Understanding the hydroxyl adsorption behavior at Pt electrode surface in high-temperature alkaline solutions

Since the application in fuel cell,the electrochemical adsorption of hydroxyl has received considerable attention in recent years.While most research mainly focus on the room temperature,in this paper,the electrochemical adsorption of hydroxyl in alkaline solution at high temperature was investigated.An unusual oxidation peak was observed at-0.27 V,suggesting new behavior of hydroxyl adsorption occurred.As is known two kinds of cation hydrated clusters exist in alkaline solution,(H_(2)O)_(x-1)M^(+)-H_(2)O-O_(ad)H and(H_(2)O)_xM^(+)-O_(ad)H.For K^(+)and Cs^(+),the cluster shows unstable structure due to the weak interaction between hydrated cation and OH^(-)especially at high temperature.However,For Li^(+),Na^(+)the cluster structure would be stable,as the interaction force between the hydrated cation and OH^(-)is so strong.It was revealed that the unusual oxidation peak has some relationship with the(H_(2)O)_(x-1)M^(+)-H_(2)O-O_(ad)H cluster(K^(+)and Cs^(+))absorbed at Pt electrode surface.When the temperature was raised,(H_(2)O)_(x-1)M^(+)-H_(2)O-and-O_(ad)H was disconnected,then the O_(ad)H absorbed at Pt surface got oxidated.Based on the SEM observation,it was showed the unusual electrochemical oxidation reaction would generate platinum oxides,blocking the reactive sites at Pt electrode surface,thus reducing the electrochemical reactivity of Pt electrode.Accordingly,parameters of alkaline concentration and temperature were systematically studied,it was found that increase temperature or alkaline concentration was in favor of the unusual oxidation reaction.This study provides more understanding of hydroxyl adsorption behavior at Pt electrode surface for the high temperature water solution environment.

Corrosion-wear behavior of nanocrystalline Fe88Si12 alloy in acid and alkaline solutions

The corrosion-wear behavior of a nanocrystalline Fe_（88）Si_（12） alloy disc coupled with a Si_3N_4 ball was investigated in acid（pH 3） and alkaline（pH 9） aqueous solutions. The dry wear was also measured for reference. The average friction coefficient of Fe_（88）Si_（12） alloy in the pH 9 solution was approximately 0.2, which was lower than those observed for Fe_（88）Si_（12） alloy in the pH 3 solution and in the case of dry wear. The fluctuation of the friction coefficient of samples subjected to the pH 9 solution also showed similar characteristics. The wear rate in the pH 9 solution slightly increased with increasing applied load. The wear rate was approximately one order of magnitude less than that in the pH 3 solution and was far lower than that in the case of dry wear, especially at high applied load. The wear traces of Fe_（88）Si_（12） alloy under different wear conditions were examined and analyzed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The results indicated that the tribo-chemical reactions that involve oxidation of the worn surface and hydrolysis of the Si_3N_4 ball in the acid solution were restricted in the pH 9 aqueous solution. Thus, water lubrication can effectively improve the wear resistance of nanocrystalline Fe_（88）Si_（12） alloy in the pH 9 aqueous solution.

Effects of applied potential on the stress corrosion cracking behavior of 7003 aluminum alloy in acid and alkaline chloride solutions

Potentiodynamic polarization tests and slow strain rate test（SSRT） in combination with fracture morphology observations were conducted to investigate the stress corrosion cracking（SCC） behavior of 7003 aluminum alloy（AA7003） in acid and alkaline chloride solutions under various applied potentials（Ea）. The results show that AA7003 is to a certain extent susceptible to SCC via anodic dissolution（AD） at open-circuit potential（OCP） and is highly susceptible to hydrogen embrittlement（HE） at high negative Ea in the solutions with p H levels of 4 and 11. The susceptibility increases with negative shift in the potential when Ea is less than-1000 m V vs. SCE. However, the susceptibility distinctly decreases because of the inhibition of AD when Ea is equal to-1000 m V vs. SCE. In addition, the SCC susceptibility of AA7003 in the acid chloride solution is higher than that in the alkaline solution at each potential. Moreover, the effect of hydrogen on SCC increases with increasing hydrogen ion concentration.

Selective recovery of lead from zinc oxide dust with alkaline Na_2EDTA solution

The selective recovery of lead from the zinc oxide dust using an alkaline Na2EDTA solution was investigated. The effects of temperature, leaching time, Na2EDTA concentration and initial NaOH concentration on the leaching rates of lead and zinc were studied. The following optimized leaching conditions were obtained： liquid-to-solid ratio 5：1 mL/g, stirring speed 650 r/min, Na2EDTA concentration 0.12 mol/L, initial NaOH concentration 0.5 mol/L, leaching temperature 70 ℃, leaching time 120 min. Under the optimized conditions, the average leaching rates of lead, zinc, fluoride and chloride are 89.92%, 0.94%, 62.84% and 90.02%, respectively. The filtrate was used to electrowin lead powders. The average current efficiency of electrowinning is about 93% and lead content is higher than 98% under the conditions of temperature of 60 ℃, current density of 200 A/m2, H3PO4 concentration of 1.5 g/L, and lead ion concentration of above 5 g/L. The consumption of Na2EDTA and the direct current are about respectively 0.218 kg and 0.958 kW·h for per kilogram of lead powder.

The interaction mechanism between zein and folic acid in alkaline aqueous solutions:an experimental and molecular simulation study

Objectives:Folic acid is a vitamin that is not highly soluble in water and is sensitive to the environment.Therefore,it is important to find suitable carriers.This study aimed to exemplify the interaction of folic acid with zein in alkaline aqueous solutions and shed light on how zein can be used as a carrier for folic acid.Materials and Methods:Zein and folic acid were separately dissolved in NaOH solutions with a PH of 11.5.Zein solution and folic acid solution were combined in specific ratios.Various methods including multi-spectroscopy,dynamic light scattering,and electron microscopy combining with molecular dynamics simulations were used to study the interaction mechanism between zein and folic acid in alkaline aqueous solutions.Results:Fluorescence spectroscopy showed that the quenching of zein by folic acid was mainly static,and the main driving force behind this interaction was van der Waals forces and hydrogen bonds.The formation of zein–folic acid complexes was confirmed by ultraviolet–visible spectroscopy,Fourier transform infrared spectroscopy,and circular dichroism spectroscopy.The results also showed that the structure of zein changed when it interacted with folic acid.Dynamic light scattering analysis revealed that the addition of folic acid caused proteins to aggregate.The aggregates of the complexes had an irregular shape and were large,as observed by scanning electron microscopy and transmission electron microscopy.Molecular simulation was used to further investigate the interaction mechanisms.According to these findings,the folic acid molecule interacted with zein in a shallow recess near the protein surface.The dominant forces at play in the zein–folic acid interaction were van der Waals forces and electrostatic forces,including hydrogen bonding.Conclusion:The zein alkali-soluble system is very suitable for folic acid delivery.

Effects of additives on zinc electrodeposition from alkaline zincate solution

The effects of additives on the surface and cross-sectional morphologies of zinc deposits on iron substrate from alkalinezincate solution were characterized by scanning electron microscope(SEM).The cathodic reaction mechanisms under variousconcentrations of additives were investigated using cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)techniques.It is found that with increasing the additive A content in the bath solution,the nucleation overpotential(NOP)value isobviously increased and the inhibition effect is strengthened.This may be mainly due to the adsorption of additive A on the cathodicelectrode surface,which can cover the active sites and block the discharge reduction.The results of EIS analysis indicate that therate-determining step of zinc electrodeposition process is changed from mixed control step into electrochemical reduction step in thepresence of additive A.However,any quantity of additive B has little effect on the NOP value and the inhibition effect is not obvious.Furthermore,addition of additive A and additive B at the same time displays the strongest inhibition effect and shows a strongsynergism because of their co-adsorption on the cathodic electrode surface.

Polyaniline Formed in Alkaline Solution─A New Luminous Material

Electropolymerization of aniline in KOH solution and properties of the polymer are studied by using in situ reflex ellipsometry, cyclic voltammetry and fluorescence spectroscopic method. The change patterns of ellipsometric parameters and the thickness of film in the process of electropolymerization are investigated. The complex refractive indices and the fluorescence spectra of PAN indicate that the PAN is a new kind of luminous material.

3D Se-doped NiCoP nanoarrays on carbon cloth for efficient alkaline hydrogen evolution

The exploration of stable and highly efficient alkaline hydrogen evolution reaction(HER)electrocatalysts is imperative for alkaline water splitting.Herein,Se-doped NiCoP with hierarchical nanoarray structures directly grown on carbon cloth(Se-NiCoP/CC)was prepared by hydrothermal reaction and phosphorization/selenization process.The experimental results reveal that Se doping could increase the electrochemical active sites and alter the electronic structure of NiCoP.The optimized Se-NiCoP/CC electrode exhibits outstanding HER activity in alkaline electrolyte,which only needs a low overpotential of 79 mV at the current density of 10 mA/cm^(2).When serving as anode and cathode electrode simultaneously,the Se-NiCoP/CC electrodes achieve current density of 50 mA/cm^(2) at a low voltage of only 1.62 V.This work provides a feasible way to rationally design high active HER electrocatalysts.

Corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding in alkaline solution

This study was done to evaluate the nugget zone(NZ)corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding(FSLW)in a solution of 0.015 mol/L borax(pH 9.3).To this end,dissimilar copper/brass plates were welded with two dissimilar heat inputs(low and high)during the welding procedure.The high and low heat inputs were conducted with 710 r/min,16 mm/min and 450 r/min,25 mm/min,respectively.Using open circuit potential(OCP)measurements,electrochemical impedance spectroscopy(EIS)and Tafel polarization tests,the electrochemical behavior of the specimens in borate buffer solution was assessed.With the help of scanning electron microscope(SEM),the morphology of welded specimen surfaces was examined after immersion in the test solution.According to the results,the NZ grain size and resistance improvement reduced due to the nugget zone corrosion with a decreased heat input.The results obtained from Tafel polarization and EIS indicated the improved corrosion behavior of the welded specimen NZ with a decrease in the heat input during the welding process unlike the copper and brass metals.Furthermore,an increased heat input during the welding process shows a reduction in the conditions for forming the passive films with higher protection behavior.

Passivation kinetics of Mg-Nd-Gd-Zn-Zr(EV31A)and Mg-Y-Nd-Gd-Zr(WE43C)in NaOH solutions

Passivation kinetics of two Mg-RE alloys,such as Mg-Nd-Gd-Zn-Zr(EV31A),and Mg-Y-Nd-Gd-Zr(WE43C)were investigated in two different heat treated conditions(solution treated and overaged)in 0.01-1.0 M NaOH solutions under potentiostatic conditions.Negative reaction order was observed in dilute NaOH which transitioned to positive values as the passivation time increased and in the 1 M NaOH as well.The passive layers showed platelet morphology and the size of the platelets decreased with increase in the NaOH concentration.The hydrogen evolution reaction(HER)kinetics was not improved on the passive layer covered surface of the Mg-RE alloys in contrast to the improvements reported on the hydroxide covered pure magnesium.The electrochemical impedance increased with increase in the NaOH concentration in the solution treated condition of both Mg-RE alloys,whereas the overaged EV31A alloy showed a reverse trend.The passive layer of EV31A showed almost 100%higher charge carrier density than the film formed on the WE43C in the overaged condition.A better passivation behavior was observed in the solution treated condition than that in the overaged condition which could be attributed to the uniform distribution of the RE elements in the solution treated specimens.The WE43C alloy revealed better corrosion resistance in the alkaline solution than the EV31A alloy.

Concentration and separation of vanadium from alkaline media by strong alkaline anion-exchange resin 717

With strong alkaline anion-exchange resin 717 as the sorbent and NaOH solution as the eluent, a study on the sorption from alkaline solution and elution of vanadium（V）, silicon（iv）, and aluminium（III） was carried out. Different parameters affecting the sorption and elution process, including temperature, pH values as well as the ratio of resin to solution, were investigated. The results show that sorption degree of vanadium（V） increases with a decrease ofpH values, and V（V） ions are easier sorbed than Si（IV） and AI（III） ions under the same conditions. The sorption degree ofV（V）, Si（IV）, and AI（III） at pH 9.14 for 15 man are 90.6%, 33.5%, and 21.6%, respectively. Si（IV）, AI（III）, and V（V） ions sorbed on 717 resin were eluted by use of 2 mol·L^-1 NaOH solution; the desorption degree ofV（V）, Si（IV）, and AI（III） for 5 min are 81.7 %, 99.1%, and 99.3%, respectively.

Synthesis of Zeolites by Alkaline Activation of Fly Ash

In terms of mineral transformation, and chemical composition of acid-soluble component as a function of reaction time, the effect of alkaline solution on zeolite-like fly ash was studied by employing fly ash and NaOH solution as starting materials. When fly ash and 1-10 mol/L NaOH solution were processed at 100 degreesC for 24 h with 1:10 W/S ratio in a relatively closed system, powder XRD patterns of resulting products indicated the formation of various zeolites. Zeolite P crystallized early at low alkaline concentration, which was replaced then by zeolites X and A. At high concentration, hydroxy sodalite was the only new phase. Quartz, in fly ash and NaOH solution system, gradually dissolved, and mullite, however, remained stable. It was concluded that, with Al/Si and Na/Si finally reaching equilibrium in molar ratio, composition of starting mixtures affects the crystallization of zeolite from fly ash.

Electrocatalytic Activity of Ni/C Electrodes Prepared by Metal Vapor Synthesis For Hydrogen Evolution in Alkaline Solution

The metal vapor synthesis (MVS) methed was used to prepare activatedcarbon supported nickel electrode. The electrocatalytic activity of the electrode forhydrogen evolution reaction(HGR) in alkaline solution was studied. Cathodicpolarization curves showed the electrocatalytic activity of Ni/C electrode prepared byMVS method was higher than that of the one prepared by conventional method.

Enhancing hydrogen electrocatalytic oxidation on Ni_(3)N/MoO_(2)in-plane heterostructures in alkaline solution

Nickel(Ni)-based materials act as one of the most promising candidates as platinum-group-metal-free(PGM-free)electrocatalysts for hydrogen oxidation reaction(HOR)in alkaline solution.Nevertheless,the electrocatalytic activity of pure Ni is significantly limited due to the sluggish kinetics under alkaline condition.To accelerate the kinetics,constructing heterostructures and nitride structures have been developed as two representative strategies.Here,we combined the two methods and presented a facile synthesis of the sheet-like Ni_(3)N/MoO_(2)in-plane heterostructures for enhanced HOR in alkaline electrolytes.Relative to Ni or Ni_(3)N,the Ni_(3)N/MoO_(2)in-plane heterostructures exhibited a significantly increased mass activity by 8.6-fold or 4.4-fold,respectively.Mechanistic studies revealed that the enhanced activity of Ni_(3)N/MoO_(2)could be attributed to the weakened hydrogen adsorption and strengthened hydroxyl adsorption.This work provides a facile approach to design high-efficiency catalysts for hydrogen-oxidation catalysis and beyond.

Corrosion behavior of Cu/Al casting-rolled clad plates in different alkaline solution

The effect of pH value and different kinds of anions on the corrosion behavior of Cu/Al casting-rolled clad plates in the alkaline solution was evaluated by means of scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray diffraction(XRD),weight loss analysis,3D confocal laser scanning microscopy(CLSM)and electrochemical test.Results show the corrosion mainly occurs on the aluminum side.The corrosion resistance of the Cu/Al decreases as the pH value increases.When pH≥12,the dissolution of the film layer is faster than the passivation process.The addition of Cl^(-)ions reduces the corrosion resistance of the Cu/Al clad plates,which leads to pitting corrosion.The higher the concentration of Cl^(-)ions,the more prone the pitting to occur.The addition of SO_(4)^(2-)ions causes the denudation of the samples.The corrosion resistance of the Cu/Al is better in the alkaline solution containing NO_(3)^(-)ions than that in the solution containing Cl^(-)ions or SO_(4)^(2-)ions.When adding SO_(4)^(2-),NO^(3)^(-)and Cl^(-)to the pure alkaline solution,the corrosion resistance of the Cu/Al clad plates decreases.

POLAROGRAPHIC CHARACTERISTICS OF TELLURIUM(Ⅳ)IN ALKALINE DYE-ACID SOLUTION

Polarographic characteristics of Te(Ⅳ)-alkaline dye were investiga- ted at mercury electrode in acidic solution.It was found that the mechanism of the electrode process depended on the concentration of Te(Ⅳ).

Electrochemical Performance of Zn（002） and Zn（100） Single Crystals in 6.0mol·L^-1 KOH

In this article, the electrochemical performance of the electrodes of zinc polycrystal, Zn（002） and Zn（100） single crystals were studied by the Tafel line extrapolation of the potentio-dynamic polarization curves, the cyclic voltammetry and the charge/discharge experiment. The results shows that in 6.0 mol·L^-1 KOH solution the corrosion rate of Zn polycrystal, Zn（100） and Zn（002） single crystals decreases in turn; and the reversibility and the charge/discharge performance of Zn single crystal was superior to Zn polycrystal. The dendrite growth of the surface of Zn polycrvstal was easier than Zn single crystal during the stages of charge/discharge.

Characterization of Zinc Passive Film by Sonication in 7 M KOH Solution

The influence of 40 kHz ultrasound radiation on the passivation behavior of zinc in 7 M KOH is presented. The results of potentiodynamic and potentiostatic measurements combined with the current oscillation caused by the irradiation were examined to explain the mechanism and the sequence of formation of the oxide films during passivation. In this study, sonication was also used to investigate both effects of the passivation duration and passivation potential on the structure of the oxide layers; the adherence of the layers was found to depend strongly on both parameters. Scanning electron microscopy-energy dispersive X-ray （SEM-EDX） analysis of the zinc surface provided complementary information on the oxide layer composition and structure.

THE ELECTROCHEMICAL PREPARATION OF POLYPHENOL WITH CONDUCTIBILITY

Polyphenol film deposited on platinum foil can continuously grow with time during the electrolysis of a phenol solution consisting of 0.1 mol L-1 phenol, 3 mol L-1 NaOH and 0.5 mol L-1 Na2SO4, as has been proved by the methods of sweep potential, constant potential and constant current, and visible spectra during the electrolysis of phenol. A polyphenol film with thickness of 0.11 mm was obtained by the electrolysis of phenol at a constant potential of 0.70 V (versus Ag/AgCl with saturated KCl solution). Polyphenol film is inactive and stable in 2 mol L-1 H2SO4 solution, neutral solution and 3 mol L-1 NaOH solution and in the potential range between -0.95 and 1.35 V. The usable potential range is dependent on the pH value. Polyphenol has an ESR signal with a g factor of 2.0049. The conductivity of polyphenol is 1.2 x 10(-4) S cm(-1). In the solution of polyphenol dissolved in DMSO, the mobility of polyphenol anions is 8 x 10(-9) m(2) s(-1) V-1 at 20degreesC.

Fabrication of 3D structure by combining AFM and chemical etching on crystalline silicon surface

AFM is used for forming silicon dioxide as a layer (mask) on the silicon wafer surface (100) during the cutting process in ambient atmosphere. The silicon dioxide is made through reaction of silicon and oxygen in the atmosphere. As a result of the anisotropic behavior of single crystalline silicon, the etching rates in alkaline solution depend greatly on the various crystal orientations. The anisotropic etching behaviors in KOH solution and reasons of crystalline silicon are described. Effect of etching conditions such as etching temperature and KOH concentration of the alkaline solution on height of the micro-protuberances has been described.