II)/Ni Research Articles

β-Functionalized Dibenzoporphyrins with Mixed Substituents Pattern: Facile Synthesis, Structural, Spectral, and Electrochemical Redox Properties.

A new series of mixed β-substituted dibenzoporphyrins were synthesized, and the effect of β-substitution on the spectral and electrochemical redox properties of the macrocycle was elucidated. The synthetic route to β-tetrasubstituted dibenzoporphyrins begins with the regioselective bromination of NiTPP(Benzo)2 to afford NiTPP(Benzo)2Br4, followed by Pd catalyzed coupling reaction to access NiTPP(Benzo)2(R)4 (R = phenyl (Ph) and phenylethynyl (PE)). Synthesized benzoporphyrins exhibited red-shifted absorption spectral features with tunable redox properties. These benzoporphyrins displayed pronounced electronic effects of β-substituents on the macrocyclic skeleton. NiTPP(Benzo)2(PE)4 exhibited the lowest HOMO-LUMO gap among the series due to extended π-conjugation. Intrestingly, metal-centered oxidation of Ni(II)/Ni(III) was observed for NiOPP(Benzo)2 and NiOPP(Benzo)Br2 after an initial conversion of the neutral porphyrin to its dicationic form under electrochemical conditions.

Highly Sensitive Electrocatalytic Determination of Formaldehyde Using a Ni/Ionic Liquid Modified Carbon Nanotube Paste Electrode

In this study, ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate was applied as additives to fabricate a novel ionic liquid/carbon nanotube paste electrode (IL/CNPE). This electrode was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. Results showed that the electron transfer rate and reversibility of the electrode were increased by the ionic liquid. The morpho-logy of prepared IL/CNPE was studied by scanning electron microscopy. Nickel/ionic liquid modified carbon nanotube paste electrode (Ni/IL/CNPE) was also constructed by immersion of the IL/CNPE in nickel sulfate solution. Ionic liquid showed significant effect on the accumulation of nickel species on the surface of the electrode. Also, the values of electron transfer coefficient, charge-transfer rate constant and electrode surface coverage for Ni(II)/Ni(III) redox couple of the Ni/IL/CNPE were found to be 0.32 and 2.37×10-1 s-1 and 2.74×10-8 mol.cm-2, respectively. The Ni/IL/CNPE was applied successfully to highly efficient electrocatalytic oxidation of formaldehyde in alkaline medium. The effects of various factors on the efficiency of electrocatalytic oxidation of formaldehyde were optimized. Under the optimized condition, cyclic voltammetry of formaldehyde at the modified electrode exhibited two linear dynamic ranges in the concentration ranges of 7.00×10-6 to 9.60×10-5 mol.L-1 and 9.60×10-5 to 32.00×10-3 mol.L-1 with excellent detection limit of 9.50×10-7 mol.L-1 (3σ/slope), respectively. Also, the method was successfully applied for formaldehyde measurement in real sample.

Secondary battery inspired NiO nanosheets with rich Ni(III) defects for enhancing persulfates activation in phenolic waste water degradation

Sulfate radicals (SO4−) with broad pH tolerance and strong oxidation capacity are promising for Fenton-like reaction degradation of phenolic waste water. Ni-based catalysts and its compounds have been seldom reported as catalysts for the sulfate radical activation from persulfates (PDS) due to its inappropriate redox potential windows. A secondary battery inspired NiO nanosheets with rich Ni(III) defects were developed for Fenton-like catalysis via the charge/discharge process of NiOx/NiOx(OH)y redox cycle. The redox potential of Ni(II)/Ni(III) in NiOx/NiOx(OH)y cycle is high enough to activate S2O82− for the generation of SO4−. The Fenton-like performance of the defect-rich NiO nanosheets is most robust among the well-known sulfate radical activation catalysts of Co3O4, α-Fe2O3, MnOOH, and CuO. The enhancement effect of NiO was attributed to the formed Ni(III) defects, which could facilitate the discharge process of Ni(III) to Ni(II) and then enhance the Ni(III)/Ni(II) cycle during the Fenton-like process. The stability and recovery of defect-rich NiO nanosheets was also studied. Its high stability in chemical structure contributed to the low Ni leaching during the reaction process in basic or neutral condition. The recovery of defect-rich NiO nanosheets could be easily realized via the annealing treatment. In all, the secondary battery inspired defect-rich NiO nanosheets with outstanding sulfate radical activation would be a promising Fenton-like catalyst for environmental remediation.

A Ni(II) derivative incorporating tetradentate Schiff base precursor: Structure, spectral, electrochemical and DFT interpretation

The Ni(II) derivative, namely Ni [L]⋅ClO4 (1) is afforded incorporating the Schiff base precursor, (HL) = [2-((E)-(2-(2-aminoethylamino)ethylimino)methyl)-6-methoxyphenol]. Single crystal X-ray structure reveals that in 1, the central Ni(II) atom is surrounded by N3O donor set and possesses on a distorted square-planar environment. EPR spectra confirms that compound 1 is diamagnetic due to square-planar geometrical nature having a spin state S = 0. DFT computational studies are in good agreement with the structural and spectral data. The electrochemical study of compound 1 shows one quasi-reversible oxidative peak at 0.92 V vs Ag/AgCl due to a redox couple of Ni(II)/Ni(III); nd a weak oxidation peak at −0.72 V vs Ag/AgCl which might be assigned to Ni(I/II) couple.

Designing Smart Materials for Efficient Electrosynthesis of Fuels and Environmental Remediation: The Story of Transition Metal Chalcogenides

Energy harvesting from solar and water has created ripples in materials energy research for the last several decades, complemented by the rise of Hydrogen as a clean fuel. Another aspect that has become more relevant is the electroreduction of atmospheric carbon dioxide into fuel or other value-added chemicals, thereby offering environmental remediation without the need to store large amounts of pressurized CO2. It has become very apparent that hydrogen-on-demand technology needs to be developed to complement the growth of hydrogen fuel economy without adding on to the process cost by storing hydrogen in pressurized tanks or non-reactive framework. In this regards, water electrolysis leading to generation of oxygen and hydrogen on demand, has been one of the most promising routes towards sustainable alternative energy generation and storage without depleting fossil-fuel based natural resources. However, the efficiency and practical feasibility of water electrolysis is limited by the anodic oxygen evolution reaction (OER), which is a kinetically sluggish, electron-intensive uphill reaction. A slow OER process also slows the other half-cell reaction, i.e. the hydrogen evolution reaction (HER) at the cathode. Hence, designing efficient catalysts for OER and HER process from earth-abundant resources has been one of the primary concerns for advancing solar water splitting. In the Nath group we have focused on transition metal chalcogenides as efficient electrocatalysts for several energy conversion processes. Recently we have discovered that these transition metal selenides are highly efficient electrocatalyst for electroreduction of CO2 to higher hydrocarbons such as ethanol, acetic acid, and acetaldehyde at reasonably low potential (-0.7 to -1.5 V) under ambient conditions. In this presentation we will first present that CO2 electroreduction with Ni, Cu and V-based selenides, and present a thorough investigation of the reaction products and their evolution as a function of applied potential and reaction time. We will also discuss about the selectivity of product formation by controlling catalyst composition and applied potential. For water splitting reactions, we had proposed the idea that these chalcogenides, specifically, selenides and tellurides will show much better OER catalytic activity due to increasing covalency around the catalytically active transition metal site, compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chemical potential around the transition metal center, [e.g. lowering the Ni2+ --> Ni3+ oxidation potential in Ni-based catalysts where Ni3+ is the actually catalytically active species]. Based on such hypothesis, we have synthesized a plethora of transition metal selenides including those based on Ni, Ni-Fe, Co, Cu, and Ni-Co, which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA/cm2 [Ni3Se2 - 200 - 290 mV; Co7Se8 - 260 mV; FeNi2Se4-NrGO - 170 mV (NrGO - N-doped reduced graphene oxide); NiFe2Se4 - 210 mV; CoNi2Se4 - 190 mV; Ni3Te2 – 180 mV]. We will also highlight the importance of this increasing covalency in enhancing OER catalytic activity with the help of experimental evidence in the chalcogenide series (Ni3S2, Ni3Se2, Ni3Te2). We will illustrate how the Ni(II) --> Ni(III) oxidation potential is indeed lowered within the selenide coordination compared to the oxide, in pure single crystals of the seleno-based coordination complex which is devoid of any surface impurities and adsorbates. To complement the experimental observations, we have also performed DFT calculation and will discuss how the OH adsorption energy varied between the oxide and chalcogenides surfaces and the implication of such variation in terms of catalytic activity. The later part of the talk will be focused on designing nanostructures for these catalysts and integrating them with nanostructured photoanode arrays to create an efficient solar-to-fuel energy conversion device as well as artificial photosynthetic units. We will illustrate growth of nanostructured (nanopillars and nanotubes) photoanode arrays through confined electrodeposition on lithographically patterned nanoelectrodes, and decorating them with nanostructured chalcogenide based electroctalaysts, and how this technique can be utilized for a hybrid energy conversion device. Results encompassing efficient photoelectrocatalytic performance of CdSe-NiSe, CdTe-Ni3Te2, CuInSe2-NiSe2 and Fe3Se4-NiSe hybrid nanocomposite will be presented.

Nickle-cobalt composite catalyst-modified activated carbon anode for direct glucose alkaline fuel cell

Glucose is the most abundant monosaccharide in nature and has great potential as high-density hydrogen carrier for fuel cells. However, the practical application of direct glucose alkaline fuel cell (DGAFC) is hampered by lack of cost-effective anode catalyst. In this study, nickel-cobalt composite catalysts were prepared by NaBH4 reduction method and electrochemical, morphological and chemical properties of catalysts were characterized by LSV, EIS, SEM, TEM, XRD and XPS techniques. The nickel-cobalt composite catalyst and modified activated carbon anode was evaluated in one-chamber DGAFC. Our results demonstrated that the DGAFC performance was greatly improved with the addition of Ni-Co composite catalyst in the anode. Fuel cell achieved the peak power density of 23.97 W m−2 under the condition of 1 M glucose, 3 M KOH and ambient temperature. The enhancement of the anode performance could be attributed to the synergic effect of two reversible redox systems, Ni(II)/Ni(III) and Co(II)/Co(III), which improved interfacial charge-transfer kinetics. Our study may facilitate the development of cost-effective renewable energy devices.

Rare trinuclear NiII2MII complexes (MII = Mn, Fe and Co) with a reduced Schiff base ligand: Synthesis, structures and magnetic properties

Abstract Three new trinuclear hetero-metallic NiII2MII complexes with MII = Mn, Fe and Co have been synthesized using a [NiLR] “metalloligand”, where H2LR = N,N′-bis(2-hydroxybenzyl)-1,3-propanediamine. All complexes have been characterized by elemental analysis, spectroscopic methods, single crystal XRD and magnetic and electrochemical studies. In the three complexes, in addition to the double phenoxido bridges, the two terminal NiII atoms are linked to the central MII [M = Mn(1), Fe(2) and Co(3)] ion by means of a bridging carboxylato co-anion, giving rise to a linear NiII-MII-NiII structure. Variable temperature magnetic susceptibility measurements show the presence of weak ferromagnetic and antiferromagnetic exchange interactions mediated through the double phenoxido bridges with J values of +8.5 and −3.0 cm−1 for complexes 1 and 2, respectively. Compound 3 shows the presence of antiferromagnetic interactions. Cyclic voltammetry shows a common quasi-reversible one electron oxidation corresponding to the Ni(II)/Ni(III) process in 1–3 and an irreversible M(II)/M(III) oxidation for Mn(1) and Fe(2).

Ni(II)-chelated thio-crown complex as a single redox couple for non-aqueous flow batteries

The Ni(II)-chelated thio-crown complex cation (nickel(II)-1,4,8,11-tetrathiacyclotetradecane), Ni([14]aneS4)2+ was tested as a single redox couple for non-aqueous flow batteries. The solid samples were synthesized with three different counter anions. Of the anions, bis(trifluoromethane)sulfonamide (TFSI−) provides the highest solubility (0.62M in the organic carbonate-based electrolyte solution). The anion-dependent solubility can be accounted for by the weaker cation/anion Coulombic interaction with larger anions. The complex cation participates in two redox reactions: Ni(II)↔Ni(III) at E1/2=1.11V (vs. Fc/Fc+) and Ni(II)↔Ni(I) at E1/2=−0.80V (vs. Fc/Fc+), which enables the working voltage of the redox flow cell with the complex cation as a single redox couple to be 1.91V. The complex cation exhibits very stable redox behavior without any degradation. The advantage of the high working voltage and superior stability cannot, however, be fully implemented because the used electrolyte is not stable against oxidative decomposition on the positive electrode.

Synthesis, spectroscopic characterization, luminescence and NLO properties of heterometallic M(II)-Ru(II) (M=Ni and Zn) hybrid complexes composed of coordination and organometallic sites

The heterometallic complexes of the type [Ni(L1-3)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] (1a-c) and [Zn(L1-3)NC5H4-C≡C-C6H3-1,3-{C≡C-trans-RuCl(dppe)2}2] (2a-c) (Where, L1 = 2-{(E)-[(2-hydroxyphenyl)imino]methyl}phenol, L2 = 2-{[(E)-(2-hydroxyphenyl) methylideneamino}-5-methoxyphenol and L3 = 2-{[(E)-(2-hydroxyphenyl)methylidene]amino}-5-nitrophenol and dppe = 1,2-bis(diphenylphosphinoethane)) have been prepared and characterized by elemental analysis, FTIR, Uv–Visible, 1H NMR, 31P NMR and mass spectral studies. The thermal stabilities of the complexes 1a-c and 2a-c were studied by thermogravimetric analysis (TGA). Quasireversible redox behaviour is observed for all complexes corresponding to Ru(II)/Ru(III) and Ni(II)/Ni(III) couple for 1a-c and Ru(II)/Ru(III) couple for 2a-c. All the complexes are emissive in solution at room temperature revealing the influence of substituents and solvent polarity on emission properties of the complexes. The second harmonic generation (SHG) efficiency of the complexes was investigated by Kurtz-powder technique demonstrating that all complexes flaunt the second harmonic generation property.

Coordination-organometallic hybrid materials based on the trinuclear M(II)-Ru(II) (M=Ni and Zn) complexes: Synthesis, structural characterization, luminescence and electrochemical properties

A new series of trinuclear complexes of the type Ni[R-C6H4NCH(O)C6H3CCRu(dppe)2Cl]2 (1a-c) and Zn[RC6H4NCH(O)C6H3CCRu(dppe)2Cl]2 (2a-c) have been prepared from the reaction of trans-[RuCl(dppe)2CCC6H3(OH)(CHO)] (1) with aniline, 4-nitroaniline and 4-methoxyaniline (R1-3) in presence of nickel acetate and zinc acetate in CH2Cl2/MeOH (1:1) mixture. The structural properties of the complexes have been characterized by elemental analyses and spectroscopic techniques viz. FTIR, UV-Visible, 1H NMR and 31P NMR spectral studies. The crystal structure and morphology of the hybrid complexes was investigated with the help of X-ray powder diffraction (XRPD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The thermal properties of 1a-c and 2a-c were studied by thermogravimetric (TG) analysis. The electrochemical behaviour of the complexes reveals that all complexes displayed a quasireversible redox behaviour corresponding to Ru(II)/Ru(III) and Ni(II)/Ni(III) couples for 1a-c and only Ru(II)/Ru(III) couple for 2a-c. All complexes are emissive in solution at room temperature revealing the influence of substituents and solvent polarity on emission properties of the complexes.

Structural and Compositional Optimization of the LiNi0.8Co0.2O2 Electrode by New Synthesis Conditions

The optimization of Citrate Precursor Method to obtain the LiNi0.8Co0.2O2 oxide from the thermal decomposition of the citrate precursor (NH4)3LiNi0.8Co0.2(C6H5O7) is presented. The optimization procedure consists of both the lithium atmosphere and the reaction time control during the decomposition of the citrate precursor. Were obtained and characterized two kind of the (Li1-xNix)(Ni0.8Co0.2)O2 oxides, with and without optimized synthesis conditions, identified as A and B oxides, respectively. The A and B oxides are characterized by compositional, structural and electrochemical studies. The results showed that is possible to reach the ordered oxide phase at smaller reaction time if the lithium atmosphere is controlled. From the combination of the chemical analysis by ICP and the DRX Rietveld structural refinement it is possible to establish the Li, Ni(II), Ni(III) and Co(III) composition with great accuracy. The resulted structural and compositional transformations have a close relation with technological parameters of the rechargeable lithium battery using Li Ni0.8Co0.2O2 oxide as cathode.

Water-soluble NNN-pincer complexes of cobalt, nickel and palladium: Solid-state structures and catalytic activity

Neutral NNN-pincer ligand 1 based on a pyridyl core and cyclic amidine pendant arms was synthesized via a straightforward condensation reaction. Its square-planar palladium acetate complex 2 was prepared in methanol and featured a cyclic, hexameric solid-state structure assembled through moderately strong N⋯H⋯O hydrogen bonds involving the ligand backbone and the non-coordinated acetate group. The octahedral, diamagnetic Co(III) complex 3 was prepared via in-situ air oxidation of its Co(II) analog. Its solid-state structure confirmed the oxidation state of the metal and revealed the presence of weak bridging and terminal NH⋯Cl hydrogen bonds. Paramagnetic nickel complex 4 was prepared in a similar fashion to 1 and was postulated to have a covalent attachment of the acetate moieties to the metal. Derivatives 2 and 3 had excellent water solubility and stability while 4 was sparingly soluble in water. Cyclic voltammetry revealed electrochemically reversible electron transfer steps corresponding to the Co(II)/Co(III) and Ni(II)/Ni(III) redox couples at −0.31V and 1.04V versus SHE, respectively. Complex 4 displayed catalytic competency towards the thiolation of iodobenzene with dimethyldisulfide and zinc in DMF. In water, 4 was able to catalyze the Negishi cross-coupling of iodobenzene.

Synthesis characterization and antibacterial activity of Cr (III), Co (III), Fe (II), Cu (II), Ni (III) complexes of 4-(2-(((2-hydroxy-5-nitrophenyl) diazenyl) (phenyl) methylene) hydrazinyl) benzene sulfonic acid based formazan dyes and their applications on leather

A novel series of un-metallized and metal complexes formazan dye (12–17) have been synthesized in an aqueous system, without using Buffers, with cost-effectiveness and improved fastness properties. The synthetic methodology involved the synthesis of 4-(2-(((2-hydroxy-5-nitrophenyl) diazenyl) (phenyl) methylene) hydrazinyl) benzene sulfonic acid followed by diazotization of 4-nitroamisnophenol which further coupled with coupler reagent i.e. 4-[(2Z)-2-benzylidenehydrazinyl] benzene sulfonic acid. Multichromic metal complexes of 4-(2-(((2-hydroxy-5-nitrophenyl) diazenyl) (phenyl) methylene) hydrazinyl) benzene sulfonic acid (1:1 and 2:1) were synthesized with the salts of Chromium, Iron, Cobalt, Copper and Nickel. Newly synthesized metal complexes were characterized by Ultraviolet–visible (UV–Vis), Fourier transforms infrared (FT-IR), Proton nuclear magnetic resonance (1H NMR), C13-nuclear magnetic resonance (13C NMR), powder X-ray crystallography (XRD) and elemental analysis. Their performance as colorant material for different fastness properties like light fastness, wash fastness, perspiration fastness were evaluated on leather fabric and were shown to possess good fastness properties 3–5, 4–5, 3–5, and 4–5 respectively. The synthesized formazan dyes were also demonstrated the high percentage value of exhaustion and fixation on leather ranging from 91–97% and 90–98% respectively. The synthesized un-metallized and metal complex formazan dyes were ranged in color from Blue, violet, Green, Brown to Red. Antibacterial activity of synthesized formazan dyes was determined in solution by agar well diffusion method and on leather using the dyed leather fabric with synthesized dyes as model system. Maximum antibacterial activity in solution with ZOIs (19 ± 0.05 mm, 25 ± 0.07 mm, 23 ± 0.09 mm, 27 ± 0.03 mm) and significant % reduction in bacterial growth on leather (56 ± 0.03%, 65 ± 0.07%, 70 ± 0.05%, and 72 ± 0.08%) was demonstrated by chromium complex (15) against E. coli, S. aureus, Klebsiella and B. subtilis respectively.

Catalytic Activity and Durability for Oxygen Evolution on La-Ni-O / Ni for Alkaline Water Electrolysis Under Potential Cycling

Introduction Alkaline water electrolysis (AWE) produces hydrogen without any carbon dioxide emission with renewable electric power supply. Anode of AWE is usually used Ni based material which is stable under steady electrolysis. Although fluctuating electricity from renewable energy enhances deterioration of Ni anode, high temperature prepared (Li)NiO/Ni anode has high stability under fluctuated power supply1). LaNiO3 is known as high electric conductivity and activity of oxygen evolution reaction (OER) in alkaline electrolyte2), however durability of LaNiO3 has never investigated under potential cycling. In this study, we have investigated the OER activity and durability of a lanthanum nickel oxide coated on Ni (La-Ni-O/Ni) using various precursors under potential cycling. Experimental Working electrodes were the La-Ni-O/Nis prepared with thermal decomposition coating of various composition precursors. The precursors were aqueous solutions of La(CH3COO)3・1.5H2O (Junsei Chemical Co. Ltd., 99.9%), Ni(NO3)2・6H2O (Junsei Chemical Co. Ltd., 98.0%) with nominal composition of La: Ni = 1.7: 1.0, 1.4: 1.0, 1.2: 1.0 and 1.0: 1.0 in mole fraction to get intermediate composition of La2NiO4, La3Ni2O7, La4Ni3O10 and LaNiO3, and the La-Ni-O/Nis were referred to as La/Ni_1.7, 1.4, 1.2 and 1.0, respectively. The precursor was coated on a Ni plate (The Nilaco corp., 99. +%) with etching to clean up its surface. The process of the coating, drying, and 873 K for 10 min of thermal decomposition were repeated 20 times. Finally, it was baked at 1173 or 873 K for 1 h in air to get a La/Ni_1.7~1.2 or La/Ni_1.0, respectively. Counter and Reference electrode were a Ni coil and a reversible hydrogen electrode (RHE), respectively. All measurements were performed with a three-electrode electrochemical cell at 303±1 K in 7.0 M (= mol dm-3) of KOH. Cyclic voltammetry was applied for 100 cycles between 0 and 1.0 V vs. RHE with the scan rate of 100 mVs-1 as electrochemical pretreatment. The catalytic activity of the OER and the resistance of surface oxide film (R f) were evaluated by slow scan voltammetry between 0.5 and 1.8 V vs. RHE with the scan rate of 5 mVs-1 and the AC impedance spectroscopy with higher frequency arc at 1.6 V vs. RHE during the duration protocol of potential cycling between 0.5 and 1.8 V vs. RHE with the scan rate of 1 Vs-1. The electrodes were analyzed by XRD and SEM before and after electrochemical measurements. Results and discussion Figure 1 shows dependence of the R f as a function of the potential cycle number. The R fs were much larger than expected from the resistivity La-Ni-Os and thickness of the oxide with the SEM images, therefore the R fs were affected by formation of NiO, which was confirmed with XRD. The R f of La/Ni_1.0 was much smaller than others, which were baked at higher temperature than La/Ni_1.0. These values were almost the same during potential cycling. Therefore, the R fs would be able to reduce by improvement of preparation procedure. Figure 2 shows the iR free polarization curves of the La/Ni_1.7~1.0 and Ni before (a) and after (b) potential cycling. Here, the R is the higher frequency intercept on the real axis, which correspond to the electrolyte resistance. The tails of Ni(II)/Ni(III) redox were observed below 1.45 V vs. RHE, and the R fs seems to be affect to the difference from the liner region around 1.55 V vs. RHE at higher potential region. The Tafel slope of the La/Ni_1.7~1.0 were almost same around 1.55 V vs. RHE. On the other hand, the current in the Tafel region, which corresponds to the OER activity, of La/Ni_1.0 was much larger than others. According to XRD, the coating of the La/Ni_1.2 and 1.0 was LaNiO3, that of the La/Ni_1.4 was mixture of LaNiO3 and La2NiO4 and that of the La/Ni_1.7 was mixture of LaNiO3, La4Ni3O10 and La2NiO4. OER currents of the La/Ni_1.7~1.0 before potential cycling were almost the same, and they increased during the potential cycling until 4000 cycles at least, although OER currents of Ni dramatically decreased with potential cycling. Therefore, La-Ni-Os are much higher durability than Ni, and LaNiO3 would be the highest OER activity in La-Ni-Os because of the largest current around 1.55 V vs. RHE. Reference H. Ichikawa, K. Matsuzawa, Y. Kohno, I. Nagashima, Y. Sunada, Y. Nishiki, A. Manabe, and S. Mitsushima, ECS Trans, 58(33), 9 (2014).R. N. Singh, L. Bahadur, J. P. Pander, and S. P. Singh, J. Appl. Electrochem., 24, 149 (1994). Figure 1

Activated biochar: Preparation, characterization and electroanalytical application in an alternative strategy of nickel determination

This work reports for the first time the use of chemically activated biochar as electrode modifier for nickel determination. The biochar activation was performed by refluxing with HNO3, which promoted a higher nickel preconcentration compared to unmodified and modified biochar precursor electrodes. Morphological and structural characterization revealed the increase of surface acid groups, surface area and porosity of biochar after activation. Nickel determination was investigated adopting an alternative voltammetric methodology based on monitoring the Ni(II)/Ni(III) redox couple. In the proposed method, it was not necessary to use a complexing agent and the biochar itself was responsible for the analyte preconcentration. A linear response for Ni(II) concentration range from 1.0 to 30 μmol L−1 and a limit of detection of 0.25 μmol L−1 were obtained. The method was successfully applied for Ni(II) determination in spiked samples of bioethanol fuel and discharge water, with recoveries values between 103 and 109%.

X-ray photoelectron spectroscopy investigation of nanoporous NiO electrodes sensitized with Erythrosine B

Nanoporous NiO thin films were prepared onto FTO glass substrates by means of screen-printing and were sensitized with Erythrosine B (EryB) dye. The obtained material was electrochemically treated and characterized with ex-situ X-ray photoelectron spectroscopy in order to gain information beneficial to the application of sensitized NiO as photocathodes of p-type dye-sensitized solar cells (p-DSCs). In particular, EryB-sensitized NiO films underwent a series of electrochemical treatments in LiClO4/Acetonitrile (ACN) electrolyte devised so as to simulate possible conditions the electrode might encounter during operation in the photoelectrochemical cell. Upon potential-cycling in a range where the two NiO faradic events Ni(II)→Ni(III) and Ni(III)→Ni(IV) occur, X-ray photoelectron spectroscopy revealed that Erythrosine B dye experiences a partial detachment from the NiO surface. This detachment seems to be paralleled by the formation of stable (Ni)+(ClO4)− couples. Overall, the EryB dye displayed an acceptable electrochemical stability onto the surface of NiO electrode up to 50 cyclic voltammetries in the range −0.27÷+1.13V vs. Ag/AgCl. These results are useful for the evaluation of electrochemical stability of the dye when this is immobilized onto an electrode surface and are beneficial for a better comprehension of the degradation phenomena operating in real photoconversion device.

Investigating Transition Metal Chalcogenides for Efficient Oxygen Evolution Electrocatalysis: The Effect of Covalency and Directionality

Water electrolysis leading to generation of oxygen and hydrogen, has been one of the most promising routes towards sustainable alternative energy generation and storage, with applications ranging from metal-air batteries, fuel cells, to solar-to-fuel energy conversion systems. Oxygen and Hydrogen evolution reaction (OER and HER respectively) are the two half reactions for water electrolysis, amongst which OER is the most challenging uphill process with a high electron count. Hence, designing efficient catalysts for OER process from earth-abundant resources has been one of the primary concerns for advancing this field. Recently transition metal chalcogenides has been identified as efficient OER electrocatalysts. We have synthesized a plethora of transition metal selenides including those based on Ni, Ni-Fe, Co, and Ni-Co, which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA/cm2 [Ni3Se2 - 200 - 290 mV; Co7Se8 - 260 mV; FeNi2Se4-NrGO - 170 mV (NrGO - N-doped reduced graphene oxide); NiFe2Se4 - 210 mV; NiCo2Se4 - 190 mV]. We have proposed the idea that one of the primary reasons these selenides show a much better OER catalytic activity is due to increasing covalency in the metal-selenium bond compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chemical potential around the transition metal center, specifically, lowering the Ni2+ --> Ni3+ oxidation potential (Ni3+ being the actually catalytically active species). In this presentation we will highlight the importance of this increasing covalency in enhancing the catalytic activity with the help of experimental evidence in selenide compositions ranging from binary Ni-selenides (Ni3Se2, NiSe2, NiSe), ternary mixed metal selenides (Ni-Co-Se, Ni-Fe-Se) as well as seleno-based molecular complex containing NiSe4 tetrahedral core. We will illustrate how the Ni(II) --> Ni(III) oxidation potential is indeed lowered within the selenide coordination compared to the oxide, in pure single crystals of the seleno-based coordination complex which is devoid of any surface impurities and adsorbates. We will also emphasize the lattice-plane-dependent catalytic activity through the example of electrodeposited NiSe2 which shows that if grown along the <311> direction exposing the Ni-rich terminating lattice plane, this catalyst can exhibit lowest overpotential at 10 mA/cm2 (140 mV) that has been reported so far for OER in alkaline medium. All of these selenide electrocatalysts has been characterized with pxrd, SEM, TEM, Raman, XPS, EDS and detailed electrochemical studies including LSV, CV, chronoameprometry, chronopotentiometry, determination of Faradaic efficiency, and ECSA. Through this presentation we will offer insight into possible reasons these selenides outperform most of the known OER electrocatalysts, which will hopefully initiate discussion and efforts to fully understand and utilize their full potential.

Honeycomb layered oxide Na3Ni2SbO6 for high performance pseudocapacitor

Abstract In this study, Na3Ni2SbO6 was synthesized by simple solid state method and its electrochemical behaviour was examined as a supercapacitor electrode for the first time. Na3Cu2SbO6 was also synthesized by the same preparation method in order to compare with the Na3Ni2SbO6. The structure and morphology of the samples were characterized by XRD, XPS and SEM analysis. The results shows O3-type honeycomb layered Na3Ni2SbO6 with microcrystal morphology. Electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The results showed that the specific capacitance of the Na3Ni2SbO6 and Na3Cu2SbO6 electrodes were 397 F/g and 50 F/g at the current density of 0.5 A/g respectively. The high pseudocapacitive nature of Na3Ni2SbO6 can be attributed to reversible redox reaction of Ni(II)/Ni(III).

Surface properties of nanostructured NiO undergoing electrochemical oxidation in 3-methoxy-propionitrile

Nanostructured nickel oxide (NiO) was deposited in the configuration of thin film (thickness, l=2–6μm) onto fluorine-doped tin oxide (FTO) substrates via plasma-assisted rapid discharge sintering (RDS). Electrochemical cycling of RDS NiO in 3-methoxy-propionitrile (3-MPN) revealed two characteristic peaks of NiO oxidation which were associated to the surface-confined redox processes Ni(II)→Ni(III) and Ni(III)→Ni(IV). Grazing angle X-ray photoelectron spectroscopy (XPS) was conducted ex-situ on NiO electrodes in both pristine and oxidized states. Oxidized NiO samples for XPS experiments were obtained in the potentiostatic mode through the polarization of NiO at its two characteristic potentials of oxidation. The XPS analysis allowed to ascertain the electronic structure of the nanoporous NiO framework, and verify the adsorption of perchlorate and chloride anions onto NiO surface due to the compensation of the charge stored in oxidized NiO.XPS also revealed that the spectrum within the region characteristic of Ni 2p ionization does not vary considerably with the state of charge of the nickel centres. This finding is in evident contrast to what has been observed for the same system when it undergoes electrochemical oxidation in aqueous electrolyte.

Reflux-based synthesis and electrocatalytic characteristics of nickel phosphate nanoparticles

This is a first report on the synthesis of nickel phosphate nanoparticles (N-NiPh) from its precursors using a reflux-based route at 90 °C and its use for destruction and conversion of urea (a biochemical species) to useful fuel (H2 gas). The prepared particles are characterized by different techniques including: X-ray diffraction (XRD), scanning electron microscopy (SEM), FTIR spectroscopy and BET surface area determination. The particle size is found to have an average value of ∼70 nm with surface area of 22.3 m2/g. According to the XRD pattern and FTIR spectrum, the obtained phase structure of the NiPh nanoparticles is Ni3(PO4)2.8H2O with a monoclinic crystallographic form. Using cyclic voltammetry (CV) (and also EIS), the N-NiPh modified glassy carbon electrode (GC/N-NiPh) is activated upon potential cycling in 0.5 M KOH for 75 cycles. This is obtained at the maximum attainable enrichment of the N-NiPh surface by Ni(II)/Ni(III) species. The GC/N-NiPh shows superior electrocatalytic activity towards urea oxidation from alkaline solution compared to the corresponding Ni(OH)2-based electrodes. The oxidation process is analyzed in the light of the measured and collected electrochemical data.