Journal of Electrochemistry

Table of Contents

2018, 24(3): 0.

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DFT Study of Water Assisted Hydrogen Dissociation on Gold Nanoparticles

CHEN Jia-li, ZHANG Xia-guang, WU De-yin, TIAN Zhong-qun

2018, 24(3): 199-206. doi:10.13208/j.electrochem.170918

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The gold nanoparticles (GNPs) show special activity toward hydrogen (H₂) dissociation, comparing with bulk gold. Such activity is significantly affected by the existence of water. To inspect the influence of water on GNPs catalyzed H₂ dissociation, we carried out density functional theory (DFT) calculations along the reaction paths for water clusters (H₂O)_m (m = 1, 2, 3, 7) assisted H₂ dissociation on gold clusters (Au_n^δ, n = 3 ~ 5; δ = 0, 1). Our calculated results show that water benefits to the H₂ dissociation. The dissociation mechanism varies with the size of water clusters, from the homolytic cleavage of the H-H bond to the oxidation dissociation mechanism on the small gold clusters. We also suggest Raman and IR spectroscopies can be used to characterize the products of those two mechanisms.

Co₃(HCOO)₆@rGO as a Promising Anode for Lithium Ion Batteries

JIANG Heng, FAN Jing-min, ZHENG Ming-sen, DONG Quan-feng

2018, 24(3): 207-215. doi:10.13208/j.electrochem.170412

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Metal–organic framework(MOF) is a kind of novel electrode materials for lithium ion batteries. Here, a composite material Co₃(HCOO)₆@rGO was synthesized for the first time by in situ loading of Co₃(HCOO)₆ on rGO (reduced oxide graphene) through a solution chemistry method. As an anode material for lithium ion batteries, it exhibited an excellent cycle stability as well as a large reversible capacity of 926 mAh·g^-1 at a current density of 500 mA·g^-1 after 100 cycles within the voltage range of 0.02 ~ 3.0 V vs. Li/Li⁺with a good rate capability. The results of cyclic voltammetry and XPS measurements revealed that both Co²⁺ and formate ions in Co₃(HCOO)₆@rGO uderwent reversible electrochemical reactions during the charge and discharge process. Compared with Co₃(HCOO)₆ synthesized through the same method, it was found that rGO could activate the electrochemical reaction of formate ion, which improved the Co₃(HCOO)₆ rate performance.A new route was demonstrated through this work to enhance the specific capacity and rate capability of MOFs by introducing rGO.

Influences of FEC-based Electrolyte on Electrochemical Performance of High Voltage Cathode Material Li₂CoPO₄F

WANG Zhi-gang, ZHAO Wei-min, WANG Hong-chun, LIN Min, GONG Zheng-liang, YANG Yong

2018, 24(3): 216-226. doi:10.13208/j.electrochem.170509

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The effects of fluoroethylene carbonate (FEC) as co-solvent on the electrochemical performance of high voltage cathode material Li₂CoPO₄F are investigated. Compared with traditional carbonate based electrolyte (1 mol·L^-1 LiPF₆ EC/DMC (1:1, m:m)), the FEC/DMC based electrolyte can significantly improved the electrochemical performance of Li₂CoPO₄F. After 100 cycles between 3V and 5.4 V at 1 C rate, the capacity retention of Li₂CoPO₄F electrode in 1 mol·L^-1 LiPF₆ EC/DMC (1:1, m:m) was 52.6 % , while that in the EC/DMC based electrolyte was only 14.5 %. Possible functional mechanisms of FEC improving the electrochemical performance of Li₂CoPO₄F were studied by LSV, EIS, SEM and XPS measurements. It was shown that compared with the traditional EC/DMC based electrolyte, the FEC/DMC based electrolyte exhibited higher stability at high voltage, which suppressed the side reactions at electrode/electrolyte interface when charged to high voltage, and improved the structure stability of Li₂CoPO₄F during cycling, thus, significantly enhanced the electrochemical performance of Li₂CoPO₄F.

Chemical Stability Investigations of Catalyst Layer in PEMFC

GAO Yan-yan, HOU Ming, JIANG Yong-yi, LIANG Dong, AI Jun, ZHENG Li-min

2018, 24(3): 227-234. doi:10.13208/j.electrochem.171101

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This work was intended to study the effect of free radicals on the chemical stability of catalyst layer via ex situ accelerated stress test (AST). Fenton reagent was used as the free radical provider in this research. Apart from the decomposition of Nafion in catalyst layer, the agglomerated Pt nanoparticles and the corroded carbon support were also observed after being treated in Fenton reagent for 100 h. Firstly, the existence of fluoride (F) ions evidenced the chemical decomposation of Nafion after being attacked by trace radical species, which was supported by the intensity decrease in the C-F stretching and vibration peak (1250 cm^-1) observed in attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum. The transmission electron microscopic (TEM) studies showed that the severe Pt nanoparticles agglomeration and carbon support corrosion happened. To gain more insight, the cyclic voltammetry (CV), ATR-FTIR and single cell performance measurements were conducted. A large loss (58%) of the electrochemical active surface area (ECSA) was observed. Another meaningful finding was the reduced double layer region, which demonstrated the reduction of carbon support. Notably, further ATR-FTIR analysis revealed the disappearance in the spectra at 1719 cm^-1 ~ 1578 cm^-1 which were assigned to the hydroquinone-quinine (HQ-Q) redox couple on the oxidized carbon surface. On the bases of these results, it could be concluded that carbon support might be decayed by releasing CO₂ instead of forming oxides on its surface. Finally, the single cell performance data indicated an obvious performance loss in high current density range, due to the proton and local gas transport limitations in the decayed electrodes.

Recent Progress for Fe-N-C Electrocatalysts in Alkaline Fuel Cells

DENG Xin, CHEN Heng-quan, HU Ye，HE Qing-gang

2018, 24(3): 235-245. doi:10.13208/j.electrochem.171213

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Fuel cells are highly recommended nowadays due to their intrinsic advantages such as high energy conversion efficiency, nearly no pollution, and convenient operation. With the development of anion exchange membrane, alkaline fuel cells have gone through a renaissance thanks to their superiorities such as faster reaction kinetics, wider choices for both fuels and electrocatalysts. It is essential to find an appropriate electrocatalyst for oxygen reduction reaction (ORR) to improve the performance of alkaline fuel cells. Further commercialization of the widely used Pt-based materials has suffered from disadvantages such as scarcity and high cost. As alternatives to largely investigated Pt-based materials, Fe-N-C electrocatalysts have gained increasing attention. However, Fe-N-C electrocatalysts still face problems including imperfect stability and durability, low metal loading, unclear catalytic mechanism and active sites, which has further hindered their design and synthesis. In this review, Fe-N-C electrocatalysts for alkaline fuel cells are discussed from the following three aspects, namely, the synthesis methods, the active sites and mechanisms, and their applications in recent five years. To optimize synthetic conditions, two kinds of typical synthetic methods are overviewed and some synthetic examples in the recent five years are summarized. Three active sites such as FeN4/C, Fe-N₂₊₂/C, and Fe-N₂/C, as well as those active sites concerned more widely in recent research for Fe-N-C electrocatalysts are also reviewed, which lays a good foundation for future design of Fe-N-C electrocatalysts. Furthermore, the single cell performance data are provided for the first time in order to enhance the application of the Fe-N-C electrocatalysts in alkaline fuel cells. As a whole, this review aims at providing theoretical support and guidance for future design and synthesis of commercial Fe-N-C electrocatalysts.

A Study of Pulse Electrodeposition on Suppressing the Formation of Lithium Dendrite

GUO Wen-jun, LI Zi-qiong, KE Ruo-hao, NIU Dong-fang, XU Heng, ZHANG Xin-sheng

2018, 24(3): 246-252. doi:10.13208/j.electrochem.170503

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A pulse charge method was used to suppress the formation of lithium dendrite on the copper electrode in 0.5 mol·L^-1 LiBr/propylene carbonate (PC) electrolyte. The surface variation of lithium deposition was investigated by scanning electron microscope and impedance measurement. The SEM test showed that the lithium dendrites were formed on the copper electrode during the traditional process of electrodeposition. However, the formed dendrite was suppressed by pulse charge method. The results of the impedance measurement confirmed that the pulse electrodeposition could suppress the dendrite under the optimized duty ratio (0.5). The long single pulse deposition time decreased the resistance of SEI film and led to the lithium dendrite growth. The current density had an effect on dendrite and the dendrite could be effectively suppressed with no less than 2 mA·cm^-2 of current density.

Preparations and Electrochemical Performances of Carbon Coated Silicon/Graphite Composites

GAO Tian-yi, GONG Zheng-liang

2018, 24(3): 253-261. doi:10.13208/j.electrochem.170728

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In this work, the carbon coated silicon (Si@C) composite materials were synthesized based on the industrial silicon powder (600 meshes) via a high energy ball milling combing with in-situ carbon coating (carbonization) method. The Si@C/graphite (Si/C) composite anode materials were prepared by a simple mechanical ball-milling approach. The effects of carbon coating and the ratio of Si to graphite on electrochemical performances of Si/graphite composite materials were investigated systematically. Compared with the nano-Si/graphite composites, the Si/C composites showed higher reversible capacity, better rate capability and cycle performance. The Si@C materials composited of amorphous carbon and crystal silicon with the primary particles size of 100 ~ 200 nm. The Si/C-2-1 composite also revealed high reversible specific capacity, good rate performance and cycling stability. The Si/C-2-1 exhibited the reversible capacity of 492 mAh·g^-1 with a capacity retention of 85.8% after 100 cycles at 0.1C. Moreover, the reversible discharge capacity reached 369.7 mAh·g^-1 when cycled at 1C, corresponding to 73.9% of that at 0.1C. The Si/C-2-3 which contained 20% silicon displayed a higher reversible capacity of 600.4 mAh·g^-1 when cycled at 0.1C. However, the cycling stability of these composites decreased with increasing Si content, indicating that the graphite content played an important role to improve the cycle performance of the composite.

Pt/g-C₃N₄ Nanosheet for Visible Light –Induced Enhancement of the Activity for Formic Acid Electro-oxidation

SUN Yong-rong, DU Chun-yu, HAN Guo-kang, WANG Ya-jing, GAO Yun-zhi, YIN Ge-ping

2018, 24(3): 262-269. doi:10.13208/j.electrochem.170627

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By using graphitic carbon nitride nanosheet (g-C₃N₄ nanosheet) as a support，Pt/g-C₃N₄ nanosheet catalyst was fabricated by microwave assisted polylol process. The nanoparticles size，composition，structure and optical properties of Pt/g-C₃N₄ nanosheet were characterized by TEM，XRD，XPS and UV-Vis diffuse reflectance spectroscopy. Comparing with the catalytic activities toward formic acid electro-oxidation under dark and visible light illumination，the superior activity of Pt/g-C₃N₄ nanosheet catalyst was achieved under visible light illumination. This visible light-driven enhancement in the formic acid performance could be attributed to the plasmon-induced electron-hole separation on g-C₃N₄ with visible light illumination. The photo-generated hot electron promoted the oxidation of formic acid molecules. The current density of g-C₃N₄ nanosheet was increased under visible light illumination in the presence of formic acid. More importantly，the fast electron transfer from Pt to g-C₃N₄ nanosheet under visible light illumination adjusted the electronic structure of Pt. The “electron deficient” state of Pt could weaken the adsorption energy of CO (as a poisoning species)，facilitating CO oxidation. The rapid removal of poisoning species on Pt would provide more catalytic activity sites for the oxidation of formic acid，enhancing formic acid catalytic activity. The visible light-assisted enhancement in the electrochemical formic acid activity provides a development strategy for direct formic acid fuel cells.

Lead Modified Nanoporous Platinum Electro-Catalysts for Formic Acid Oxidation

Yuanyuan Zhang, Qingfeng Yi，Gekunkun Zuo, Tao Zou, Xiaoping Liu, Xiulin Zhou

2018, 24(3): 270-278. doi:10.13208/j.electrochem.170707

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Platinum (Pt) catalysts modified by other suitable metals significantly enhance their electrochemical activities for formic acid oxidation. In this work, a titanium-supported nanoporous network platinum (nanoPt/Ti) electrode was prepared using a hydrothermal method. The as-prepared nanoPt/Ti electrode was modified with a certain amount of lead by using cyclic voltammetry for different scan cycle numbers (n), namely, n = 10, 15, 20 and 30, to synthesize the novel lead-modified nanoporous Pt (nanoPb_(n)-Pt/Ti) electrodes. Electro-oxidation of formic acid on these electrodes was studied with cyclic voltammetry (CV), chronoamperometry and chronopotentiometry in sulfuric acid solution. CV curves showed that both nanoPt/Ti and nanoPb_(n)-Pt/Ti electrodes displayed high electrocatalytic activities for formic acid oxidation, and the onset potential of formic acid oxidation on the nanoPb₍₂₀₎-Pt/Ti electrode was -0.06 V, which was more negative than that on the nanoPt/Ti electrode (0.06 V). In addition, the first oxidation peak current density on the nanoPb₍₂₀₎-Pt/Ti electrode was 12.7 mA·cm^-2, which was far larger than that on the nanoPt electrode (4.4 mA·cm^-2). Chronoamperommetric data at 0.1 V in 0.5 mol·L^-1 H₂SO₄ + 1 mol·L^-1 HCOOH suggested that the nanoPb₍₂₀₎-Pt/Ti electrode exhibited the stable current density of 8.09 mA·cm^-2 which was 60 times higher than the nanoPt electrode, indicating the dramatic enhancement of electroactivity on the lead-modified nanoPt/Ti electrode for formic acid oxidation with comparison to the nanoPt/Ti electrode. Chronopotentiometric responses on the electrode at 1.5 mA, 2 mA, 2.2 mA and 2.5 mA in 0.5 mol·L^-1 H₂SO₄ + 1 mol·L^-1 HCOOH revealed notable electrochemical oscillations which lasted longer time than those on the nanoPt/Ti electrode. It was demonstrated that the lead-modified nanoPb₍₂₀₎-Pt/Ti electrode presented the most significant enhancement on surface anti-poisoning ability.

Carbon Composite Fe₃O₄ Nanoparticles Based Electrochemical Sensor for Hydrogen Peroxide Detection

ZHANG Si-yu, WANG Hui-juan, LI Shu-fang, QU Jian-ying

2018, 24(3): 279-284. doi:10.13208/j.electrochem.170506

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In this work, a novel hydrogen peroxide electrochemical sensor was constructed with ferroferric oxide (Fe₃O₄) magnetic nanoparticles, which demonstrated good electrocatalytic activity for hydrogen peroxide. There existed a good linear relationship between the concentration of hydrogen peroxide and the oxidation peak current in the range of 1.00 × 10^-6 ~ 1.00 × 10^-3 mol·L^-1 (R = 0.9980) with the detection limit of 6.60 × 10-7 mol·L^-1. The sensor exhibited good anti-interference ability, high reproducibility and stability.

Simulation of Fractal Growth on Metal Wire Electrode

DING Li-feng, MAO Pei-yuan, CHENG Jun, NIU Yu-lan, WEN Yu-hao, CHEN Wei

2018, 24(3): 285-291. doi:10.13208/j.electrochem.170711

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During processes of metal electrodepostion, there exist many complex morphological forms such as dendritic growing in the cathode deposited metal edge, which will seriously affect the quality of the electrodeposited product and current efficiency during machining. Investigations on dendritic crystal growing process and morphology could help controlling growth of electrolysis precipitate. In this work, Python and Matlab softwares were used, and the model of parallel electrode electrodeposition was established based on the diffusion-limited aggregation (DLA) model. By analyzing the law of fractal growth at different conditions of the particles number, probability, electrode spacing, the movement step length and orientation drift, and the inner link between simulation parameters and practical factors that affect fractal growth of electrodeposition, it was found that the simulation results can match the actual parameters by controlling the simulation parameters such as particles number, wire electrode spacing, movement step length and orientation drift probability. The inner connection between simulated parameters and actual electrodeposition factors is discussed. Finally, the specific electrodeposition experiments can be simulated by changing the computer variables, which is controllable and crucial to applying the fractal growth to industry electrolysis.

Preparation and Electrochemical Performance of Ag-TiO₂-MnO₂Composites

ZHANG Ling-xiao, ZHAO Hui-hui, ZHANG Li-juan, FU Yu

2018, 24(3): 292-299. doi:10.13208/j.electrochem.171130

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The silver-titanium dioxide co-modified manganese dioxide (Ag-TiO₂-MnO₂) cathode material was prepared through high temperature solid state reaction. The microstructure, phase composition and electrochemical performance of the prepared samples were characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FT-IR), X-ray photoelectron spectroscopy (XPS), Energy-dispersive X-ray spectroscopy (EDS), Cyclic voltammetry (CV), galvanostatic discharge and electrochemical impedance spectroscopy (EIS). Results showed that the unmodified and Ag-TiO₂ modified MnO₂ samples both exhibited β-MnO₂ structurebut with different morphologies. The EDS mapping results revealed that Ag was uniformly dispersed on the surface of manganese dioxide, while Ti was relatively non-uniform in the Ag-TiO₂-MnO₂ sample. The modified samples were effective in improving specific discharge capacities. The specific discharge capacity increased from 75 mAh·g^-1 to 115 mAh·g^-1 at the rate of 1C. The stronger bond energy of Mn-O in the modified MnO₂ could suppress the volume expansion during the discharge process, which can maintain the structural stability of the manganese dioxide material.

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ZHAN Dong-ping

2018, 24(3): 300-301.

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