Fabrication of Single-Crystal Violet Phosphorus Flakes For Ultrasensitive Photodetection.

Violet phosphorus (VP) has attracted a lot of attention for its unique physicochemical properties and emerging potential in photoelectronic applications. Although VP has a van der Waals (vdW) structure similar to that of other 2D semiconductors, direct synthesis of VP on a substrate is still challenging. Moreover, optoelectronic devices composed of transfer-free VP flakes have not been demonstrated. Herein, a bismuth-assisted vapor phase transport technique is designed to grow uniform single-crystal VP flakes on the SiO2 /Si substrate directly. The size of the crystalline VP flakes is an order of magnitude larger than that of previous liquid-exfoliated samples. The photodetector fabricated with the VP flakes shows a high responsivity of 12.5 A W-1 and response/recovery time of 3.82/3.03 ms upon exposure to 532 nm light. Furthermore, the photodetector shows a small dark current (<1 pA) that is beneficial to high-sensitivity photodetection. As a result, the detectivity is 1.38 × 1013 Jones that is comparable with that of the vdW p-n heterojunction detector. The results reveal the great potential of VP in optoelectronic devices as well as the CVT technique for the growth of single-crystal semiconductor thin films.

Achieving High-Performance Electrocatalytic Water Oxidation on Ni(OH)2 with Optimized Intermediate Binding Energy Enabled by S-Doping and CeO2 -Interfacing.

The adsorption energy of the reaction intermediates has a crucial influence on the electrocatalytic activity. Ni-based materials possess high oxygen evolution reaction (OER) performance in alkaline, however too strong binding of *OH and high energy barrier of the rate-determining step (RDS) severely limit their OER activity. Herein, a facile strategy is shown to fabricate novel vertical nanorod-like arrays hybrid structure with the interface contact of S-doped Ni(OH)2 and CeO2 in situ grown on Ni foam (S-Ni(OH)2 /CeO2 /NF) through a one-pot route. The alcohol molecules oxidation reaction experiments and theoretical calculations demonstrate that S-doping and CeO2 -interfacing significantly modulate the binding energies of OER intermediates toward optimal value and reduce the energy barrier of the RDS, contributing to remarkable OER activity for S-Ni(OH)2 /CeO2 /NF with an ultralow overpotential of 196 mV at 10 mA cm-2 and long-term durability over 150 h for the OER. This work offers an efficient doping and interfacing strategy to tune the binding energy of the OER intermediates for obtaining high-performance electrocatalysts.

Selectively Confined Black Phosphorus Nanowires in Carbon Nanotubes.

Nanoconfinement of low-dimensional materials opens up a new territory for tailoring material hybridization to produce novel geometric structures for applications in electronics, catalysis, and photonics. Despite the progress made in the encapsulation of 2D materials, exploration of their definite crystal structures into lower-dimensional nanomaterials is still largely unexplored. Herein, one-dimensional black phosphorus (BP) nanowires with an aspect ratio of over 100 produced by confining BP into the CNT (conf-BP@CNT) are reported. Notably, the unique structure and dimensions of BP were determined by confinement within the CNT and were accurately characterized by crystallography. During the spatially confined growth, the defects and capillarity effect of the CNT promote nucleation and growth of BP within the CNT. conf-BP@CNT shows surface charge localization of conf-BP and protection rendered by the CNT shell, giving rise to more efficient and stable photocatalytic rhodamine B (RhB) degradation than the bare exfoliated BP nanosheets. These results demonstrate the effectiveness of nanoconfinement in producing nanomaterials with controllable dimensions, precise spatial arrangement, and unique structures.

Single-Atom Pt Doping Induced p-Type to n-Type Transition in NiO Nanosheets toward Self-Gating Modulated Electrocatalytic Hydrogen Evolution Reaction.

Exploring highly efficient single atom catalysts with defined active centers and tunable electronic structures is highly desirable. Herein, we developed an efficient hydrogen evolution reaction (HER) electrocatalyst through a self-gating phenomenon induced by Pt single atoms (SAs) supported on ultrathin NiO nanosheets (PtSA-NiO). The Ni atoms in NiO are partially replaced by the atomically dispersed Pt atoms, leading to a transition from p-type NiO into n-type PtSA-NiO. When the n-type PtSA-NiO serves as HER electrocatalyst, the self-gating phenomenon occurs in the ultrathin nanosheets, resulting in a mixture of leakage ("active") and metal-insulator-semiconductor ("inert") regions. The "inert" region induced by the ionic gating and reverse potential is capable of accumulating relatively high surface charge carrier concentration with an ultrahigh electric field, making the PtSA-NiO highly conductive; meanwhile, the HER process occurs at the Pt SAs sites (active region) in the PtSA-NiO nanosheets. As a result, the PtSA-NiO requires only 55 mV to deliver 10 mA/cm2 in an alkaline solution with good stability.

Selective photoelectrochemical oxidation of glucose to glucaric acid by single atom Pt decorated defective TiO2.

Photoelectrochemical reaction is emerging as a powerful approach for biomass conversion. However, it has been rarely explored for glucose conversion into value-added chemicals. Here we develop a photoelectrochemical approach for selective oxidation of glucose to high value-added glucaric acid by using single-atom Pt anchored on defective TiO2 nanorod arrays as photoanode. The defective structure induced by the oxygen vacancies can modulate the charge carrier dynamics and band structure, simultaneously. With optimized oxygen vacancies, the defective TiO2 photoanode shows greatly improved charge separation and significantly enhanced selectivity and yield of C6 products. By decorating single-atom Pt on the defective TiO2 photoanode, selective oxidation of glucose to glucaric acid can be achieved. In this work, defective TiO2 with single-atom Pt achieves a photocurrent density of 1.91 mA cm-2 for glucose oxidation at 0.6 V versus reversible hydrogen electrode, leading to an 84.3 % yield of glucaric acid under simulated sunlight irradiation.

Sequential Electrodeposition of Bifunctional Catalytically Active Structures in MoO3 /Ni-NiO Composite Electrocatalysts for Selective Hydrogen and Oxygen Evolution.

Exploring earth-abundant and highly efficient electrocatalysts is critical for further development of water electrolyzer systems. Integrating bifunctional catalytically active sites into one multi-component might greatly improve the overall water-splitting performance. In this work, amorphous NiO nanosheets coupled with ultrafine Ni and MoO3 nanoparticles (MoO3 /Ni-NiO), which contains two heterostructures (i.e., Ni-NiO and MoO3 -NiO), is fabricated via a novel sequential electrodeposition strategy. The as-synthesized MoO3 /Ni-NiO composite exhibits superior electrocatalytic properties, affording low overpotentials of 62 mV at 10 mA cm-2 and 347 mV at 100 mA cm-2 for catalyzing the hydrogen and the oxygen evolution reaction (HER/OER), respectively. Moreover, the MoO3 /Ni-NiO hybrid enables the overall alkaline water-splitting at a low cell voltage of 1.55 V to achieve 10 mA cm-2 with outstanding catalytic durability, significantly outperforming the noble-metal catalysts and many materials previously reported. Experimental and theoretical investigations collectively demonstrate the generated Ni-NiO and MoO3 -NiO heterostructures significantly reduce the energetic barrier and act as catalytically active centers for selective HER and OER, synergistically accelerating the overall water-splitting process. This work helps to fundamentally understand the heterostructure-dependent mechanism, providing guidance for the rational design and oriented construction of hybrid nanomaterials for diverse catalytic processes.

Nanophase graphene frameworks.

Nanophase graphene frameworks (NGFs) assembled by interconnected domains have massive interfaces, where the interfacial interaction and the compact architectures drastically elevate the durability of graphene towards physical and chemical destruction. The excellent electrical conductivity of the NGFs can be perfectly maintained even after 1500 friction cycles or 3 h flame treatment.

Engineering 2D Architectures toward High-Performance Micro-Supercapacitors.

The rise of micro-supercapacitors is satisfying the demand for power storage in portable devices and wireless gadgets. But the miniaturization of the energy-storage components is significantly limited by their energy density. Electrode materials with adequate electrochemical active surfaces are therefore required for improving performance. 2D materials with ultralarge specific surface areas offer a broad portfolio of the development of high-performance micro-supercapacitors in spite of their several critical drawbacks. An architecture engineering strategy is therefore developed to break these natural limits and maximize the significant advantages of these materials. Based on the approaches of phase transformation, intercalation, surface modification, material hybridization, and hierarchical structuration, 2D architectures with improved conductivity, enlarged specific surface, enhanced redox activity, as well as the unique synergetic effect exhibit great promise in the application of miniaturized supercapacitors with highly enhanced performance. Herein, the architecture engineering of emerging 2D materials beyond graphene toward optimizing the performance of micro-supercapacitors is discussed, in order to promote the application of 2D architectures in miniaturized energy-storage devices.