Synthesis of Magnesium Phosphorous Trichalcogenides and Applications in Photoelectrochemical Water Splitting.

Promising applications of metal phosphorous trichalcogenides (M2 P2 X6 or MPX3 ) have been predicted in optoelectronics, photoelectrocatalysis, and water-splitting reactions, mainly due to its wide bandgap. Transition metals are widely used in the synthesis of MPX3 , however, divalent cations of alkaline earth metals can also be constituents in MPX3 2D layered structures. Herein, MgPX3 (X = S, Se) are synthesized and their photoelectrochemical (PEC) activity is tested in the hydrogen evolution and oxygen evolution reaction (OER) regions under a wide range of wavelengths. MgPSe3 photoelectrode shows the best PEC performance with a response of 1.6 ± 0.1 mA cm-2 under 420 nm. In the light-assisted OER, a 200 mV improvement is obtained in the overpotential at 10 mA cm-2 for MgPSe3 . The better performance of MgPSe3 is consistent with its lower optical bandgap (Eg  = 3.15 eV), as a result of the variation of electronegativity between selenide and sulfide.

A Decade of Germananes: Four Approaches to Their Functionalization.

Since the first synthesis of germanane (GeH) reported in 2013, two-dimensional germanium-based materials have been intensively studied. Over the past decade, several methodologies for the functionalization of germanane have been introduced. The first approach utilized exfoliation of Zintl phase CaGe2 with alkyl halides. Liu's solvothermal method was used for the synthesis of methyl germanane. Another methodology utilized Ge-H activation with sodium naphthalenide and its subsequent alkylation. All of these methods provide functionalized germananes; thus, a comparison of these methods is needed. In this paper, such a comparison of current synthetic approaches towards alkyl germananes is reported, and additionally, a new method for Ge-H activation utilizing a NaK equimolar alloy is presented as a fourth approach. For this purpose, eight alkyl reagents were chosen representing reactive benzyl bromides as well as linear esters and nitriles because they contain easily trackable functional groups. The materials were characterized using Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis, and the data were compared. The comparison of all methods revealed not only some drawbacks for each method but also their advantages. The method utilizing sodium naphthalenide provided the lowest degree of surface coverage, whereas the solvothermal method seemed to provide materials with the highest degree of functionalization; unfortunately, the functionalization was also accompanied by a high degree of surface oxidation, i.e., (Ge-OH/Ge═O) formation. The highest degree of surface coverage accompanied by the lowest degree of surface oxidation was achieved employing Goldberger's phase transfer direct exfoliation of CaGe2 as well as Ge-H activation using the NaK alloy with subsequent alkylation.

Simple Bottom-Up Synthesis of Bismuthene Nanostructures with a Suitable Morphology for Competitive Performance in the Electrocatalytic Nitrogen Reduction Reaction.

Nitrogen reduction to ammonia under ambient conditions has received important attention, in which high-performing catalysts are sought. A new, facile, and seedless solvothermal method based on a high-temperature reduction route has been developed in this work for the production of bismuthene nanostructures with excellent performance in the electrocatalytic nitrogen reduction reaction (NRR). Different reaction conditions were tested, such as the type of solvent, surfactant, reducing agent, reaction temperature, and time, as well as bismuth precursor source, resulting in distinct particle morphologies. Two-dimensional sheet-like structures and small particles displayed very high electrocatalytic activity, attributed to the abundance of tips, edges, and high surface area. NRR experiments resulted in an ammonia yield of 571 ± 0.1 µg h-1 cm-2 with a respective Faradaic efficiency of 7.94 ± 0.2% vs Ag/AgCl. The easy implementation of the synthetic reaction to produce Bi nanostructures facilitates its potential scale up to larger production yields.

High-Entropy NASICON Phosphates (Na3M2(PO4)3 and NaMPO4Ox, M = Ti, V, Mn, Cr, and Zr) for Sodium Electrochemistry.

High-entropy materials, with complex compositions and unique cocktail characteristics, have recently drawn significant attention. Additionally, a family of sodium super ion conductors (NASICONs)-structured phosphates in energy storage areas shows a comprehensive application for traditional alkaline ion batteries and, in particular, solid-state electrolytes. However, there is no precedent in fabricating this kind of NASICON-type high-entropy phase. Here, we report the successful fabrication of two well-crystallized high-entropy phosphates, namely, Na3(Ti0.2V0.2Mn0.2Cr0.2Zr0.2)2(PO4)3 (HE-N3M2P3) and Na(Ti0.2V0.2Mn0.2Cr0.2Zr0.2)2PO4Ox (HE-NMP). The prepared materials in which the transition metals (TMs) of Ti, V, Mn, Cr, and Zr occupy the same 12c Wykoff position can form a structure analogous to R3̅c Na3V2(PO4)3 that is carefully determined by X-ray diffraction, neutron diffraction, and transmission electron microscopy. Further, their performance for sodium ion batteries and sodium-based solid-state electrolytes was evaluated. The HE-N3M2P3 might exhibit a promising electrochemical performance for sodium storage in terms of its structure resembling that of Na3V2(PO4)3. Meanwhile, the HE-NMP shows considerable electrochemical activity with numerous broad redox ranges during extraction and insertion of Na+, related to the coexistence of several TM elements. The evaluated temperature-dependent ionic conductivity for HE-NMP solid electrolyte varies from 10-6 to 10-5 S cm-1 from room temperature to 398.15 K, offering high potential for energy storage applications as a new high-entropy system.

The Role of Alkali Cation Intercalates on the Electrochemical Characteristics of Nb2 CTX MXene for Energy Storage.

The intercalation of cations into layered-structure electrode materials has long been studied in depth for energy storage applications. In particular, Li+ -, Na+ -, and K+ -based cation transport in energy storage devices such as batteries and electrochemical capacitors is closely related to the capacitance behavior. We have exploited different sizes of cations from aqueous salt electrolytes intercalating into a layered Nb2 CTx electrode in a supercapacitor for the first time. As a result, we have demonstrated that capacitive performance was dependent on cation intercalation behavior. The interlayer spacing expansion of the electrode material can be observed in Li2 SO4 , Na2 SO4 , and K2 SO4 electrolytes with d-spacing. Additionally, our results showed that the Nb2 CTx electrode exhibited higher electrochemical performance in the presence of Li2 SO4 than in that of Na2 SO4 and K2 SO4 . This is partly because the smaller-sized Li+ transports quickly and intercalates between the layers of Nb2 CTx easily. Poor ion transport in the Na2 SO4 electrolyte limited the electrode capacitance and presented the lowest electrochemical performance, although the cation radius follows Li+ >Na+ >K+ . Our experimental studies provide direct evidence for the intercalation mechanism of Li+ , Na+ , and K+ on the 2D layered Nb2 CTx electrode, which provides a new path for exploring the relationship between intercalated cations and other MXene electrodes.

A Metal-Doped Fungi-Based Biomaterial for Advanced Electrocatalysis.

Nature and its highly sophisticated biomaterials are an endless source of inspiration for engineers and scientists across a wide range of disciplines. During the last decade, concepts of bioinspired synthesis of hierarchically structured nano- and micromaterials have been attracting increasing attention. In this article, we have utilized the natural ability of fungi to absorb metal ions for a bioinspired synthesis of carbonaceous material doped by selected transition metals. As an all-around metal accumulator, Hebeloma mesophaeum was selected, and it was cultivated in the presence of three transition-metal ions: NiII , FeII , and MnII . The metal-doped carbonized biomaterial possessed enhanced catalytic activity toward hydrazine oxidation, oxygen reduction, and cumene hydroperoxide reduction. Thus, we have shown possible transformation of a waste product (fungi grown on a contaminated soil) into a value-added carbonaceous material with tailored catalytic properties. This bioinspired synthesis can outline an attractive route for the fabrication of catalysts for important industrial applications on a large scale.

One-Step Synthesis of B/N Co-doped Graphene as Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction: Synergistic Effect of Impurities.

In the last decade, numerous studies of graphene doping by various metal and nonmetal elements have been done in order to obtain tailored properties, such as non-zero band gap, electrocatalytic activity, or controlled optical properties. From nonmetal elements, boron and nitrogen were the most studied dopants. Recently, it has been shown that in some cases the enhanced electrocatalytic activity of graphene and its derivatives can be attributed to metal impurities rather than to nonmetal elements. In this paper, we investigated the electrocatalytical properties of B/N co-doped graphene with respect to the content of metallic impurities introduced by the synthesis procedures. For this purpose, a permanganate (Hummers) and a chlorate (Hofmann) route were used for the preparation of the starting graphene oxides (GO). The GO used for the synthesis of B/N co-doped graphene had significantly difference compositions of oxygen functionalities as well as metallic impurities introduced by the different synthetic procedures. We performed a detailed structural and chemical analysis of the doped graphene samples to correlate their electrocatalytic activity with the concentration of incorporated boron and nitrogen as well as metallic impurities.

Fluorographene and Graphane as an Excellent Platform for Enzyme Biocatalysis.

The application of enzymes is a crucial issue for current biotechnological application in pharmaceutical, as well as food and cosmetic industry. Effective platforms for enzyme immobilization are necessary for their industrial use in various biosynthesis procedures. Such platforms must provide high yield of immobilization and retain high activity at various conditions for their large-scale applications. Graphene derivatives such as hydrogenated graphene (graphane) and fluorographene can be applied for enzyme immobilization with close to 100 % yield that can result to activities of the composites significantly exceeding activity of free enzymes. The hydrophobic properties of graphene stoichiometric derivatives allowed for excellent non-covalent bonding of enzymes and their use in various organic solvents. The immobilized enzymes retain their high activities even at elevated temperatures. These findings show excellent application potential of enzyme biocatalysts immobilized on graphene stoichiometric derivatives.

Hydrogenation of Fluorographite and Fluorographene: An Easy Way to Produce Highly Hydrogenated Graphene.

Fluorographene is an excellent precursor for the synthesis of graphene derivatives. Relative to pure graphene, fluorographene possesses higher reactivity and, in comparison with graphene oxide, is also homogenous in composition, which enables the preparation of well-defined materials. Recently, it has been shown that several graphene derivatives can be synthesized from fluorographene, thus yielding various products such as graphene acid or alkylated graphene. This study focuses on the hydrogenation of fluorographene by using various hydrogenation reactions, including the use complex hydrides and solvated electrons in different media. In addition, a comparison of these reactions shows that fluorinated graphite has significantly lower reactivity than fluorographene. The conversion rates of these reactions are higher when fluorographene is used relative to fluorographite. These reactions can be used to tune the hydrogen/fluorine composition on a graphene backbone.

Doping with Graphitic Nitrogen Triggers Ferromagnetism in Graphene.

Nitrogen doping opens possibilities for tailoring the electronic properties and band gap of graphene toward its applications, e.g., in spintronics and optoelectronics. One major obstacle is development of magnetically active N-doped graphene with spin-polarized conductive behavior. However, the effect of nitrogen on the magnetic properties of graphene has so far only been addressed theoretically, and triggering of magnetism through N-doping has not yet been proved experimentally, except for systems containing a high amount of oxygen and thus decreased conductivity. Here, we report the first example of ferromagnetic graphene achieved by controlled doping with graphitic, pyridinic, and chemisorbed nitrogen. The magnetic properties were found to depend strongly on both the nitrogen concentration and type of structural N-motifs generated in the host lattice. Graphenes doped below 5 at. % of nitrogen were nonmagnetic; however, once doped at 5.1 at. % of nitrogen, N-doped graphene exhibited transition to a ferromagnetic state at ∼69 K and displayed a saturation magnetization reaching 1.09 emu/g. Theoretical calculations were used to elucidate the effects of individual chemical forms of nitrogen on magnetic properties. Results showed that magnetic effects were triggered by graphitic nitrogen, whereas pyridinic and chemisorbed nitrogen contributed much less to the overall ferromagnetic ground state. Calculations further proved the existence of exchange coupling among the paramagnetic centers mediated by the conduction electrons.

Fluorographene Modified by Grignard Reagents: A Broad Range of Functional Nanomaterials.

Fluorographene is the youngest stoichiometric derivative of graphene; hence, its reactivity is only poorly explored. Compared to graphene, the significantly higher reactivity of C-F bonds makes this material a suitable platform for a large number of chemical modifications. Fluorographene is also the only member of the halographene family that can be prepared in the stoichiometric composition (C1 F1 ). Herein, the chemical modification of fluorographene with Grignard reagents, which are well known in organic synthesis for the formation of new C-C bonds, is presented. The reaction with alkyl magnesium bromides led to successful modification of fluorographene with ethyl, vinyl, ethynyl and propargyl groups. Chemical characterisation showed the presence of covalently bonded functional groups in a high concentration exceeding one functional group per C6 motif. The reactivity of Grignard reagents with fluorographene decreased from ethyl to ethynyl. The terminal carbon-carbon triple bonds were used for click reactions with organic azides leading to the formation of triazole rings. These findings open up a broad spectrum of opportunities for simple and robust modification of graphene by chemical reactions proceeding at room temperature under mild conditions. These results have major application potential in sensing, biomedical and energy-related applications.

2H→1T Phase Engineering of Layered Tantalum Disulfides in Electrocatalysis: Oxygen Reduction Reaction.

Tremendous attention is currently being paid to renewable sources of energy. Transition-metal dichalcogenides (TMDs) have been intensively studied for their promising catalytic activities in the hydrogen evolution reaction (HER) and the oxygen reduction reaction (ORR). In this fundamental work, we explored the catalytic properties of TMD family members 2H TaS2 and 1T TaS2 . Our findings reveal that both polytypes exhibit poor HER performance, which is even more pronounced after electrochemical reduction/oxidation. Our experimental data show that 1T TaS2 has a lower overpotential at a current density of -10 mA cm-1 , despite theoretical DFT calculations that indicated that the more favorable free energy of hydrogen adsorption should make "perfect" 2H TaS2 a better HER catalyst. Thorough characterization showed that the higher conductivity of 1T TaS2 and a slightly higher surface oxidation of 2H TaS2 explains this discrepancy. Moreover, changes in the catalytic activity after electrochemical treatment are addressed here. For the ORR in an alkaline environment, the electrochemical treatment led to an improvement in catalytic properties. With onset potentials similar to that of Pt/C catalysts, TaS2 was found to be an efficient catalyst for the ORR, rather than for proton reduction, in contrast to the behavior of Group 6 layered TMDs.

Simple Synthesis of Fluorinated Graphene: Thermal Exfoliation of Fluorographite.

Fluorinated graphene can be prepared directly by thermal exfoliation of fluorographite. The exfoliation was performed in a dynamic nitrogen atmosphere at various temperatures and the exfoliation products were analysed in detail by GC-MS. The structure and properties of all prepared fluorinated graphenes with various contents of fluorine were characterized by a number of analytical techniques. The results show both the dependence of fluorine concentration on exfoliation temperature and the suitability of this method for the synthesis of graphene with controlled concentration of fluorine. The high-temperature exfoliated fluorographite exhibits a high heterogeneous electron transfer rate and excellent catalytic properties towards the oxygen reduction reaction. These synthetic procedures can open a simple way for the synthesis of fluorinated graphene-based devices with tailored properties.

MoS2 /WS2 -Graphene Composites through Thermal Decomposition of Tetrathiomolybdate/Tetrathiotungstate for Proton/Oxygen Electroreduction.

MoS2 and WS2 have been prepared on a conductive graphene support by thermal reduction of tetrathiotungstate/tetrathiomolybdate and graphite oxide. Whereas the catalytic properties towards hydrogen evolution are strongly influenced by the Magnéli phases formed as a byproduct during the synthesis, the catalytic activity towards oxygen reduction of these composite materials is not affected by this phenomenon and these materials exhibit high catalytic activity towards this industrially important reaction.

Impedimetric detection of gut-derived metabolites using 2D Germanene-based materials.

Apart from the extensively researched graphene under the Group 14 2D materials, monolayered germanene and its derivatives have been gaining interest lately as alternative class of 2D materials owing to their facile synthesis, and attractive electronic and optical properties. Herein, three different functionalized germanene-based nanomaterials, namely Ge-H, Ge-CH3 and Ge-C3-CN were investigated on their novel incorporation in impedimetric immunosensors for the detection of gut-derived metabolites associated with neurological diseases, such as kynurenic acid (KA) and quinolinic acid (QA). The designed germanene-based immunosensor relies on an indirect competitive mechanism using disposable electrode printed chips. The competition for a fixed binding site of a primary antibody occurs between the bovine serum albumin-conjugated antigens on the electrode surface and the free antigens in the solution. Among the three materials, Ge-H displayed superior bioanalytical performance in KA and QA detection. Lower limits of detection of 5.07-11.38 ng/mL (26.79-68.11 nM) were attained for KA and QA with a faster reaction time than previously reported methods. Also, minimal cross-reactivity with interfering compounds, good reproducibility in impedimetric responses (RSD = 2.43-7.51 %) and long-term stability up to a month at 4 °C were the other attributes that the proposed Ge-H competitive impedimetric immunosensor has accomplished. The application of the developed Ge-H immunosensor to serum samples allowed an accurate KA and QA quantification at physiologically relevant levels. This work serves as a stepping-stone in the development of germanene-based nanomaterials for their implementation into cost-effective, miniaturized, portable and rapid impedimetric immunosensors, which are highly desirable for point-of-care testing in clinical settings.

Tuning Germanane Band Gaps via Cyanoethyl Functionalization for Cutting-Edge Photoactive Cathodes: Photoenhanced Hybrid Zinc-Ion Capacitor Evaluation.

Energy harvesting and storing by dual-functional photoenhanced (photo-E) energy storage devices are being developed to battle the current energy hassles. In this research work, our investigations on the photoinduced efficiency of germanane (Ge-H) and its functionalized analogue cyanoethyl (Ge-C2-CN) are assessed as photocathodes in photo-E hybrid zinc-ion capacitors (ZICs). The evaluated self-powered photodetector devices made by these germanene-based samples revealed effective performances in photogenerated electrons and holes. The photo-E ZICs findings provided a photoinduced capacitance enhancement of ∼52% (for Ge-H) and ∼26% (for Ge-C2-CN) at a scan rate of 10 mV s-1 under 100 mW cm-2 illumination with 435 nm wavelength. Further characterizations demonstrated that the photo-E ZIC with Ge-C2-CN supply higher specific capacitance (∼6000 mF g-1), energy density (∼550 mWh kg-1), and power density (∼31,000 mW kg-1), compared to the Ge-H. In addition, capacitance retention of photo-E ZIC with Ge-C2-CN is ∼91% after 3000 cycles which is almost 6% greater than Ge-H. Interestingly, the photocharging voltage response in photo-E ZIC made by Ge-C2-CN is 1000 mV, while the photocharging voltage response with Ge-H is approximately 970 mV. The observed performances in Ge-H-based photoactive cathodes highlight the pivotal role of such two-dimensional materials to be applied as single architecture in new unconventional energy storage systems. They are particularly noteworthy when compared to the other advanced photo-E supercapacitors and could even be enhanced greatly with other suitable inorganic and organic functional precursors.

Enhancing Nitrogen Reduction Reaction through Formation of 2D/2D Hybrid Heterostructures of MoS2@rGO.

Given the challenging task of constructing an efficient nitrogen reduction reaction (NRR) electrocatalyst with enhanced ambient condition performance, properties such as high specific surface area, fast electron transfer, and design of the catalyst surface constitute a group of key factors to be taken into consideration to guarantee outstanding catalytic performance and durability. Thereof, this work investigates the contribution of the 2D/2D heterojunction interface between MoS2 and reduced graphene oxide (rGO) on the electrocatalytic synthesis of NH3 in an alkaline media. The results revealed remarkable NRR performance on the MoS2@rGO 2D/2D hybrid electrocatalyst, characterized by a high NRR sensitivity (faradaic efficiency) of 34.7% with an NH3 yield rate of 3.98 ± 0.19 mg h-1 cm-2 at an overpotential of -0.3 V vs RHE in 0.1 M KOH solution. The hybrid electrocatalysts also exhibited selectivity for NH3 synthesis against the production of the hydrazine (N2H4) byproduct, hindrance of the competitive hydrogen evolution reaction (HER), and good durability over an operation period of 8 h. In hindsight, the study presented a low-cost and highly efficient catalyst design for achieving enhanced ammonia synthesis in alkaline media via the formation of defect-rich ultrathin MoS2@rGO nanostructures, consisting predominantly of an HER-hindering hexagonal 2H-MoS2 phase.

Electrochemical Intercalation and Exfoliation of CrSBr into Ferromagnetic Fibers and Nanoribbons.

Recent studies dedicated to layered van der Waals crystals have attracted significant attention to magnetic atomically thin crystals offering unprecedented opportunities for applications in innovative magnetoelectric, magneto-optic, and spintronic devices. The active search for original platforms for the low-dimensional magnetism study has emphasized the entirely new magnetic properties of two dimensional (2D) semiconductor CrSBr. Herein, for the first time, the electrochemical exfoliation of bulk CrSBr in a non-aqueous environment is demonstrated. Notably, crystal cleavage governed by the structural anisotropy occurred along two directions forming atomically thin and few-layered nanoribbons. The exfoliated material possesses an orthorhombic crystalline structure and strong optical anisotropy, showing the polarization dependencies of Raman signals. The antiferromagnetism exhibited by multilayered CrSBr gives precedence to ferromagnetic ordering in the revealed CrSBr nanostructures. Furthermore, the potential application of CrSBr nanoribbons is pioneered for electrochemical photodetector fabrication and demonstrates its responsivity up to 30 µA cm-2 in the visible spectrum. Moreover, the CrSBr-based anode for lithium-ion batteries exhibited high performance and self-improving abilities. This anticipates that the results will pave the way toward the future study of CrSBr and practical applications in magneto- and optoelectronics.

In Situ Vanadium-Deficient Engineering of V2 C MXene: A Pathway to Enhanced Zinc-Ion Batteries.

This research examines vanadium-deficient V2 C MXene, a two-dimensional (2D) vanadium carbide with exceptional electrochemical properties for rechargeable zinc-ion batteries. Through a meticulous etching process, a V-deficient, porous architecture with an expansive surface area is achieved, fostering three-dimensional (3D) diffusion channels and boosting zinc ion storage. Analytical techniques like scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller, and X-ray diffraction confirm the formation of V2 C MXene and its defective porous structure. X-ray photoelectron spectroscopy further verifies its transformation from the MAX phase to MXene, noting an increase in V3+ and V4+ states with etching. Cyclic voltammetry reveals superior de-zincation kinetics, evidenced by consistent V3+ /V4+ oxidation peaks at varied scanning rates. Overall, this V-deficient MXene outperforms raw MXenes in capacity and rate, although its capacity diminishes over extended cycling due to structural flaws. Theoretical analyses suggest conductivity rises with vacancies, enhancing 3D ionic diffusion as vacancy size grows. This work sheds light on enhancing V-based MXene structures for optimized zinc-ion storage.

Exploration of Charge Storage Behavior of Binder-Free EDL Capacitors in Aqueous Electrolytes.

Charge storage in electrochemical double-layer capacitors (EDLCs) is via the adsorption of electrolyte counterions in their positive and negative electrodes under an applied potential. This study investigates the EDLC-type charge storage in carbon nanotubes (CNT) electrodes in aqueous acidic (NaHSO4), basic (NaOH), and neutral (Na2SO4) electrolytes of similar cations but different anions as well as similar anions but different cations (Na2SO4 and Li2SO4) in a two-electrode Swagelok-type cell configuration. The physicochemical properties of ions, such as mobility/diffusion and solvation, are correlated with the charge storage parameters. The neutral electrolytes offer superior charge storage over the acidic and basic counterparts. Among the studied ions, SO4 2- and Li+ showed the most significant capacitance owing to their larger solvated ion size. The charge stored by the anions and cations follows the order SO4 2- > HSO4 - > OH- and Li+ > Na+, respectively. Consequently, the CNT//Li2SO4//CNT cell displayed outstanding charge storage indicators (operating voltage ∼0-2 V, specific capacitance ∼122 F·g-1, specific energy ∼67 W h·kg-1, and specific power ∼541 W·kg-1 at 0.5 A·g-1) than the other cells, which could light a red light-emitting diode (2.1 V) for several minutes. Besides, the CNT//Li2SO4//CNT device showed exceptional rate performance with a capacitance retention of ∼95% at various current densities (0.5-2.5 A·g-1) after 6500 cycles. The insights from this work could be used to design safer electrochemical capacitors of high energy density and power density.