Ce Site in Amorphous Iron Oxyhydroxide Nanosheet toward Enhanced Electrochemical Water Oxidation.

Iron oxyhydroxide has been considered an auspicious electrocatalyst for the oxygen evolution reaction (OER) in alkaline water electrolysis due to its suitable electronic structure and abundant reserves. However, Fe-based materials seriously suffer from the tradeoff between activity and stability at a high current density above 100 mA cm-2 . In this work, the Ce atom is introduced into the amorphous iron oxyhydroxide (i.e., CeFeOx Hy ) nanosheet to simultaneously improve the intrinsic electrocatalytic activity and stability for OER through regulating the redox property of iron oxyhydroxide. In particular, the Ce substitution leads to the distorted octahedral crystal structure of CeFeOx Hy , along with a regulated coordination site. The CeFeOx Hy electrode exhibits a low overpotential of 250 mV at 100 mA cm-2 with a small Tafel slope of 35.1 mVdec-1 . Moreover, the CeFeOx Hy electrode can continuously work for 300 h at 100 mA cm-2 . When applying the CeFeOx Hy nanosheet electrode as the anode and coupling it with the platinum mesh cathode, the cell voltage for overall water splitting can be lowered to 1.47 V at 10 mA cm-2 . This work offers a design strategy for highly active, low-cost, and durable material through interfacing high valent metals with earth-abundant oxides/hydroxides.

Ferricyanide Armed Anodes Enable Stable Water Oxidation in Saturated Saline Water at 2 A/cm2.

The direct seawater electrolysis at high current density and low overpotential affords an effective strategy toward clean and renewable hydrogen fuel production. However, the severe corrosion of anode as a result of the saturation of Cl- upon continuous seawater feeding seriously hamper the electrolytic process. Herein, cobalt ferricyanide / cobalt phosphide (CoFePBA/Co2 P) anodes with Cap/Pin structure are synthesized, which stably catalyze alkaline saturated saline water oxidation at 200-2000 mA cm-2 over hundreds of hours without corrosion. Together with the experimental findings, the molecular dynamics simulations reveal that PO4 3- and Fe(CN)6 3- generated by the electrode play synergistic role in repelling Cl- via electrostatic repulsion and dense coverage, which reduced Cl- adsorption by nearly 5-fold. The novel anionic synergy endow superior corrosion protection for the electrode, and is expected to promote the practical application of saline water electrolysis.

Recent progress on emergent two-dimensional magnets and heterostructures.

Intrinsic two-dimensional (2D) magnetic materials own strong long-range magnetism while their characteristics of the ultrathin thickness and smooth surface provide an ideal platform for manipulating the magnetic properties at 2D limit. This makes them to be potential candidates in various spintronic applications compared to their corresponding bulk counterparts. The discovery of magnetic ordering in 2D CrI3and Gr2Ge2Te6nanostructures stimulated tremendous research interest in both experimental and theoretical studies on various intrinsic magnets at 2D limit. This review gives a comprehensive overview of the recent progress on the emergent 2D magnets and heterostructures. Firstly, several kinds of typical 2D magnetic materials discovered in the last few years and their fabrication methods are summarized in detail. Secondly, the current strategies for manipulating magnetic properties in 2D materials are further discussed. Then, the recent advances on the construction of representative van der Waals magnetic heterostructures and their respective performance are provided. With the hope of motivating the researchers in this area, we finally offered the challenges and outlook on 2D magnetism.

Two-Dimensional Unipolar Memristors with Logic and Memory Functions.

Two-dimensional materials have been widely used in electronics due to their electrical properties that are not accessible in traditional materials. Here, we present the first demonstration of logic functions of unipolar memristors made of functionalized HfSe2-xOx flakes and memtransistors made of MoS2/graphene/HfSe2-xOx van der Waals heterostructures. The two-terminal memristors exhibit stable unipolar switching behavior with high switching ratio (>106), high operating temperature (106 °C), long-term endurance (>104 s), and multibit data storage and can operate as memory latches and logic gates. Benefiting from these superior memristive properties, the three-terminal heterostructure memtransistors show wide tunability in electrical switching behaviors, which can simultaneously implement logic operation and data storage. Finally, we investigate their application prospect in logical units with memory capability, such as D-type flip-flop. These results demonstrate the potential of two-dimensional materials for resistive switching applications and open up an avenue for future in-memory computing.

Layered metal phosphorous trichalcogenides nanosheets: facile synthesis and photocatalytic hydrogen evolution.

Layered transition metal phosphorous trichalcogenide (MPX3) materials have attracted immense attention due to their excellent optical and electrical properties. However, the controllable synthesis of ultrathin MPX3 nanosheets is still challenging. Here, we present a facile phosphosulfurization scheme to prepare high-quality layered FePS3 nanosheets, with ∼20 nanometers in thickness. The optical properties of the as-obtained FePS3 show good light-harvesting ability, which endows it with excellent photocatalytic hydrogen evolution performance (402.4 µmol g-1 h-1) under the simulated solar illumination. We further show that other MPX3 family members such as In2/3PS3 and CdPS3 can be also synthesized by the same approach. Our finding can offer a feasible approach for rationally designing other MPX3 materials for various applications.

Tuning Intermediates Adsorption and C─N Coupling for Efficient Urea Electrosynthesis Via Doping Ni into Cu.

Simultaneous electrochemical reduction of nitrite and carbon dioxide (CO2 ) under mild reaction conditions offers a new sustainable and low-cost approach for urea synthesis. However, the development of urea electrosynthesis thus far still suffers from low selectivity due to the high energy barrier of * CO formation and the subsequent C─N coupling. In this work, a highly active dendritic Cu99 Ni1 catalyst is developed to enable the highly selective electrosynthesis of urea from co-reduction of nitrite and CO2 , reaching a urea Faradaic efficiency (FE) and production rate of 39.8% and 655.4 µg h-1  cm-2 , respectively, at -0.7 V versus reversible hydrogen electrode (RHE). In situ Fourier-transform infrared spectroscopy (FT-IR) measurements together with density functional theory (DFT) calculations demonstrate that Ni doping into Cu can significantly enhance the adsorption energetics of the key reaction intermediates and facilitate the C─N coupling. This work not only provides a new strategy to design efficient electrocatalysts for urea synthesis but also offers deep insights into the mechanism of C─N coupling during the co-reduction of nitrite and CO2 .

Frontiers in Photoelectrochemical Catalysis: A Focus on Valuable Product Synthesis.

Photoelectrochemical (PEC) catalysis provides the most promising avenue for producing value-added chemicals and consumables from renewable precursors. Over the last decades, PEC catalysis, including reduction of renewable feedstock, oxidation of organics, and activation and functionalization of C─C and C─H bonds, are extensively investigated, opening new opportunities for employing the technology in upgrading readily available resources. However, several challenges still remain unsolved, hindering the commercialization of the process. This review offers an overview of PEC catalysis targeted at the synthesis of high-value chemicals from sustainable precursors. First, the fundamentals of evaluating PEC reactions in the context of value-added product synthesis at both anode and cathode are recalled. Then, the common photoelectrode fabrication methods that have been employed to produce thin-film photoelectrodes are highlighted. Next, the advancements are systematically reviewed and discussed in the PEC conversion of various feedstocks to produce highly valued chemicals. Finally, the challenges and prospects in the field are presented. This review aims at facilitating further development of PEC technology for upgrading several renewable precursors to value-added products and other pharmaceuticals.

Deciphering in-situ surface reconstruction in two-dimensional CdPS3 nanosheets for efficient biomass hydrogenation.

Steering on the intrinsic active site of an electrode material is essential for efficient electrochemical biomass upgrading to valuable chemicals with high selectivity. Herein, we show that an in-situ surface reconstruction of a two-dimensional layered CdPS3 nanosheet electrocatalyst, triggered by electrolyte, facilitates efficient 5-hydroxymethylfurfural (HMF) hydrogenation to 2,5-bis(hydroxymethyl)furan (BHMF) under ambient condition. The in-situ Raman spectroscopy and comprehensive post-mortem catalyst characterizations evidence the construction of a surface-bounded CdS layer on CdPS3 to form CdPS3/CdS heterostructure. This electrocatalyst demonstrates promising catalytic activity, achieving a Faradaic efficiency for BHMF reaching 91.3 ± 2.3 % and a yield of 4.96 ± 0.16 mg/h at - 0.7 V versus reversible hydrogen electrode. Density functional theory calculations reveal that the in-situ generated CdPS3/CdS interface plays a pivotal role in optimizing the adsorption of HMF* and H* intermediate, thus facilitating the HMF hydrogenation process. Furthermore, the reconstructed CdPS3/CdS heterostructure cathode, when coupled with MnCo2O4.5 anode, enables simultaneous BHMF and formate synthesis from HMF and glycerol substrates with high efficiency.

Single atomic Ru in TiO2 boost efficient electrocatalytic water oxidation to hydrogen peroxide.

Electrocatalytic two-electron water oxidation affords a promising approach for distributed production of H2O2 using electricity. However, it suffers from the trade-off between the selectivity and high production rate of H2O2 due to the lack of suitable electrocatalysts. In this study, single atoms of Ru were controllably introduced into titanium dioxide to produce H2O2 through an electrocatalytic two-electron water oxidation reaction. The adsorption energy values of OH intermediates could be tuned by introducing Ru single atoms, offering superior H2O2 production under high current density. Notably, a Faradaic efficiency of 62.8% with an H2O2 production rate of 24.2 µmol min-1 cm-2 (>400 ppm within 10 min) was achieved at a current density of 120 mA cm-2. Consequently, herein, the possibility of high-yield H2O2 production under high current density was demonstrated and the importance of regulating intermediate adsorption during electrocatalysis was evidenced.

Engineering Atomic-Scale Patterning and Resistive Switching in 2D Crystals and Application in Image Processing.

The ultrathin thickness of 2D layered materials affords the control of their properties through defects, surface modification, and electrostatic fields more efficiently compared with bulk architecture. In particular, patterning design, such as moiré superlattice patterns and spatially periodic dielectric structures, are demonstrated to possess the ability to precisely control the local atomic and electronic environment at large scale, thus providing extra degrees of freedom to realize tailored material properties and device functionality. Here, the scalable atomic-scale patterning in superionic cuprous telluride by using the bonding difference at nonequivalent copper sites is reported. Moreover, benefitting from the natural coupling of ordered and disordered sublattices, controllable piezoelectricity-like multilevel switching and bipolar switching with the designed crystal structure and electrical contact is realized, and their application in image enhancement is demonstrated. This work extends the known classes of patternable crystals and atomic switching devices, and ushers in a frontier for image processing with memristors.

Photocatalytic co-production of hydrogen gas and N-benzylidenebenzylamine over high-quality 2D layered In4/3P2Se6 nanosheets.

The concurrent photocatalytic synthesis of hydrogen gas and high-valued chemicals over two-dimensional semiconductors is extremely attractive to alleviate global energy and environmental concerns through directly using sunlight. Herein, a novel layered In4/3P2Se6 nanosheet is synthesized by a space confined chemical vapor conversion method, and it acts as a dual-functional photocatalyst to deliver the co-production of hydrogen gas and N-benzylidenebenzylamine from water reduction and selective benzylamine oxidation. The simultaneous yield of hydrogen gas and N-benzylidenebenzylamine is 895 µmol g-1 and 681 µmol g-1, respectively, within 16-hour continuous reaction involving a small amount of water in acetonitrile solvent. Moreover, 97.4% N-benzylidenebenzylamine selectivity from benzylamine oxidation can be achieved with continuous 10 hour-reaction only in acetonitrile solvent under ambient conditions. Further in situ electron paramagnetic resonance measurements and reaction optimization tests reveal that the reaction mechanism strongly relies on the conditions over the In4/3P2Se6 nanosheet photocatalyst.

Recent Trends in the Pyrolysis of Non-Degradable Waste Plastics.

Waste plastics are non-degradable constituents that can stay in the environment for centuries. Their large land space consumption is unsafe to humans and animals. Concomitantly, the continuous engineering of plastics, which causes depletion of petroleum, poses another problem since they are petroleum-based materials. Therefore, energy recovering trough pyrolysis is an innovative and sustainable solution since it can be practiced without liberating toxic gases into the atmosphere. The most commonly used plastics, such as HDPE, LDPE (high- and low-density polyethylene), PP (polypropylene), PS (polystyrene), and, to some extent, PC (polycarbonate), PVC (polyvinyl chloride), and PET (polyethylene terephthalate), are used for fuel oil recovery through this process. The oils which are generated from the wastes showed caloric values almost comparable with conventional fuels. The main aim of the present review is to highlight and summarize the trends of thermal and catalytic pyrolysis of waste plastic into valuable fuel products through manipulating the operational parameters that influence the quality or quantity of the recovered results. The properties and product distribution of the pyrolytic fuels and the depolymerization reaction mechanisms of each plastic and their byproduct composition are also discussed.

Gate-Coupling-Enabled Robust Hysteresis for Nonvolatile Memory and Programmable Rectifier in Van der Waals Ferroelectric Heterojunctions.

Ferroelectric field-effect transistors (FeFETs) are one of the most interesting ferroelectric devices; however, they, usually suffer from low interface quality. The recently discovered 2D layered ferroelectric materials, combining with the advantages of van der Waals heterostructures (vdWHs), may be promising to fabricate high-quality FeFETs with atomically thin thickness. Here, dual-gated 2D ferroelectric vdWHs are constructed using MoS2 , hexagonal boron nitride (h-BN), and CuInP2 S6 (CIPS), which act as a high-performance nonvolatile memory and programmable rectifier. It is first noted that the insertion of h-BN and dual-gated coupling device configuration can significantly stabilize and effectively polarize ferroelectric CIPS. Through this design, the device shows a record-high performance with a large memory window, large on/off ratio (107 ), ultralow programming state current (10-13 A), and long-time endurance (104 s) as nonvolatile memory. As for programmable rectifier, a wide range of gate-tunable rectification behavior is observed. Moreover, the device exhibits a large rectification ratio (3 × 105 ) with stable retention under the programming state. This demonstrates the promising potential of ferroelectric vdWHs for new multifunctional ferroelectric devices.

Subthermionic field-effect transistors with sub-5 nm gate lengths based on van der Waals ferroelectric heterostructures.

Overcoming the sub-5 nm gate length limit and decreasing the power dissipation are two main objects in the electronics research field. Besides advanced engineering techniques, considering new material systems may be helpful. Here, we demonstrate two-dimensional (2D) subthermionic field-effect transistors (FETs) with sub-5 nm gate lengths based on ferroelectric (FE) van der Waals heterostructures (vdWHs). The FE vdWHs are composed of graphene, MoS2, and CuInP2S6 acting as 2D contacts, channels, and ferroelectric dielectric layers, respectively. We first show that the as-fabricated long-channel device exhibits nearly hysteresis-free subthermionic switching over three orders of magnitude of drain current at room temperature. Further, we fabricate short-channel subthermionic FETs using metallic carbon nanotubes as effective gate terminals. A typical device shows subthermionic switching over five-to-six orders of magnitude of drain current with a minimum subthreshold swing of 6.1 mV/dec at room temperature. Our results indicate that 2D materials system is promising for advanced highly-integrated energy-efficient electronic devices.

Recent Progress in CVD Growth of 2D Transition Metal Dichalcogenides and Related Heterostructures.

In recent years, 2D layered materials have received considerable research interest on account of their substantial material systems and unique physicochemical properties. Among them, 2D layered transition metal dichalcogenides (TMDs), a star family member, have already been explored over the last few years and have exhibited excellent performance in electronics, catalysis, and other related fields. However, to fulfill the requirement for practical application, the batch production of 2D TMDs is essential. Recently, the chemical vapor deposition (CVD) technique was considered as an elegant alternative for successfully growing 2D TMDs and their heterostructures. The latest research advances in the controllable synthesis of 2D TMDs and related heterostructures/superlattices via the CVD approach are illustrated here. The controlled growth behavior, preparation strategies, and breakthroughs on the synthesis of new 2D TMDs and their heterostructures, as well as their unique physical phenomena, are also discussed. Recent progress on the application of CVD-grown 2D materials is revealed with particular attention to electronics/optoelectronic devices and catalysts. Finally, the challenges and future prospects are considered regarding the current development of 2D TMDs and related heterostructures.

A unipolar nonvolatile resistive switching behavior in a layered transition metal oxide.

Two-dimensional layered materials have been considered as promising candidates for resistive random access memory, one of the most promising next-generation nonvolatile memories. However, due to the types of defects, most of the devices still suffer from poor environmental stability, defects inducing complexity, and uncontrollability. Here, we fabricate memory cells based on synthesized high-quality two-dimensional layered transition-metal oxide (α-MoO3) nanosheets which can be thinned to 8.68 nm (∼6 layers) and find a unipolar nonvolatile resistive switching behavior. Driven by the migration of intrinsic oxygen vacancies, the devices show a large memory window (∼105), good memory voltage stability, long-term endurance (for durations of over 3 days and 50 manual DC switching cycles) and multi-bit memory states. Furthermore, we find the devices with an excellent temperature tolerance of lower SET/RESET voltages and a larger memory window (>104 at 380 K) at higher temperatures, suggesting their potential in practical applications. Finally, all 2D memory devices are demonstrated using graphene/α-MoO3/graphene heterostructures.

Synthesis and Optoelectronic Applications of a Stable p-Type 2D Material: α-MnS.

α-MnS, as a nonlayered p-type material with a wide band gap of 2.7 eV, has been expected to supplement the scarcity of two-dimensional (2D) p-type semiconductors, which are desperately required for constructing atomically thin p-n junctions. However, the preparation and property investigation of 2D α-MnS has scarcely been reported so far. Herein, we report the controlled synthesis of ultrathin large-scale α-MnS single crystals down to 4.78 nm via a facile chemical vapor deposition (CVD) method. Importantly, top-gating field-effect transistors based on the as-synthesized α-MnS nanosheets show p-type transport behavior with an ultrahigh on/off ratio exceeding 106, surpassing most reported p-type 2D materials. Meanwhile, α-MnS phototransistors exhibit an ultrahigh detectivity of 3.2 × 1014 Jones, as well as an excellent photoresponsivity of 139 A/W and a fast response time of 12 ms. Besides, outstanding environmental stability and admirable flexibility have also been demonstrated in the as-synthesized α-MnS nanosheets. We believe that this work broadens the scope of the CVD synthesis strategy for various p-type 2D materials and demonstrates their significant application potentials in electronics and optoelectronics.

Anti-Ambipolar Transport with Large Electrical Modulation in 2D Heterostructured Devices.

Van der Waals materials and their heterostructures provide a versatile platform to explore new device architectures and functionalities beyond conventional semiconductors. Of particular interest is anti-ambipolar behavior, which holds potentials for various digital electronic applications. However, most of the previously conducted studies are focused on hetero- or homo- p-n junctions, which suffer from a weak electrical modulation. Here, the anti-ambipolar transport behavior and negative transconductance of MoTe2 transistors are reported using a graphene/h-BN floating-gate structure to dynamically modulate the conduction polarity. Due to the asymmetric electrical field regulating effect on the recombination and diffusion currents, the anti-ambipolar transport and negative transconductance feature can be systematically controlled. Consequently, the device shows an unprecedented peak resistance modulation factor (≈5 × 103 ), and effective photoexcitation modulation with distinct threshold voltage shift and large photo on/off ratio (≈104 ). Utilizing this large modulation effect, the voltage-transfer characteristics of an inverter circuit variant are further studied and its applications in Schmitt triggers and multivalue output are further explored. These properties, in addition to their proven nonvolatile storage, suggest that such 2D heterostructured devices display promising perspectives toward future logic applications.