Anode Microstructure Research Articles

Production of carbon anodes by high-temperature mould pressing

Laboratory-scale carbon anodes were produced by a new method of high temperature mould pressing, and their physico-chemical properties were studied. The influence of mould pressing conditions and coal pitch addition on the bulk density, crushing strength, and oxidation resistance was analyzed. The microstructure of carbon anodes was investigated by scanning electron microscopy (SEM), and the mechanism of producing carbon anodes by high-temperature mould pressing was analyzed. The results show that when the anodes are produced by high-temperature mould pressing, coal pitch can expand into the coke particles and fill the pores inside the particles, which is beneficial for improving the quality of prebaked anodes. The bulk density of carbon anodes is 1.64–1.66 g/cm3, which is 0.08–0.12 g/cm3 higher than that of industrial anodes, and the oxidation resistance of carbon anodes is also significantly improved.

Effect of Different Ca Content on Microstructure and Electrochemical Performance of As-Cast AZ31 Magnesium Alloy Sacrificial Anodes

The effect of ca on the as-cast microstructure and electrochemical performance of AZ31 anode was investigated. The results show that addition of Ca to AZ31 anodes can result in not only grain refinement, but also a change in both morphology and volume fraction of the second phases. And grain refinement by Ca addition can be explained by the GRF mechanism. 0.4%Ca addition to as-cast AZ31 anode can increase the effective current capacity and current efficiency, and meet the requirements of magnesium sacrificial anode, but open circuit potential is lower than the nation standards. AZ31-0.4Ca anode will have a broad marketing application prospect.

Improved microstructure and performance of Ni-based anode for intermediate temperature solid oxide fuel cells

Three kinds of anodes prepared by NiO impregnation, (Ni, Mg)O impregnation and conventional sintering methods are investigated under the conditions of anodic current polarization and redox cycling. The optimized NiO loading in the NiO-impregnated anode is 40 wt%; and the minimum polarization resistance is 1.40, 0.71 and 0.60 Ω cm2 at 700, 750 and 800 °C, respectively, due to the increased triple phase boundary and conductivity that promote the charge-transfer process of H2 oxidation reaction. The conventional Ni–YSZ cermet anode is less sensitive to the current polarization at 200 mA cm−2; however, its polarization resistance is much higher than those of the impregnated anodes. (Ni, Mg)O impregnation improves the performance durability and redox-ability at 800 °C, with a low polarization resistance of 0.93 Ω cm2 after 48 h of current polarization and of 0.71 Ω cm2 after 10 redox cycles. The addition of Mg lowers the reducibility of (Ni, Mg)O particles; and its improved electrochemical performance and redox cycling resistance are attributed to its stabilized microstructure consisting of nano-scale Ni particles distributed on the surface of the pre-sintered YSZ scaffold. The agglomeration of fine Ni particles is suppressed by the unreduced (Ni, Mg)O in the anode.

Influence of Ga and In on microstructure and electrochemical properties of Mg anodes

The influence of Ga and In on the electrochemical properties of Mg anode materials were investigated by the polarization and galvanostatic curve tests. The microstructure and the corroded surface of the Mg-In-Ga alloys were observed by scanning electron microscopy (SEM). The corrosion product of the Mg-0.8%In (mass fraction) and Mg-0.8%Ga-0.3%In alloy were determined by X-ray diffraction. The results show that no second phase exists in the Mg-xIn (x=0–0.8%) allloys. Intergranular compounds containing Ga and In elements occur in the Mg-0.8%In-xGa (x=0–0.8%) alloys. The addition of In into Mg as well as the addition of 0.05%–0.5%Ga into Mg-In alloy promotes the corrosion resistance. The addition of Ga into Mg-In alloys also promotes the electrochemical activity. The Mg-0.8%In-0.8%Ga alloy has the most negative mean potential, −1.682 V, which is more negative than −1.406 V in AZ91D. The corrosion type of the Mg-In-Ga alloys is general corrosion and the corrosion product is Mg(OH)2.

Quantification of double-layer Ni/YSZ fuel cell anodes from focused ion beam tomography data

Three-dimensional microstructure reconstructions of Ni–yttria-stabilized zirconia (Ni/YSZ) anodes are presented, all of which are based on focused ion beam tomography data.The reconstruction procedure, starting from a series of 2D scanning electron micrographs, is investigated step by step and potential sources of error are identified. The distinction between Ni phase, YSZ phase and pore phase is solved by an advanced algorithm, which belongs to the region-growing image segmentation methods. This improves the accuracy of automated grayscale segmentation especially for images with low contrast, which is characteristic of both solid phases in Ni/YSZ anodes.Critical microstructure parameters like material fractions, surface areas, particle size and distribution of Ni, YSZ, and pore phase, as well as phase connectivity and triple-phase boundary density, are evaluated and discussed.In this contribution, two types of high-performance Ni/YSZ anodes – differing in thickness of both the anode functional layer and the anode substrate – are reconstructed and compared to each other. For the first time, the anode functional layer adjacent to the thin film electrolyte is separately quantified. The presented methods are qualified to quantitatively compare different anode microstructures and relate the result to their electrochemical performance.

In situ TEM observation of buffering the anode volume change by using NiTi alloy during electrochemical lithiation/delithiation

A novel Ti3Sn/NiTi shape memory alloy anode with a sandwich structure was fabricated by arc melting. In order to characterize in situ the Ti3Sn/NiTi anode microstructure changes and phase transformations during cycling, a nanoscale lithium battery was set up inside a transmission electron microscope, which consists of Li metal as the cathode, the native Li2O layer on the surface of Li metal as the solid electrolyte, and the Ti3Sn/NiTi as the anode. Only the Ti3Sn intermetallic compound experienced the electrochemical reaction, while the NiTi alloy (inactive with Li+) was applied for buffering the Ti3Sn volume change during cycling. An obvious reaction front of Ti3Sn migrated from one end to the other during lithiation, which can also return after delithiation. It provides direct evidence that the NiTi alloy can effectively accommodate the anode volume change during electrochemical lithiation and delithiation.

Effect of microstructure refinement on performance of Ni/Ce0.8Gd0.2O1.9 anodes for low temperature solid oxide fuel cell

Abstract To clarify the role of milling process on polarization resistance of Ni/GDC cermet anodes for low temperature solid oxide fuel cell (LT-SOFC), an anode with the structure of NiO/Ce 0.8 Gd 0.2 O 2− δ (NiO/GDC20) was prepared via two different milling processes, including conventional ball-milling (CBM) and high energy ball-milling (HEBM). NiO/GDC20 anode composites were fabricated by screen-printing of the milled powders on the dense sintered GDC electrolyte substrate. By employing electrochemical impedance spectroscopy analysis, the effect of the milling process intensity on the LT-SOFC anode performance was examined using a symmetric Ni–GDC20/GDC20/Pt electrolyte-supported cell at 400–600 °C. Microstructural studies of NiO/GDC composite powders showed effectiveness of HEBM method on disintegration of CBM aggregates. HEBM powder with much finer particle size showed smaller crystallites than the CBM powder, which led to a finer-grained uniformly-distributed Ni/GDC anode microstructure. In comparison with the anode prepared by CBM powder, the resulted cermet anode showed further GDC lattice expansion, lower anodic polarization resistance, and also decreased activation energy for hydrogen oxidation reaction. Detailed anode impedance analysis showed dominant role of the charge transfer process and rate determining step of dissociation/adsorption/diffusion in hydrogen-oxidation reaction of both Ni/GDC anodes. In addition, evaluation of activation energy showed enhancement of the charge transfer and dissociation/adsorption/diffusion steps with finer-grained microstructure. It is found that the refinement of microstructure has a significant role on the anode polarization resistance and related electrochemical processes.

Development of the anode pore structure and its effects on the performance of solid oxide fuel cells

Microstructural features, especially pore structure, has a substantial effect on the properties of the anode layer determining the electrochemical performance of the solid oxide fuel cells (SOFCs). Distinct anode pore structures were obtained by removal of various pyrolyzable pore formers (e.g. flake graphite, spheroidal graphite, spherical polymethyl methacrylate, random shaped sucrose, and spherical polystyrene particles). Determined processing parameters for the constituent layers allowed fabrication of Ni-YSZ anodes and complete multilayer fuel cells without macro defects (i.e. cracks, blisters and warpage). A systematic comparison was performed on the anode microstructures, as the fabricated fuel cells consisted of identical component layers (i.e. electrolyte, cathode and current collectors) supported by an anode layer with various pore structures. Voltammetric measurements and analyses of the corresponding impedance spectra on the developed fuel cells along with the investigations on the resultant microstructures using scanning electron microscopy and mercury intrusion porosimetry techniques led to the identification of the relationships between the anode pore structure and the electrochemical performance of the fuel cells. It was revealed that the anode pore structure has critical effects on the properties of the formed anode layers such as electrical conductivity, gas permeability and electrochemical polarization. The novel findings on the anode pore structure allowed increasing the power density of the fuel cells with identical components from 0.45 W/cm2 to power densities over 1.75 W/cm2 at 800 °C using diluted hydrogen (10% H2 in Ar) as fuel.

Effect of Composition Ratio of Ni‐YSZ Anode on Distribution of Effective Three‐Phase Boundary and Power Generation Performance

AbstractNi‐YSZ anode of solid oxide fuel cells (SOFCs) with three different compositions are examined and compared through electrochemical measurement, microstructural analysis, and numerical simulation. Three‐dimensional (3D) microstructure of the porous anodes is directly observed using focused ion beam and scanning electron microscope (FIB‐SEM), and microstructural parameters such as phase connectivity and three‐phase boundary (TPB) density are quantified to correlate the microstructure to the performance. 3D numerical simulation using the obtained microstructure is conducted considering the various transport phenomena and the electrochemical reaction in the anodes to predict their overall electrochemical performance. The performance of the Ni:YSZ = 30:70 anode is measured significantly lower than those of the Ni:YSZ = 50:50 and 70:30 anodes, which is attributed to the elongation of the ionic transport pathways. The poor connectivity of the Ni phase in the Ni:YSZ = 30:70 anode shifts the electrochemically active region far from the anode–electrolyte interface, resulting in higher Ohmic loss. The amount and distribution of the effective TPB associated with the phase connectivity are essentially important to explain the anode performance. The 3D numerical simulation qualitatively reproduces the anode performance and gives detailed information about the internal states of the anodes such as the distribution of the charge‐transfer current.

Effect of pass deformation on microstructure, corrosion and electrochemical properties of aluminum alloy anodes for alkaline aluminum fuel cell applications

The effect of pass deformation in rolling processes on the microstructure, corrosion resistance and electrochemical activity of Al-Mg-Bi-Sn-Ga-In alloy anodes operated in an alkaline solution (85 °C, 5 mol·L−1 NaOH with addition of NaSnO3) with current density of 800 mA·cm−2 was investigated. To analyze the microstructure of aluminum alloy anodes, we used scanning electron microscope, transmission electron microscope and electron backscatter diffraction techniques. We also used the hydrogen evolution method and electrochemical testing techniques to investigate the corrosion and electrochemical behavior of aluminum alloy anodes. The results showed that uniform microstructures with homogeneous distribution of fine active segregated phases as well as an excellent electrochemical performance of the aluminum alloy anodes were achieved by the dynamic recrystallization under pass deformation of 40%. We found that the aluminum alloy anodes (under pass deformation of 40%) had the lowest hydrogen evolution rate (0.092 mL·min−1·cm−2) and the most negative electrode potential (−1.585 V).

Low Temperature Electrode Materials Synthesized by Citrate Precursor Method for Solid Oxide Fuel Cells

AbstractHomogeneous nanocrystalline NiO–Ce0.9Ln0.1O2–δ (Ln = La, Sm, Gd, and Pr) composite anode and nanocrystalline Ce0.9Gd0.1O2–δ electrolyte material have been successfully synthesized by citrate precursor method. LSCF has been synthesized by conventional solid state method and used as cathode material in our studies. The synthesized powders have been characterized by powder X‐ray diffraction, microscopy, and surface area studies. The average crystallite size of the anode materials has been found to be in the range of 5–15 nm by HRTEM. Highly dense electrolyte and porous electrode materials have been observed by FESEM and confirmed by BET surface area studies. Three cells have been fabricated successfully. Based on the performance of the three cells containing three different anode materials we have achieved better electrochemical characteristics in Ni–GDC with maximum power density of 302 mW cm–2 and open circuit voltage of 1.012 V at 500 °C. The difference in the performance of the cells containing Ni–GDC as compared to Ni–LDC and Ni–SDC anode is due to changes in the microstructure and crystallite size of anode which affects the electrochemical performance of the cells. The performances of all the cells containing nanocomposite powders are suitable anode materials for low temperature SOFCs.

Ni<sub>0.75</sub>Co<sub>0.25</sub>/(Gd<sub>2</sub>O<sub>3</sub>–CeO<sub>2</sub>) Anodes for Solid Oxide Fuel Cells

Electrochemical performance of solid oxide fuel cells based on Ni0.75Co0.25-GDC (Gd0.1Ce0.9O1.95) and Ni-GDC anodes were investigated and compared in order to understand the effects of (i) alloying Ni with Co and (ii) anode microstructure on the cell performance under hydrogen fuel. At the sintering temperature of 1300°C for 5 h, the Ni0.75Co0.25-GDC anode showed a superior distribution and connection of grains to the Ni-GDC anode which had grain clustering structure in general. Grain growth and connection were found in both anodes when the sintering temperature was increased to 1350°C for 3 h. This resulted in significant improvement of the anodic polarization resistance for the Ni-GDC anode but only minor change for the Ni0.75Co0.25-GDC anode. This research, however, showed that the Ni-GDC anode had higher anodic polarization resistance than the Ni0.75Co0.25-GDC anode, resulting in the better cell power density at all sintering conditions. The maximum power density obtained at 800°C for the cell with the Ni0.75Co0.25-GDC anode was 118 mW•cm-2. Impedance spectroscopy analysis showed that the total cell resistance of both cell types became progressively larger when the operation time was prolonged to 10 h at 800°C, while the microstructure change was not observable by the SEM. The reason for the fast degradation will thus require further investigation.

THREE--LAYER CO--FIRING FABRICATION OF LaCrO<SUB>3</SUB>--BASED CERAMIC INTERCONNECT, COMPOSITE ANODE SUPPORT AND YSZ ELECTROLYTE

Developing cost–effective methods to prepare dense ceramic interconnect membrane for solid oxide fuel cell (SOFC) stacks is currently considered as a major technical obstacle. In order to improve the co–firing compatibility of LaCrO3–based interconnects with the traditional YSZ–based SOFC anode support NiO/YSZ, interconnect material of La0.7Ca0.3Cr0.97O3−δ (LCC) was introduced to NiO/YSZ anode. Triple–phase composite NiO/YSZ/LCC was prepared, and then examined as novel anode support. Sintering character, microstructure, electrical conductivity, and thermal expansion coefficient of the composite anode were investigated in detail as a function of LCC addition, respectively. Results indicated that the NiO/YSZ/LCC composite anode had excellent overall performance. Furthermore, by using a simple drop–coating process, LCC and YSZ wet membranes were prepared on the opposite surfaces of NiO/YSZ/LCC support, respectively. Followed by three–layer co–firing at 1400 in air for 4 h, dense La0.7Ca0.3Cr0.97O3−δ interconnect and * 21171131, 1208085QE84, 2012SQRL190ZD KJ2011B185 : 2012–02–24, : 2012–04–06 ! : , , 1973 , , DOI: 10.3724/SP.J.1037.2012.00097

CFD model of a methane fuelled single cell SOFC stack for analysing the combined effects of macro/micro structural parameters

A fully coupled CFD model of a direct internal reforming single cell SOFC stack previously designed by Ceramic Fuel Cell Ltd (CFCL) has been developed. In this model, an innovative solution technique for accelerating finite volume treatment of the electrodes as two distinct layers, a diffusion layer and a catalyst layer, is taken to analyse the combined effects of the macro/microstructural parameters on distribution of fields and each of the reactions involved in the process. To assess the simulation results, the model is not only evaluated with the CFCL experimental data that was reported from the similar geometry, but it is also assessed for the effects of the reforming and water gas shift reactions. It is found that a 3D model is more representative of the global reforming reaction rate. Furthermore, distributions of the key parameters along different spatial domains disclose the complex interaction between the anode flow field design and microstructural parameters of the anode diffusion layer. In fact, an optimal set of the anode microstructure that promotes the reforming reaction rate will not automatically result in improved SOFC performance. The developed model is a powerful tool to study complex fuel cell related problems and to optimize fuel cells’ structure.

I111 3DプリンタによるSOFC電極微構造の拡大再構築と拡散実験への適用可能性評価(OS-5:燃料電池・二次電池関連研究の新展開(1))

The porous microstructure of SOFC electrodes significantly affects the SOFC performance. It is necessary to understand the diffusion process through the complex microstructure in order to improve the performance of SOFC. 3D-printed enlarged models based on practical microstructure of SOFC anode obtained by FIB-SEM observation were prepared for possible application to diffusion experiments. The 3D models were evaluated in the point of gas tightness and strength. Furthermore, reproducibility of the complex microstructure by a 3D printer was tested by examining the difference between the original FIB-SEM data and the 3D-printed microstructure. The result shows both the possibilities and limitations of this method.

Simulation of Solid Oxide Fuel Cell Anode Microstructure Evolution Using Phase Field Method

In the present study, a phase field method is used to simulate the microstructural evolution of nickel-yttria stabilized zirconia composite anode of solid oxide fuel cell based on three-dimensional microstructures reconstructed by focused ion beam-scanning-electron-microscopy technique. A three-dimensional reconstruction of the anode sample after initial reduction is used as the initial microstructure. By implementing efficient semi-implicit Fourier spectral method in the phase field simulation with different periodic boundary conditions, the computation efficiency is improved in orders of magnitude. In order to quantitatively study the correlation between the anode microstructure evolution and the resulting electrochemical performance degradation, the evolution of three-phase boundary and nickel specific surface area and the nickel and pore phase tortuosity factors are quantitatively calculated in simulations. For comparison, different real time experiments have been conducted and the simulation results showed good agreement with the real time experimental data.

Directed Transport as a Route to Improved Performance in Micropore-Modified Encapsulated Multilayer Silicon Electrodes

Energy storage is an increasingly critical component of modern technology, with applications that include energy infrastructure, transportation systems, and portable electronics. Improvements to lithium-ion battery energy/power density through the adoption of silicon anodes—promising both gravimetric and volumetric capacities that far exceed traditional carbon-based anodes—has been limited by ∼300% strains and poor coulombic efficiency during charge and discharge ((dis)charge) cycling which result in short operational lifetimes. We examine encapsulated micropore-modified silicon anodes that define lithium mass-transfer dynamics to constrain strain evolution and improve capacity retention during (dis)charge cycling. Fully integrated cells incorporating this silicon anode and a commercial grade LiCoO2 cathode maintain their capacity for 110 cycles with >99% average coulombic efficiency from cycles 5 to 100. Anodes with thicknesses up to 50 μm resulted in area-normalized capacities of up to 12.7 mAhcm−2. When the silicon anode microstructure pitch is varied, a direct relationship is found to exist between the rate capability and volumetric capacity of the anode. Helium-ion Microscopy, Secondary Ion Mass Spectrometry, and Scanning Electron Microscopy, used as ex-situ characterization methods for the evolution of the electrode's structure on cycling, reveal significant changes in nanoscale morphology that otherwise retain the essential laminate micropore motif of the initial Si anode.

A more efficient anode microstructure for SOFCs based on proton conductors

While the desired microstructure of the state-of-the-art Ni-YSZ anode for a solid oxide fuel cell (SOFC) based on YSZ is well known, the anode microstructure for a SOFC based on a proton conductor is yet to be optimized. In this study, we examined the effect of anode porosity on the performance of a SOFC based on BaZr0.1Ce0.7Y0.1Yb0.1O3� d (BZCYYb), a mixed ion (proton and oxygen anion) conductor with high ionic conductivity at intermediate temperatures. Three cells with Ni-BZCYYb cermet anodes of different porosities (37%, 42%, and 50%) and identical electrolytes and cathode components were fabricated and tested. Under typical fuel cell operating conditions, the cell with anode of the lowest porosity (37%), prepared without pore former, achieved the highest performance, demonstrating a peak power density of 1.2 W/cm 2 at 750

The Effects of Nd on Lead Anode for Zinc Electrowinning

A detailed investigation of the effects of Nd on the microstructure, mechanical properties and electrochemical properties of lead anode in 160g.L-1 at 35°C was carried out. Galvanostatic polarization and Chronopotentiometry (CP) were used to study the electrochemical behavior ( such as anodic potential, corrosion rate and the composition of passive film) of the Pb and Pb-Nd anodes. The metallographic structure and passive film morphology of Pb and Pb-Nd anodes were observed and analyzed using polarizing microscope and scanning electronic microscopy (SEM), respectively. The experimental results show the grains become smaller and aggregation of PbxNdy become severe as the content of Nd increases. The addition of Nd enhances the formation of PbO2, inhibits the formation of PbSO4 and PbO and reduces the anodic potential. However, Holes presenting on rough passive film of high Nd content Pb-Nd anodes accelerate the corrosion.

Investigation of the microstructural effect of Ni–yttria stabilized zirconia anode for solid-oxide fuel cell using micro-beam X-ray absorption spectroscopy analysis

The microstructural effect of the solid-oxide fuel cell (SOFC) anode on fuel cell performance has been investigated using X-ray absorption spectroscopy (XAS). Anodes were examined after the fuel cell had operated at 600–700 °C using H2 fuel. The microstructure of micro tubular anodes consisting of conventional Ni–yittria stabilized zirconia (YSZ) has been controlled by altering the co-sintering temperature with the zirconia electrolyte. Impedance analysis has clearly shown that the overpotentials for the gas transport and the electrochemical reactions improve for the anode prepared at lower co-sintering temperatures. Using data from the X-ray absorption near edge structure (XANES) energy region, the metallic Ni fraction as a function of distance from the electrolyte has also been measured for those samples. XANES observation has shown the oxidation status of Ni in the anode is quite sensitive to position relative to the anode/electrolyte interface. These results may be an indication of the positions of the reaction sites for oxide ions and the fuel: assuming the oxidation state of nickel (Ni–O) designates the active triple phase boundary.