicates that it is promising to develop the tandem gasochromic-Pd-WO3/graphene/Si structure for room-temperature high-performance low-cost hydrogen sensors.

To meet the increasing requirements of minimizing circuits, the development of novel device architectures that use ultra-thin two-dimensional materials is encouraged. Here, we demonstrate a non-volatile black phosphorus (BP) PNP junction in a BP/h-BN/graphene heterostructure in which BP acts as a transport channel layer, hexagonal boron nitride (h-BN) serves as a tunnel barrier layer and graphene is the charge-trapping layer. The device architecture is designed such that only the middle part of the BP is aligned over the graphene flake, enabling the flexible tuning of the charge carriers in the BP over the graphene charge-trapping layer. Thus, the device exhibits the ability to work in two different operating modes (PNP and PP+P). Each operating mode can be retained well and demonstrates non-volatile behavior, and each can be programmed by using the control-gate.