“Deactivation of copper electrode” in electrochemical reduction of CO2

Metallic Cu electrode can electrochemically reduce CO₂ to CH₄, C₂H₄ and alcohols with high yields as revealed by the present authors. Many workers reported that formation of CH₄ and C₂H₄ rapidly diminishes during electrolysis of CO₂ reduction. This paper shows that such deactivation of Cu electrode is reproduced with electrolyte solutions prepared from reagents used by these workers. Deactivated Cu electrodes recovered the electrocatalytic activity for CO₂ reduction by anodic polarization at −0.05 V versus she in agreement with the previous reports. Features of the deactivation depend greatly on the individual chemical reagents. Purification of the electrolyte solution by preelectrolysis with a Pt black electrode effectively prevents the deactivation of Cu electrode. Anode stripping voltammetry of Cu electrodes, which were deactivated during electrolysis of CO₂ reduction, showed anodic oxidation peaks at ca. −0.1 or −0.56 V versus she. The severer the deactivation of the Cu electrode was, the higher electric charge of the anodic peak was observed. It is presumed that some impurity heavy metal, originally contained in the electrolyte, is deposited on the Cu electrode during the CO₂ reduction, poisoning the electrocatalytic activity. On the basis of the potential of the anodic peaks, Fe²⁺ and Zn²⁺ are assumed to be the major contaminants, which cause the deactivation of the Cu electrode. Deliberate addition of Fe²⁺ or Zn²⁺ to the electrolyte solutions purified by preelectrolysis exactly reproduced the deactivation of a Cu electrode in CO₂ reduction. The amount of the deposited Fe or Zn on the electrode was below the monolayer coverage. Electrothermal atomic absorption spectrometry (etaas) showed that Fe originally contained in the electrolyte solution is effectively removed by the preelectrolysis of the solution. Mechanistic difference is discussed between Fe and Zn in the deterioration of the electrocatalytic property of Cu electrode in the CO₂ reduction. The concentration of the impurity substances originally contained in the chemical reagents as Fe or Zn is estimated to be far below the standard of the impurity levels guaranteed by the manufacturers. Presence of trimethylamine in the electrolyte solution also severely poisons a Cu electrode in the CO₂ reduction. It was concluded that the deactivation of Cu electrode in CO₂ reduction is not caused by adsorption of the products or the intermediates produced in CO₂ reduction.     

X‐ray absorption spectroscopy study of synthetic cobalt blue pigments similar to Kangxi blue and white porcelain

A series of cobalt blue pigments, which were synthesized based on the chemical compositions of the blue pigments in Kangxi blue and white porcelain, were investigated by Co, Mn, and Fe K‐edge and L_2,3‐edge X‐ray absorption spectroscopy to determine the oxidation states and species of the elements and to discern their impact on the blue color. The results reveal that Co is bivalent and mainly located at tetrahedral sites, which is the main parameter controlling the blue color. Mn is mainly present as Mn²⁺, or Co_xZn_1‐xAl₂O₄ and Fe is mainly present as Fe³⁺. In particular, Fe³⁺ substitutes the Al in CoAl₂O₄ and occupies octahedral sites with a high Mn content. All the synthetic cobalt blue pigments can form a solid solution with various end‐members or an intermediate solution spinel. The spectroscopic determination of the oxidation states and speciation of Co, Mn, and Fe furthers understanding of the coloration of blue pigments in blue and white porcelain.     

Synthesis of a magnesium/aluminum/iron layered double hydroxide and its flammability characteristics in halogen‐free,flame‐retardant ethylene/vinyl acetate copolymer composites

Mg–Al–Fe ternary hydrotalcites were synthesized by a coprecipitation method and characterized with powder X‐ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The flame‐retardant effects of Mg/Al–CO₃ layered double hydroxides (LDHs) and Mg/Al/Fe–CO₃ LDHs in an ethylene/vinyl acetate copolymer (EVA) were studied with the limited oxygen index (LOI), the UL‐94 test, and the cone calorimeter test (CCT), and the thermal degradation behavior of the composites was examined by thermogravimetric analysis. The results showed that the LOI values of the EVA/(Mg/Al/Fe–CO₃ LDH) composites were basically higher than those of the EVA/(Mg/Al–CO₃ LDH) composites at the same additive level. In the UL‐94 test, there was no rating for the EVA/(Mg/Al–CO₃ LDH) composite at the 50% additive level, and a dripping phenomenon occurred. However, the EVA/(Mg/Al/Fe–CO₃ LDH) composites at the same loading level of LDHs containing a suitable amount of Fe³⁺ ion reached the V‐0 rating, the dripping phenomenon disappearing. The CCTs indicated that the heat release rate (HRR) of the EVA composites with Mg/Al/Fe–CO₃ LDHs containing a suitable amount of Fe³⁺ decreased greatly in comparison with that of the composites with Mg/Al–CO₃ LDHs. The introduction of a given amount of Fe³⁺ ion into Mg/Al–CO₃ LDHs resulted in an increase in the LOI, a decrease in the HRR, and the achievement of the UL‐94 V‐0 rating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The fate of iron during the alkali‐activation of synthetic (CaO‐)FeOx‐SiO2 slags: An Fe K‐edge XANES study

Slags from the nonferrous metals industry have great potential to be used as feedstocks for the production of alkali‐activated materials. Until now, however, only very limited information has been available about the structural characteristics of these materials. In the work presented herein, synthetic slags in the CaO–FeO_x–SiO₂ system, representing typical compositions of Fe‐rich slags, and inorganic polymers (IPs) produced from the synthetic slags by activation with alkali silicate solutions have been studied by means of X‐ray absorption near‐edge structure (XANES) spectroscopy at the Fe K‐edge. The iron in the slags was largely Fe²⁺, with an average coordination number of approximately 5 for the iron in the amorphous fraction. The increase in average oxidation number after alkali‐activation was conceptualized as the consequence of slag dissolution and IP precipitation, and employed to calculate the degrees of reaction of the slags. The degree of reaction of the slags increased with increasing amorphous fraction. The iron in the IPs had an average coordination number of approximately 5; thus, IPs produced from the Fe‐rich slags studied here are not Fe‐analogs of aluminosilicate geopolymers, but differ significantly in terms of structure from the latter.     

Preparation of block copolymers via metal‐free visible‐light‐induced ATRP for the detection of lead ions

Polyacrylamide‐b‐poly(methacrylic acid) was prepared on the surface of Au electrode (Au/PAM/PMAA) for Pb²⁺ ion electrochemical sensing via metal‐free visible‐light‐induced atom transfer radical polymerization, which was very simple, convenient, and environmentally friendly. Au/PAM/PMAA was carefully examined by cyclic voltammetry, electrochemical impedance spectroscopy, and X‐ray photoelectron spectroscopy. Further, Au/PAM/PMAA was successfully used for the determination of Pb²⁺ ion by differential pulse anodic stripping voltammetry. Under the optimal conditions, a linear response from 1.0 × 10^?11 to 1.0 × 10^?4 mol/L with detection limit of 2.5 × 10^?12 mol/L (S/N = 3) was achieved from the results of experiments. Comparing with similar Pb²⁺ sensors, the broader linear range and lower detection limit suggested the promising prospect of Au/PAM/PMAA. In a word, the work of this article had an important significance for the polymer‐modified electrodes and the sensitive detection of Pb²⁺. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45863.     

Effect of chemical inhomogeneity on domains and ferroelectric properties of Fe‐modified 0.77Bi0.5Na0.5TiO3–0.23SrTiO3

Lead‐free 0.77(Bi_0.5Na_0.5)TiO₃–0.23Sr(Ti_1?xFe_x)O₃ (x = 0, 0.04) (BNT–23STF_x) was prepared using a conventional solid‐state reaction route. The effects of Fe‐modification on the chemical homogeneity from a μm scale perspective, the core‐shell domains structures, and the ferroelectric properties were investigated. The chemical homogeneity was analyzed using energy dispersive X‐ray mapping in scanning transmission electron microscopy mode, and the field‐dependent behaviors of strain and polarization were obtained to determine the ferroelectric properties. Substituting Fe³⁺ for Ti⁴⁺ resulted in completely different electrical behavior and properties, despite similar XRD patterns and microstructures. The Fe‐substitution promoted the mobility of Sr²⁺ ions in the BNT phase and, as a consequence, the chemical homogeneity increased and the core‐domains collapsed. Extending the ceramic processing, such as milling time and sintering time, affected domain distribution and compositional inhomogeneity, which led to a gradual transformation from ferroelectric to relaxor.     

Formation of structural defects and strain in electrodegraded Fe‐doped SrTiO3 crystals due to oxygen vacancy migration

We report on our investigation of structural defect and strain formation in electrodegraded reduced and oxidized, Fe‐doped SrTiO₃ (Fe:STO) single crystals using optical second harmonic generation (SHG) and confocal Raman spectroscopy. SHG and Raman spectra reveal structural and electrochemical inhomogeneity resulting from the formation of Fe⁴⁺/oxygen ion and Fe³⁺/oxygen vacancy aggregation sites along the degraded anode and cathode interfaces, respectively. We show that mixed Fe³⁺/Fe⁴⁺ states and structural strain gradients are generated across the color fronts. These results, as well as oxygen sublattice differences between the anodic and cathodic bulk, present the color front as an interface between two dominant oxygen bonding distortions. The strain near the color front shows a strong dependence on oxygen vacancy concentration and diffusion within the crystals. Our characterization of structural and electrochemical changes due to electric field‐induced strain and oxygen vacancy migration advances knowledge of electrodegradation in perovskite‐based titanate single crystals.     

Raman Vibrations,Domain Structures,and Photovoltaic Effects in A‐Site La‐Modified BiFeO3 Multiferroic Ceramics

Micro‐Raman spectroscopy, X‐ray diffraction, high‐resolution transmission electron microscopy (TEM), oxygen vacancies, synchrotron X‐ray absorption spectroscopy, magnetizations, optical band gaps, and photovoltaic (PV) effects have been studied in (Bi_1?xLa_x)FeO₃ (BFO100xL) ceramics for x = 0.0, 0.05, 0.10, and 0.15. XRD, Raman spectra, and TEM confirm a rhombohedral R3c symmetry with the tilted FeO₆ oxygen octahedra in all compounds. The low‐frequency Raman vibrations become broader and shift toward higher frequency as La³⁺ increases. Fe K‐edge synchrotron X‐ray absorptions reveal that Fe³⁺ valence and Fe–O–Fe bond angle are not modified by the La³⁺ substitution. All compounds exhibit a linear antiferromagnetic feature. Optical transmission reveals band gaps in the range of 2.22–2.24 eV. The heterostructures of indium tin oxide (ITO) film/(Bi_1?xLa_x)FeO₃ ceramics/Au film show a p–n junction‐like I–V characteristic behavior. The maximal PV power conversion efficiency can reach 0.19% in ITO/BFO15L/Au under illumination of λ = 405 nm. A junction‐like theoretical model can reasonably describe open‐circuit voltage and short‐circuit current as a function of illumination intensity.     

Synthesis and Characterization of 3,4,5‐Triamino‐1,2,4‐Triazolium 5‐Nitrotetrazolate

3,4,5‐Triamino‐1,2,4‐triazolium 5‐nitrotetrazolate ( 2 ) was synthesized in high yield from 3,4,5‐triamino‐1,2,4‐triazole (guanazine) ( 1 ) and ammonium 5‐nitrotetrazolate. The new compound 2 was characterized by vibrational (IR and Raman) and multinuclear NMR spectroscopy (¹H, ¹³C, ¹⁵N), elemental analysis and single crystal X‐ray diffraction (triclinic, P(‐1), a=0.7194(5), b=0.8215(5), c=0.8668(5) nm, α=75.307(5), β=70.054(5), γ=68.104(5)°, V=0.4421(5) nm³, Z=2, ϱ=1.722 g cm⁻¹, R₁=0.0519 [F>4σ(F)], wR₂(all data)=0.1154). The ¹⁵N NMR spectrum and X‐ray crystal structure (triclinic, P‐1, a=0.5578(5), b=0.6166(5), c=0.7395(5) nm, α=114.485(5)°, β=90.810(5)°, γ=97.846(5)°, V=0.2286(3) nm³, Z=2, ϱ=1.658 g cm⁻¹, R₁=0.0460 [F>4σ(F)], wR₂(all data)=0.1153) of 1 were also determined.     

Structural features of iron‐phosphate glass

This paper reports a study and discusses the role of Fe ions in the inhibition of corrosion of iron phosphate glasses. The structure of the 40Fe₂O₃–60P₂O₅ (mol%) glass, having a confirmed dissolution rate in aqueous solution at 90°C superior to borosilicate glasses, was investigated. Samples were crystallized at characteristic temperatures defined by differential thermal analysis and analyzed by X‐ray diffraction. Crystalline phases of Fe₂Fe[P₂O₇]₂ and Fe₄[P₂O₇]₃ were detected. The hyperfine parameters from the Mössbauer spectrum indicate that both Fe²⁺ and Fe³⁺ ions are in octahedral coordination, and 18% of the Fe³⁺ ions in the starting batch are reduced to Fe²⁺ ions after melting. The broad and symmetric spectra centered in g≈2.0 from the EPR measurements indicate the presence of two or more Fe interacting ions occupying sites of relatively high local symmetry.     

Characterization of in situ prepared nano‐hydroxyapatite/polyacrylic acid (HAp/PAAc) biocomposites

Nanoparticles hydroxyapatite (HAp) was prepared via an in situ biomimetic process with polyacrylic acid (PAAc) as a host polymeric material. Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, X‐ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were used to test the physical and chemical characteristics of biocomposites. The formation of HAp is confirmed by energy dispersion X‐ray analysis. Chemical binding between inorganic HAp and PAAc was investigated and discussed. HAp formation was initiated through the interaction of Ca²⁺ ions with the negative side groups of the polymer surface. The results showed that the biocomposites were formed with good homogeneity and thermal stability. Nanoparticles of HAp were uniformly distributed in the polymeric matrices. The resulting new materials are hoped to be applicable in the biomedical fields. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

In Situ Measurements on Solid Oxide Fuel Cell Cathodes – Simultaneous X‐Ray Absorption and AC Impedance Spectroscopy on Symmetrical Cells

A solid oxide fuel cell in operando is a complex multiphasic entity under electrical polarization and operating at high temperatures. In this work, we reproduce these conditions while studying transition metal redox chemistry in situ at the cathode. This was achieved by building a furnace that allowed for X‐ray absorption near‐edge structure and AC impedance spectroscopy data to be obtained simultaneously on symmetrical cells while at operating temperatures. The cell electrodes consisted of phases from the Ruddlesden–Popper family; La₂NiO_4+δ, La₄Ni₃O_10–δ, and composites thereof. The redox chemistry of nickel in these cathodes was probed in situ through investigation of changes in the position of the X‐ray absorption K‐edge. An oxidation state reduction (Ni³⁺ to Ni²⁺) was observed on heating the cells; this was correlated to changing concentrations of ionic charge carriers in the electrode. Polarizing the cells resulted in dramatic changes to their electrical performance but not to the bulk redox chemistry of the electrode. The implications of this with respect to explaining the polarization behavior are discussed.     

Local microstructure characterization of rare earth‐doped PMMA with low‐ion content by fluorescence EXAFS

Fluorescence‐extended X‐ray absorption fine structure (EXAFS), and emission spectrum and excitation spectrum (ESES) were used to characterize the local structure of rare earth‐doped poly(methyl methacrylate)s (Re‐PMMAs) with ion concentration of 600–1000 ppm. Fluorescence EXAFS shows that the chemical state of Sm in Sm‐PMMA is the same as that in Sm₂O₃ and samarium octanoate (SOA), while that of Eu in Eu‐PMMA is different from that in Eu₂O₃ and europium octanoate. ESES also proves the concomitance of Eu²⁺ with Eu³⁺ ions in Eu‐PMMA. And, the almost identical peak positions of Eu L₃ edge at ～6976.7 eV in fluorescence EXAFS of Eu‐PMMA with various Eu content suggests the proportions of Eu²⁺ to Eu³⁺ are the same in these samples. The simulation of fluorescence EXAFS shows that the first‐shell coordination number of Sm³⁺ in Sm‐PMMA is 9.12, and the average first‐shell distance around Sm³⁺ in Sm‐PMMA is 2.43 Å. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1294–1298, 2006     

Electrochemical behavior of La0.8Sr0.2FeO3 electrode with different porosities under cathodic and anodic polarization

Electrochemical behavior of La_0.8Sr_0.2FeO₃ (LSF) electrode with different porosities under cathodic and anodic current polarization has been investigated by electrochemical impedance spectroscopy and the galvanostatic method. The activation and degradation behavior of the LSF electrode may be related to the partial reduction and oxidation of the Fe ions under cathodic and anodic polarization, especially in the LSF electrodes with high porosities. The performance of the LSF electrode has been found to depend on the oxygen vacancies at the LSF surface, which would promote the transport of oxygen intermediate species at the LSF surface close to the triple-phase boundary (TPB) region. Results show that the polarization resistance (Rp) of the LSF electrode decreases at the beginning with the increase of cathodic polarization time, while Rp always increases with the increase of anodic polarization time. The effect of cathodic and anodic polarization becomes predominant with the increasing of the porosities of the LSF electrode, which is ascribed to the decrease of the interface area between electrode and electrolyte.     

In situ UV–VIS spectroelectrochemical study of polyaniline degradation

The degradation of polyaniline at anodic potentials was studied with in situ UV–Vis spectroscopy of polymer‐coated ITO glass electrodes. Spectral changes at high potential values were observed and discussed. Degradation follows first‐order kinetics, with rate constants ranging from 8.40 × 10⁻⁶ to 2.93 × 10⁻³ s⁻¹ at electrode potentials of E_NHE = +0.85 to +1.20 V. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 287–294, 1999     

Synthesis of Nano‐γ‐Ferric Oxide by Thermolysis of the 2‐Mercapto‐5‐Methylpyridine‐N‐Oxide‐Iron(III) Complex via Factorial Design

2‐Mercapto‐5‐methylpyridine‐N‐oxide (MMPNO) and its sodium salt (NaMMPNO) were synthesized. The reaction of the latter with Fe³⁺ generates Fe(MMPNO)₃ chelate. The thermolysis of this chelate at 350 °C yielded highly pure reddish‐brown γ‐Fe₂O₃ nanocrystallites with an average particle size of 6.2 nm, a particle size range of 4.2 to 14.8 nm, and a specific surface area of 51.5 m²g^–1. The thermolysis process was optimized using the 2² fractional design. Quantitative tests and characterization of products were carried out by UV‐vis spectroscopy, XRD, LLS, SEM, TGA, BET, TEM, FT‐IR, elemental microanalysis, and classical analytical measurements.     

Physicochemical and structural effects of electrolyte‐induced delamination on polyethylene teraphthalate‐coated steel plates

This research evaluated the in situ physicochemical changes and alterations occurring in an electrolytic chromium coated steel (ECCS), surface protected by polyethylene teraphthalate (PET) copolymer, after inducing a fracture on the coating in an acid acetic‐acetate medium. The delamination was characterized in the front of the failure by means of anodic and cathodic electrochemical mechanisms, and the resistance and degradation of the metal‐polymer composite's substrates were analyzed by means of Raman vibrational spectroscopy. The application of an electrochemical cell to generate in situ delamination, simulating the formation of pores or artificial defects, provided information on the activity inside the substrates of the PET‐coated ECCS composite as a result of the effect of the acetic acid. The anodic delamination mechanism is based on the diffusion of the electrolyte through the metal‐polymer interface and the pre‐existence of pores on the polymer layer. The cathodic delamination mechanism is based on the mechanical action of the gaseous hydrogen as a result of the reduction of H⁺. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

An in situ spectroelectrochemical Raman investigation of Au electrodeposition and electrodissolution in KAu(CN)2 solution

Spectroelectrochemical behaviour of CN^– on a Au electrode in a KAu(CN)₂ bath at pH 6.3 was studied by in situ confocal Raman spectroscopy. Internal (CN stretch) and external (Au–CN) CN^–-related frequencies were investigated under potentiostatic control in a potential interval spanning cathodic and anodic ranges (–1800 to +1200 mV vs Ag/AgCl). Electrochemical behaviour was assessed by cyclic voltammetry. Stark-shifted Au–NC^– species are the dominating ones under cathodic polarization. Above the hydrogen evolution potential a Au–H stretch band can also be observed. At open circuit Au–CN^– species tend to prevail, while anodic conditions relate to the enhanced formation of Au(CN)₂ ^– and OCN^–.     

Effect of electrode materials on the kinetics of the electro-reduction of peroxyacetic acid

Electrochemical behavior of peroxyacetic acid (PAA) and hydrogen peroxide (H₂O₂) was examined at various metal and carbon electrodes (i.e., Au, Ag, Cu, Pt, Pd, Rh, Ti, W, Hg, Ni, Fe, glassy carbon (GC), and basal-plane pyrolytic graphite (BPG)) in 0.1 M acetate buffer solution (pH 5.5) using potentiostatic (i.e., cyclic voltammetry and rotating disk electrode voltammetry) and galvanostatic techniques. It was found that the electro-reductions of PAA and H₂O₂ are highly sensitive to electrode material. Both species were found to be electrochemically and separately reduced at Au, Ag, Cu, Pt, Pd, GC, and BPG electrodes. On the other hand, at Fe, Ni, Hg, Rh, Ti, and W electrodes, voltammetric response for the PAA reduction was not obviously observed. The kinetics of electro-reduction of PAA in 0.1 M acetate buffer solution was studied at Au, Ag, and GC electrodes in details, and the relevant kinetic parameters (i.e., the exchange current density, j₀, the standard rate constant, k⁰, and cathodic transfer coefficient, α_c) were estimated from the Tafel plots. The cyclic voltammetric reduction peak potentials obtained for the PAA reduction at Au, Ag, and GC electrodes were compared with those calculated using the kinetic and thermodynamic parameters obtained under the same experimental conditions. The measured and calculated reduction peak potentials at each electrode were found to be in agreement with each other, indicating that the evaluated values of kinetic parameters for the reduction of PAA at Au, Ag, and GC electrodes are reasonable.     

Syntheses and characterization of polystyrene‐supported 2,5‐dimercapto‐1,3,4‐thiodiazole and its sorption behavior for Pd(II), Pt(IV), and Au(III)

A type of chelating resin crosslinking polystyrene‐supported 2,5‐dimercapto‐1,3,4‐thiodiazole (also called bismuththiol I, BMT), containing sulfur and nitrogen atoms, was prepared. The structure of PS‐BMT was confirmed by FTIR, elemental analysis, and X‐ray photoelectron spectroscopy (XPS). Adsorption of Pd(II), Pt(IV), and Au(III) was investigated. The capacity of PS‐BMT to adsorb Pd(II) and Pt(IV) was 0.190 and 0.033 mmol/g, respectively. The adsorption dynamics of Pd(II) showed that adsorption was controlled by liquid film diffusion and that the apparent activation energy, E_a, was 32.67 kJ/mol. The Langmuir model was better than the Freundlich model in describing the isothermal process of Pd(II), and the ΔG, ΔH, and ΔS values calculated were ?0.33 kJ/mol, 26.29 kJ/mol, and 87.95 J mol^?1 K^?1, respectively. The mechanisms of adsorption of Pd(II), Pt(IV), and Au(III) were confirmed by XPS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 631–637, 2006