Solid Oxide Fuel Cell Anode Research Articles

In-situ Ni exsolution from NiTiO3 as potential anode for solid oxide fuel cells

Sample NiTiO3 (NTO) is prepared by the molten salts synthesis route as a potential anode material for solid oxide fuel cell (SOFC) applications. An additional sample impregnated with 5 mol%Ni (N-NTO) is also presented. Structural characterization reveal a pure NiTiO3 phase upon calcination at 850 °C and 1000 °C. Redox characterization by temperature programmed reduction tests indicate the transition from NiTiO3 to Ni/TiO2 at ca. 700 °C. Ni nanoparticles (ca. 26 nm) are exsolved in-situ from the structure after a reducing treatment at 850 °C. Catalytic activity tests for partial oxidation of methane performed in a fixed bed reactor reveal excellent values of activity and selectivity due to the highly dispersed Ni nanoparticles in the support surface. Time-on-stream behavior during 100 h operation in reaction conditions for sample N-NTO yield a stable CH4 conversion. Electrolyte supported symmetrical cells are prepared with both materials achieving excellent polarization resistance of 0.023 Ω cm2 in 7%H2/N2 atmosphere at 750 °C with sample N-NTO. The maximum power density achieved is of 273 mW cm−2 at 800 °C with a commercial Pt ink used as a reference cathode, indicating further improvement of the system can be achieved and positioning the N-NTO material as a promising SOFC anode material.

Multi-functionalities enabled fivefold applications of LaCo0.6Ni0.4O3−δ in intermediate temperature symmetrical solid oxide fuel/electrolysis cells

A solid oxide cell (SOC) integrating solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) usually utilizes two different materials as the anode and cathode prepared by the costly multi-elements co-doping process. In this work, LaCo0.6Ni0.4O3−δ (LCN) is employed as the contact material and the electrode for the symmetrical SOC and exhibits good catalytic activities towards the four typical reactions, i.e., oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), oxygen evolution reaction (OER), and CO2 reduction reaction (CO2RR). The LCN-GDC electrode has the low activation energies of 1.18 and 0.55 eV as the cathode and anode of SOFC, respectively. High peak power densities (PPDs) of 1.896 and 0.562 W cm−2 are obtained at 800 °C for the Ni-YSZ (8 mol.% Y2O3 stabilized ZrO2) anode-supported and YSZ (200 μm)-supported symmetrical SOFCs, respectively. An electrolysis current density (ECD) of 2.316 A cm−2 is obtained at 800 °C and 2.0 V and a robust operation for over 120 h with a degradation rate of about 0.5 mV h−1 is achieved with LCN as the current collector in air side at 750 °C for the symmetrical SOECs. Such a multi-functional material shows attractive competitiveness and successfully achieves fivefold applications in SOCs. The protocol described herein affords a new vision towards material development basing on the consideration of enhancing the chemical compatibility and lowering the cost of the whole SOC but not just one electrode.

Accelerating Net Zero chemical manufacturing series: investment in low-carbon infrastructure will play a major role

Sr- and Mo-deficiency Sr1.95TiMo1−xO6–δ (STM1−xO; x = 0–0.075) double perovskites are prepared and applied as potential anodes for solid-oxide fuel cells (SOFCs) operated in sulfur-containing syngas. The effect of Sr- and Mo- deficiency on the crystalline nature, electrical and thermal properties and electrochemical performance are investigated. The STM0.925O crystallizes in a single-phase cubic perovskite structure and has excellent thermal and chemical compatibilities with Ce0.9Gd0.1O1.95, Ce0.8Sm0.2O1.9 and La0.9Sr0.1Ga0.8Mg0.2O3–δ electrolytes. The conductivities of STM0.925O in H2 at 550 °C–850 °C are higher than 160 S cm−1. The polarization resistance (Rp) of STM0.925O is recorded as 1.451 Ω cm2 at 850 °C in H2, which is 51% lower than that in pristine Sr2TiMoO6, and the maximum power density (Pmax) at 800 °C in H2 shows 41% increment as compared to Sr2TiMoO6. The electrochemical performance of STM0.925O is further enhanced by impregnation of Pd: the Rp is decreased from 0.73 Ω cm2 to 0.33 Ω cm2 for STM0.925O and Pd-impregnated STM0.925O (Pd-STM0.925O) anodes, while the corresponding Pmax in H2 increased from 649 to 1051 mW cm−2 at 850 °C. The Pd-STM0.925O shows high electrochemical property and durability in simulated coal syngas containing sulfur (3% H2O), making it a promising anode for hydrocarbon-fueled SOFCs.

Lanthanum Ferrites-Based Exsolved Perovskites as Fuel-Flexible Anode for Solid Oxide Fuel Cells.

Exsolved perovskites can be obtained from lanthanum ferrites, such as La0.6Sr0.4Fe0.8Co0.2O3, as result of Ni doping and thermal treatments. Ni can be simply added to the perovskite by an incipient wetness method. Thermal treatments that favor the exsolution process include calcination in air (e.g., 500 °C) and subsequent reduction in diluted H2 at 800 °C. These processes allow producing a two-phase material consisting of a Ruddlesden–Popper-type structure and a solid oxide solution e.g., α-Fe100-y-zCoyNizOx oxide. The formed electrocatalyst shows sufficient electronic conductivity under reducing environment at the Solid Oxide Fuel Cell (SOFC) anode. Outstanding catalytic properties are observed for the direct oxidation of dry fuels in SOFCs, including H2, methane, syngas, methanol, glycerol, and propane. This anode electrocatalyst can be combined with a full density electrolyte based on Gadolinia-doped ceria or with La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) or BaCe0.9Y0.1O3-δ (BYCO) to form a complete perovskite structure-based cell. Moreover, the exsolved perovskite can be used as a coating layer or catalytic pre-layer of a conventional Ni-YSZ anode. Beside the excellent catalytic activity, this material also shows proper durability and tolerance to sulfur poisoning. Research challenges and future directions are discussed. A new approach combining an exsolved perovskite and an NiCu alloy to further enhance the fuel flexibility of the composite catalyst is also considered. In this review, the preparation methods, physicochemical characteristics, and surface properties of exsoluted fine nanoparticles encapsulated on the metal-depleted perovskite, electrochemical properties for the direct oxidation of dry fuels, and related electrooxidation mechanisms are examined and discussed.

The Role of Bi-Polar Plate Design and the Start-Up Protocol in the Spatiotemporal Dynamics during Solid Oxide Fuel Cell Anode Reduction

Start-up conditions largely dictate the performance longevity for solid oxide fuel cells (SOFCs). The SOFC anode is typically deposited as NiO-ceramic that is reduced to Ni-ceramic during start-up. Effective reduction is imperative to ensuring that the anode is electrochemically active and able to produce electronic and ionic current; the bi-polar plates (BPP) next to the anode allow the transport of current and gases, via land and channels, respectively. This study investigates a commercial SOFC stack that failed following a typical start-up procedure. The BPP design was found to substantially affect the spatiotemporal dynamics of the anode reduction; Raman spectroscopy detected electrochemically inactive NiO on the anode surface below the BPP land-contacts; X-ray computed tomography (CT) and scanning electron microscopy (SEM) identified associated contrasts in the electrode porosity, confirming the extension of heterogeneous features beyond the anode surface, towards the electrolyte-anode interface. Failure studies such as this are important for improving statistical confidence in commercial SOFCs and ultimately their competitiveness within the mass-market. Moreover, the spatiotemporal information presented here may aid in the development of novel BPP design and improved reduction protocol methods that minimize cell and stack strain, and thus maximize cell longevity.

Rationally structuring proton-conducting solid oxide fuel cell anode with Ni metal catalyst and porous skeleton

In response to the urgent demand for highly active anodes for lower-temperature proton-conducting solid oxide fuel cells (H–SOFCs) and with the aim to explore the function of metal catalysts and porous skeletons, two series anode-supported BaZr0.1Ce0.7Y0.2O3-δ (BZCY)-based single cells with varying Ni catalysts and pore formers were assembled and evaluated comparably. In the exploration of Ni catalyst variable, the NBZCY65-35-20SS (65 wt% NiO in NiO-BZCY prepared with adding 20 wt% starch) anode possesses the highest performance, for the 1:1 vol ratio of Ni-BZCY could offer the maximum effective triple-phase boundary (TPB) area in the prerequisite of having abundant pores achieved with the 20 wt% pore former as a constant. In addition, both the NBZCY65-35-15SS and NBZCY65-35-25SS anode demonstrate inferior electrochemical properties separately due to the inadequate reducing gas transmission channels and reaction sites. The BZCY cell assembled with NBZCY65-35-20SS reveals an excellent performance, in which the peak power densities (PPDs) were 660, 539, 413, 272 mW cm−2 and the polarization resistances (RP) were 0.061, 0.126, 0.28, 0.652 Ω cm2 at 700, 650, 600, 550 °C, respectively. NBZCY65-35-20SS, which has both a superior TPB area and a fine porous anode skeleton, is a preferable option for anode-supported H–SOFCs. On the whole, the scientific regulations governing metal catalysis and pore-forming could be beneficial to the architecture of fine H–SOFC anode structures.

Synthesis and characterization of NiO colloidal ink solution for printing components of solid oxide fuel cells anodes

A synthesis of NiO colloidal ink solution for printing of the main anode component of solid oxide fuel cells (SOFCs) by commercial printer was shown in the work. The ink was synthesized by a single step chemical reaction of the dissolved nickel nitrate hexahydrate and ammonium carbonate solution with the addition of Triton X-100 surfactant. Results revealed that the obtained ink was stable for at least 4 months contained almost the same NiO nanoparticles with the size at the range of 7–9 nm. These nanoparticles structural and morphology investigation was conducted by high resolution transmission electron microscopy (HR-TEM), Raman spectroscopy and selected area electron diffraction (SAED) analytical methods. Detected rheological properties of the ink revealed that materials for anode in SOFC can be deposited using a commercial printer followed by calcination at 900 °C. Processes occurred during calcination were investigated by TGA and DSC analytical techniques. Finally, the printed coating was subjected to the investigation using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM).

Pores for thought: generative adversarial networks for stochastic reconstruction of 3D multi-phase electrode microstructures with periodic boundaries

The generation of multiphase porous electrode microstructures is a critical step in the optimisation of electrochemical energy storage devices. This work implements a deep convolutional generative adversarial network (DC-GAN) for generating realistic n-phase microstructural data. The same network architecture is successfully applied to two very different three-phase microstructures: A lithium-ion battery cathode and a solid oxide fuel cell anode. A comparison between the real and synthetic data is performed in terms of the morphological properties (volume fraction, specific surface area, triple-phase boundary) and transport properties (relative diffusivity), as well as the two-point correlation function. The results show excellent agreement between datasets and they are also visually indistinguishable. By modifying the input to the generator, we show that it is possible to generate microstructure with periodic boundaries in all three directions. This has the potential to significantly reduce the simulated volume required to be considered “representative” and therefore massively reduce the computational cost of the electrochemical simulations necessary to predict the performance of a particular microstructure during optimisation.

Thermo-mechanical stress analyses of solid oxide fuel cell anode based on three-dimensional microstructure reconstruction

During high-temperature operation of a solid oxide fuel cell, the stresses caused by mismatch of thermal expansion coefficients between different materials and external mechanical loads may cause the rising of damage risk of nickel-yttria-stabilized zirconia anode. It is quite difficult to quantify the mechanical characteristics of a composite anode without investigating on the stress distribution in its real microstructure. However, the high operating temperature and extremely complex microstructure in micro-scale determine the high difficulty in in-situ measurement of thermo-mechanical stress distribution. In this work, the microstructures of six different anode samples, fabricated by using identical nickel oxide-yttria-stabilized zirconia powder mixture, are reconstructed in three-dimension based on the dual-beam focused-ion-beam-scanning-electron-microscopy. The three-dimensional thermo-mechanical stress distributions of different microstructures are conducted at operating temperature based on the finite element method. The effects of both thermal expansion coefficients mismatch between nickel and yttria-stabilized zirconia and external mechanical loads are analyzed. The mechanical failure probabilities of yttria-stabilized zirconia phase in different reconstructions are estimated based on the obtained stress distributions to investigate the influence of microstructure characterizations on nickel-yttria-stabilized zirconia anode strength.

Effect Analysis of Various Gradient Particle Size Distribution on Electrical Performance of Anode-Supported SOFCs With Gradient Anode

Abstract Gradient particle size anode has shown great potential in improving the electrical performance of anode-supported solid oxide fuel cells (SOFCs). In this study, a 3D comprehensive model is established to study the effect of various gradient particle size distribution on the cell electrical performance for the anode microstructure optimization. The effect of homogeneous particle size on the cell performance is studied first. The maximum current density of homogeneous anode SOFC is obtained for the comparison with the electrical performance of gradient anode SOFC. Then the effect of various gradient particle size distribution on the cell molar fraction, polarization losses, and electronic current density distribution is analyzed and discussed in detail. Results show that increasing the particle diameter gradient can effectively reduce the anodic concentration overpotential. Decreasing the particle diameter of anode functional layer 2 is beneficial for reducing the activation and ohmic overpotentials. On these bases, the comprehensive electrical performance of SOFCs with gradient particle size anode and homogeneous anode is compared to highlight the optimal gradient particle diameter distribution. In the studied cases of this work, the gradient particle diameter of 0.7 μm, 0.4 μm, and 0.1 μm at anode support layer (ASL), anode functional layer 1, and anode functional layer 2 (case 3) is the optimal particle size distribution.

Composition-considered Woschni heat transfer correlation: Findings from the analysis of over-expected engine heat losses in a solid oxide fuel cell–internal combustion engine hybrid system

An over-expected amount of heat losses occurred in the internal combustion engine (ICE) of a solid oxide fuel cell (SOFC)–ICE hybrid system and achieving the target efficiency of the hybrid system was seriously impeded by these heat losses. The objectives of this study are to understand the causes of these over-expected heat losses and to propose a new engine heat transfer correlation applicable to engine operation with unconventional fuels, including but not limited to SOFC anode off-gas. First, the effects of composition on the gas convection coefficient were analysed; the engine intake gas in the hybrid system was analysed to have a 1.3–1.4 times larger convention coefficient than general engine intake gas because of its unusual composition. Second, considering the effects of composition, we proposed a new engine heat transfer correlation, named ‘composition-considered Woschni’. Third, to validate this new correlation, experiments and simulations of engine operation were conducted while varying the composition of intake gas. The simulation results using the composition-considered Woschni correlation showed much better predictivity than those using the original Woschni correlation. The total root mean square values of the error rates of the main performance indices for all operating conditions decreased from 12.4% to 5.6% by applying this new correlation.

Development of solid oxide fuel cells using high-frequency plasma spraying technologies

The paper describes the topical issues and the latest achievements in the development of materials with high electrochemical characteristics for single cells and small assemblies of solid oxide fuel cells (SOFC). The authors propose planar SOFC technology which includes sequential deposition of all layers of a thin-film cell on a porous metallic substrate by plasma techniques. The method allows developing porous SOFC anode and cathode, which increases the active area of electrochemical reaction, reduces the spread of technological parameters (in particular, the spread in thickness and porosity of a solid electrolyte), improves SOFC performance and reduces the mass and size of SOFC assemblies. The paper also describes the physics of plasma spraying process in individual cells and SOFC structures. The proposed method is an alternative to traditional SOFC production methods; it eliminates the necessity to use agglomeration technology or other heat treatment. Moreover, it opens up the prospects for automated continuous production process. The appropriate SOFC production equipment is developed, for stationary and mobile use. Further studies will be focused on the task of reducing the weight of SOFC assemblies, which allows using them as an auxiliary power unit for on-board power supply, for example, for cars, airplanes and spaceships.

Catalytic characteristics of Ni(B)-coated YSZ powder by neutral electroless plating

In this study, an eco-friendly, electroless, and neutral (pH 7.0) process of nickel plating at low temperature (40 °C) was used to develop an anode catalyst for a solid oxide fuel cell (SOFC). Electroless Ni(B) plating on yttria-stabilized zirconia (YSZ) particles resulted in the formation of a Ni(B)/YSZ core–shell. We examined the crystallinity and uniformity of the Ni(B) layer on the plated core–shell powder and found that it had an amorphous-like structure. In addition, we evaluated the rate of carbon deposition and characteristics of the SOFC anode catalyst: the carbon deposition rate was 19.42%, H2 selectivity was nearly 88% at 800 °C, and methane conversion was maintained at 100% at temperatures above 850 °C. It was ascertained that in the high-temperature region, which is the main operating temperature of SOFCs, the amorphous-like microstructure of the Ni(B) layer on the Ni(B)–YSZ core–shell powder played an important role in enhancing these properties.

Positive Effects of H2O on the Hydrogen Oxidation Reaction on Sr2Fe1.5Mo0.5O6−δ-Based Perovskite Anodes for Solid Oxide Fuel Cells

The steam is commonly supplied with H2 to the anodes of Ni-based solid oxide fuel cells (SOFCs). Humidified H2 is also widely used for emerging perovskite anodes of SOFCs, although the influences o...

Generating C4 Alkenes in Solid Oxide Fuel Cells via Cofeeding H2 and n-Butane Using a Selective Anode Electrocatalyst

Solid oxide fuel cells (SOFCs) offer opportunities for the application as both power sources and chemical reactors. Yet, it remains a grand challenge to simultaneously achieve high efficiency of transforming higher hydrocarbons to value-added products and of generating electricity. To address it, we here present an ingenious approach of nanoengineering the triple-phase boundary of an SOFC anode, featuring abundant Co7W6@WOx core–shell nanoparticles dispersed on the surface of black La0.4Sr0.6TiO3. We also developed a cofeeding strategy, which is centered on concurrently feeding the SOFC anode with H2 and chemical feedstock. Such combined optimizations enable effective (electro)catalytic dehydrogenation of n-butane to butenes and 1,3-butadiene. The C4 alkene yield is higher than 50% while the peak power density of the SOFC reached 212 mW/cm2 at 650 °C. In addition, coke formation is largely suppressed and little CO/CO2 is produced in this process. While this work shows new possibility of chemical–electricity coupling in SOFCs, it might also open bona fide avenues toward the electrocatalytic synthesis of chemicals at higher temperatures.

Noise suppressed and bias field corrected image segmentation method for porous Ni-YSZ anode microstructure

Accurate three-phase identification from Solid Oxide Fuel Cell (SOFC) anode micrograph is challenged by both noise and intensity inhomogeneity. In this paper, a novel framework is proposed for porous Ni-YSZ cermet anode Optical Microscopy (OM) image segmentation. The proposed framework takes advantage of a statistical model in which an observed image is decomposed into two multiplicative components (bias field and true image) and one additive component (noise). A two-stage Principal Component Analysis with Local Pixel Grouping (LPG-PCA) denoising algorithm is firstly performed to suppress additive noise, it can preserve more image local structural features by modeling a pixel and its nearest neighbors as a vector variable and selecting training samples with similar contents to this variable in a local window for PCA transformation. In order to enhance the robustness to noise, uneven illumination and other outliers, a kernel metric is introduced into fuzzy clustering method embedded with bias field correction for image segmentation. The proposed method has been compared to other state-of-the-art segmentation algorithms on both simulated images and real SOFC anode OM images. Extensive experiments results have demonstrated that the proposed framework can successfully eliminate the influence of both uneven illumination and noise on real Ni/YSZ anode OM images to obtain a better three-phase identification accuracy. The high-quality segmentation results lay firm foundation for accurate microstructural parameter extraction.

The tortuosity factor effect on solid oxide fuel cell performance

In this work, the three-dimensional (3-D) microstructure of Solid Oxide Fuel Cell (SOFC) composite electrode is reconstructed by a random particle packing procedure and a geometrical dilating process, based on which the different tortuosity factors (τ) are calculated by solving the steady state charge conservation equation in different percolated networks. After that, the effects of the different τ on cell performance are analyzed by a one-dimensional (1-D) SOFC performance simulation model, in which the electrochemical reactions and the gas/ion/electron transport are coupled. The results indicate that the tortuosity factor of the ion-conducting phase in SOFC cathode (τio,c) plays the most important role and up to 62% SOFC performance improvement can be expected by decreasing τio,c. In addition, by decreasing the tortuosity factor of the gas phase (τgas,a) and the ion-conducting phase in SOFC anode (τio,a), 1.7% and 17% performance improvement can be achieved, respectively. This work could help improving SOFC performance by modifying the tortuous transport paths in SOFC porous electrodes.

Simulation of Solid Oxide Fuel Cell Anode in Aspen HYSYS—A Study on the Effect of Reforming Activity on Distributed Performance Profiles, Carbon Formation, and Anode Oxidation Risk

A distributed variable model for solid oxide fuel cell (SOFC), with internal fuel reforming on the anode, has been developed in Aspen HYSYS. The proposed model accounts for the complex and interactive mechanisms involved in the SOFC operation through a mathematically viable and numerically fast modeling framework. The internal fuel reforming reaction calculations have been carried out in a plug flow reactor (PFR) module integrated with a spreadsheet module to interactively calculate the electrochemical process details. By interlinking the two modules within Aspen HYSYS flowsheeting environment, the highly nonlinear SOFC distributed profiles have been readily captured using empirical correlations and without the necessity of using an external coding platform, such as MATLAB or FORTRAN. Distributed variables including temperature, current density, and concentration profiles along the cell length, have been discussed for various reforming activity rates. Moreover, parametric estimation of anode oxidation risk and carbon formation potential against fuel reformation intensity have been demonstrated that contributes to the SOFC lifetime evaluation. Incrementally progressive catalyst activity has been proposed as a technically viable approach for attaining smooth profiles within the SOFC anode. The proposed modeling platform paves the way for SOFC system flowsheeting and optimization, particularly where the study of systems with stack distributed variables is of interest.

Fabrication of a micropatterned composite electrode for solid oxide fuel cells via ultraviolet nanoimprint lithography

A micropatterned object composed of La0.75Sr0.25Co0.50Mn0.50O3/Gadolinium-doped Ceria (LSCM/GDC) nanocomposite was fabricated for anode of solid oxide fuel cells (SOFCs) via ultraviolet nanoimprint lithography (UV-NIL). The LSCM/GDC nanocomposite particles were mixed with UV-curable resin and then UV imprinted on a dense yttria-stabilized zirconia (YSZ) substrate. The UV-NIL derived micropillars kept their structure on the YSZ substrate after the UV-curable resin was removed in the sintering process. After fabrication of the patterned SOFC anode electrode, its impedance was experimentally investigated. The ability of the developed method to fabricate micropatterned composite SOFC materials was demonstrated.

Direct reforming of Methane–Ammonia mixed fuel on Ni–YSZ anode of solid oxide fuel cells

To control the temperature distribution in the Ni–YSZ (yttria-stabilized zirconia) anode of solid oxide fuel cells (SOFCs) by efficiently utilizing the heat generated by electrochemical reactions, the supply of methane–ammonia mixed fuel is proposed. The reaction characteristics of reforming/decomposition of the mixed fuel on a Ni–YSZ catalyst are experimentally investigated. A mixture gas of methane, steam, ammonia, and balance argon is supplied to a packed bed catalyst placed in a quartz tube in an electric furnace. The crushed Ni–YSZ anode of SOFCs is used as the catalyst. The exhaust gas composition is analyzed by gas chromatography and the streamwise temperature distribution of the catalyst bed is measured by an infrared camera. It is found that ammonia decomposition preferentially proceeds and steam methane reforming becomes active after sufficient ammonia has been consumed. A low-temperature region is formed by steam methane reforming owing to its strongly endothermic nature. Its position moves downstream while its magnitude decreases as the ammonia concentration in the fuel increases. This shows that the local temperature distribution can be controlled by tuning the ratio of methane to ammonia in the mixed fuel. It is also found that, at a certain mixture ratio, the mixed fuel realizes a hydrogen production rate higher than that for only methane or ammonia.