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28 December 2017, Volume 23 Issue 6

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Table of Contents-2017,Vol 23(6)

2017, 23(6):  0. 

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Articles



Core-shell Pd@Pt Ultrathin Nanowires as Durable Oxygen Reduction Electrocatalysts

WANG Xin, XIONG Yun-jie, ZOU Liang-liang, HUANG Qing-hong, ZOU Zhi-qing, YANG Hui

2017, 23(6):  619-626.  doi:10.13208/j.electrochem.170113

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This paper describes a simple CO-assisted reduction approach for the controllable synthesis of ultrathin Pd nanowires along the one-dimensional (1D) direction. Ultrathin Pt films from one to several atomic layers were successfully decorated onto ultrathin Pd nanowires by utilizing Cu UPD deposition, and followed by in-situ redox replacement reaction of UPD Cu by Pt. The core–shell structure and composition of the Pd@Pt ultrathin nanowires have been verified using transmission electron microscopy and energy dispersive X-ray spectrometry. The core–shell Pd@Pt ultrathin nanowires exhibited comparative electrocatalytic activity and improved durability for the oxygen reduction reaction in comparison with commercial Pt black. The enhanced durability of the core-shell Pd@Pt catalyst could be ascribed to 1D structural stability.



Cobalt-Based Nitrogen-Doped Carbon Non-Noble Metal Catalysts for Oxygen Reduction Reaction

JIANG Meng-xiu, ZHANG Jing, LI Yue-hua, ZHANG Rong

2017, 23(6):  627-637.  doi:10.13208/j.electrochem.170105

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Transition metal-nitrogen co-doped carbon catalysts have attracted significant attention because of their reasonable activity and remarkable selectivity toward oxygen reduction reaction (ORR) as cathodic reaction in fuel cells. However, the role of transition metal in the active sites of the catalysts still is uncertain. In this work, the Co_x-N_y/C-T catalysts were prepared with BP2000 as a carbon source, urea (Ur) as a nitrogen source and Co(OAc)₂•4H₂O as a metal precursor by a simple chemical method. Meanwhile, in order to optimize the ORR activity, the catalysts were synthesized with different amounts of Co and urea, and heat-treated at different temperatures from 600-1000 ℃. SEM, TEM, BET, XRD and XPS techniques were used to characterize the catalysts in terms of structures and compositions, as well as the catalytic active sites. CV and LSV were measured to compare the ORR activity and to obtain the electron transfer number. The peak potential for oxygen reduction was approximately 0.829 V (vs. RHE) on the optimum Co_0.13-N_0.3/C-800 catalyst in an alkaline electrolyte. The results indicated that Co-N-C was potentially catalytic active site and responsible for the ORR catalytic activity in an alkaline electrolyte. The overall electron transfer number for ORR catalyzed by the optimum Co-N/C catalyst was determined to be 3.7, suggesting that the ORR catalyzed by Co-N/C was a mixture of 2- and 4-electron transfer pathways, dominated by a 4-electron transfer process. Furthermore, the Co_x-N_y/C-T catalysts also exhibited excellent methanol tolerance and stability.



Effect of allyl thiourea on nickel electrodeposition from solution containing ammonia and chloride

HE Ya-ning, YUAN Liang,DING Zhi-ying, LIU Shi-jun

2017, 23(6):  638-644.  doi:10.13208/j.electrochem.161217

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The effects of allylthiourea (ATU) concentration on the cathodic polarization behaviour, nucleation and surface morphology of nickel electrodeposited on the glassy carbon electrode from ammonia-ammonium chloride-water (NH₃-NH₄Cl-H₂O) solutions were investigated by cyclic voltammogry, cathodic polarization and current transient methods. The results revealed that the addition of ATU inhibited nickel deposition, which was enhanced with an increase in ATU concentration from 5 to 50 mg•L^-1. The initial deposition kinetics corresponded to a model including instantaneous nucleation and diffusion controlled growth. In the presence of ATU, the initial nucleation of nickel electrocrystallisation remained unchanged. However, the number density of nuclei increased and the crystal growth rate decreased. Furthermore, the addition of ATU apparently made the grains finer, leading to the formation of a more compact and uniform nickel deposit as compared with that without ATU.



Kinetics and Mechanism toward Electrochemical Reductions of Sodium Bromide and Methanol over Iron Electrodes

LIAO Qun ZHANG Shu-feng LENG Wen-hua

2017, 23(6):  645-653.  doi:10.13208/j.electrochem.161017

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It is of technological value and scientific interest to the electro-synthesis of ferrocene, conversion of carbon dioxide (CO₂) and organic electro-synthesis in non-aqueous solutions by investigating the kinetics and mechanism toward electrochemical reductions of sodium bromide (NaBr) and methanol over iron electrodes. However, few reports in the related researches are available. In this article, the kinetics and mechanism toward electrochemical reductions of NaBr and methanol over iron electrodes were examined in detail by carrying out the polarization curve and electrochemical impedance spectroscopic measurements. The results showed that methanol was the reactant, while Na⁺ ions were functioned only as conducting species; the electrode potential was the only status variable, and its impact on the rate constants of the electro-reduction of methanol followed classic Arrhenius’s equation; the reduction was not limited by concentration diffusion, but mainly by the Ohmic polarization; the amount of H₂ gas production obeyed the Faraday’s law and the activation energy was evaluated to be ~26.2 kJ•mol^-1.



Effect of PEG-Coating on Properties of Lithium-Sulfur Battery Cathode Material Containing Carbon Fiber Conductive Agent

TAN Jiecheng, TIAN Yanhong, ZHANG Xuejun, FAN Kaile

2017, 23(6):  654-660.  doi:10.13208/j.electrochem.160928

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The composite materials contained high modulus carbon fiber (HMCF) were successfully prepared by employing a ball-milling process based on the coating treatment of polyethylene glycol (PEG), and their structures and morphologies were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques．The influences of PEG content on sulfur cathode capacity, cycle stability and rate performance were systematically studied. It was found that by the pre-coating of PEG, the cathode exhibited the high initial discharge specific capacity of 1312.5 mAh•g^-1 at a current rate of 0.2C, and the reversible discharge capacity of 650 mAh•g^-1 was obtained after 50 cycles at a current rate of 200 mA•g^-1, showing the remarkably improved cycling stability.



Effects of jet milling and classifying process on the performance of LiFePO₄/C in full batteries

LIU Xing-liang, YANG Mao-ping,WANG Wei-wei, CAO Yong

2017, 23(6):  661-666.  doi:10.13208/j.electrochem.160930

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The carbon coated lithium iron phosphate (LiFePO₄/C) composite cathode material was prepared by using iron phosphate process. The effects of jet milling and classifying process on the electrochemical performance of LiFePO₄/C cathode material in full batteries were investigted. Scanning electron microscopic analyses suggested that the globose secondary particles were crustily crushed during the jet milling and classifying process, which would further result in lower tap density and carbon content. The LiFeP₄/C composite cathode materials with different physical characteristics were further tested in full batteries to evaluate the electrochemical properties. The results showed no obvious differences in capacity, AC resistance, DC resistance and power density. However, the globose LiFePO₄/C exhibited far better performances in low temperature discharge capacity retention rate and high temperature cycle retention than that of granulated composite cathode, which probably arisen from the certain delamination and destruction of conductive network during the jet milling and classifying process.



Preparation of NiS₂ nanosheet and its application in asymmetric supercapacitor

Wang Yuan-you, Liu Ya-nan，JIN Dang-qin

2017, 23(6):  667-674.  doi:10.13208/j.electrochem.170103

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In this work, the NiS₂ nanosheets have been synthesized using Ni(OH)₂  as a precursor through a sacrificial template method. The microstructure and chemical composition of as-prepared NiS₂ were characterized by XRD, EDS, BET, SEM and TEM techniques. The results showed that both Ni(OH)₂  and NiS₂  were composed of nanoplates. The electrochemical tests revealed that NiS₂ exhibited the high specific capacitance of 1067.3 F•g^-1 at a current density of 1 A•g^-1 and excellent rate performance. Furthermore, in order to evaluate the practical application of NiS₂, an asymmetric supercapacitor, NiS₂ as the positive electrode and AC as the negative electrode, displayed high energy density of 38.4 Wh•kg^-1 with a power density of 0.8 kW•kg^-1. Meanwhile, the asymmetric supercapacitor showed a superior cycling performance and 93.7% of the specific capacitance was retained after 3000 charge-discharge cycles.



Capacity Fading Analyses of LiNi _0.5Co _0.2Mn _0.3O₂and LiNi _0.5Co _0.2Mn _0.3O₂/LiFePO₄ Cathode Materials for Lithium-Ion Battery

HU Yi HE Xiang-zhu DENG Zhong-de KONG Ling-yong SHANG Wei-li

2017, 23(6):  675-683.  doi:10.13208/j.electrochem.161229

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The LiNi _0.5Co _0.2Mn _0.3O₂/LiFePO₄ (NMC532/LFP) composite cathode material for lithium-ion battery was prepared by wet ball-milling. The capacity fading behaviors of LiNi _0.5Co _0.2Mn _0.3O₂ (NMC532) and LiNi _0.5Co _0.2Mn _0.3O₂/LiFePO₄ (NMC532/LFP) were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), charge/discharge and electrochemical impedance spectroscopy (EIS) tests. The results indicated that the capacity retention values of NMC532/LFP were 97.80% and 86.48%, respectively, after 50 cycles and 60℃ high temperature storage. The NMC532/LFP exhibited better cycle performance and high temperature storage performance. Charge transfer impedance (Rct) values increased obviously after 50 cycles and high temperature storage, in particular, the R_ct value of NMC532/LFP was smaller. The I(003)/I(104) values of NMC532 and NMC532/LFP were reduced, while that of NMC532/LFP became larger, illustrating the cation mixed phenomenon was improved. There were no apparent particle cracking and particle fracture phenomena observed after 50 cycles, however, some NMC532 powder particles were obtained. The cracks were obaerved on the surface of NMC532 particles and among particles after high temperature storage, and the slight pulverization occurred on the surface of NMC532/LFP particles. Less ordered material structure, higher degree of cation mixing and increased charge transfer resistance might be mainly responsible for the capacity fading behaviors of NMC532 and NMC532/LFP.



Engineering the Electrochemical Capacitive Properties of Activated Carbon by Correct Selection of Ionic-Liquid Electrolytes

ZHANG Qiu-hong, SHEN Bao-shou, ZUO Song-lin, WEI Xin-yu

2017, 23(6):  684-693.  doi:10.13208/j.electrochem.161215

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In order to improve the electrochemical capacitive properties and to apply coconut shell activated carbon (AC) serving as electrode materials in ionic liquid (IL)-based supercapacitor (SC), the coconut shell AC material was re-activated using a steam as an activating agent in this work, forming a secondary AC (W-AC). The results showed that the specific capacitance of the W-AC electrode was much larger than that of the raw activated carbon electrode (R-AC) in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]BF₄). The electrochemical techniques including cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) measurement, and electrochemical impedance spectroscopy (EIS) were used to systematically study the capacitive properties of W-AC electrode in a series of ILs composed of different cations and anions. The electrochemical performances of the W-AC electrode using different ILs as electrolytes varied because of the different ion diameters, liquid viscosities and ionic conductivities for various ILs. Among them, the IL electrolytes composed of EMIM+, BMIM⁺ and BF₄^-, TFSI- were found to be most suitable for W-AC electrode. The specific capacitance of W-AC electrode reached 153 F•g^-1 in [EMIM]BF4 IL electrolyte, and the as–assembled SCs could achieve a high energy density of 57 Wh•kg^-1 with a potential window of 3.5 V in [BMIM]BF₄. These results may provide valuable information for selecting appropriate ionic liquids and designing high-performance supercapacitors to meet different needs.



Applications of N-methyl-N-butyl-pyrrolidinium bromide and N-methyl-N-ethyl-pyrrolidinium bromide in Zn-Br Flow Batteries

ZHANG Qi, ZHANG Miao-miao, MENG Lin

2017, 23(6):  694-701.  doi:10.13208/j.electrochem.161027

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It is extremely important for battery performance and safety in Zn-Br flow battery to use quaternary ammonium salts as complex agents for bromine. In this work, the effects of electrolyte compositions and concentrations on the electrode reactions and battery performances were studied in the absence and presences of N-methyl-N-ethyl-pyrrolidinium bromide (MEP) or N-methyl-N-butyl-pyrrolidinium bromide (MBP). The conductivities in the electrolytes containing different constitutions and concentrations were measured by EIS method. The charge-discharge performance for the battery and the complex ability for bromine in different electrolytes were also investigated. The results showed that the electrolyte containing MBP was better than that containing MEP for the battery performance and bromine complex ability.



Effect of Fe²⁺/Fe³⁺Interconvertion on Reduction Behavior of Fe³⁺ in Acidic Electrolytes

QIN Jian-xin, LIN Feng, LIU Wen-ping, CHEN Chao, REN Meng-de

2017, 23(6):  702-707.  doi:10.13208/j.electrochem.161129

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The influences of ferrous/ferric (Fe²⁺/Fe³⁺) interconvertion on electrochemical reduction and electrode reaction of Fe³⁺ were investigated by using linear sweep voltammetry, potentiostatic method and cyclic voltammetry (CV) in acidic electrolytes containing chloride ion (Cl^- ) and sulfate ion (SO₄^2-). It was shown that the reduction process of Fe³⁺/Fe²⁺ would take place in two independent stages: (1) the reduction of Fe³⁺ to Fe²⁺ at E=0.35V and (2) the co-precipitation of Fe²⁺ by forming Fe(OH)₂ (E≤-0.3 V) instead of Fe. The major effect of Fe²⁺/Fe³⁺ interconvertion on the reduction is the |ipa/ipc| of quasi-reversible and equilibrium potential in the first stage. Practically speaking, the |ipa/ipc| values increased with the increase of c(Fe³⁺ )/c(Fe²⁺ ), and the values of |ipa/ipc| at fast sweep rates were less strongly affected than those at slow sweep rates. The least variation in |ipa/ipc| (|i_pa/i_pc|≈1.20) with sweep rate was observed in 0.50 mol·L^-1 Fe²⁺ and 0.50 mol·L^-1  Fe³⁺ solutions. Meanwhile, the equilibrium potential was also affected by c(Fe³⁺ )/c(Fe²⁺ ). The equilibrium potential shifted more positively from E₁=0.501 V in No. ① to E₅=0.565 V in No. ⑤ among the five samples studied in this work.



Electroactivities of Pd/Fe₃O₄-C catalysts for electro-oxidation of methanol, ethanol and propanol

ZOU Tao, YI Qing-feng, ZHANG Yuan-yuan, LIU Xiao-ping, XU Guo-rong, NIE Hui-dongand ZHOU Xiu-lin

2017, 23(6):  708-717.  doi:10.13208/j.electrochem.161104

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Development of palladium (Pd) catalysts with high electroactivity for alcohol oxidation is significant for alcohol fuel cells. In this work, Pd nanoparticles were formed by sodium borohydride (NaBH₄) reduction method and subsequently deposited on the surface of carbon supported ferriferrous oxide (Fe₃O₄/C) composites to obtain the Pd/Fe₃O₄-C catalysts with different Fe₃O₄ loadings. Their transmission electron microscopic (TEM) images show that the Pd nanoparticles were uniformly dispersed on the Fe₃O₄/C. Electroactivities of the prepared Pd/Fe₃O₄-C catalysts toward oxidations of C1-C3 alcohols (methanol, ethanol, n-propanol and iso-propanol) in alkaline media were investigated by cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy. Among the prepared catalysts (Pd/Fe₃O₄(2%)-C, Pd/Fe₃O₄(5%)-C, Pd/Fe₃O₄(10%)-C and Pd/C), the Pd/Fe₃O₄(5%)-C catalyst presented the highest electro-oxidation current density for oxidations of C1-C3 alcohols. According to the CV data, the anodic peak current densities for oxidations of methanol, ethanol, n-propanol and iso-propanol on the Pd/Fe₃O₄(5%)-C catalyst were over 1.7, 1.4, 1.7 and 1.3 times larger than that on the Pd/C catalyst, respectively. Furthermore, the charge transfer resistance of ethanol oxidation on the Pd/Fe₃O₄(5%)-C catalyst was much lower than that on the Pd/C catalyst. For all of the prepared catalysts, the decreases in electro-oxidation current density of the tested C1-C3 alcohols followed the order of n-propanol >ethanol > methanol >iso-propanol. In addition, the presence of Fe₃O₄ nanoparticles in the carbon powder improved the electrochemical stability of the Pd nanoparticles.



Electrochemical Behaviors of Ce³⁺/Ce⁴⁺ Couple in a Mixed-Acid Medium of CH₃SO₃H and H₂SO₄

LI Zhao-hua, XU Jiao-long，WU Ting

2017, 23(6):  718-723.  doi:10.13208/j.electrochem.160827

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In order to determine the optimum molar ratio between methanesulfonic acid (MSA) and sulfuric acid, linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behaviors of cerium (III)/cerium (IV) (Ce³⁺/Ce⁴⁺couple on a Pt electrode in a mixed acid solution. Various concentrations of sulfuric acid were considered in the experiments, while the concentration of MSA was fixed at 1.0 mol·L^-1. It was found that the optimum concentration of sulfuric acid was 0.8 mol·L^-1 since the current response was the highest in the control groups and Ce³⁺ was easier to be oxidized to Ce⁴⁺. In the mixed acid solution, the solubility of cerium (III) increased to 0.95 mol·L^-1 from 0.25 mol·L^-1 in 1.3 mol·L^-1 sulfuric acid solution. Electrolytic experiment and liquid-phase oxidation had been taken to explore the application of the mixed acid medium. The results revealed that Ce³⁺ exhibited the excellent electrochemical activity and Ce⁴⁺demonstrated a stronger oxidation capacity in the mixed acid solution.



Effect of Calcium on Atmospheric Corrosion Resistance of Bridge Steel

LI Dong-liang, FU Gui-qin, ZHU Miao-yong

2017, 23(6):  724-731.  doi:10.13208/j.electrochem.161020

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The corrosion behavior of bridge steel in simulated hot and humid industrial-marine atmosphere was investigated by mass loss analysis, XRD, SEM, electrochemical methods and a wet/dry alternate immersion corrosion test using 0.1 mol•L^-1 NaCl+0.01 mol•L^-1 NaHSO₃ solutions. The corrosion depth (W) of experimental steels before and after calcium treatment versus time (t) curves showed a good agreement with the power function of W=Atⁿ. The corrosion products were mainly composed of amorphous phase and a small amount of crystals including α-FeOOH, β-FeOOH, γ-FeOOH and Fe₃O₄. Trace calcium could promote the formation of ferrite and strengthen the protective film on steel surface to prevent the rapid corrosion of bare steel. It could also refine the grain of steel structure and inhibit the crystal transformation of corrosion products, accordingly, refine the particles of corrosion products and reduce the defects in rust layer, and finally, improve the density of rust layer.