2D Ultrathin Nanosheets Research Articles

Electro-functionalized 2D nitrogen-carbon nanosheets decorated with symbiotic cobalt single-atoms/clusters

Two-dimensional (2D) materials loaded with single atoms and clusters are being set at the forefront of catalysis due to their distinctive geometric and electronic features. However, the usually-complicated synthesis procedures impede in-depth clarification of their catalytic mechanisms. To this end, herein we developed an efficient one-step dimension-reduction carbonization strategy, with which we successfully architected a highly-efficient catalyst for oxygen reduction reaction (ORR), featured with symbiotic cobalt single atoms and clusters decorated in two-dimensional (2D) ultra-thin (3.5 nm thickness) nitrogen-carbon nanosheets. The synergistic effects of the two components afford excellent oxygen reduction activity in alkaline media (E1/2=0.823 V vs. RHE) and thereof a high power density (146.61 mW cm−2) in an assembled Zn-air battery. As revealed by theoretical calculations, the cobalt clusters can regulate electrons surrounding those individual atoms and affect the adsorption of intermediate species. As a consequence, the derived active sites of single cobalt atoms lead to a significant improvement of the ORR performance. Thus, our work may fuel interests to delicate architecture of single atoms and clusters coexisting 2D support toward optimal electrocatalytic performance.

Microwave absorption parameters over 2–18 GHz frequency range for the MXene composite – Ti3C2Tx @MnCo2O4

The great potential for electromagnetic wave (EMW) absorption is revealed in two-dimensional (2D) Ti3C2Tx (MXene) thin sheets that have numerous surface flaws and an extensive spectrum of functional groups. In this study, Ti3AlC2 (MAX Phase) is etched, and then ultrasonic exfoliation is used to create 2D ultrathin Ti3C2Tx nanosheets; a type of MXene. The MnCo2O4 spherical particles were grown on the layered structure of Ti3C2Tx via a one-pot hydrothermal process. The synthesized Ti3C2Tx/MnCo2O4 composite provides superior bulk-to-surface and interfacial charge transfer capabilities due to their short charge transfer distance and extensive interface contact area to the EMW. This article thoroughly evaluates the loss impact in Ti3C2Tx/MnCo2O4 absorbers as -44.4dB of reflection loss at 16.04GHz with a thickness of 5.114mm for the first time, which is essential for fabricating an effective microwave absorber.

Nonradical peroxymonosulfate activation via high-level pyrrolic-nitrogen and electron-deficient carbon at 2D ultrathin carbonaceous nanosheets for efficient BPA removal

Activation of persulfate by N-doped carbon is an emerging advanced oxidation process (AOP) for removing organic pollutants from water via singlet oxygen (1O2)-dominated non-radical way, however, the efficient generation of 1O2 is a hot topic worth deep exploration. In this study, glucose was used as an additional carbon and oxygen of prefabricated supramolecular melamine-cyanuric acid precursor, the final co-thermal polymerization products completely changed from conventional graphitic carbon nitride to ultrathin carbonaceous materials when the mass of glucose up to 0.72 g. The simple one-pot strategy can easily generate active electron-deficient carbon sites due to nitrogen and oxygen doping by modulating the electronic structure of the carbon framework, which is critical for the activation of peroxymonosulfate (PMS) to produce 1O2. The glucose content can adjust the degree of disorder of the amorphous carbonaceous nanosheet, and significantly improve the exposure of active pyrrolic nitrogen sites (27.47 %) and doped oxygen through the defective structure, which is another essential factor for the generation of 1O2 in the activation of PMS. The MCAG-0.72/ PMS exhibited excellent performance in BPA degradation, 95 % BPA (20 mg L−1) can be removed in 60 min with 1.0 mM PMS with reaction constant k=0.0209 min−1. Furthermore, MCAG-0.72 also demonstrated excellent BPA degradation in different actual water metrics and performance well in the four consecutive cycles. This study provides a novel convenient strategy to synthesize cost-effective N/O co-doped carbonaceous material for efficient activating PMS to remove refractory organics in water and wastewater, it sheds light on practical large-scale industrial applications in PMS-based AOPs.

Highly Efficient, Flexible, and Self-Healable Moisture-Driven Energy Harvester Based on 2D Vanadium Pentoxide Nanosheets

The ubiquitous source of atmospheric moisture brought about a fascinating research avenue of extracting atmospheric water to generate sustainable electricity. Energy may be extracted from ambient moisture with obvious and substantial advantages. This point-of-use technology provides a decentralized alternative to meet the energy needs in isolated off-grid places. Unlike traditional energy generators which predominantly rely upon fossil fuel, moisture-induced energy generators can extract energy from moisture in a sustainable and eco-friendly way. Herein, we demonstrated a self-healable moist electric generator (MEG) based on vanadium pentoxide (V2O5) 2D nanosheet membranes. Lamellar membranes of V2O5 nanosheets have been shown to be excellent cation conductors and excellent materials for harvesting energy from ambient moisture. Ultra-thin 2D nanosheets of V2O5 was obtained by treatment of bulk V2O5 crystals with hydrogen peroxide. V2O5 nanosheet membrane was fabricated by vacuum-assisted filtration of 2D V2O5 nanosheets dispersion over a PTFE support membrane. The V2O5 membrane was easily peeled off from the support membrane on drying to obtain a flexible and freestanding V2O5 membrane. The V2O5 membrane consisting of percolated nanofluidic channels was sandwiched between a bottom solid copper foil and a perforated copper foil as the bottom electrode. The top electrode is perforated for exposure to atmospheric humidity. As the atmospheric water molecules come in contact with the V2O5 surface, an open-circuit voltage of 0.5 Volts and a short-circuit current of 0.3 microamperes is generated. The generated voltage and current is attributed to the preferential flow of cations through the V2O5 nanochannels. The exposed surface and edges of V2O5 nanosheets have a high negative surface charge which results in the splitting of water molecules into H3O+ and OH- ions. An electrical double layer (EDL) is established at the V2O5/water interface which selectively permits H3O+ ions through the channels. The mobile ions of the EDL transport through the nanofluidic channels creating a gradient between the two electrodes, resulting in a constant potential difference between the top and bottom electrodes which is harvested as electric current. The MEGs can be easily connected in parallel or series to enhance the current and voltage respectively. We demonstrate ten MEGs connected in series to power small electronic devices such as calculators and humidity meters. One of the key features of the V2O5 MEG is its ability to repair any physical damage to the active material owing to the water-assisted healing characteristics V2O5 membrane. Figure 1

Self-standing 3D rose-like bimetallic oxides modified nitrogen-doped graphite aerogels as a robust catalyst for efficient oxygen evolution

FeNi bimetallic oxides are considered as a potential catalyst candidate material for efficient oxygen evolution. However, low conductivity, rapid structural collapse, and metal ion release always lead to electrochemical performance and poor stability, which become major challenges in the electrochemical process. Herein, we synthesized self-standing 3D rose-like bimetallic oxides modified nitrogen-doped graphite aerogels (FeNiOx@N/GA) by the facile layer-by-layer self-assembled method. The unique 2D/3D structure composed of 2D ultrathin graphene nanosheets decorated 3D microflowers can provide a large active area and a rapid charge transfer rate. Moreover, both oxidation and nitrogen doping can improve the reaction kinetics of the material, thereby exhibiting higher catalytic activity. FeNiOX@N/GA exhibits excellent oxygen evolution reaction (OER) performance (η10=291 mV) and low Tafel slope (39 mV dec−1) in the 1 M KOH. This work can be expected to provide a novel and valid method for rational design and manufacture of advanced bimetallic oxides-based positive electrode toward efficient OER. Meanwhile, FeNiOx@N/GA is loaded on nickel foam and displays good electrochemical properties as an air-cathode in Zn-Air battery, demonstrating outstanding practicability.

A two-dimensional Aurivillius oxide for enhanced solar energy driven hydrogen evolution and waste water treatment

Bi2WO6 has attracted extensive attention in photocatalysts in recent years as a typical Aurivillius oxide. However, it suffers from severe electron-hole recombination due to the large charge transfer distance from bulk to surface. Unfortunately, strong chemical bonds between the neighboring layers in Aurivillius oxides lead to difficulties in the construction of 2D materials. Here, a facile NaBH4-assisted hydrothermal method is developed to construct 2D Bi2WO6 nanosheets with adjustable thickness from 4.03 to 1.51 nm and O vacancies density (named as BWO-x, x = 15, 30, 45, 60). By balancing the thickness and the O vacancy density in the nanosheets, the charge separation efficiency can be tuned and consequently, the photocatalytic activity can be optimized, leading to over 11 times enhancement in photocatalytic hydrogen evolution. Furthermore, the best performed nanosheets demonstrate universality in dye polluted water treatment. Nearly 100% degradation can be reached after only 5, 50, and 30 min with degradation rate constant of 29.73, 3.21, and 6.62 min−1g−1 for Rhodamine B, methyl orange, and methylene blue, respectively. This work provides a comprehensive approach to produce ultrathin 2D nanosheets of Aurivillius photocatalysts for enhanced charge separation and photocatalytic activity.

Ultrafast and Parts-per-Billion-Level MEMS Gas Sensors by Hetero-Interface Engineering of 2D/2D Cu-TCPP@ZnIn2S4 with Enriched Surface Sulfur Vacancies.

The primary challenge for resonant-gravimetric gas sensors is the synchronous improvement of the sensitivity and response time, which is restricted by low adsorption capacity and slow mass transfer in the sensing process and remains a great challenge. In this study, a novel 2D/2D Cu-TCPP@ZnIn2S4 composite is successfully constructed, in which Cu-TCPP MOF is used as a core substrate for the growth of 2D ultrathin ZnIn2S4 nanosheets with well-defined {0001} crystalline facets. The Cu-TCPP@ZnIn2S4 sensor exhibited high sensitivity (1.5 Hz@50 and 2.3 Hz@100 ppb), limit of detection (LOD: 50 ppb), and ultrafast (9 s @500 ppb) detection of triethylamine (TEA), which is the lowest LOD and the fastest sensor among the reported TEA sensors at room temperature, tackling the bottleneck for the ultrafast detection of the resonant-gravimetric sensor. These above results provide an innovative and easily achievable pathway for the synthesis of heterogeneous structure sensing materials.

Electrocatalytic and Selective Oxidation of Glycerol to Formate on 2D 3d-Metal Phosphate Nanosheets and Carbon-Negative Hydrogen Generation.

In the landscape of green hydrogen production, alkaline water electrolysis is a well-established, yet not-so-cost-effective, technique due to the high overpotential requirement for the oxygen evolution reaction (OER). A low-voltage approach is proposed to overcome not only the OER challenge by favorably oxidizing abundant feedstock molecules with an earth-abundant catalyst but also to reduce the energy input required for hydrogen production. This alternative process not only generates carbon-negative green H2 but also yields concurrent value-added products (VAPs), thereby maximizing economic advantages and transforming waste into valuable resources. The essence of this study lies in a novel electrocatalyst material. In the present study, unique and two-dimensional (2D) ultrathin nanosheet phosphates featuring first-row transition metals are synthesized by a one-step solvothermal method, and evaluated for the electrocatalytic glycerol oxidation reaction (GLYOR) in an alkaline medium and simultaneous H2 production. Co3(PO4)2 (CoP), Cu3(PO4)2 (CuP), and Ni3(PO4)2 (NiP) exhibit 2D sheet morphologies, while FePO4 (FeP) displays an entirely different snowflake-like morphology. The 2D nanosheet morphology provides a large surface area and a high density of active sites. As a GLYOR catalyst, CoP ultrathin (∼5 nm) nanosheets exhibit remarkably low onset potential at 1.12 V (vs RHE), outperforming that of NiP, FeP, and CuP around 1.25 V (vs RHE). CoP displays 82% selective formate production, indicating a superior capacity for C-C cleavage and concurrent oxidation; this property could be utilized to valorize larger molecules. CoP also exhibits highly sustainable electrochemical stability for a continuous 200 h GLYOR operation, yielding 6.5 L of H2 production with a 4 cm2 electrode and 98 ± 0.5% Faradaic efficiency. The present study advances our understanding of efficient GLYOR catalysts and underscores the potential of sustainable and economically viable green hydrogen production methodologies.

Tunable 2D Conjugated Porous Organic Polymer Films for Precise Molecular Nanofiltration and Optoelectronics.

Structural design of 2D conjugated porous organic polymer films (2D CPOPs), by tuning linkage chemistries and pore sizes, provides great adaptability for various applications, including membrane separation. Here, four free-standing 2D CPOP films of imine- or hydrazone-linked polymers (ILP/HLP) in combination with benzene (B-ILP/HLP) and triphenylbenzene (TPB-ILP/HLP) aromatic cores are synthesized. The anisotropic disordered films, composed of polymeric layered structures, can be exfoliated into ultrathin 2D-nanosheets with layer-dependent electrical properties. The bulk CPOP films exhibit structure-dependent optical properties, triboelectric nanogenerator output, and robust mechanical properties, rivaling previously reported 2D polymers and porous materials. The exfoliation energies of the 2D CPOPs and their mechanical behavior at the molecular level are investigated using density function theory (DFT) and molecular dynamics (MD) simulations, respectively. Exploiting the structural tunability, the comparative organic solvent nanofiltration (OSN) performance of six membranes having different pore sizes and linkages to yield valuable trends in molecular weight selectivity is investigated. Interestingly, the OSN performances follow the predicted transport modeling values based on theoretical pore size calculations, signifying the existence of permanent porosity in these materials. The membranes exhibit excellent stability in organic solvents at high pressures devoid of any structural deformations, revealing their potential in practical OSN applications.

Solution-processed 2D van der Waals networks: Fabrication strategies, properties, and scalable device applications

Solution-based processing of two-dimensional (2D) materials has garnered significant interest as a facile and versatile route for the large-scalable production of 2D material films. Despite the benefits in process, these films were not considered suitable for device applications during the early stages of research because their electronic properties were far from those of 2D materials obtained through micromechanical exfoliation or chemical vapor deposition. Due to the small lateral dimensions and polydisperse thickness of constituent 2D nanosheets, the resulting film tends to be porous and exhibits numerous inter-sheet junctions, primarily contacting edge-to-edge. This nanosheet morphology leads to poor electrical conductivity of the network, and also hinders the film functioning as a semiconductor or an insulator. To produce ultrathin 2D nanosheets with narrow thickness distribution and large lateral sizes, various chemical exfoliation strategies have been explored, but these are limited by long process times, involvement of harsh chemicals, and/or undesired structural damage or phase changes. Recent breakthroughs in electrochemical exfoliation using tetraalkylammonium intercalants enabled the production of high-quality 2D nanosheets with structural characteristics favorable for producing ultrathin, conformal films of 2D materials, which allow for scalable production of high-performance electronic components that can readily be assembled into functional devices via solution-processing. In this review article, we aim to offer an extensive introduction solution-based processing techniques for acquiring 2D nanosheets, their subsequent assembly into thin films, and their diverse applications, primarily focusing on electronics and optoelectronics but also extending to other fields. Remaining challenges and potential avenues for advancement will also be discussed.

Facile construction of MoS2 decorated CdS hybrid heterojunction with enhanced hydrogen generation performance

Promoting the charge separation to improve photocatalytic performance of semiconductor photocatalysts is very important in the field of artificial photosynthesis. Here, a novel MoS2/CdS 2D–2D ultrathin nanosheet heterostructure was fabricated via a one-pot solvothermal route. The obtained 2D–2D MoS2/CdS nanojunction has not only provided large contact areas, but also shortened the charge transport distance, resulting in significantly enhanced photocatalytic H2 evolution property. The composites that were synthesized were examined using X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), Transmission electron microscope (TEM), UV-vis diffuse reflectance spectra (DRS), Photoluminescence (PL) and X-ray photoelectron spectra (XPS) analysis. By optimizing the 2D MoS2 amounts in the heterojunction, the 5 wt.% 2D/2D MoS2/CdS heterojunction displayed the maximal photocatalytic H2 evolution rate of 4449 μmolh−1g−1 under visible light irradiation in the presence of lactic acid as the sacrificial reagent, which was 6 times higher than that of pristine 2D CdS. Based on the photoelectrochemical and photoluminescence spectra tests, it could be deduced that the charge separation and transfer of 2D/2D MoS2/CdS heterojunction was tremendously improved, and the recombination of photoinduced electron-hole pairs was effectively impeded. Moreover, the 2D MoS2 was used as a cocatalyst to provide the abundant active sites and lower the overpotential for H2 generation reaction. The current work would offer an insight to fabricate the 2D/2D heterojunction photocatalysts for splitting H2O into H2.

Tailoring Bi2Se3 Topological Insulator for Visible-NIR Photodetectors with Schottky Contacts Using Liquid Phase Exfoliation.

Layered semiconductors of the V-VI group have attracted considerable attention in optoelectronic applications owing to their atomically thin structures. They offer thickness-dependent optical and electronic properties, promising ultrafast response time, and high sensitivity. Compared to the bulk, 2D bismuth selenide (Bi2Se3) is recently considered a highly promising material. In this study, 2D nanosheets are synthesized by prolonged sonication in two different solvents, such as N-methyl-2-pyrrolidone (NMP) and chitosan-acetic acid solution (CS-HAc), using the liquid-phase exfoliation (LPE) method. X-ray diffraction confirms the amorphous nature of exfoliated 2D nanosheets with maximum peak intensity at the same position (015) crystal plane as that obtained in its bulk counterpart. SEM confirms the thin 2D nanosheet-like morphology. Successful exfoliation of Bi2Se3 nanosheets up to five layers is achieved using CS-HAc solvent. The as-synthesized 2D nanosheets in different solvents are employed to fabricate the photodetector. At minimum selected power density, the photodetector fabricated using exfoliated ultrathin 2D nanosheets exhibits the highest range of responsivity, varying from 15 to 2.5 mA/W, and detectivity ranging from 2.83 × 109 to 6.37 × 107. Ultrathin 2D Bi2Se3 nanosheets have fast rise and fall times, ranging from 0.01 to 0.12 and 0.01 to 0.06 s, respectively, at different wavelengths. Ultrathin Bi2Se3 nanosheets have improved photodetection parameters as compared to multilayered nanosheets due to the high surface to volume ratio, reduced recombination and trapping of charge carrier, improved carrier confinement, and faster carrier transport due to the thin layer.

Exfoliation of a Coordination Polymer Based on a Linear π-Conjugated Ligand into an Ultrathin Nanosheet for Glyphosate Sensing.

Owing to the large-scale consumption of pesticides and their potential threats to the environment and human health, the development of sensing materials for pesticides has attracted considerable attention in recent years. In this work, a novel Cd(II)-based coordination polymer (CP) with the formula [Cd(H2O)2(L)]·DMF (Cd-1, DMF = N,N-dimethylformamide, H2L = 4,4'-[(2,5-dimethoxy-1,4-phenylene)di-2,1-ethenediyl]bis-benzoic acid) was synthesized under solvothermal conditions. Structural analysis revealed that coordination between central Cd2+ cations and the ligand L2- formed two-dimensional (2D) networks, which were further assembled by noncovalent hydrogen bonds into a three-dimensional (3D) supramolecular framework. Through ultrasonic treatment in isopropyl alcohol, Cd-1 was exfoliated to afford an ultrathin CP-based 2D nanosheet (Cd-1-NS) with a thickness of less than 1.8 nm. Compared to the bulk materials, the prepared Cd-1-NS exhibited enhanced fluorescence emission properties and superior sensing performance toward glyphosate (Glyph) in water with high selectivity, sensitivity, anti-interference, fast response, and good recyclability via the turn-off effect. The limit of detection (LOD) of Cd-1-NS for Glyph was as low as 41 nM (7 ppb) in the low-concentration range of 0-2.4 μM. In addition, the Cd-1-NS also showed excellent practicability and reliability for the detection of Glyph in real samples, including lake water, tap water, cabbage, and watermelon skin, and could realize the rapid visualized sensing of Glyph residues on the surfaces of vegetables and fruits.

Ultrathin 2D As2Se3 Nanosheets for Photothermal-Triggered Cancer Immunotherapy.

Arsenic trioxide (As2O3) has achieved groundbreaking success in the treatment of acute promyelocytic leukemia (APL). However, its toxic side effects seriously limit its therapeutic application in the treatment of solid tumors. To detoxify the severe side effects of arsenic, herein we synthesized innovative 2D ultrathin As2Se3 nanosheets (As2Se3 NSs) with synergistic photothermal-triggered immunotherapy effects. As2Se3 NSs are biocompatible and biodegradable under physiological conditions and can release As(III) and Se(0). Furthermore, selenium increases the immunomodulatory efficacy of arsenic treatments, facilitating reprogramming of the tumor microenvironment by As2Se3 NSs by enhancing the infiltration of natural killer cells and effector tumor-specific CD8+ T cells. The synergistic combination of photothermal therapy and immunotherapy driven by As2Se3 NSs via a simple but effective all-in-one strategy achieved efficient anticancer effects, addressing the key limitations of As2O3 for solid tumor treatment. This work demonstrates not only the great potential of selenium for detoxifying arsenic but also the application of 2D As2Se3 nanosheets for cancer therapy.

Mild chemistry synthesis of ultrathin Bi2O2S nanosheets exhibiting 2D-ferroelectricity at room temperature.

Modern technology demands miniaturization of electronic components to build small, light, and portable devices. Hence, discovery and synthesis of new non-toxic, low cost, ultra-thin ferroelectric materials having potential applications in various electronic and optoelectronic devices are of paramount importance. However, achieving room-temperature ferroelectricity in two dimensional (2D) ultra-thin systems remains a major challenge as conventional three-dimensional ferroelectric materials lose their ferroelectricity when the thickness is brought down below a critical value owing to the depolarization field. Herein, we report room-temperature ferroelectricity in ultra-thin single-crystalline 2D nanosheets of Bi2O2S synthesized by a simple, rapid, and scalable solution-based soft chemistry method. The ferroelectric ground state of Bi2O2S nanosheets is confirmed by temperature-dependent dielectric measurements as well as piezoelectric force microscopy and spectroscopy. High resolution transmission electron microscopy analysis and density functional theory-based calculations suggest that the ferroelectricity in Bi2O2S nanosheets arises due to the local distortion of Bi2O2 layers, which destroys the local inversion symmetry of Bi2O2S.

In situ conversion of Co–CoN nanowires into ultrathin 2D nanosheets for highly effective catalytic hydrogenation

Ultrathin 2D Co–CoN heterojunction nanosheets were prepared by a novel route based on in situ conversion of Co–CoN nanowires. The nanosheets exhibit excellent catalytic activity and stability towards aromatic nitro compounds.

Creation of robust oxygen vacancies in 2D ultrathin BiOBr nanosheets by irradiation through photocatalytic memory effect for enhanced CO2 reduction

An interesting photocatalytic memory effect was found in 2D ultrathin BiOBr nanosheets, which endowed them the capability to trap photogenerated electrons on Bi3+ and Br- in this material system for an extended period of time and resulted in the creation of stable oxygen vacancies (Ov) by just visible light irradiation due to the charge balance requirement. Thus, a broader visible light absorption, more negative conduction band minimum, stronger piezoelectric response, better charge carrier separation and transfer, and enhanced CO2 adsorption and activation were occurred in these BiOBr nanosheets with prior visible light irradiation, all of which were beneficial for their enhanced CO2 reduction performances in photocatalysis, piezocatalysis, and photopiezocatalysis, respectively, than their counterparts without it. This work demonstrated a novel approach to create oxygen vacancies by light irradiation through the photocatalytic memory effect, which could be readily applied to similar photocatalyst systems to boost their performances and generate novel functionalities.

Surfactant-assisted Fe-anchored and N-doped ultrathin graphene nanosheets for enhanced electrocatalytic oxygen reduction

Exploration of tremendous electrocatalysts for oxygen reduction reaction (ORR) as promising alternatives is urgent in various electrochemical applications. As a result, one catalyst of homogeneously dispersed Fe, N sites anchored on two-dimensional (2D) ultrathin graphene nanosheets (Fe-N@C) is rationally designed and synthesized via a surfactant-assisted pyrolysis approach. Water-soluble F127 surfactant facilitates the uniform dispersion of Fe and restrains the aggregation of Fe-based particles during pyrolysis treatment, which promotes the formation of plentiful FeNx species. The 2D ultrathin structure is beneficial to expose more FeNx and make the most use of these active sites. Therefore, the developed Fe-N@C catalyst demonstrates enhanced catalytic properties in alkaline media with an approximate 4e− pathway and more positive half-wave potential (E1/2, 0.85 V), which is plus 0.04 V than commercial 20 % Pt/C catalyst. Besides, the target catalyst also exhibits superb poison resistance and long-term stability. This work presents a practical direction for the fabrication of other high-efficient catalysts and a new insight into ORR.

Ultrathin and porous CoP nanosheets as an efficient electrocatalyst for boosting hydrogen evolution behavior at a broad range of pH

Designing highly-efficient, stable and low-cost catalysts for electrocatalytic hydrogen evolution reaction (HER) plays an important role in renewable energy conversion technology. The particularly ultrathin and porous 2D architecture can provide plentiful activation sites, short delivery channels to improve reaction kinetic and promote HER procedure. High-performance transition metal phosphide (CoP) combined with unique and holey 2D ultrathin nanosheet structure is prepared by successively hydrothermal reaction, oxidation and phosphorization techniques, which presents remarkable stability and electrocatalytic HER properties in a wide pH range. The thickness and pore dimension of ultrathin and porous CoP nanosheets are ∼15 and 3–17 nm. The optimized CoP nanosheets only require 60, 128, 90 mV overpotentials to drive the current density of 10 mA cm−2 in acidic, neutral and alkaline environment, respectively, much better than those of oxide counterpart and the previously reported transition metal-based electrocatalysts. Moreover, the small Tafel slopes of porous CoP nanosheets are 54, 69.9 and 62.9 mV dec−1 in acidic, neutral and alkaline media. CoP nanosheets also exhibit high conductivity, large Cdl, and long-term stability for 20 h in pH-universal electrolyte.

Nanosheet-assembled transition metal sulfides nanoflowers derived from CoMo-MOF for efficient oxygen evolution reaction

Oxygen evolution reaction (OER) is a multi-electron transfer process, whose intrinsic sluggish dynamic restricts the whole process of overall water splitting (OWS). To address this issue, a porous transition metal sulfide (TMS) catalyst with rich heterojunctions was prepared by vulcanization and trace Fe doping of CoMo-based metal–organic framework (MOF). In this work, the nanoflower composed of ultrathin 2D nanosheets anchored on a nickel foam presents a layered interface that contributes to the exposure of active regions. The resulting electrode denoted as Fe@CoMo2S4/Ni3S2/NF required a low overpotential (η10 = 167 mV @ 10 mA cm−2, η50 = 260 mV @ 50 mA cm−2) in 1.0 M KOH for OER and a small cell voltage (E = 1.513 V @ 10 mA cm−2) to power OWS when coupled with commercial Pt/C. It also exhibited splendid morphological and chemical stability with virtually invariant polarization curve and flower-like appearance after 1000 CV cycles, as well as long-term durability over 100 h with a constant current density of 10 mA cm−2. This work revealed the multi-anionic regulation mechanism in the surface reconstruction of sulfide electrocatalysts, and verified that Co/Mo/Ni-based oxysulfide was the true active substance of OER, which inspired the understanding and design of multi-anionic regulated electrocatalysts.