Nanofluidic devices have turned out to be exemplary systems for investigating fluidic transport properties in a highly restricted area, where the electrostatic interactions or chemical reactions between nanochannel and flowing species strongly dominate the ions and flow transport. Numerous nanofluidic devices have recently been explored to manipulate ion currents and construct electronic devices. Enlightened by electronic field effect transistors, utilizing the electric field effect of nanopore nanochannels has also been adopted to develop versatile nanofluidic devices. Here, we report a nanopore-based nanofluidic unijunction transistor composed of a conical glass nanopipette with the biomaterial polydopamine (PDA) coated at its outer surface. The as-fabricated nanofluidic device exhibited negative differential resistance (NDR) and ion current oscillation (ICO) in ionic transport. The pre-doped copper ions in the PDA moved toward the tip as increasing the potential, having a robust shielding effect on the charge of the tip, thus affecting the surface charge density of the nanopore in the working zone. Finite element simulation based on a continuum model coupled with Stokes–Brinkman and Poisson–Nernst–Planck (PNP) equations revealed that the fluctuations in charge density remarkably affect the transport of ionic current in the nanofluidic device. The as-prepared nanofluidic semiconductor device was a ready-to-use equipment that required no additional external conditions. Our work provides a versatile and convenient way to construct nanofluidic electronic components; we believe by taking advantage of advanced surface modification methods, the oscillation frequency of the unijunction transistors could be controlled on demand, and more nanofluidic devices with resourceful functions would be exploited.

Isolated active metal atoms anchored on nitrogen-doped carbon matrix have been developed as the efficient catalyst for accelerating sluggish reaction kinetics of oxygen reduction reaction (ORR). The facile rational structure engineering with abundant isolated active metal atoms is highly desirable but challenging. Herein, we demonstrate that atomically dispersed Fe sites (Fe-N₄ moieties) on the hierarchical porous nitrogen-doped carbon matrix (Fe-SA-PNC) for high ORR activity can be achieved by a dual-template assisted strategy. By thermal decomposition of NH₄Cl template, the nitrogen-doped carbon matrix is generated based on the interaction with carbon precursor of citric acid. Meanwhile, the introduction of NaCl template facilitates the formation of hierarchical porous structures, which enable more active sites exposed and improve the mass transfer. Interestingly, the dual-template strategy can inhibit the formation of iron carbide nanoparticles (NPs) by generating porous structures and avoiding of the rapid loss of nitrogen during pyrolysis. The as-made Fe-SA-PNC catalysts with well-defined Fe-N₄ active sites exhibit highly efficient ORR activity with a half-wave potential of 0.838 V versus the reversible hydrogen electrode, as well as good stability and methanol tolerance, outperforming the commercial Pt/C. The zinc-air battery (ZAB) constructed by Fe-SA-PNC also shows a higher peak power density and specific discharging capacity than that of Pt-based ZAB. The present work provides the facile strategy for tailoring nitrogen doping and porous structures simultaneously to prevent the formation NPs for achieving the well-dispersed and accessible single-atom active sites, paving a new way to design efficient electrocatalysts for ORR in fuel cells.

Transition-metal phosphides, as the promising alternatives to noble metal catalysts, have been widely used as efficient electrocatalysts for hydrogen evolution reaction (HER). In this work, three kinds of cobalt-8-hydroxyquinoline (Coq_x) with different size and nanostructures are synthesized by varying the hydrothermal conditions, which was named as Coq_x-L, Coq_x-M and Coq_x-S according to the decreased size. Accordingly, the Co_xP/NC with three different size nanostructures (Co_xP/NC-L, Co_xP/NC-M and Co_xP/NC-S) are obtained by the sequential carbonization and phosphidation of Coq_x. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results imply the identical chemical composition in these catalysts with different morphologies. Thus, systematic study is carried out to reveal the relationship between catalytic performance and morphologies of materials with the same chemical composition. The experimental result indicates that the morphology of Co_xP/NC plays a crucial role on the surface area and electron transfer. Finally, the catalyst of Co_xP/NC-S with the smallest size nanostructrue exhibits the best HER performance with a low overpotential at current density of 10 mA/cm² (η = 56.9 and 115.6 mV) and a small Tafel slope (52.3 and 69.3 mV/dec) in both 0.1 M HClO₄ and 1.0 M KOH as well as long-term stability.

As an attempt to minimize the usage amounts of noble metals in catalysis, PtAg alloy nanocrystals with a porous nanosheet morphology were fabricated through a galvanic replacement reaction. During the reaction, ascorbic acid was added to the solution to protect the Ag triangular nanoplates from being totally etched. Structural characterizations indicated that the obtained nanocrystals had thin porous basal planes and winding edges with abundant bulges. Such unique two-dimensional porous architectures endowed this nanomaterial with plenty of catalytically active sites and structural benefits in electron and mass moving, as well as morphology stability. Electrochemical tests proved that the PtAg porous nanosheets had superior catalytic activity and durability towards methanol electrooxidation in basic media. Specifically, the mass and specific activities of the PtAg porous nanosheets were 4.5 and 2.7 times higher than those of a commercial Pt/C catalyst. In addition to the special structures, the introduction of Ag enhanced the catalytic performances of the PtAg porous nanosheets.

The preparation of nanomaterials with superior catalytic properties through simple and rapid protocols is a task of great importance. In the present study, we demonstrate the direct synthesis of trimetallic PdRuPt nanowire networks through the reduction of the corresponding metal precursors with NaBH₄, in the presence of KBr and polyvinylpyrrolidone (PVP). The elemental composition of the final products could be easily tuned by varying the added amounts of metal precursors. The obtained nanomaterials were then used as catalysts for methanol electrooxidation in an acidic medium. Among the synthesized PdRuPt and PtPd nanowire networks, Pd_0.97Ru_0.44Pt exhibits the highest catalytic activity and durability, along with a specific activity 3.5 times higher than that of commercial Pt/C. The enhanced catalytic properties of the present nanowiresystems are attributed to their unique structures and the introduction of Ru into PtPd nanocrystals with outstanding properties.

Enhanced cellular uptake efficiency of nanoparticles is important for their biomedical applications, including photothermal therapy (PTT) for cancer. In this study, a one-pot method was used to construct a positively charged and magnet-responsive nanocomposite comprising reduced graphene oxide anchoring iron oxide (RGI) with a polyethylenimine (PEI) modification, to improve the efficiency of cell internalization. The surface charge can be finely tuned using PEIs of different molecular weights. The obtained RGI_1.8k composite (RGI modified by 1.8 kDa PEI) could load indocyanine green (ICG) at a high mass ratio of 10:3 and ablate cancer cells using low-density laser irradiation because of its positively charged surface. In addition, the hybrids of RGI_1.8k and ICG could kill most cancer cells at a laser density of 0.7 W/cm² in vitro and 0.3 W/cm² in vivo. At the same time, cell viability could be controlled by converting the external magnetic-field direction because of the enrichment of the magnet-responsive composite in vitro and in vivo. Furthermore, RGI_1.8k-ICGs could be used as T₂-weighted magnetic resonance and infrared thermal imaging agents. Coupled with the magnetic target effect, the imaging signal could be improved significantly. Therefore, RGI_1.8k-ICGs represent a new highly efficient PTT and imaging agent with great potential for cancer treatment.

Scalable production of earth-abundant, easy-to-prepare, and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is essential for sustainable energy-based systems. Herein, we systematically studied the electrocatalytic HER performance of a self-supported ternary Co_0.5Mn_0.5P/carbon cloth (CC) nanomaterial prepared using a hydrothermal reaction and phosphorization process. Electrochemical tests demonstrated that the ternary Co_0.5Mn_0.5P/CC nanomaterial could be a highly active electrocatalyst in acidic media, with overpotentials of only 41 and 89 mV, affording current densities of 10 and 100 mA·cm^-2, respectively, and a Tafel slope of 41.7 mV·dec^-1. Furthermore, the electrocatalyst exhibited superior stability, with 3, 000 cycles of cyclic voltammetry from -0.2 to 0.2 V at a scan rate of 100 mV·s^-1 and 40 h of static polarization at a fixed overpotential of 83 mV, indicating its potential for large-scale hydrogen production.

Using Te nanowires as a sacrificial template, we developed a facile wet-chemical method for the synthesis of bimetallic PtCu nanowires. The as-prepared PtCu nanowires possess a porous structure and high aspect ratio. Transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, energy dispersive X-ray spectrum elemental mapping, inductively coupled plasmamass spectroscopy, and X-ray photoelectron spectroscopy (XPS) measurement techniques are used to analyze the structure and composition of the as-prepared nanowires. The XPS results verify that the incorporation of Cu led to the modified electronic state of Pt. Electrocatalytic results prove that the as-prepared nanowires present superior activity for methanol and ethanol electrooxidation in an alkaline solution.