Electrochemical performance characteristics and optimum design strategies of a solid oxide electrolysis cell system for carbon dioxide reduction

An analytical model is developed to study the electrochemical characteristics of a solid oxide electrolysis cell (SOEC) for carbon dioxide reduction, in which the activation overpotential, concentration overpotential, and ohmic overpotential are considered as the main sources of voltage losses. The Bulter-Volmer equation, DGM model, and Ohm's law are employed to characterize the three overpotentials, respectively. The theoretical model is validated by comparing the simulation results with the experimental data from the literature. The anode-supported configuration SOEC is found to be the most favorable design. The effects of the cathode inlet gas molar fraction on the cathode overpotential and the cell potential are discussed in detail. It is found that there exists an optimum molar fraction for the cathode inlet gas at which the cathode concentration overpotential attains its minimum for given operation conditions. Moreover, the effects of some importantly operating parameters such as the current density, temperature and pressure on the cell potential are discussed. Thermal-electrochemical analysis shows that the Joule heat generated from the irreversibilities in the SOEC may be larger than, equal to, or smaller than the thermal energy needed for the carbon dioxide reduction reaction, and consequently, a system layout with five different design strategies to implement the carbon dioxide electrolysis is put forward.     

Study on stability of self-breathing DFMC with EIS method and three-electrode system

In this paper, direct methanol fuel cell's (DMFC's) electrochemical process was successfully investigated in situ using Electrochemical Impedance Spectroscopy (EIS) method. Under three-electrode system, anode and cathode's polarization overpotential, charge transferring resistance and active surface were independently measured in order to reveal the degradation factors after 50 h stability testing. The results showed that Ru's dispersing, membrane's swelling and water flooding were main reasons resulting in performance decline. And SEM images confirmed these conclusions. Moreover, cathode's degradation was less serious than anode and it could be recovered. Traditional equivalent circuit model of self-breathing DMFC was modified according to a fact that the dielectric relaxation phenomenon of porous electrode occurred at cathode rather than anode.     

Structural characterization and electrochemical hydrogen storage properties of Ti2−xZrxNi (x = 0, 0.1, 0.2) alloys prepared by mechanical alloying

Nominal Ti₂Ni was synthesized under argon atmosphere at room temperature using a planetary high-energy ball mill. The effect of milling time and Zr substitution for Ti on the microstructure was characterized by XRD, SEM and TEM, and the discharge capacities of Ti_2−xZr_xNi (x = 0, 0.1, 0.2) were examined by electrochemical measurements at galvanostatic conditions. XRD analysis shows that amorphous phase of Ti₂Ni can be elaborated by 60 h of milling, whereas Zr substitution hinders amorphization process of the system. The products of ball milling nominal Ti_2−xZr_xNi (x = 0.1, 0.2) were austenitic (Ti, Zr)Ni and partly TiO, despite the fact that the operation was carried out under argon atmosphere. By comparing the SEM micrographs, it is found that the amorphous phase of Ti₂Ni was formed in the stage of cold-welding during milling, while with Zr substitution particles were flaky and finer, inhomogeneous in size distribution with massive agglomeration. TEM analysis was carried out and confirmed the observations via XRD. In the electrochemical tests, amorphous Ti₂Ni shows the best discharge capacity at 102 mAh/g at a current density of 40 mA/g. Without need of activation, it exhibits extraordinary cycling stability under room temperature. On the other hand, the effect of Zr substitution on the electrochemical property of Ti₂Ni is tricky, as superficially the discharge capacity drops drastically with Zr substitution, but with increase of Zr content (from x = 0.1 to x = 0.2), the discharge capacity increases generally, which credits to larger unit-cell-volume provided by ZrNi compared to TiNi. It is also found that the Ti–Ni system becomes significantly susceptible to oxidation when Zr is introduced to the initial powders as mechanical alloying is deployed as a synthesis method.     

La2−xSrxCoO4−δ (x = 0.9, 1.0, 1.1) Ruddlesden-Popper-type layered cobaltites as cathode materials for IT-SOFC application

La_2−xSr_xCoO_4−δ (x = 0.9, 1.0, 1.1) compounds with Ruddlesden-Popper K₂NiF₄-type structure have been investigated as potential cathode materials for IT-SOFC application. Materials have been prepared by citrate-nitrate combustion method. Structural evolution analysed by XRD shows a shortened Co–O–Co bond length within the perovskite layer as Sr substitution increases, while the interlayer distance at the same time increases. An oxygen stoichiometry close to 4 has been found for all compositions at room temperature. Thermal expansion coefficients have been obtained from temperature-dependent XRD analysis and show large values (>20 × 10⁻⁶ K⁻¹) compared to the currently utilized electrolyte materials. Electrochemical characterisation has been performed by means of impedance spectroscopy on symmetric cells with CGO electrolyte. Pure electrodes have a high Area Specific Resistance, probably due to limited oxygen ion diffusion. By using composite electrode (50 wt.% CGO), an Area Specific Resistance of 0.25 Ω cm² is obtained at approximately 700 °C for all the three compounds suggesting promising electrochemical properties for IT-SOFCs.     

Identification of oxygen reduction processes at (La,Sr)MnO3 electrode/La9.5Si6O26.25 apatite electrolyte interface of solid oxide fuel cells

Oxygen reduction reaction of (La,Sr)MnO₃ (LSM) cathode on La_9.5Si₆O_26.25 apatite (LSO) electrolyte is studied over the temperature range 750–900 °C and the oxygen partial pressure range 0.01–1 atm by electrochemical impedance spectroscopy. The impedance responses show two separable arcs and are analyzed in terms of two different equivalent circuits with comparable information on the electrode processes at high and low frequencies. The electrode process associated with the high frequency arc (σ₁) is basically independent of oxygen partial pressure. The activation energy of σ₁ is 188 ± 15 kJ mol⁻¹ for the O₂ reduction reaction on the LSM electrode sintered at 1150 °C, and decreases to 120 kJ mol⁻¹ for the O₂ reduction reaction on the LSM electrode sintered at 850 °C, which is close to 80–110 kJ mol⁻¹ observed for the same electrode process at LSM/YSZ interface. The reaction order with respect to PO₂$P_{{\text{O}}_2}$ and the activation energy of the electrode process associated with low frequency arc (σ₂) are generally close to that of σ₂ at the LSM/YSZ interface. The activation process of the cathodic polarization treatment is noticeably slower for the reaction at LSM/LSO interface as compared to that at LSM/YSZ interface. The impedance responses of O₂ reduction reaction at the LSM/LSO interface are significantly higher than that at the LSM/YSZ interface due to the silicon spreading. The impedance responses decrease with the decrease of the sintering temperature of LSM electrode on LSO electrolyte. At the sintering temperature of 1000 °C, the impedance responses of O₂ reduction reaction is 1.74 Ω cm² at 900 °C, which is significantly smaller than that of LSM electrode sintered at 1150 °C.     

Graphene nanoribbons as a novel support material for high performance fuel cell electrocatalysts

Graphene nanoribbons (GNRs) were first used as a novel support material for Pt nanoparticles (NPs) based catalyst for methanol electro-oxidation. Upon oxidation and cutting of multiwall carbon nanotubes (MWCNTs), highly dispersive graphene oxide nanoribbons (GONRs) were obtained, on which metal ions such as PtCl₆²⁻ can be homogenously deposited. The hybrid catalyst of GNRs supported Pt NPs (Pt/GNR) was further prepared through facile in-situ chemical co-reduction, with a homogeneous distribution of Pt NPs (2–3 nm) on the nanoribbons. Compared to Pt/MWCNT and commercial Pt/XC72R catalysts, Pt/GNR hybrids show much larger electrochemically active surface area, higher electrochemical stability, and better CO tolerance towards electro-oxidation of methanol. Therefore, GNR is a promising alternative two-dimensional support material for electrocatalysts in direct methanol fuel cells.     

新型铁碳活性焦处理工业废水的应用分析

介绍了新型铁碳活性焦相对传统微电解填料具有的优点及其在污水处理中的应用,分析了铁碳活性焦微电解技术的反应机理及影响因素,并对如何提高废水的综合处理效率进行了探索.     

电弧喷涂金属层电化学性能研究

本文采用电化学测试方法,分析比对电弧喷涂涂层的腐蚀电位、腐蚀电流,进而比较它们对基体金属的牺牲阳极保护作用及腐蚀性能,以期为钢结构长效防腐复合涂层体系的设计提供参考。     

Electrochemical behavior of tungsten in （NaCI-KCI-NaF-W03） molten salt

Abstract The electrochemical reaction mechanism and electrocrystaUization process of tungsten in the NaCl- KCl-NaF-WO3 molten salt were investigated at 973 K （700℃） by means of cyclic voltammetry, chronopotentiometry, and chronoamperometry techniques. The results show that the electrochemical reaction process of tungsten in the NaCl-KCl-NaF-WO3 molten salt system is a quasireversible process mix-controlled by ion diffusion rate and electron transport rate. Tungsten ion in this system is reduced to W（0） in two steps. The electrocrystallization process of tungsten is found to be an instantaneous, hemispheroid three-dimensional nucleation process and the tungsten ion diffusion coefficient of 2.361 × 10^-4 cm2.s^-1 is obtained at experimental conditions.     

Corrosion Behavior of 5A05 Aluminum Alloy in NaCl Solution

The corrosion behavior of 5A05 aluminum alloy in 3.5 wt.%NaCl solution was investigated by scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),Fourier transform-infrared(FT-IR)spectroscopy and electrochemical impedance spectroscopy(EIS)test,and the corrosion mechanism was also discussed.The results showed that the corrosion rates of the 5A05 alloy were low and decreased with the increase in immersion time.Under the conditions of exposure studied,this alloy sufered from pitting corrosion that took place from or around the intermetallic particles existing in the alloy.The number and size of the hemispherical corrosion pits on the sample surfaces increased with the increase of the test time.The dark-grey layer of corrosion products formed on 5A05 aluminum alloy in 3.5%NaCl solution contained many microcracks.Furthermore,XPS and FT-IR analysis proved that the corrosion products were mainly composed of Al2O3,Al(OH)3 and AlCl3.