Production of hydrogen by electrochemical water splitting has been hindered by the high cost of precious metal catalysts, such as Pt, for the hydrogen evolution reaction (HER). In this work, novel hierarchical β-Mo2 C nanotubes constructed from porous nanosheets have been fabricated and investigated as a high-performance and low-cost electrocatalyst for HER. An unusual template-engaged strategy has been utilized to controllably synthesize Mo-polydopamine nanotubes, which are further converted into hierarchical β-Mo2 C nanotubes by direct carburization at high temperature. Benefitting from several structural advantages including ultrafine primary nanocrystallites, large exposed surface, fast charge transfer, and unique tubular structure, the as-prepared hierarchical β-Mo2 C nanotubes exhibit excellent electrocatalytic performance for HER with small overpotential in both acidic and basic conditions, as well as remarkable stability.

Carrier doping of MoS2 nanoflakes was achieved by functional self-assembled monolayers (SAMs) with different dipole moments. The effect of SAMs on the charge transfer between the substrates and MoS2 nanoflakes was studied by Raman spectroscopy, field-effect transistor (FET) measurements, and Kelvin probe microscope (KFM). Raman data and FET results verified that fluoroalkyltrichlorosilane-SAM with a large positive dipole moment, acting as hole donors, significantly reduced the intrinsic n-doping characteristic of MoS2 nanoflakes, while 3-(trimethoxysilyl)-1-propanamine-SAMs, acting as electron donors, enhanced the n-doping characteristic. The additional built-in electric field at the interface between SiO2 substrates and MoS2 nanoflakes induced by SAMs with molecular dipole moments determined the charge transfer process. KFM results clearly demonstrated the charge transfer between MoS2 and SAMs and the obvious interlayer screening effect of the pristine and SAM-modified MoS2 nanoflakes. However, the KFM results were not fully consistent with the Raman and FET results since the externally absorbed water molecules were shown to partially shield the actual surface potential measurement. By eliminating the contribution of the water molecules, the Fermi level of monolayer MoS2 could be estimated to modulate in a range of more than 0.45-0.47 eV. This work manifests that the work function of MoS2 nanoflakes can be significantly tuned by SAMs by virtue of affecting the electrostatic potential between the substrates and MoS2 nanoflakes.

Development of low‐cost, high‐performance, and bifunctional electrocatalysts for water splitting is essential for renewable and clean energy technologies. Although binary phosphides are inexpensive, their performance is not as good as noble metals. Adding a third metal element to binary phosphides (Ni‐P, Co‐P) provides the opportunity to tune their crystalline and electronic structures and thus their electrocatalytic properties. Here, ternary phosphide (NiCoP) films with different nickel to cobalt ratios via an electrodeposition technique are synthesized. The films have a triple‐layered and hierarchical morphology, consisting of nanosheets in the bottom layer, ≈90–120 nm nanospheres in the middle layer, and larger spherical particles on the top layer. The ternary phosphides exhibit versatile activities that are strongly dependent on the Ni/Co ratios and Ni0.51Co0.49P film is found to have the best electrocatalytic activities for both hydrogen evolution reactions and oxygen evolution reactions. The high performance of the ternary phosphide film is attributed to enhanced electric conductivity so that reaction kinetics is accelerated, enlarged surface area due to the hierarchical and three‐layered morphology, and increased local electric dipole so that the energy barrier for the water splitting reaction is lowered.

A dual-band self-powered photodetector (SPPD) with high sensitivity is realized by a facile combination of InSe Schottky diode and Au plasmonic nanoparticle (NP) arrays. Comparing with pristine InSe devices, InSe/Au photodetectors possess an additional capability of photodetection in visible to near-infrared (NIR) region. This intriguing phenomenon is attributed to the wavelength selective enhancement of pristine responsivities by hybridized quadrupole plasmons resonance of Au NPs. It is worth pointing out that the maximum of enhancement ratio in responsivity reaches up to ∼1200% at a wavelength of 685 nm. In addition, owing to a large Schottky barrier difference formed between active layer and two asymmetric electrodes, the responsivities of dual-band InSe/Au photodetector could reach up to 369 and 244 mA/W at the wavelength of 365 and 685 nm under zero bias voltage, respectively. This work would provide an additional opportunity for developing multifunctional photodetectors with high performance based on two-dimensional materials, upgrading their capacity of photodetection in a complex environment.

Piezoelectric two-dimensional (2D) van der Waals (vdWs) materials are highly desirable for applications in miniaturized and flexible/wearable devices. However, the reverse-polarization between adjacent layers in current 2D layered materials results in decreasing their in-plane piezoelectric coefficients with layer number, which limits their practical applications. Here, we report a class of 2D layered materials with an identical orientation of in-plane polarization. Their piezoelectric coefficients (e22) increase with layer number, thereby allowing for the fabrication of flexible piezotronic devices with large piezoelectric responsivity and excellent mechanical durability. The piezoelectric outputs can reach up to 0.363 V for a 7-layer α-In2Se3 device, with a current responsivity of 598.1 pA for 1% strain, which is one order of magnitude higher than the values of the reported 2D piezoelectrics. The selfpowered piezoelectric sensors made of these newly developed 2D layered materials have been successfully used for real-time health monitoring, proving their suitability for the fabrication of flexible piezotronic devices due to their large piezoelectric responses and excellent mechanical durability.