Comparative performance analysis of a direct ammonia-fuelled anode supported flat tubular solid oxide fuel cell: A 3D numerical study

Solid oxide fuel cells that are designed in different geometrical structures (planar, tubular, flat-tubular, etc.) are dirt-free, quiet, and efficient cells that run using different fuels including contagions fuels. In this work, the performance of a 3D model of direct ammonia feed anode supported flat-tubular solid oxide fuel cell having six fuel supply channels was developed, investigated, and elucidated numerically in comparison with hydrogen fuels at different operating conditions using COMOSOL Multiphysics. The finding of this study is revealed that the performance of the developed model that is running with direct ammonia is better than hydrogen feed one using the same geometrical dimensions and operating parameters. It is also confirmed that direct ammonia feed anode supported flat-tubular solid oxide fuel cell has outstanding performance over the corresponding anode supported tubular solid oxide fuel cell using the same active cell surface area, gas channel length, and operating conditions. Parametric sweep analyses have been also performed on selected operating parameters and the outcomes revealed that the working temperature and the amount of reactant gases have a powerful impact on cell performance. Thus, ammonia is a green auspicious, and profitable candidate to use as a carbon-neutral fuel for anode supported flat-tubular solid oxide fuel cells in the near future.     

Lignite as a fuel for direct carbon fuel cell system

Lignite, also known as brown coal, and char derived from lignite by pyrolysis were investigated as fuels for direct carbon solid oxide fuel cells (DC-SOFC). Experiments were carried out with 16 cm² active area, electrolyte supported solid oxide fuel cell (SOFC), using pulverized solid fuel directly fed to DC-SOFC anode compartment in a batch mode, fixed bed configuration. The maximum power density of 143 mW/cm² was observed with a char derived from lignite, much higher than 93 mW/cm² when operating on a lignite fuel. The cell was operating under electric load until fuel supply was almost completely exhausted. Reloading fixed lignite bed during a thermal cycle resulted in a similar initial cell performance, pointing to feasibility of fuel cell operation in a continuous fuel supply mode. The additional series of experiments were carried out in SOFC cell, in the absence of solid fuels, with (a) simulated CO/CO₂ gas mixtures in a wide range of compositions and (b) humidified hydrogen as a reference fuel composition for all cases considered. The solid oxide fuel cell, operated with 92%CO + 8%CO₂ gas mixture, generated the maximum power density of 342 mW/cm². The fuel cell performance has increased in the following order: lignite (DC-SOFC) < char derived from lignite (DC-SOFC) < CO + CO₂ gas mixture (SOFC) < humidified hydrogen (SOFC).     

Design of industrially scalable microtubular solid oxide fuel cells based on an extruded support

The current work describes the adaptation of an existing lab-scale cell production method for an anode supported microtubular solid oxide fuel cell to an industrially ready and easily scalable method using extruded supports. For this purpose, Ni–YSZ (yttria stabilized zirconia) anode is firstly manufactured by Powder Extrusion Moulding (PEM). Feedstock composition, extruding parameters and binder removal procedure are adapted to obtain the tubular supports. The final conditions for this process were: feedstock solid load of 65 vol%; a combination of solvent debinding in heptane and thermal debinding at 600 °C. Subsequently, the YSZ electrolyte layer is deposited by dip coating and the sintering parameters are optimized to achieve a dense layer at 1500 °C during 2 h. For the cathode, an LSM (lanthanum strontium manganite)–YSZ layer with an active area of ∼1 cm² is deposited by dip coating. Finally, the electrochemical performance of the cell is measured using pure humidified hydrogen as fuel. The measured power density of the cell at 0.5 V was 0.7 W cm⁻² at 850 °C.     

Influence of anode's microstructure on electrochemical performance of solid oxide direct carbon fuel cells

The microstructure of anode has a significant influence on the whole electrochemical performance of solid oxide direct carbon fuel cells (SO-DCFCs). The tubular SO-DCFCs based on cathode supported solid oxide fuel cells was fabricated by dip-coating and co-sintering techniques. As the anode porosity mainly came from the pore former (graphite) in the dip-coating process, different contents of graphite were added into the anode slurries. When the graphite was 10.1% wt., the SO-DCFCs showed the best performance and stability. The peak power density reached 242 mW cm⁻² at 850 °C, with carbon black (located 5% Fe) as the fuel and air as the oxidant.     

Nanoporous nickel thin film anode optimization for low-temperature solid oxide fuel cells

Thin film solid oxide fuel cells (TF–SOFCs) having anode–substrate nanostructure that was optimized for the low-temperature operation were fabricated. Nickel thin film anodes with four different anode thicknesses were deposited on anodic aluminum oxide templates, nanoporous substrates having two different pore sizes, by the sputtering method. Subsequently, a yttria-stabilized zirconia (YSZ) electrolyte and platinum cathode were deposited on them, which completed the entire fuel cell structure. The anode nanostructure of fuel cells in six combinations was analyzed by the cross-sectional view, surface microscopy method, and three-dimensional morphology observation. Those investigations enabled the anode nanostructure to be identified, such as the anode porosity and the roughness of the interface between anodes and electrolytes. Then, the six TF–SOFCs were electrochemically characterized in a 500 °C operating environment. The maximum power densities were obtained through the i–V–P curves, and the highest performance of 294.1 mW/cm² was measured in the cell having a combination of 200 nm–sized porous aluminum anodic oxide (AAO) and 1200 nm–thick Ni anode. This showed up to 20.1% improvement over the other cells. EIS analysis showed that the optimized ohmic and faradaic resistance originated from each part of the unique TF–SOFC structure.     

Exploring MnCr2O4–Gd0.1Ce0.9O2-δ as a composite electrode material for solid oxide fuel cell

Symmetrical solid oxide fuel cell (SOFC) adopting the same material at both electrodes is potentially capable of promoting thermomechanical compatibility between near components and lowering stack costs. In this paper, MnCr₂O₄–Gd_0.1Ce_0.9O_2-δ (MCO-GDC) composite electrodes prepared by co-infiltration method for symmetrical electrolyte supported and anode supported solid oxide fuel cells are evaluated at a temperature range of 650–800 °C in wet (3% H₂O) hydrogen and air atmospheres. Without any alkaline earth elements and cobalt, the co-infiltrated MCO-GDC composite electrode shows excellent activity for oxygen reduction reaction but mediocre activity for hydrogen oxidation reaction. With MCO-GDC as the cathode, the Ni-YSZ (Y₂O₃ stabilized ZrO₂) anode supported asymmetrical cell demonstrates a peak power density of 665 mW cm⁻² at 800 °C. The above results suggest MCO-GDC is a promising candidate cathode material for solid oxide fuel cells.     

Fabrication, electrochemical characterization and thermal cycling of anode supported microtubular solid oxide fuel cells

This work describes the manufacture and electrochemical characterization of anode supported microtubular SOFC's (solid oxide fuel cells). The cells consist of a Ni-YSZ anode tube of 400 μm wall-thickness and 2.4 mm inner diameter, a YSZ electrolyte of 15-20 μm thickness and a LSM-YSZ cathode. The microtubular anode supporting tubes were prepared by cold isostatic pressing. The deposition of thin layers of electrolyte and cathode are made by spray coating and dip coating respectively. The cells were electrochemically characterized with polarization curves and complex impedance measurements using 5% H₂/95% Ar and 100% of H₂, humidified at 3% as reactant gas in the anodic compartment and air in the cathodic one at temperatures between 750 and 900 °C. The complex impedance measurements show an overall resistance from 1 to 0.42 Ω cm² at temperatures between 750 and 900 °C with polarization of 200 mA cm⁻². The I-V measurements show maximum power densities of 0.3-0.7 W cm⁻² in the same temperature interval, using pure H₂ humidified at 3%. Deterioration in the cathode performance for thin cathodes and high sintering temperatures was observed. They were associated to manganese losses. The cell performance did not present considerable degradation at least after 20 fast shut-down and heating thermal cycles.     

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.     

Mixed ionic electronic conducting perovskite anode for direct carbon fuel cells

The conversion of carbonaceous materials to electricity in a Direct Carbon Fuel Cell (DCFC) offers the most efficient process with theoretical electric efficiency close to 100%. One of the key issues for fuel cells is the continuous availability of the fuel at the triple phase boundaries between fuel, electrode and electrolyte. While this can be easily achieved with the use of a porous fuel electrode (anode) in the case of gaseous fuels, there are serious challenges for the delivery of solid fuels to the triple junctions. In this paper, a novel concept of using mixed ionic electronic conductors (MIEC) as anode materials for DCFCs has been discussed. The lanthanum strontium cobalt ferrite, La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) was chosen as the first generation anode material due to its well known high mixed ionic and electronic conductivities in air. This material has been investigated in detail with respect to its conductivity, phase and microstructural stability in DCFC operating environments. When used both as the anode and cathode in a DCFC, power densities in excess of 50 mW/cm² were obtained at 804 °C in electrolyte supported small button cells with solid carbon as the fuel. The concept of using the same anode and cathode material has also been evaluated in electrolyte supported thick wall tubular cells where power densities around 25 mW/cm² were obtained with carbon fuel at 820 °C in the presence of helium as the purging gas. The concept of using a mixed ionic electronic conducting anode for a solid fuel, to extend the reaction zone for carbon oxidation from anode/electrolyte interface to anode/solid fuel interface, has been demonstrated.     

Performance analysis of hollow fibre-based micro-tubular solid oxide fuel cell utilising methane fuel

Solid oxide fuel cell (SOFC) has been studied as one of the most amazing development in energy production that could work directly with hydrocarbon fuel without reforming procedure. This study was conducted to analyse the micro-tubular solid oxide fuel cell (MT-SOFC) in terms of its performance by utilising methane as the fuel, subsequently compared with hydrogen. MT-SOFC that was investigated in this work consisted of thin cathode layer, coated onto co-extruded anode/electrolyte dual-layer hollow fibre (HF); in which its anode was made of nickel (Ni), coupled with cerium-gadolinium oxide (CGO) as an electrolyte, whereas the cathode was lanthanum strontium cobalt ferrite (LSCF) and CGO. The physical analyses carried out were three-point bending test and scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was further conducted to examine the carbon deposition in HFs. In evaluating the performance of HFs, current-voltage (IV) measurement, as well as impedance analysis of various temperatures range from 500 °C to 700 °C were performed. Based on the results, the OCV, maximum power density and ohmic ASR of MT-SOFC exposed to methane fuel, were at 0.79 V, 0.22 W cm⁻² and 0.31 Ω cm²; compared to the other that was exposed to hydrogen fuel, recorded at 0.89 V, 0.67 W cm⁻² and 0.19 Ω cm² respectively. This indicates that there was a significant reduction in cell performance when methane was used as the fuel, due to the carbon deposition as proven by SEM, three-point bending and XRD.     

Optimization of process parameters using response surface methodology (RSM) for power generation via electrooxidation of glycerol in T-Shaped air breathing microfluidic fuel cell (MFC)

The present work focuses on the optimization of operating parameters using Box Behnken design (BBD) in RSM to obtain maximum power density from a glycerol based air-breathing T-shaped MFC. The major parameters influencing the experiment for enhancing the cell performance in MFC are glycerol/fuel concentration, anode electrolyte/KOH concentration, anode electrocatalyst loading and cathode electrolyte/KOH concentration. The ambient oxygen is used as the oxidant. The acetylene black carbon (C_AB) supported laboratory synthesized electrocatalyst Pd–Pt (16:4)/C_AB is used as anode electrocatalyst and commercial Pt (40 wt%)/C_HSA as the cathode electrocatalyst. The quadratic model predicts the appropriate operating conditions to achieve highest power density from the laboratory designed T-shaped MFC. The p-value of less than 0.0001 and F-value of greater than 1 i.e., 26.32 indicate that the model is significant. The optimum conditions predicted by the RSM model were glycerol concentration of 1.07 M, anode electrolyte concentration of 1.62 M anode electrocatalyst loading of 1.12 mg/cm² and cathode electrolyte concentration of 0.69 M. The negligible deviation of only 1.07% between actual/experimental power density (2.76 mW/cm²) and predicted power density (2.79 mW/cm²) was recorded. This model reasonably predicts the optimum conditions using Pd–Pt (16:4)/C_AB electrocatalyst to obtain maximum power density from glycerol based MFC.     

Fabrication and performance evaluation of planar solid oxide fuel cell with large active reaction area

Anode-supported planar solid oxide fuel cells (SOFCs) with dimension from 5 × 5 cm² to 15 × 15 cm² have been successfully fabricated by tape casting, screen-printing and single-step co-firing technologies, which shows a potential way of cost-effective for mass production. The performance of the cells has been investigated at operating temperature between 650 °C and 750 °C. The typical cell with dimension of 10 × 10 cm² (active reaction area of 9 × 9 cm²) obtained open circuit voltage (OCV) of 1.15 V and power density of 770 mW/cm² at current density of 950 mA/cm² at 750 °C. The performance degradation of the cell is lower than 1.56%/1000 h. When external reformed methane gas was used as fuel, the cell showed no obvious performance decrease compared to that using pure hydrogen as fuel. The test results have demonstrated that the as-prepared large size cells have excellent performance and reliability, which is ready for SOFC stack assembly.     

Testing of a cathode fabricated by painting with a brush pen for anode-supported tubular solid oxide fuel cells

We have studied the properties of a cathode fabricated by painting with a brush pen for use with anode-supported tubular solid oxide fuel cells (SOFCs). The porous cathode connects well with the electrolyte. A preliminary examination of a single tubular cell, consisting of a Ni-YSZ anode support tube, a Ni-ScSZ anode functional layer, a ScSZ electrolyte film, and a LSM-ScSZ cathode fabricated by painting with a brush pen, has been carried out, and an improved performance is obtained. The ohmic resistance of the cathode side clearly decreases, falling to a value only 37% of that of the comparable cathode made by dip-coating at 850 °C. The single cell with the painted cathode generates a maximum power density of 405 mW cm⁻² at 850 °C, when operating with humidified hydrogen.     

Fabrication and optimization of LSM infiltrated cathode electrode for anode supported microtubular solid oxide fuel cells

In this study, anode supported microtubular solid oxide fuel cells (SOFCs) with LSM (lanthanum strontium manganite) catalyst infiltrated LSM-YSZ (yttria stabilized zirconia) cathodes are developed to increase the density of triple/three phase boundaries (TPBs) in the cathode, thereby to improve the cell performance. For this purpose, two different porous YSZ layers are formed on the dense YSZ electrolyte, i.e., one is with co-sintering while the other one is not. Incorporation of LSM into these porous YSZ layers is achieved via dip coating of a sol-gel based infiltration solution. The effects of the fabrication method for porous YSZ, LSM solution dwelling time and the thickness of the porous YSZ layer on the cell performance are experimentally investigated and optimized in the given order. A reference cell having a conventional dip coated cathode prepared by mixing the commercial LSM and YSZ powders is also fabricated for comparison. The results show that among the cases considered, the highest peak power density of 0.828 W/cm² can be obtained from the cell, whose single dip coated porous electrolyte layer co-sintered with the dense electrolyte is impregnated with LSM for a dwelling time of 45 min. On the other hand, the peak power density of the reference cell is measured as only 0.558 W/cm². These results reveal that ～50% increase in the maximum cell performance compared to that of the reference cell can be achieved by LSM infiltration after the optimizations.     

Dependence of polarization in anode-supported solid oxide fuel cells on various cell parameters

The performance of solid oxide fuel cells (SOFCs) is affected by various polarization losses, namely, ohmic polarization, activation polarization and concentration polarization. Under given operating conditions, these polarization losses are largely dependent on cell materials, electrode microstructures, and cell geometric parameters. Solid oxide fuel cells (SOFC) with yttria-stabilized zirconia (YSZ) electrolyte, Ni–YSZ anode support, Ni–YSZ anode interlayer, strontium doped lanthanum manganate (LSM)–YSZ cathode interlayer, and LSM current collector, were fabricated. The effect of various parameters on cell performance was evaluated. The parameters investigated were: (1) YSZ electrolyte thickness, (2) cathode interlayer thickness, (3) anode support thickness, and (4) anode support porosity. Cells were tested over a range of temperatures between 600 and 800 °C with hydrogen as fuel, and air as oxidant. Ohmic contribution was determined using the current interruption technique. The effect of these cell parameters on ohmic polarization and on cell performance was experimentally measured. Dependence of cell performance on various parameters was rationalized on the basis of a simple analytical model. Based on the results of the cell parameter study, a cell with optimized parameters was fabricated and tested. The corresponding maximum power density at 800 °C was ∼1.8 W cm⁻².     

Experimental investigation on DMFCs using reduced noble metal loading with NiTiO3 as supportive material to enhance cell performances

In this present work, the effect of anode electrocatalyst materials is investigated by adding NiTiO₃ with Pt/C and Pt-Ru/C for the performance enhancement of direct methanol fuel cells (DMFCs). The supportive material NiTiO₃/C has been synthesized first by wet chemical method followed by incorporation of Pt and Pt-Ru separately. Experiments are conducted with the combination of four different electrocatalyst materials on the anode side (Pt/C, Pt-NiTiO₃/C, PtRu/C, Pt-Ru-NiTiO₃/C) and with commercial 20 wt % Pt/C on the cathode side; 0.5 mg_pt/cm² loading is maintained on both sides. The performance tests of the above catalysts are conducted on 5 cm² active area with various operating conditions like cell operating temperatures, methanol/water molar concentrations and reactant flow rates. Best performing operating conditions have been optimized. The maximum peak power densities attained are 13.30 mW/cm² (26.6 mW/mg_pt) and 14.60 mW/cm² (29.2 mW/mg_pt) for Pt-NiTiO₃/C and Pt-Ru-NiTiO₃/C at 80 °C, respectively, with 0.5 M concentration of methanol and fuel flow rate of 3 ml/min (anode) and oxygen flow rate of 100 ml/min (cathode). Besides, 5 h short term stability tests have been conducted for PtRu/C and Pt-NiTiO₃/C. The overall results suggest that the incorporation of NiTiO₃/C supportive material to Pt and Pt-Ru appears to make a promising anode electrocatalysts for the enhanced DMFC performances.     

A novel doped CeO2–LaFeO3 composite oxide as both anode and cathode for solid oxide fuel cells

A novel composite oxide Ce(Mn,Fe)O₂-La(Sr)Fe(Mn)O₃ (CFM-LSFM) was synthesized and evaluated as both anode and cathode materials for solid oxide fuel cells. The cell with CFM-LSFM electrodes was fabricated by tape-casting and screen printing technique. The power-generating performance of this cell was comparable to that of the cell with Ni-SSZ anode and LSM-SSZ cathode. During the 120 h long-term test in hydrogen at 800 °C, the performance increased by 8.6% from 256 to 278 mW cm⁻². This was attributed to the decrease of polarization resistance and ohmic resistance during the test. The XRD results showed the presence of Fe, MnO and some unknown second phases after heat-treating the electrode materials in H₂ which may be beneficial to the anode electrochemical process. The gradual decrease of polarization resistance as increasing the current density possibly resulted from the increasing content of water in the anode.     

Air-breathing membraneless laminar flow-based fuel cell with flow-through anode

This paper describes a detailed characterization of laminar flow-based fuel cell (LFFC) with air-breathing cathode for performance (fuel utilization and power density). The effect of flow-over and flow-through anode architectures, as well as operating conditions such as different fuel flow rates and concentrations on the performance of LFFCs was investigated. Formic acid with concentrations of 0.5 M and 1 M in a 0.5 M sulfuric acid solution as supporting electrolyte were exploited with varying flow rates of 20, 50, 100 and 200 μl/min. Because of the improved mass transport to catalytic active sites, the flow-through anode showed improved maximum power density and fuel utilization per single pass compared to flow-over planar anode. Running on 200 μl/min of 1 M formic acid, maximum power densities of 26.5 mW/cm² and 19.4 mW/cm² were obtained for the cells with flow-through and flow-over anodes, respectively. In addition, chronoamperometry experiment at flow rate of 100 μl/min with fuel concentrations of 0.5 M and 1 M revealed average current densities of 34.2 mA/cm² and 52.3 mA/cm² with average fuel utilization of 16.3% and 21.4% respectively for flow-through design. The flow-over design had the corresponding values of 25.1 mA/cm² and 35.5 mA/cm² with fuel utilization of 11.1% and 15.7% for the same fuel concentrations and flow rate.     

Experimental investigation on the effect of anode functional layer on the performance of anode supported micro-tubular SOFCs

In this study, anode supported micro-tubular solid oxide fuel cells (SOFCs) are fabricated by extrusion method and the effects of powder size, thickness and sintering temperature of the anode functional layer (AFL) on the electrochemical performance is experimentally investigated. For this purpose, four different commercial NiO powders are tested as initial powder for the fabrication of the anode functional layer. The thickness of AFL is also considered by varying the number of coatings. After deciding the optimum initial NiO powder size used in AFL and AFL thickness, the effect of pre-sintering temperature is examined. The performance tests are performed at an operating temperature of 800 °C under hydrogen and air. The microstructures of the samples are also investigated by a scanning electron microscope. The best peak power density is obtained as ～0.5 W/cm² from the cell having a single layer anode functional layer pre-sintered at 1250 °C prepared by NiO powders with 4 m²/g surface area.     

Performance of direct ammonia fuel cell with PtIr/C,PtRu/C,and Pt/C as anode electrocatalysts under mild conditions

While ammonia (NH₃) is an attractive alternative to pure hydrogen, its direct use in fuel cells is fraught with difficulties. A direct ammonia fuel cell (DAFC) with PtIr/C (Pt:Ir = 1:1), PtRu/C (Pt:Ru = 1:1), and Pt/C anode electrocatalyst was investigated at 25 °C and 100 kPa inlet gas pressure. Due to the synergistic and electronic effects of the PtIr alloy, their open-circuit voltages (OCVs) were rated as PtIr/C > PtRu/C > Pt/C, with the DAFC with PtIr/C anode achieving the highest OCV of 0.50 V and peak power density (PPD) of maximum 1.68 mW cm^?2. Meanwhile, an online Fourier transform infrared (FTIR) spectrometer detected an increase in ammonia permeation in the cathode exhaust gas, indicating a possibility of fuel permeation and cathode electrocatalyst degradation. The degradation of DAFC efficiency with rising cycle numbers may be due to ammonia cross-over and poisoning over the surface of the electrocatalyst.