Supercapacitor Electrodes from the in Situ Reaction between Two-Dimensional Sheets of Black Phosphorus and Graphene Oxide

Two-dimensional materials show considerable promise as high surface area electrodes for energy-storage applications such as supercapacitors. A single sheet of graphene possesses a large specific surface area because of its atomically thin thickness. However, to package this area efficiently in a device, it must be confined within a finite three-dimensional volume without restacking of the sheet faces. Herein, we present a method of maintaining the high surface area through the use of a hybrid thin film in which few-layer-exfoliated black phosphorus (BP) reduces graphene oxide (GO) flakes. When the film is exposed to moisture, a redox reaction between the BP and the GO forms an interpenetrating network of reduced GO (RGO) and a liquid electrolyte of intermediate phosphorus acids H _xPO _y. The presence of the liquid H _xPO _y electrolyte in the RGO/H _xPO _y film stabilizes and preserves an open-channel structure enabling rapid ion diffusion, leading to an excellent charging rate capability (up to 500 mV s^-1 and retaining 62.3% of initial capacitance at a large current density of 50 A g^-1) when used as electrodes in supercapacitors.

Fully printed high performance humidity sensors based on two-dimensional materials

Fully printed humidity sensors based on two-dimensional (2D) materials are described. Monolayer graphene oxide (GO) and few-layered black phosphorus (BP) flakes were dispersed in low boiling point solvents suitable for inkjet printing. The humidity sensors were fabricated by printing GO and BP sensing layers on printed silver nanoparticle electrodes. The electrical response of the GO and BP sensors to humidity levels ranges from 11 to 97% relative humidity, which revealed a high capacitance sensitivity of 4.45 × 104 times for the GO sensor and 5.08 × 103 times for the BP sensor at 10 Hz operation frequency. Response/recovery times of the GO and BP sensor were found to be 2.7/4.6 s and 4.7/3.0 s respectively. These sensors also showed sensitive and fast response to a proximal human fingertip, showing potential applications in contactless switching.

Solution processing of two-dimensional black phosphorus

Phosphorene, or two-dimensional (2D) black phosphorus (BP) was the first synthetic 2D elemental allotrope beyond graphene to be isolated and studied. It is useful due to its high p-type carrier mobility and direct band gap that is tunable in the range ca. 0.3-2 eV thus bridging the energy gap between graphene and transition metal dichalcogenides such as molybdenum disulfide. Beyond the 'Scotch-Tape' method that was used to isolate the first samples of 2D BP for prototype studies, a range of potentially scalable solution processing techniques emerged later that can produce electronics grade material. This feature article focuses on such solution-process routes to 2D BP and highlights challenges in processing the material, mainly caused by its susceptibility to oxidation, as well as illuminating new avenues and opportunities in the area.

Black phosphorus with near-superhydrophobic properties and long-term stability in aqueous media

We present the use of a polymeric stabilizer which stymies the degradation of black phosphorus nanosheets in aqueous media as well as imparting superhydrophobic properties to immobilised nanosheets.

Precursor determined lateral size control of monolayer MoS2 nanosheets from a series of alkylammonium thiomolybdates: a reversal of trend between growth media

The growth of ligand-free MoS₂ nanosheets with mean lateral sizes below 5 nm at 270 °C is reported. Nanosheets grown from a melt of tetraalkylammonium tetrathiomolybdates, [R₄N]₂[MoS₄] (R = n-butyl, n-hexyl or n-octyl) vary in width between mean lateral sizes of 4.35 and 2.1 nm. Inclusion of the precursors into a polymer matrix shows the opposite trend in lateral dimensions with sheet widths ranging from 3.5 to 4.8 nm.

Asymmetric MoS2 /Graphene/Metal Sandwiches: Preparation, Characterization, and Application

The polarizable organic/water interface is used to construct MoS₂ /graphene nanocomposites, and various asymmetrically dual-decorated graphene sandwiches are synthesized. High-resolution transmission electron microscopy and 3D electron tomography confirm their structure. These dual-decorated graphene-based hybrids show excellent hydrogen evolution activity and promising capacitance performance.

Nanostructured Aptamer-Functionalized Black Phosphorus Sensing Platform for Label-Free Detection of Myoglobin, a Cardiovascular Disease Biomarker

We report the electrochemical detection of the redox active cardiac biomarker myoglobin (Mb) using aptamer-functionalized black phosphorus nanostructured electrodes by measuring direct electron transfer. The as-synthesized few-layer black phosphorus nanosheets have been functionalized with poly-l-lysine (PLL) to facilitate binding with generated anti-Mb DNA aptamers on nanostructured electrodes. This aptasensor platform has a record-low detection limit (∼0.524 pg mL(-1)) and sensitivity (36 μA pg(-1) mL cm(-2)) toward Mb with a dynamic response range from 1 pg mL(-1) to 16 μg mL(-1) for Mb in serum samples. This strategy opens up avenues to bedside technologies for multiplexed diagnosis of cardiovascular diseases in complex human samples.

On the stability of surfactant-stabilised few-layer black phosphorus in aqueous media

The stability of few-layer black phosphorus has been studied in aqueous media using a range of spectroscopic techniques. The material is meta-stable, degrading over time mainly to phosphoric acids.

Tin(II) Sulfide (SnS) Nanosheets by Liquid-Phase Exfoliation of Herzenbergite: IV-VI Main Group Two-Dimensional Atomic Crystals

The liquid-phase exfoliation of tin(II) sulfide to produce SnS nanosheets in N-methyl-2-pyrrolidone is reported. The material is characterized by Raman spectroscopy, atomic force microscopy, lattice-resolution scanning transmission electron microscope imaging, and energy dispersive X-ray spectrum imaging. Quantum chemical calculations on the optoelectronic characteristics of bulk and 10-layer down to monolayer SnS have been performed using a quantum chemical density functional tight-binding approach. The optical properties of the SnS and centrifugally fractionated SnS nanosheet dispersions were compared to that predicted by theory. Through centrifugation, bilayer SnS nanosheets can be produced size-selectively. The scalable solution processing of semiconductor SnS nanosheets is the key to their commercial exploitation and is potentially an important step toward the realization of a future electronics industry based on two-dimensional materials.

Production of few-layer phosphorene by liquid exfoliation of black phosphorus

We report the liquid exfoliation of black phosphorus to form few-layer phosphorene nanosheets.