Electronegative Elements Research Articles

Role of fluoride and fluorocarbons in enhanced stability and performance of halide perovskites for photovoltaics

Fluorine is the most electronegative element and its small size and highly polar bonding enable it to play a unique and vital role in many materials. In this Research Update, the authors review the potential for fluorine, when incorporated at interfaces, to address fundamental materials challenges to the stability and photophysical properties of halide perovskites, a burgeoning class of photovoltaic absorber materials. While the halide perovskite electronic structure is considered to be defect-tolerant in the bulk, defects at surfaces and grain boundaries are sites of carrier recombination and phase degradation due to their greater reactivity towards moisture and oxygen. Fluoride and fluorocarbons can directly prevent defects by increasing the bonding strength at grain boundaries as well as by acting as a hydrophobic physicochemical barrier. Less direct benefits are also discussed, such as morphological and cell band alignment improvements. Our discussion covers partial incorporation in the perovskite lattice of fluoride as a halide substitution and substitution of the native cations for fluorocarbon cations, as well as the inclusion of molecular fluorocarbons.

Suppressing the surface passivation of Pt-Mo nanowires via constructing Mo-Se coordination for boosting HER performance

Modulating the surface coordination environment of Pt based nanocrystals at the atomic level is of great importance to obtain good electrocatalytic performance. Given the fundamental understandings of surface structure degeneration of Pt based nanocrystals, introducing a weak electronegative element to the surface of Pt-based catalysts is beneficial for suppressing surface passivation and improving hydrogen evolution reaction performance of Pt. Density functional theory results reveal that the energy barrier of water dissociation process can be greatly reduced by using Se element as the surface modifier to replace the O. This hypothesis is further validated by experiments that ultralong Pt85Mo15-Se nanowires were fabricated to suppress the excessive passivation behavior of transition metals of Pt based alloy. The Pt85Mo15-Se nanowires exhibit higher activity with 4.98 times the specific activity and 4.87 times the mass activity of commercial Pt/C, as well as a better stability towards alkaline hydrogen evolution reaction. The deep exploration of X-ray photoelectron spectroscopy and theoretical calculations disclose that Se element could maintain the electron-rich state around the electronic orbit of Pt. This study provides a new insight to advance the fundamental understanding on electrocatalytic materials, which exhibits a promising approach to protect the surface chemical environment of Pt based nanocrystals.

Elemental Core Level Shift in High Entropy Alloy Nanoparticles via X-ray Photoelectron Spectroscopy Analysis and First-Principles Calculation.

High entropy alloy nanoparticles (HEA-NPs) are expanding their influence in many fields. To explore the electronic structures in such multielemental systems, HEA-NPs were synthesized on two different carbon substrates through carbothermal shock and in situ reduction methods. The relationship between the apparent core level energy shifts (negative or positive) and the electron density changes among the components of quinary-metal HEA-NPs was investigated by X-ray photoelectron spectroscopy (XPS) analysis and first-principles electronic structure calculations. It was found that Cu displays a negative core level shift while Fe, Co, Mg, Cr, and Mn display a positive core level shift. While experiments show an apparent positive core level shift for Ni, electronic structure calculations reveal that this arises from shifts in the Fermi level and that the electron density redistribution in Ni behaves more like Cu than the other elements. The findings show that the electron density redistribution in the NPs occurs from less electronegative elements to more electronegative ones. This work should guide the design of HEA-NPs to expand their potential applications in mechanical structures, medicine, catalysis, and energy storage/conversion.

Spotlight on Alkali Metals: The Structural Chemistry of Alkali Metal Thallides

Alkali metal thallides go back to the investigative works of Eduard Zintl about base metals in negative oxidation states. In 1932, he described the crystal structure of NaTl as the first representative for this class of compounds. Since then, a bunch of versatile crystal structures has been reported for thallium as electronegative element in intermetallic solid state compounds. For combinations of thallium with alkali metals as electropositive counterparts, a broad range of different unique structure types has been observed. Interestingly, various thallium substructures at the same or very similar valence electron concentration (VEC) are obtained. This in return emphasizes that the role of the alkali metals on structure formation goes far beyond ancillary filling atoms, which are present only due to charge balancing reasons. In this review, the alkali metals are in focus and the local surroundings of the latter are discussed in terms of their crystallographic sites in the corresponding crystal structures.

Effect of Ligand Adsorption on the Electronic Properties of the PbS(100) Surface.

A first-principles density functional theory calculation was carried out to study the adsorption of acetic acid, methyl amine, methanethiol, and hydrogen iodide on the (100) surface of PbS. All four ligands are common capping agents used in colloidal PbS quantum dot-based photovoltaics. Interestingly, among the considered adsorbates, dissociative adsorption was energetically preferred for hydrogen iodide, while associative adsorption was favorable for the rest. Associative adsorption was driven by strong interactions between the electronegative elements (Y) in the respective ligands and the Pb surface atoms via Pb 6p-Y np bond hybridization (n represents the valence quantum number of the respective electronegative elements). Importantly, the adsorption of ligands altered the work function of PbS, with contrasting trends for associative (decrease in the work function) versus dissociative (increase in the work function) adsorption. The changes in the work function correlates well with a corresponding shift in the 5d level of surface Pb atoms. Other important observations include variations in the work function that linearly change with increasing the surface coverage of adsorbed ligands as well as with the strength of the adsorption of ligands.

Effects of metal fluoride/sulfide microparticles generated by consecutive high-pulse-power breakdowns on the insulating performance in compressed SF6

Spark gas switches (SGS) are widely used in various pulsed power applications where sulfur hexafluoride (SF6) is still dominant because of its excellent insulating performance. However, particle contamination generated by SF6 possesses some special properties that can greatly reduce the effectiveness of the gas switches. The objective of this paper is to study the effects of particles generated spontaneously by consecutive breakdowns of high-pulse-power SGS on the insulating performance in compressed SF6. A double electrode/double pulse method, coupled with laser scattering and laser shadow photography, is adopted to detect the particles and examine their specific roles in the breakdown process. Many large particles in SF6, of approximately 150 μm in diameter, are observed at about 80 milliseconds after a single breakdown. Furthermore, numerous particles gradually suspend and accumulate in the gap after consecutive breakdowns. Particles generated by SF6 can reach tens of micrometers in size. They have rough microtopography covered by abundant floccules, and contain rich electronegative elements: fluorine and sulfur. Moreover, particle-involved abnormal breakdowns in SF6 usually occur with nearly equal threshold and probability in spite of the increasing consecutive breakdowns, and conversely, the abnormal breakdowns in N2 appear more frequently and unsteadily with a high dispersibility. The analysis of field enhancement caused by these large metal-fluoride/sulfide particles shows that they can directly cause significant field emission (FE) due to their properties of surface-field enhancement and causticity. Such FE further triggers micro-discharge. Subsequently, this behavior eventually leads to abnormal breakdowns at a lower threshold.

Stereochemistry of Transition Metal Complexes Controlled by the Metallo-Anomeric Effect.

The use of stereoelectronic interactions to control reactivity and selectivity has a long history in chemistry. The anomeric effect, one of the fundamental concepts in organic chemistry, describes the preferences of a substituent at the anomeric carbon in glycosides to adopt axial configuration when the anomeric group is an electronegative element such as oxygen or a halogen. The origin of the anomeric effect has been the subject of intense debate. Explanations capitalizing on either the delocalization of the endocyclic oxygen lone pair into the antibonding σ*(C-X) orbital or the minimization of the dipole-dipole interactions are currently the two leading theoretical models. Although the majority of experimental and theoretical studies have focused on the elements from groups 6 and 7, little is known about conformational preferences of tetrahydropyran rings substituted with a transition metal at the anomeric carbon and the role of these interactions in stereoselective synthesis. Here, we report studies on conformational and configurational preferences of organometallic complexes stabilized by vicinal heteroatoms. We provide computational evidence that late transition metals adopt the axial position in heterocycles or synclinal geometry in acyclic systems. Furthermore, the anomeric preferences of late transition metals correlate with the oxidation state of the metal and can be explained by hyperconjugative interactions between endocyclic heteroatom and the σ* acceptor orbitals of the C-M bond. In a broader context, this discovery provides insight into the role of previously unanticipated stereoelectronic effects that can be harnessed in the design of stereoselective reactions, including chemical glycosylation and enantioselective catalysis.

Hierarchical Highly Wrinkled Trimetallic NiFeCu Phosphide Nanosheets on Nanodendrite Ni3S2/Ni Foam as an Efficient Electrocatalyst for the Oxygen Evolution Reaction.

The sluggish oxygen evolution reaction (OER) and costly noble-metal oxide catalysts hinder the vast usage of environmentally friendly water splitting for hydrogen production. Elemental doping by partial replacing of parent metal elements with elements of higher electronegativity is considered to be one of the most efficient strategies to promote the electrocatalytic OER performance. In this work, we synthesize an efficient hierarchical highly wrinkled NiFeCu phosphide nanosheet on nanodendrite Ni3S2/NiF substrates through partial replacement of Cu instead of Ni and Fe in NiFeP@Ni3S2/NiF by using a facile electrodeposition method. The NiFeCuP@Ni3S2/NiF electrocatalyst needs only 230, 282, and 351 mV to reach 10, 50, and 100 mA × cm-2, respectively. Notably, this electrocatalyst shows one of the lowest OER overpotentials at 10 mA/cm-2 for metal phosphides and endured the OER at 20 mA × cm-2 for 18 h with negligible voltage elevation. The X-ray photoelectron spectroscopy (XPS), double-layer capacitance (Cdl) plots, and electrochemical impedance spectroscopy show that the partial Cu doping in NiFeP@Ni3S2/NiF not only can change the electron density around Ni and Fe but also can increase the electrochemically active surface area and conductivity of electrocatalysts.

Observation of light and secondary ion emissions from surfaces irradiated with highly charged ions

Visible light and secondary ions emitted from various sample surfaces (Si, HOPG, Cu, and Teflon) were observed after irradiation with highly charged ions (HCIs). HCIs were produced using an electron beam ion source (Kobe EBIS) at Kobe University. Visible emissions were detected using a liquid nitrogen cooled CCD detector. The mass spectrum of secondary ions was obtained using a quadrupole mass analyzer. The major constituent in both light and secondary ion emissions was hydrogen. Balmer lines were the dominant form of light emission as observed from spectra, and proton signals were the most intense peaks in SIMS spectra. The emission intensity of Balmer light and the proton signal intensity (as observed from the SIMS spectrum) both increased as the charge state of the incident HCI increased. Both intensities were roughly proportional to the third to fourth power of the charge state. Spatial distribution of Balmer light was measured and the kinetic energy of hydrogen sputtered from the surface was estimated to be ∼20 eV. The SIMS measurement results for the Teflon sample demonstrate the advantage of using SIMS with an HCI probe for detecting electronegative elements.

Influence of Hydrofluoric Acid Leaching and Roasting on Mineralogical Phase Transformation of Pyrite in Sulfidic Mine Tailings

Under the oxidative roasting process, pyrite, as a major mineral in sulfidic mine tailings, can transform to iron oxides. Generated iron oxides, if exhibiting enough magnetic properties, can be recovered via magnetic separation resulting in partial mine tailings valorization. However, due to the presence of various minerals and sintering possibility, it is advantageous to remove impurities and increase the pyrite content of mine tailings prior to the roasting procedure. In this case, hydrofluoric acid that has no influence on pyrite can be used to leach most inorganic minerals, including aluminosilicates. Therefore, this study investigated and compared the influence of the roasting process with and without hydrofluoric acid leaching pretreatment on mineralogical phase transformation of pyrite and magnetic properties of thermally generated minerals. Several tests and analyses were performed to study mineralogical phase transformation, morphology, elemental composition, surface characterization, and magnetic properties. Results of this study indicated that without acid leaching pretreatment, pyrite was mainly transformed to hematite. However, via acid leaching, fluorine, as a more electronegative element over oxygen, entered the compound and neglected the role of oxygen in thermal oxidation, instead reducing sulfur content of pyrite to only form pyrrhotite.

Synthesis, Anticancer, and Antibacterial Studies of Benzylidene Bearing 5-substituted and 3,5-disubstituted-2,4-Thiazolidinedione Derivatives

To develop novel compounds having potent anticancer and antibacterial activities. Several studies have proved that benzylidene analogues of clinical 2,4-TZDs, such as troglitazone and ciglitazone, have more potent antiproliferative activity than their parent compounds. Literature studies also revealed that the attachment of more heterocyclic rings, containing nitrogen on 5th position of 2,4-TZD, can enhance the antimicrobial activity. Hence, attachment of various moieties on the benzylidene ring may produce safe and effective compounds in the future. The objective of the present study was to synthesize a set of novel benzylidene ring containing 5- and 3-substituted-2,4-thiazolidinedione derivatives and evaluate them for their anticancer and antibacterial activity. The synthesized compounds were characterized by IR, NMR, mass, and elemental studies. The in vitro cytotoxicity studies were performed for human breast cancer (MCF-7) and human lung cancer (A549) cells and HepG2 cell-line and compared to standard drug doxorubicin by MTT assay. Antimicrobial activity of the synthesized 2,4-thiazolidinediones derivatives was carried out using the cup plate method with slight modification. The results obtained showed that TZ-5 and TZ-13 exhibited good antiproliferative activity against A549 cancer cell-line, whereas TZ-10 exhibited moderate antiproliferative activity against HepG2 cell-line when compared to standard drug doxorubicin. TZ-5 also exhibited reasonable activity against the MCF-7 cell-line with doxorubicin as standard. TZ-4, TZ-5, TZ-6, TZ-7, and TZ- 16 exhibited remarkable antibacterial activity against Gram positive and moderate activity against Gram negative bacteria with the standard drug ciprofloxacin. Attachment of heterocyclic rings containing nitrogen as the hetero atom improves the anticancer and antimicrobial potential. Attachment of electronegative elements like halogens can also enhance the antimicrobial activity. Further structure modifications may lead to the development of more potent 2,4-TZD leads that can be evaluated for further advanced studies.

Designing a Deep-UV Nonlinear Optical Fluorooxosilicophosphate

Structures composed of SiOxF6-x (x = 1, 2, 3, 4, 5) or SiOxF4-x (x = 1, 2, 3) species have thus far been observed in only a few compounds, and their functional properties are completely unknown in silicate chemistry. By introducing the least electronegative element, cesium, and the most electronegative element, fluorine, into the silicophosphate system, we successfully designed the first noncentrosymmetric fluorooxosilicophosphate with Si-F bonds, CsSiP2O7F, whose structure consists of an unprecedented SiP2O10F moiety containing hexacoordinate SiO5F species. The experimental results highlight CsSiP2O7F as the first fluorooxosilicophosphate deep-UV nonlinear optical (NLO) material. The first-principles calculations reveal that the SiP2O10F moiety is a new type of NLO-active unit and that both cesium and fluorine increase the deep-UV transparency of CsSiP2O7F. This work provides a new source of deep-UV NLO materials and insights into obtaining noncentrosymmetric structures that are indispensable to functional materials in nonlinear optics, piezoelectricity, ferroelectric, pyroelectricity, etc.

Changes of the band structure of Mg2Si induced by interstitial doping with nonmetallic elements

The electronic structures and the densities of states of Mg8Si4X1 were calculated by using density functional theory, where semiconducting Mg2Si and a nonmetallic element, X, form interstitial alloys. When X is an inert gas element, the electronic structure is basically the same as that of Mg8Si4, but the bandgap increases (X = He or Ne) or decreases (X = Ar) depending on the degree of volume expansion caused by the interstitial alloying. In the case of X = electronegative element (O, F, or Cl), X works as an electron acceptor, which causes the transition of Mg2Si from an intrinsic semiconductor to a p-type semiconductor. This is also the case for X = H. When the electronegativity of X is intermediate (X = C, Si, N, P, or S), the bandgap at the R point of the reciprocal lattice of Mg8Si4 becomes negligible. When X = B, a transition to an n-type semiconductor is predicted as in the case of doping with electropositive metal elements such as Li and Al, but the bandgap at the R point of the reciprocal lattice of Mg8Si4 becomes negligible, as in the case of elements with intermediate electronegativities.

Regulating electrodeposition morphology of lithium: towards commercially relevant secondary Li metal batteries.

Lithium, the lightest and most electronegative metallic element, has long been considered the ultimate choice as a battery anode for mobile, as well as in some stationary applications. The high electronegativity of Li is, however, a double-edged sword-it facilitates a large operating voltage when paired with essentially any cathode, promising a high cell-level energy density. It is also synonymous with a high chemical reactivity and low reduction potential. The interfaces a Li metal anode forms with any other material (liquid or solid) in an electrochemical cell are therefore always mediated by one or more products of its chemical or electrochemical reactions with that material. The physical, crystallographic, mechanical, electrochemical, and transport properties of the resultant new material phases (interphases) regulate all interfacial processes at a Li metal anode, including electrodeposition during battery recharge. This Review takes recent efforts aimed at manipulating the structure, composition, and physical properties of the solid electrolyte interphase (SEI) formed on an Li anode as a point of departure to discuss the structural, electrokinetic, and electrochemical requirements for achieving high anode reversibility. An important conclusion is that while recent reports showing significant advances in the achievement of highly reversible Li anodes, e.g. as measured by the coulombic efficiency (CE), raise prospects for as significant progress towards commercially relevant Li metal batteries, the plateauing of achievable CE values to around 99 ± 0.5% apparent from a comprehensive analysis of the literature is problematic because CE values of at least 99.7%, and preferably >99.9% are required for Li metal cells to live up to the potential for higher energy density batteries offered by the Li metal anode. On this basis, we discuss promising approaches for creating purpose-built interphases on Li, as well as for fabricating advanced Li electrode architectures for regulating Li electrodeposition morphology and crystallinity. Considering the large number of physical and chemical factors involved in achieving fine control of Li electrodeposition, we believe that achievement of the remaining ∼0.5% in anode reversibility will require fresh approaches, perhaps borrowed from other fields. We offer perspectives on both current and new strategies for achieving such Li anodes with the specific aim of engaging established contributors and newcomers to the field in the search for scalable solutions.

Testing the limits of radical-anionic CH-amination: a 10-million-fold decrease in basicity opens a new path to hydroxyisoindolines via a mixed C-N/C-O-forming cascade.

An intramolecular C(sp3)–H amidation proceeds in the presence of t-BuOK, molecular oxygen, and DMF. This transformation is initiated by the deprotonation of an acidic N–H bond and selective radical activation of a benzylic C–H bond towards hydrogen atom transfer (HAT). Cyclization of this radical–anion intermediate en route to a two-centered/three-electron (2c,3e) C–N bond removes electron density from nitrogen. As this electronegative element resists such an “oxidation”, making nitrogen more electron rich is key to overcoming this problem. This work dramatically expands the range of N-anions that can participate in this process by using amides instead of anilines. The resulting 107-fold decrease in the N-component basicity (and nucleophilicity) doubles the activation barrier for C–N bond formation and makes this process nearly thermoneutral. Remarkably, this reaction also converts a weak reductant into a much stronger reductant. Such “reductant upconversion” allows mild oxidants like molecular oxygen to complete the first part of the cascade. In contrast, the second stage of NH/CH activation forms a highly stabilized radical–anion intermediate incapable of undergoing electron transfer to oxygen. Because the oxidation is unfavored, an alternative reaction path opens via coupling between the radical anion intermediate and either superoxide or hydroperoxide radical. The hydroperoxide intermediate transforms into the final hydroxyisoindoline products under basic conditions. The use of TEMPO as an additive was found to activate less reactive amides. The combination of experimental and computational data outlines a conceptually new mechanism for conversion of unprotected amides into hydroxyisoindolines proceeding as a sequence of C–H amidation and C–H oxidation.

Band bending at the ZnO(0001)-Zn surface produced by electropositive, electronegative and atmospheric adsorbates

We have analysed the surface band bending (SBB) at the clean ZnO(0001)-Zn surface and after its modification by electropositive, electronegative and atmospheric adsorbates. The evolution of the band bending with increasing adsorption was monitored by measuring core-level and valence-band X-ray photoelectron spectra. We found that the SBB produced by the adsorption of electropositive elements was always downwards, reaching in all cases the limit imposed by the crossing of the conduction-band minimum with the Fermi level. The adsorption of electronegative elements produced always upward band bending, but in this case a pinning of the SBB was observed that kept the valence-band maximum far from the Fermi level. A self-consistent equation relating the adsorbate level occupation with the band bending is shown to qualitatively reproduce the observed SBB pinning effect. In contrary to the commonly assumed upwards SBB for the ZnO/air interface, a downward SBB was observed after exposing the clean surface to atmospheric air. A downward SBB was also observed when the surface was bombarded with 1 keV Ar+ in vacuum.

A review on fluoride induced organotoxicity and genotoxicity in mammals and zebrafish

Fluorine is a highly reactive electronegative element and naturally found in a combined form with other elements. In water, it remains as fluoride. It can be present in soil and air also. Beside the natural abundance, anthropogenic activities e.g. use of pesticides, fertilizers, sewage, coal burning etc. can increase the fluoride concentration in the environment. According to the World Health Organization, Permissible limit of fluoride in drinking water is 1.5 ppm (mg/L). When presence of fluoride in drinking water is within the permissible limit, it exerts beneficial effects on teeth, preventing dental caries; while, chronic exposure of fluoride beyond the permissible limit causes mild to severe form of dental and skeletal fluorosis. Apart from these hard tissues, chronic fluoride exposure beyond the permissible limit causes detrimental effect on soft tissues e.g. liver, kidney, spleen, gastrointestinal tract, reproductive organ etc. Studies also indicate that fluoride induces significantly genotoxic effect both in vivo and in vitro. Although various techniques have been developed for defluoridation of water but each one has limitations. Unfortunately, till date, there is no effective strategy of fluorosis treatment. In order to develop an effective therapeutic strategy, thorough understandings on the molecular mechanism of fluoride induced toxicity should be unravelled. This review enlightens both beneficial and toxic effects of fluoride emphasizing its molecular mechanism of action.

Room Temperature Fluoride Ion Batteries

Fluorine is highly electronegative (+2.84 V vs. SHE) element and possess low weight. Fluoride is monovalent, and it has high charge density. Consequently, it enables high ionic conductivity similar to Li+ in certain solids. However, fluorine is a corrosive and toxic gas, which forbids it as one of the electrodes. Nevertheless, fluoride ions can be transported between a metal and a metal fluoride through a fluoride transporting electrolyte, and fluoride-ion batteries (FIB) can be realized. FIB offers high specific energy, energy density, thermal stability, and safety compared to state of the art lithium-ion batteries (LIBs). Primary batteries based on fluoride transport were demonstrated earlier [1]. Recently we have demonstrated first rechargeable FIB that was operable at 150 °C [2]. Several challenges need to be addressed to realize its full potential of FIBs. We have been working on various aspects related to FIB with the aim of developing sustainable fluoride ion batteries [3-5]. Recently, for the first time, we have demonstrated room-temperature (RT) rechargeable fluoride-ion batteries using BaSnF4 as fluoride transporting solid electrolyte [6]. BaSnF4 shows high fluoride conductivity of 3.5x10–4 S cm–1, but limited electrochemical stability window. To be compatible with BaSnF4, we have utilized low electropositive Sn, Zn as anode materials to demonstrate RT FIB. However, to enable cells with high operating potentials, the electrolyte should be compatible with highly electropositive metals (e.g., Mg, Ce). Toward this, we developed a new interlayer electrolyte that is compatible with highly electropositive metals like Ce and Mg. Further, utilizing the interlayer electrolyte, we demonstrate the functioning of first high potential RT FIB.

Aromaticity‐promoted C−F Bond Activation in Rhodium Complex: A Facile Tautomerization

Fluorine is the most electronegative element in the periodic table. Thus, activation of the carbon-fluorine (C-F) bond, the strongest single bond to carbon, has attracted considerable interest from both experimentalists and theoreticians. In comparison with numerous approaches to activate C-F bonds, the aromaticity-promoted method is less developed. Herein, we demonstrate that the C-F bond activation could be achieved by a facile tautomerization, benefitting from aromaticity, which can stabilize both the transition states and products. Our findings highlight an important application of aromaticity in the C-F bond activation, providing experimentalists with an alternative approach to activate C-F bonds.

Inductive Effect in Mn-Doped NiO Nanosheet Arrays for Enhanced Capacitive and Highly Stable Hybrid Supercapacitor

The inductive effect related to foreign metal substitution has great effect on the redox behavior of transition metal oxides, which plays an important role in their electrochemical activities. In this work, we demonstrate the inductive effect in nickel oxide nanosheet arrays (NSAs) via doping with the lower electronegative element Mn, which has greatly improved their electrochemical capacitance and stability. Density functional theory (DFT) calculations show that the inductive effect in Mn–NiO increases the electron transport efficiency, enhances the adsorption energy of OH–, and also makes the compound more covalent. Therefore, Mn–NiO NSAs demonstrated a dramatically improved specific capacitance twofold better than that of pure NiO NSAs at a current density of 5 mA cm–2 and higher stability without any decay of capacitance after 10 000 cycles at 30 mA cm–2. Moreover, the hybrid supercapacitor device of Mn–NiO NSAs//graphene–CNT exhibited an excellent recycling stability after 50 000 cycles of charging/d...