Molecular Precursor Routes for Ag-Based Metallic, Intermetallic, and Metal Sulfide Nanoparticles: Their Comparative ORR Activity Trend at Solid|Liquid and Liquid|Liquid Interfaces.

The electrochemical conversion of oxygen to water is a crucial process required for renewable energy production, whereas its first two-electron step produces a versatile chemical and oxidant─hydrogen peroxide. Improving performance and widening the limited selection of the potential catalysts for this reaction is a step toward the implementation of clean-energy technologies. As silver is known as one of the most effective catalysts of oxygen reduction reaction (ORR), we have designed a suitable molecular precursor pathway for the selective synthesis of metallic (Ag), intermetallic (Ag3Sb), and binary or ternary metal sulfide (Ag2S and AgSbS2) nanomaterials by judicious control of reaction conditions. The decomposition of xanthate precursors under different reaction conditions in colloidal synthesis indicates that carbon-sulfur bond cleavage yields the respective metal sulfide nanomaterials. This is not the case in the presence of trioctylphosphine when the metal-sulfur bond is broken. The synthesized nanomaterials were applied as catalysts of oxygen reduction at the liquid-liquid and solid-liquid interfaces. Ag exhibits the best performance for electrochemical oxygen reduction, whereas the electrocatalytic performance of Ag and Ag3Sb is comparable for peroxide reduction in an alkaline medium. Scanning electrochemical microscopy (SECM) analysis indicates that a flexible 2-electron to 4-electron ORR pathway has been achieved by transforming metallic Ag into intermetallic Ag3Sb.

Surface Engineered Peroxidase-Mimicking Gold Nanoparticles to Subside Cell Inflammation.

The smart design of nanoparticles with varying surfaces may open a new avenue for potential biomedical applications. Consequently, several approaches have been established for controlled synthesis to develop the unique physicochemical properties of nanoparticles. However, many of the synthesis and functionalization methods are chemical-based and might be toxic to limit the full potential of nanoparticles. Here, curcumin (a plant-derived material) based synthesis of gold (Au) nanoparticles, followed by the development of a suitable exterior corona using isoniazid (INH, antibiotic), tyrosine (Tyr, amino acid), and quercetin (Qrc, antioxidant), is reported. All these nanoparticles (Cur-Au, Cur-AuINH, Cur-AuTyr, and Cur-AuQrc) possess inherent peroxidase-mimicking natures depending on the surface corona of respective nanoparticles, and they are found to be excellent candidates for free radical scavenging action. The peroxidase-mimicking nanoparticle interactions with red blood cells and mouse macrophages confirmed their hemo- and biocompatible nature. Moreover, these surface-engineered Au nanoparticles were found to be suitable in subsiding key pro-inflammatory cytokines such as interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interleukin-1ß (IL-1ß). The inherent peroxidase-mimicking behavior and anti-inflammatory potential without any significant toxicity of these nanoparticles may open new prospects for nanomedicine.

Precursor Engineering for the Synthesis of Mixed Anionic Metal (Cu, Mn) Chalcogenide Nanomaterials via Solvent-Less Synthesis.

Metal-organic ligands with mixed chalcogenides are potential compounds for the preparation of mixed anionic metal chalcogenide alloys. However, only a few of such ligands are known, and their complexes are not well explored. We have prepared homo- and hetero-dichalcogenoimidodiphosphinate [(EE'PiPr2NH)] (E, E' = Se, Se; S, S; S, Se) complexes of manganese and copper through metathetical reactions. The X-ray single crystal structure of [Mn{(SePiPr2)2N}2] 1 revealed a triclinic crystal system, with a MnSe4 core unit, whereas the crystal structure determination of [Mn{(SPiPr2)(SePiPr2)N}2] 2 indicated a triclinic crystal system with a Mn(S/Se)2 unit. Both metal centers are tetrahedral, with two deprotonated bidentate ligands forming the coordination sphere. The free ligand was found to exhibit a gauche configuration in the solid state. The energies of the various rotamers of dithio-analogue were studied by DFT calculations. The decomposition behavior of complexes with homo- and heterochalcogenides was investigated, and the complexes were employed as single-source precursors to generate manganese and copper chalcogenides through solvent-less melt reactions between 500 and 550 °C. The deposited powders were characterized by powder X-ray diffraction (p-XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscopy (TEM), and elemental mapping. MnS, MnSe2, and MnSSe phases were obtained from the decomposition of respective manganese complexes. In contrast, the decomposition of copper-based complexes yielded Cu2-xSe and the sulfur-doped Cu3Se2 phase from seleno- and mixed thio/seleno-complexes of Cu, respectively. The morphology ranged from random sheet-like structures to agglomerated platelets, while the selected area electron diffraction (SAED) revealed the crystalline nature of the materials. Depending on the nature of the complex and the temperature, different amounts of phosphorus were present as an impurity in the synthesized products.

Selective Synthesis of Bismuth or Bismuth Selenide Nanosheets from a Metal Organic Precursor: Investigation of their Catalytic Performance for Water Splitting.

The development of cost-effective, functional materials that can be efficiently used for sustainable energy generation is highly desirable. Herein, a new molecular precursor of bismuth (tris(selenobenzoato)bismuth(III), [Bi(SeOCPh)3]), has been used to prepare selectively Bi or Bi2Se3 nanosheets via a colloidal route by the judicious control of the reaction parameters. The Bi formation mechanism was investigated, and it was observed that the trioctylphosphine (TOP) plays a crucial role in the formation of Bi. Employing the vapor deposition method resulted in the formation of exclusively Bi2Se3 films at different temperatures. The synthesized nanomaterials and films were characterized by p-XRD, TEM, Raman, SEM, EDX, AFM, XPS, and UV-vis spectroscopy. A minimum sheet thickness of 3.6 nm (i.e., a thickness of 8-9 layers) was observed for bismuth, whereas a thickness of 4 nm (i.e., a thickness of 4 layers) was observed for Bi2Se3 nanosheets. XPS showed surface oxidation of both materials and indicated an uncapped surface of Bi, whereas Bi2Se3 had a capping layer of oleylamine, resulting in reduced surface oxidation. The potential of Bi and Bi2Se3 nanosheets was tested for overall water-splitting application. The OER and HER catalytic performances of Bi2Se3 indicate overpotentials of 385 mV at 10 mA cm-2 and 220 mV, with Tafel slopes of 122 and 178 mV dec-1, respectively. In comparison, Bi showed a much lower OER activity (506 mV at 10 mA cm-2) but a slightly better HER (214 mV at 10 mA cm-2) performance. Similarly, Bi2Se3 nanosheets were observed to exhibit cathodic photocurrent in photoelectrocatalytic activity, which indicated their p-type behavior.

Triphenylphosphine-Assisted Transformation of NiS to Ni2P through a Solvent-Less Pyrolysis Route: Synthesis and Electrocatalytic Performance.

Straightforward synthetic routes to the preparation of transition metal phosphides or their chalcogenide analogues are highly desired due to their widespread applications, including catalysis. We report a facile and simple route for the preparation of a pure phase nickel phosphide (Ni2P) and phase transformations in the nickel sulfide (NiS) system through a solvent-less synthetic protocol. Decomposition of different sulfur-based complexes (dithiocarbamate, xanthate, and dithiophosphonate) of nickel(II) was investigated in the presence and absence of triphenylphosphine (TPP). The optimization of reaction parameters (nature of precursor, ratio of TPP, temperature, and time) indicated that phosphorus- and sulfur-containing inorganic dithiophosphonate complexes and TPP (1:1 mole ratio) produced pure nickel phosphide, whereas different phases of nickel sulfide were obtained from dithiocarbamate and xanthate precursors in the presence or absence of TPP. A plausible explanation of the sulfide or phosphide phase formation is suggested, and the performance of Ni2P was investigated as an electrocatalyst for supercapacitance and overall water-splitting reactions. The performance of Ni2P with the surface free of any capping agents is not well explored, as common synthetic methods are solution-based routes; therefore, the electrocatalytic performance was also compared with metal phosphides, prepared by other routes. The highest specific capacitance of 367 F/g was observed at 1 A/g, and the maximum energy and power density of Ni2P were calculated to be 17.9 Wh/kg and 6951 W/kg, respectively. The prepared nickel phosphide required overpotentials of 174 and 316 mV along with Tafel slopes of 115 and 95 mV/dec to achieve a current density of 10 mA/cm2 for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively.

Flexible Molecular Precursors for Selective Decomposition to Nickel Sulfide or Nickel Phosphide for Water Splitting and Supercapacitance.

Herein, the synthesis of three nickel(II) dithiophosphonate complexes of the type [Ni{S2 P(OR)(4-C6 H4 OMe)}2 ] [R=H (1), C3 H7 (2)] and [Ni{S2 P(OR)(4-C6 H4 OEt}2 ] [R=(C6 H5 )2 CH (3)] is described; their structures were confirmed by single-crystal X-ray studies. These complexes were subjected to surfactant/solvent reactions at 300 °C for one hour as flexible molecular precursors to prepare either nickel sulfide or nickel phosphide particles. The decomposition of complex 2 in tri-octylphosphine oxide/1-octadecene (TOPO/ODE), TOPO/tri-n-octylphosphine (TOP), hexadecylamine (HDA)/TOP, and HDA/ODE yielded hexagonal NiS, Ni2 P, Ni5 P4 , and rhombohedral NiS, respectively. Similarly, the decomposition of complex 1 in TOPO/TOP and HDA/TOP yielded hexagonal Ni2 P and Ni5 P4 , respectively, and that of complex 3 in similar solvents led to hexagonal Ni5 P4 , with TOP as the likely phosphorus provider. Hexagonal NiS was prepared from the solvent-less decomposition of complexes 1 and 2 at 400 °C. NiS (rhom) had the best specific supercapacitance of 2304 F g-1 at a scan rate of 2 mV s-1 followed by 1672 F g-1 of Ni2 P (hex). Similarly, NiS (rhom) and Ni2 P (hex) showed the highest power and energy densities of 7.4 kW kg-1 and 54.16 W kg-1 as well as 6.3 kW kg-1 and 44.7 W kg-1 , respectively. Ni5 P4 (hex) had the lowest recorded overpotential of 350 mV at a current density of 50 mA cm-2 among the samples tested for the oxygen evolution reaction (OER). NiS (hex) and Ni5 P4 (hex) had the lowest overpotentials of 231 and 235 mV to achieve a current density of 50 mA cm-2 , respectively, in hydrogen evolution reaction (HER) examinations.

Tannic acid-derivatized graphitic carbon nitride quantum dots as an "on-off-on" fluorescent nanoprobe for ascorbic acid via copper(II) mediation.

A microwave-assisted hydrothermal route was employed to prepare fluorescent tannic acid (TA)-derivatized graphitic carbon nitride quantum dots. The resulting dots display blue fluorescence (best measured at excitation/emission wavelengths of 350/452 nm) with a quantum yield as high as ~44%. The incorporated TA imparts a fluorescence switching behavior in that very low concentrations of Cu(II) can quench the fluorescence, while (AA) can restore it. It is presumed that AA causes Cu(II) to be transformed to Cu(I). Based on these findings, a fluorometric method was designed for AA detection. The probe allows AA to be detected with a 50 pM limit of detection and a linear analytical range that extends from 0.1 to 200 nM of AA. Real and spiked samples were successfully assayed by the probe to demonstrate its analytical applicability. Graphical abstract Schematic presentation of fluorescent graphitic carbon nitride quantum dots functionalized with tannic acid. Their fluorescence is quenched by Cu2+ and recovered by ascorbic acid (AA). This is exploited in an assay with a picomolar detection limit.

Microwave-assisted synthesis of thymine-functionalized graphitic carbon nitride quantum dots as a fluorescent nanoprobe for mercury(II).

A microwave-assisted hydrothermal method was employed to prepare thymine-modified graphitic carbon nitride quantum dots (T-gCNQDs) which are shown to be a novel fluorescent nanoprobe for Hg(II). They exhibit excellent optical properties (blue emission with a fluorescence quantum yield of 46%) and water solubility. The incorporation of thymine into the gCNQDs results in an enhancement in photoluminescence properties. It is found that fluorescence, best measured at excitation/emission wavelengths of 350/445 nm, is much more strongly quenched by Hg(II) compared to the thymine-free nanoprobe. The quenching is highly selective even in the presence other metal ions. This is ascribed to the formation of T-Hg(II)-T base complexes. Fluorescence drops linearly in the 1.0 to 500 nM Hg(II) concentration range, and the limit of detection is 0.15 nM. The method was applied to the determination of Hg(II) in spiked samples of tap and pond water. Recoveries were found to be >95%, thus demonstrating the practical applicability of the assay. Graphical abstract A microwave-assisted hydrothermal route was employed to prepare thymine-functionalized graphitic carbon nitride QDs (T-gCNQDs). A selective fluorescence quenching mechanism occurred between T-gCNQDs and Hg(II) due to thymine functionalization. T-gCNQDs was utilized to detect Hg(II) in real samples.

Heterocyclic Bismuth(III) Dithiocarbamato Complexes as Single-Source Precursors for the Synthesis of Anisotropic Bi2 S3 Nanoparticles.

New complexes catena-(µ2 -nitrato-O,O')bis(piperidinedithiocarbamato)bismuth(III) (1) and tetrakis(µ-nitrato)tetrakis[bis(tetrahydroquinolinedithiocarbamato)bismuth(III)] (2) were synthesised and characterised by elemental analysis, FTIR spectroscopy and thermogravimetric analysis. The single-crystal X-ray structures of 1 and 2 were determined. The coordination numbers of the Bi(III) ion are 8 for 1 and ≥6 for 2 when the experimental electron density for the nominal 6s(2) lone pair of electrons is included. Both complexes were used as single-source precursors for the synthesis of dodecylamine-, hexadecylamine-, oleylamine and tri-n-octylphosphine oxide-capped Bi2 S3 nanoparticles at different temperatures. UV/Vis spectra showed a blueshift in the absorbance band edge characteristic of a quantum size effect. High-quality, crystalline, long and short Bi2 S3 nanorods were obtained depending on the thermolysis temperature, which was varied from 190 to 270 °C. A general trend of increasing particle breadth with increasing reaction temperature and increasing length of the carbon chain of the amine (capping agent) was observed. Powder XRD patterns revealed the orthorhombic crystal structure of Bi2 S3 .

Cysteine-capped gold nanoparticles suppress aggregation of proteins exposed to heat stress.

Gold nanoparticles show a lot of promise as potential agents for drug delivery and disease diagnosis. Because of this, it is important that the interaction between gold nanoparticles and biomolecules be well characterized to avoid undesirable consequences. In this study, gold nanoparticles were synthesized by the reduction of gold salt by sodium borohydride in the presence of cysteine as the capping agent. The physical features of the nanoparticles were analyzed using Ultraviolet-Visible spectrophotometry and transmission electron microscopy. The interaction between gold nanoparticles and the following proteins: bovine serum albumin, citrate synthase, malate dehydrogenase, and human heat shock protein 70 was investigated by UV-Vis spectrophotometry. The stability of the proteins against heat stress was assessed by monitoring their aggregation at 48 °C, either in the presence or absence of gold nanoparticles. The gold nanoparticles were capable of suppressing the heat-induced aggregation of the proteins. Furthermore, apart from possessing independent protein-aggregation suppression function, the AuNPs also augmented the chaperone function of human heat shock protein 70. Findings from this study demonstrate that cyteine-coated gold nanoparticles exhibit chaperone-like activity and have the capability to stabilize proteins to which they may be conjugated.

Eco-friendly mixed metal (Mg-Ni) ferrite nanosheets for efficient electrocatalytic water splitting.

Eco-friendly and cost-effective catalysts with multiple active sites, large surface area, high stability and catalytic activity are highly desired for efficient water splitting as a sustainable green energy source. Within this line, a facile synthetic approach based on solventless thermolysis was employed for the simple and tunable synthesis of Ni1-xMgxFe2O4 (0 ≤ x ≤ 1) nanosheets. The characterization of nanosheets (via p-XRD, EDX, SEM, TEM, HRTEM, and SAED) revealed that the pristine ferrites (NiFe2O4 and MgFe2O4), and their solid solutions maintain the same cubic symmetry throughout the composition regulation. Elucidation of the electrochemical performance of the nanoferrite solid solutions showed that by tuning the local chemical environment of Ni in NiFe2O4 via Mg substitution, the intrinsic catalytic activity was enhanced. Evidently, the optimized Ni0.4Mg0.6Fe2O4 catalyst showed drastically enhanced HER activity with a much lower overpotential of 121 mV compared to the pristine NiFe2O4 catalyst. Moreover, Ni0.2Mg0.8Fe2O4 catalyst exhibited the best OER performance with a low overpotential of 284 mV at 10 mA/cm2 in 1 M KOH. This enhanced electrocatalytic activity could be due to improved electronic conductivity caused by the partial substitution of Ni2+ by Mg2+ in the NiFe2O4 matrix as well as the synergistic effect in the Mg-substituted NiFe2O4. Our results suggest a feasible route for developing earth-abundant metal oxide-based electrocatalysts for future water electrolysis applications.

An in vitro assessment of the interaction of cadmium selenide quantum dots with DNA, iron, and blood platelets.

Cadmium selenide (CdSe) quantum dots have gained increased attention for their potential use in biomedical applications. This has raised interest in assessing their toxicity. In this study, water-soluble, cysteine-capped CdSe nanocrystals with an average size of 15 nm were prepared through a one-pot solution-based method. The CdSe nanoparticles were synthesized in batches in which the concentration of the capping agent was varied with the aim of stabilizing the quantum dot core. The effects of the CdSe quantum dots on DNA stability, aggregation of blood platelets, and reducing activity of iron were evaluated in vitro . DNA damage was observed at a concentration of 200 µg/mL of CdSe quantum dots. Furthermore, the CdSe nanocrystals exhibited high reducing power and chelating activity, suggesting that they may impair the function of haemoglobin by interacting with iron. In addition, the CdSe quantum dots promoted aggregation of blood platelets in a dose dependent manner.

Facile synthesis of organically capped CdTe nanoparticles.

A simple method for the preparation of tri-n-octylphosphine oxide (TOPO) and hexadecylamine (HDA) capped CdTe particles have been employed in this study. The method involves the reduction of tellurium in water followed by the addition of the cadmium salt and thermolysis in TOPO and HDA. The influence of the reduction time (2, 4 and 6 h) of tellurium on the optical properties was investigated. The particles were characterised by electron microscopy and X-ray diffraction techniques.

Tuning composition of CuCo2S4-NiCo2S4 solid solutions via solvent-less pyrolysis of molecular precursors for efficient supercapacitance and water splitting.

Mixed metal sulfides are increasingly being investigated because of their prospective applications for electrochemical energy storage and conversion. Their high electronic conductivity and high density of redox sites result in significant improvement of their electrochemical properties. Herein, the composition-dependent supercapacitive and water splitting performance of a series of Ni(1-x)Cu x Co2S4 (0.2 ≤ x ≤ 0.8) solid solutions prepared via solvent-less pyrolysis of a mixture of respective metal ethyl xanthate precursors is reported. The use of xanthate precursors resulted in the formation of surface clean nanomaterials at low-temperature. Their structural, compositional, and morphological features were examined by p-XRD, SEM, and EDX analyses. Both supercapacitive and electrocatalytic (HER, OER) properties of the synthesized materials significantly vary with composition (Ni/Cu molar content). However, the optimal composition depends on the application. The highest specific capacitance of 770 F g-1 at a current density of 1 A g-1 was achieved for Ni0.6Cu0.4Co2S4 (NCCS-2). This electrode exhibits capacitance retention (C R) of 67% at 30 A g-1, which is higher than that observed for pristine NiCo2S4 (838 F g-1 at 1 A g-1, 47% C R at 30 A g-1). On the contrary, Ni0.4Cu0.6Co2S4 (NCCS-3) exhibits the lowest overpotential of 124 mV to deliver a current density of 10 mA cm-2. Finally, the best OER activity with an overpotential of 268 mV at 10 mA cm-2 was displayed by Ni0.8Cu0.2Co2S4 (NCCS-1). The prepared electrodes exhibit high stability, as well as durability.

Double functionalized haemocompatible silver nanoparticles control cell inflammatory homeostasis.

Infection, trauma, and autoimmunity trigger tissue inflammation, often leading to pain and loss of function. Therefore, approaches to control inflammation based on nanotechnology principles are being developed in addition to available methods. The metal-based nanoparticles are particularly attractive due to the ease of synthesis, control over physicochemical properties, and facile surface modification with different types of molecules. Here, we report curcumin conjugated silver (Cur-Ag) nanoparticles synthesis, followed by their surface functionalization with isoniazid, tyrosine, and quercetin, leading to Cur-AgINH, Cur-AgTyr, and Cur-AgQrc nanoparticles, respectively. These nanoparticles possess radical scavenging capacity, haemocompatibility, and minimal cytotoxicity to macrophages. Furthermore, the nanoparticles inhibited the secretion of pro-inflammatory cytokines such as interleukin-6, tumor necrosis factor-α, and interleukin-1ß from macrophages stimulated by lipopolysaccharide (LPS). The findings reveal that the careful design of surface corona of nanoparticles could be critical to increasing their efficacy in biomedical applications.

Colloidal synthesis of metal chalcogenide nanomaterials from metal-organic precursors and capping ligand effect on electrocatalytic performance: progress, challenges and future perspectives.

Renewable and sustainable functional nanomaterials, which can be employed in alternative green energy sources, are highly desirable. Transition metal chalcogenides are potential catalysts for processes resulting in energy generation and storage. In order to optimize their catalytic performance, high phase purity and precise control over shape and size are indispensable. Metal-organic precursors with pre-formed bonds between the metal and the chalcogenide atoms are advantageous in synthesizing phase pure transition metal chalcogenides with controlled shape and sizes. This can be achieved by the decomposition of metal-organic precursors in the presence of suitable surfactants/capping agents. However, the recent studies on electrocatalysis at the nanoscale level reveal that the capping agents attached to their surface have a detrimental effect on their efficiency. The removal of surfactants from active sites to obtain bare surface nanoparticles is necessary to enhance catalytic activity. Herein, we have discussed the properties of different metal-organic precursors and the role of surfactants in the colloidal synthesis of metal chalcogenide nanomaterials. Moreover, the effect of surfactants on their electrocatalytic performance, the commonly used strategies for removing surfactants from the surface of nanomaterials and the future perspectives are reviewed.

Comparative study on the effect of precursors on the morphology and electronic properties of CdS nanoparticles.

Cadmium dithiocarbamate and cadmium ethyl xanthate complexes were synthesized and characterized by microanalysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analyses. The complexes were employed as molecular precursors for the fabrication of CdS nanoparticles in hexadecylamine (HDA) and oleylamine (OLA) at a temperature of 250 °C. Spherical and oval shaped particles with sizes ranging from 9.93 ± 1.89 to 16.74 ± 2.78 nm were obtained in OLA while spherical, oval and rod shaped particles with sizes ranging from 9.40 ± 1.65 to 29.90 ± 5.32 nm were obtained in HDA. Optical properties of the nanoparticles showed blue shifts as compared to the bulk CdS, with the OLA capped nanoparticles slightly more blue shifted than the corresponding HDA capped nanoparticles. Results of crystallinity patterns revealed hexagonal phase of CdS.

Low temperature scalable synthetic approach enabling high bifunctional electrocatalytic performance of NiCo2S4 and CuCo2S4 thiospinels.

Ternary metal sulfides are currently in the spotlight as promising electroactive materials for high-performance energy storage and/or conversion technologies. Extensive research on metal sulfides has indicated that, amongst other factors, the electrochemical properties of the materials are strongly influenced by the synthetic protocol employed. Herein, we report the electrochemical performance of uncapped NiCo2S4 and CuCo2S4 ternary systems prepared via solventless thermolysis of the respective metal ethyl xanthate precursors at 200 and 300 °C. The structural, morphological and compositional properties of the synthesized nanoparticles were examined by powder X-ray diffraction (p-XRD), transmission electron microscopy (TEM), high-resolution TEM, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX) techniques. Electrochemical studies indicate that NiCo2S4 nanoparticles synthesized at 300 °C exhibit superior energy storage characteristics with a high specific capacitance of ca. 2650 F g-1 at 1 mV s-1, as compared to CuCo2S4 nanoparticles, which showcased a specific capacitance of ca. 1700 F g-1 at the same scan rate. At a current density of 0.5 A g-1, NiCo2S4 and CuCo2S4 nanoparticles displayed specific capacitances of 1201 and 475 F g-1, respectively. In contrast, CuCo2S4 nanoparticles presented a higher electrocatalytic activity with low overpotentials of 269 mV for oxygen evolution reaction (OER), and 224 mV for the hydrogen evolution reaction (HER), at 10 mA cm-2. The stability of the catalysts was examined for 2000 cycles in which a negligible change in both OER and HER activities was observed.

Solventless synthesis of nanospinel Ni1-x Co x Fe2O4 (0 ≤ x ≤ 1) solid solutions for efficient electrochemical water splitting and supercapacitance.

The formation of solid solutions represents a robust strategy for modulating the electronic properties and improving the electrochemical performance of spinel ferrites. However, solid solutions have been predominantly prepared via wet chemical routes, which involve the use of harmful and/or expensive chemicals. In the present study, a facile, inexpensive and environmentally benign solventless route is employed for the composition-controlled synthesis of nanoscopic Ni1-x Co x Fe2O4 (0 ≤ x ≤ 1) solid solutions. The physicochemical characterization of the samples was performed by p-XRD, SEM, EDX, XPS, TEM, HRTEM and UV-Vis techniques. A systematic investigation was also carried out to elucidate the electrochemical performance of the prepared nanospinels towards energy generation and storage. Based on the results of CV, GCD, and stability tests, the Ni0.4Co0.6Fe2O4 electrode showed the highest performance for the supercapacitor electrode exhibiting a specific capacitance of 237 F g-1, superior energy density of 10.3 W h kg-1 and a high power density with a peak value of 4208 W kg-1, and 100% of its charge storage capacity was retained after 4000 cycles with 97% coulombic efficiency. For HER, the Ni0.6Co0.4Fe2O4 and CoFe2O4 electrodes showed low overpotentials of 168 and 169 mV, respectively, indicating better catalytic activity. For OER, the Ni0.8Co0.2Fe2O4 electrode exhibited a lower overpotential of 320 mV at a current density of 10 mA cm-2, with a Tafel slope of 79 mV dec-1, demonstrating a fast and efficient process. These results indicated that nanospinel ferrite solid solutions could be employed as promising electrode materials for supercapacitor and water splitting applications.

Synergistically enhanced performance of transition-metal doped Ni2P for supercapacitance and overall water splitting.

Cost-effective and readily available catalysts applicable for electrochemical conversion technologies are highly desired. Herein, we report the synthesis of dithiophosphonate complexes of the type [Ni{S2P(OH)(4-CH3OC6H4)}2] (1), [Co{S2P(OC4H9)(4-CH3OC6H4)}3] (2) and [Fe{S2P(OH)(4-CH3OC6H4)}3] (3) and employed them to prepare Ni2P, Co-Ni2P and Fe-Ni2P nanoparticles. Ni2P was formed by a facile hot injection method by decomposing complex 1 in tri-octylphosphine oxide/tri-n-octylphosphine at 300 °C. The prepared Ni2P was doped with Co and Fe employing complexes 2 and 3, respectively, under similar experimental conditions. Doping Ni2P with Co and Fe demonstrated synergistic improvement of Ni2P performance as an electrocatalyst in supercapcitance, hydrogen evololution and oxygen evolution reactions in alkaline medium. Cobalt doping improved the Ni2P charge storage capacity with a supercapacitance of 864 F g-1 at 1 A g-1 current density. Fe doped Ni2P recorded the lowest overpotential of 259 mV to achieve a current density of 10 mA cm-2 and a Tafel slope of 80 mV dec-1 for OER, better than the undoped Ni2P and the benchmark IrO2. Likewise, Fe-doped Ni2P electrode required the lowest overpotential of 68 mV with a Tafel slope of 110 mV dec-1 to attain the same current density for HER. All catalysts showed excellent stability in supercapacitance and overall water splitting reactions, indicating their practical use in energy conversion technologies.