Conventional Ni-YSZ Research Articles

Correlation Between Microstructure and Performance of GDC-Based Electrodes

Gadolinium doped ceria (GDC) gains increasing attention as a promising material for both solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). The GDC-based electrodes demonstrate positive features, e.g. enhanced electrochemical performance in low operation temperatures, resistivity to sulfur poisoning and carbon deposition, etc. As GDC is a mixed electronic-ionic conductor in reducing atmosphere, electrochemical reactions can be supported by the double phase boundary (DPB) at the GDC surface. Several studies demonstrated that the DPB reaction may dominate the electrochemical performance over triple phase boundary (TPB) reaction in Ni-GDC electrodes, where it can account for as much as 95 % of the total reaction depending on the cermet microstructure [1]. Recent studies even show that pure ceria electrodes can achieve substantial power density [2,3]. In this context, the microstructure design principle for GDC-based electrodes should focus on maximizing GDC surface area. Particularly, GDC electrodes with infiltrated GDC nanoparticles or electro-catalytic nanoparticles may achieve competitive performance compared with the conventional Ni-YSZ electrodes. Although many strategies have been proposed to improve performance of GDC-based electrodes, it is difficult to quantitatively compare all the reported results. Furthermore, the correlation between microstructure and performance of pure GDC electrode are still scarce.Several different types of GDC-based electrodes are fabricated and tested in the unified characterization procedure in this study. Four basic designs are considered, i.e. Ni-GDC, GDC-perovskite composites, GDC electrodes with deposited Ni nanoparticles and pure GDC electrodes. Several strategies to modify the GDC surface area are discussed. In addition, the substantial enhancements in the DPB density and electrochemical performance were achieved by precipitating Ni-nanoparticles directly on sub-micron GDC powders at 2wt.% loading. The performance of electrodes was evaluated by electrochemical impedance spectra measurements with various humidity and temperature conditions. The results showed clear dependance between GDC surface area and electrode performance. At the same time, it should be noted that the electrode active thickness depends on the electrode microstructure. In particular, it is in the range of 5 µm for the pure nano-GDC electrode. When the GDC electrode is thicker than the active thickness, it results in large Ohmic resistance due to the electronic conduction in the porous electrode.[1] A. Nenning, M. Holzmann, J. Fleig, A.K. Opitz, Mater. Adv. 2 (2021) 5422–5431.[2] M. Ouyang, A. Bertei, S.J. Cooper, Y. Wu, P. Boldrin, X. Liu, M. Kishimoto, H. Wang, M. Naylor Marlow, J. Chen, X. Chen, Y. Xia, B. Wu, N.P. Brandon, J. Energy Chemistry. 56 (2021) 98–112.[3] W. Jung, K.L. Gu, Y. Choi, S.M. Haile, Energy Env. Sci. 7 (2014) 1685–1692.

Comparison of the Electrochemical and Degradation Behaviour of Ni-YSZ and Ni-GDC Electrodes Under Steam, Co- and CO2 Electrolysis

The mixed ionic and electronic conductive property of Ni-GDC has ensured that the electrochemical reaction zones of the electrode extend beyond the triple phase boundary of Ni/GDC/fuel gas to the double phase boundary of the GDC and the fuel gas [1, 2]. In addition, ceria has shown good carbon suppression properties when operated in carbon-containing fuels[3, 4]. For these reasons, Ni-GDC has emerged as a possible replacement for the conventional Ni-YSZ electrode. However, a direct comparison of the performance and long-term degradation of Ni-GDC with literature values of the Ni-YSZ would be ambiguous. On one hand, different reports utilize different fuel gas compositions, operating temperatures as well as current densities. On the other hand, the fabrication of fuel electrode-supported Ni-GDC is still a challenge due to the well-known inter-diffusion [5, 6] between the YSZ and the GDC oxide phase at a high sintering temperature (1400 °C) of YSZ electrolytes. Hence, most of the electrode fabrication has remained on electrolyte support. Thus, a direct comparison of electrolyte-supported Ni-GDC with the conventional fuel electrode-supported Ni-YSZ is ineffective due to different degradation behaviour.Therefore, this present study aims to investigate and compare the long-term stability of Ni-GDC and Ni-YSZ under three different electrolysis modes; steam-electrolysis, co-electrolysis and CO2-electrolysis. Firstly, electrolyte-supported single cells of Ni-GDC (NiO-GDC//8YSZ//GDC//LSCF) and Ni-YSZ (NiO-GDC//8YSZ//GDC//LSCF) were fabricated and investigated using electrochemical impedance spectroscopy (EIS) from 750-900 °C temperature range. Furthermore, the impedance data were also recorded under polarization (0.7 to 1.4V) as well as at OCV by varying the partial pressure of steam, CO2 and oxygen (, pH20, pCO2 and pO2). Finally, stability tests of the single cells were carried out under steam electrolysis (H2O: H2, 50:50) and co-electrolysis (H2O: CO2:H2, 40:40:20) conditions at 900 °C with 0.5 A/cm2 current density for 500 h [7]. For the CO2-electrolysis (CO2:CO, 80:20), the stability test was performed up to 1000 h. The post-test characterization of the operated cells was carried out using both SEM-EDX as well as FIB-SEM. The results reveal that Ni-GDC exhibits higher current density than Ni-YSZ in all the electrolysis modes. In the post-test analysis, loss of GDC percolation was observed and the Ni particles were observed to be covered by the GDC oxide phase. Furthermore, both electrodes demonstrate that Ni is migrating away from the electrolyte in all the electrolysis modes. The detailed electrochemical and microstructural properties of the operated cells will be presented and discussed.

Conditional GAN for Generation of 3D SOFC Electrode Microstructure Dataset

Synthetic three-dimensional porous structures of solid oxide fuel cell anode are generated using the deep convolutional conditional generative adversarial neural network (DCCGAN). The developed network consists of a generator that produces an artificial structure dataset from random numbers, so-called latent variables, and a discriminator that judges whether the input structure dataset is real or fake. The generator and discriminator are alternately trained to improve their performance in an adversarial manner so that the generator can eventually create realistic structures indistinguishable from the real ones. The training process is performed using the real structure dataset of conventional Ni-YSZ anodes with different solid volume ratios, i.e., Ni: YSZ = 70:30, 50:50, and 30:70. In this study, additional training is performed for the generator to control the volume fraction of the generated structures. First, the values of the volume fractions are input to the generator alongside the latent variables. Then, the volume fraction loss is calculated from the difference between the volume fractions of the generated structure and the input values. Finally, the volume fraction loss is used to train the generator in addition to the ordinal training process. The trained network is validated by comparing the generated structures with the real structures in terms of microstructural parameters such as volume fraction, surface area density, and triple-phase boundary density. This comparison is conducted not only for the structures used for the training but also those that are not used for the training, i.e., a solid volume ratio of Ni: YSZ = 40:60 and 60:40. It is found from the results that the volume fractions of the generated structures are in good agreement with the specified input values to the generator. Also, other microstructural parameters quantified from the artificial microstructures are similar to those of the real structures. In addition, since the developed network does not contain fully-connected layers, and is hence categorized as a fully-convoluted network, structures with arbitrary sizes can be generated using the same generator by changing the dimension of the latent variables. The generated structures are confirmed to be free from digital artifacts such as noise, disconnectivity, and periodicity in structures.

Life Testing and Redox Cycling of Ni- and Ru-Doped Strontium Iron Titanate Exsolution Fuel Electrodes in Electrolyte-Supported Solid Oxide Cells

Oxide exsolution fuel electrodes for solid oxide cells (SOCs) have shown good initial electrochemical performance compared with conventional Ni-YSZ. Few studies have focused on investigating the long-term durability of these materials and no long-term reversible operation has ever been conducted on cells with these exsolution fuel electrodes. In this study, life tests on electrolyte-supported full and symmetric cells with Sr0.95Ti0.3Fe0.63Ni0.07O3- d (STFN) and Sr0.95Ti0.3Fe0.63Ru0.07O3- d (STFRu) fuel electrodes were conducted under different testing conditions. STFN fuel electrodes tested with 97% H2 +3% H2O showed worse initial stability than cells tested with 50% H2 +50% H2O; this is attributed to a more extensive perovskite-RP phase transformation, as suggested by in-situ X-ray diffraction (XRD) analyses. STFRu was also tested with 97% H2 +3% H2O and showed better stability than STFN.

Solid oxide cells with cermet of silver and gadolinium-doped-ceria symmetrical electrodes for high-performance power generation and water electrolysis

A cermet of silver and gadolinium-doped-ceria (Ag-GDC) is investigated as novel symmetrical electrode material for (ZrO2)0.92(Y2O3)0.08 (YSZ) electrolyte-supported solid oxide cells (SOCs) operated in fuel cell (SOFC) and electrolysis (SOEC) modes. The electrochemical performances are evaluated by measuring the current density-voltage characteristics and impedance spectra of the SOCs. The activity of hydrogen and air electrodes is investigated by recording overpotential versus current density in symmetrical electrode cells, respectively in hydrogen and air, using a three-electrode method. Conventional hydrogen electrode, Ni-YSZ, and oxygen electrode, LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ)-GDC, are tested as comparison. The results show that, as an oxygen electrode, Ag-GDC is more active than LSCF-GDC in catalyzing both oxygen reduction reaction (ORR) in an SOFC and oxygen evolution reaction (OER) in an SOEC. As a hydrogen electrode, Ag-GDC is more active than Ni-YSZ in catalyzing hydrogen oxidation reaction (HOR) in an SOFC and hydrogen evolution reaction (HER) in an SOEC, especially in high steam concentration. An SOC with symmetrical Ag-GDC electrodes operated in a fuel cell mode, with 3% H2O humidified H2 as the fuel, displays a peak power density of 395 mWcm−2 at 800 °C. Its polarization resistance at open circuit voltage is 0.21 Ω cm2. Ag-GDC electrode can be operated even at pure steam. An SOEC operated for electrolyzing 100% H2O, the current density reaches 720 mA cm−2 under 1.3 V at 800 °C.

Highly flexible solid oxide fuel cells using phase-controlled electrolyte support

Flexible solid oxide fuel cells (SOFCs) have attracted increasing attention due to their excellent mechanical stability and lightness. An essential electrolyte material for developing highly flexible SOFCs is 3 mol% yttria-stabilized zirconia (3YSZ), but there remain some difficulties in its application to SOFCs. We report a phase-controlled, bendable, ultra-thin 3YSZ electrolyte with a thickness of ~22 µm, high flexural strength, and improved ohmic resistance that surpasses that of 8 mol% YSZ electrolytes. A flexible cell (total thickness < 60 µm) is fabricated through simple and reproducible methods such as tape casting and screen printing. The highest cell performance is achieved among the reported flexible SOFCs, with the maximum power density of 0.86 W cm−2 at 900 °C using conventional cermet electrodes, Ni-YSZ anode, and LSM-YSZ cathode. Our study provides a well-defined framework for developing flexible SOFCs as next-generation power sources for mobile devices with high volumetric power.

Insights on a Ruddlesden-Popper phase as an active layer for a solid oxide fuel cell fed with dry biogas

Solid oxide fuel cell (SOFC) is a mature opportunity for producing power energy in remote areas like islands, where access to the electrical grid is not favoured, and gas distribution is the only viable approach. In this context, generally, biogas represents the most convenient fuel resources in these areas. However, the direct use of biogas in SOFCs is still an issue to be solved due to its negative effect on the conventional Ni-YSZ anode. In this study, to overcome this issue, we suggested using a protective layer coated on the anode of a commercial SOFC. A nickel manganite showing mixed ionic and electronic conductivity tailored specifically for this approach was investigated. The preliminary characterisations showed that the formation of a Ruddlesden-Popper (RP) n = 1 structure supporting fine encapsulated particles based on Ni was formed around 800 °C in consequence of the reducing environment. The electrochemical experiments carried out for 270 h demonstrated for the coated cell significant stability in the presence of dry biogas, albeit an ageing effect was noticed in the electrical percolation of both cell electrodes. The post mortem analyses revealed an attractive redox property for the nickel manganite, which partially returned to the RP n = 2 phase. Moreover, the absence of carbon deposits on the anode suggests possible applications for this approach.

Effects of mass fraction of La0.9Sr0.1Cr0.5Mn0.5O3-δ and Gd0.1Ce0.9O2-δ composite anodes for nickel free solid oxide fuel cells

The optimal anode mass fraction of La0.9Sr0.1Cr0.5Mn0.5O3-δ (LSCM) and Gd0.1Ce0.9O2-δ (GDC) is evaluated in this study. The anodes with GDC share of 30–100 wt.% are investigated. Initial polarization resistance decreased as the GDC share increased. However, anodes with GDC share over 80 wt.% significantly deteriorated in the degradation tests. Nano-scale cracks were observed in the GDC phase at the grain boundaries after the test. These nano-cracks were not observed in composite anodes, from which it is implied that LSCM has stabilization effect on GDC structure. The mass fraction of LSCM : GDC = 30 : 70 wt.% is found to be optimal in terms of initial electrochemical performance and stability. The optimal LSCM-GDC shows lower polarization resistance than conventional Ni-YSZ at low temperatures, which is comparable to Ni-GDC anode.

Surface oxidation of Ni-cermet electrodes by CO2 and H2O and how to moderate it

The oxidation of porous Ni-yttria-stabilized zirconia (YSZ) and Ni-gadolinia-doped ceria (GDC) ceramic-metal (cermet) electrodes in H2O and CO2 atmospheres was studied by near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). We show that the oxidation of nickel by the two gases is not similar, as is commonly believed, but it depends on the ceramic type. Nickel is vulnerable to oxidation in H2O but it resists to CO2 in Ni-GDC, as compared to the Ni-YSZ electrode. Inspired by this observation we conceptualize and fabricate Ni-YSZ electrodes modified by ceria nanoparticles, which show significantly higher resistance to CO2 oxidation as compared with conventional Ni-YSZ electrodes. The preparation of tailor-made cermet electrodes with identical bulk/mechanical characteristics but very different surface properties offers a promising fabrication strategy for high-performance and durability solid oxide electrolysis cells for CO2 conversion.

Microstructure and Performance of Ni-Free Nano La0.75Sr0.25Cr0.5Mn0.5O3 - Gd0.2Ce0.8Ox Composite Anode

The correlation between microstructure and performance of La0.75Sr0.25Cr0.5Mn0.5O3 - Gd0.2Ce0.8Ox (LSCM-GDC) solid oxide fuel cell (SOFC) anode is investigated. The fuel electrode is fabricated with the nano-composite powder prepared through colloidal-processing-based approach. The well dispersed nano-powder results in the limited particle coarsening during sintering and fine electrode microstructure. The influences of sintering temperature and electrode thickness on polarization resistance are investigated. The lowered sintering temperature results in particle size below 100 nm, which improves electrochemical performance. On the other hand, porosity over 57% inhibits percolation of the solid phases, in particular the LSCM. The performance of thinner composite electrode is superior, which is in good agreement with the deteriorated LSCM and GDC percolations. The electrochemical performance of the optimized electrode is competitive to the conventional Ni-YSZ, Ni-GDC, and LSCM-GDC anodes fabricated with submicron powders.

Fabrication of Durable Ni-YSZ Hydrogen Electrode for High-Temperature Solid Electrolyzer Cells.

Solid oxide electrolyzer cells with an Ni-Fe-yttria-stabilized zirconia (Ni-Fe-YSZ) hydrogen electrode as the cathode, lanthanum strontium ferrite (LSCF)-gadolinia-doped ceria (GDC) air electrode as the anode, and YSZ as the electrolyte were fabricated, and the oxidation protection effect of sacrificial Fe particles was investigated. X-ray diffraction analysis indicated that Ni was protected from oxidation under a water vapor atmosphere by sacrificial Fe. Scanning electron microscopy observations suggested that the Ni particles accumulated in the Ni-YSZ hydrogen electrode, which might have been associated with the partial oxidation of Ni during cell operation at 700 °C in 50% H₂O/15% H₂/35% Ar atmosphere. No appreciable microstructural changes were observed for the Ni-Fe-YSZ hydrogen electrode. Furthermore, the presence of the sacrificial Fe particles could be responsible for the superior durability of the cell, compared with that of the cell featuring the conventional Ni-YSZ hydrogen electrode.

Surface decorated La0.43Ca0.37Ni0.06Ti0.94O3−d as an anode functional layer for solid oxide fuel cell applications

Surface decorated La0.43Ca0.37Ni0.06Ti0.94O3−d (LCNT) perovskite oxide was investigated as an anode functional layer (AFL) for anode-supported solid oxide fuel cells (SOFCs). The surface exsolved Ni nano particles on LCNT scaffold enlarged electrochemically active triple phase boundaries (TPBs) without any agglomeration and mechanical failure. The Ni particles with 60 nm in diameter were homogeneously exsolved from LCNT perovskite. The Ni-YSZ anode supported cell with LCNT anode functional layer (AFL) exhibited a maximum power density of 0.94 W/cm2, similar to that of the conventional Ni-YSZ AFL cell at 900 °C. The activation polarization resistance of the LCNT AFL cell was effectively reduced compared to that of the Ni-YSZ AFL cell, though it had higher Ohmic resistance due to thicker YSZ electrolyte and lower electrical conductivity. Our study suggests the potential use of LCNT with exsolved nano particles as an active and durable AFL for high-temperature SOFCs.

High performance of direct methane-fuelled solid oxide fuel cell with samarium modified nickel-based anode

Natural gas is one of the most attractive fuels for solid oxide fuel cell (SOFC), while the anode activity for methane fuel has a great influence on the performance and stability of SOFC. Samarium is a good catalyst promoter for methane reforming. In this work, samarium is used to modify nickel catalyst, which results in small nickel oxide particles. The SmNi-YSZ (yttria-stabilized zirconia) anode has smaller particles and better interfacial contact between nickel and YSZ compared with conventional Ni-YSZ anode. The fine structure of SmNi-YSZ anode results in high activity for electrochemical oxidation of hydrogen and low polarization resistance of the cell. The performance of SmNi-YSZ anode cell with humidified methane as fuel is greatly improved, which is similar to that with hydrogen as fuel. The maximum power densities of SmNi-YSZ anode cell are 1.56 W cm−2 for humidified hydrogen fuel and 1.54 W cm−2 for humidified methane fuel at 800 °C. The maximum power density is increased by 221% when samarium is used to modify Ni-YSZ anode for humidified methane fuel at 650 °C. High cell performance results in good stability of SmNi-YSZ anode cell and the cell runs stably for more than 600 min for humidified methane fuel.

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.

Co-fired anode-supported solid oxide fuel cell for internal reforming of hydrocarbon fuel

Hydrocarbon-based solid oxide fuel cell (SOFC) is being projected as one of the possible alternatives to conventional internal combustion engines. However, the conventional Ni–YSZ anode is prone to carburization in the presence of hydrocarbon fuels. In the present study, an optimized Ni–Cu-based anode composition (Ni0.9–Cu0.1–YSZ0.95–GDC0.05) has been evolved based on accelerated carburization studies and phase analysis by X-ray diffractometry and X-ray photoelectron spectroscopy. The electrochemical parameters have been derived for the optimized anode composition, and its exchange current density is estimated to be 76.3 mA cm−2 at 780 °C. The main advantage of the optimized anode is its suitability for co-firing with the electrolyte. Using the optimized anode composition, anode-supported SOFC single cells (ASCs) have been fabricated and their electrical and electrochemical performances have been evaluated and compared with conventional ASC. The anode-supported co-cast SOFC with the optimized anode composition exhibits a power density of 436 mW cm−2 at 850 °C and 0.5 V with methane as fuel.

Solid oxide fuel cells fueled by simulated biogas: Comparison of anode modification by infiltration and reforming catalytic layer

• Conventional Ni-YSZ anodes were modified by infiltration and a catalytic layer. • Detailed comparison between the modified cells and the bare cell was made. • The GDC infiltration on anode is beneficial only in certain cases. • Enhancement of cell performance and stability was achieved by the catalytic layer. Solid oxide fuel cell (SOFC) provides a new method for clean and efficient conversion and utilization of hydrocarbon fuels due to its high fuel flexibility. The utilization of biogas fuel through direct internal reforming (DIR) allows for a simplification of the SOFC system since no external reformer appears strictly necessary. Despite its considerable convenience and potential, at present, direct internal dry reforming is still not considered as a competitive process for commercial application, which is limited by the reaction difficulty and high risk of carbon deposition. To address the problem, in this study, conventional Ni-yttrium stabilized zirconia (YSZ) anodes of SOFCs are modified by two methods, i.e. Ce 0.9 Gd 0.1 O 2-δ (GDC) infiltration and a Ni-GDC reforming catalytic layer. A comparative study between the modified cells and the bare cell is made under operation with humidified H 2 and simulated biogas. Both of these two modification methods lead to a slight but acceptable decrease of the cell performance under humidified H 2 . In the case of simulated biogas, results show that GDC infiltration is only beneficial to the cell performance with very low or very high CO 2 /CH 4 molar ratio. While with a moderate CO 2 /CH 4 ratio of 0.5–1.5, GDC infiltration instead results in a decrease of cell performance. However, the cell modified by a Ni-GDC catalytic layer shows superior performance towards the direct utilization of simulated biogas than the bare one and the one modified by GDC infiltration. The anode modification by a Ni-GDC catalytic layer can also improve the stability of the cell under simulated biogas, which is verified under different operating currents, although serious carbon deposition is detected in the catalytic layer afterwards.

Enhancing the partial oxidation of gasoline with Mo-doped Ni catalysts for SOFC applications: An integrated experimental and DFT study

We introduce a small amount of Mo atoms into a Ni/YSZ catalyst for the partial oxidation reaction of gasoline. We find that a Ni-Mo/YSZ catalyst displays a high reforming activity and stability with an isooctane conversion of 90 % and H2 yield of 76 % with less degree of coking and sintering as compared to a Ni/YSZ catalyst. Our XRD results indicate that a Ni-Mo solid solution is formed. Raman results also suggest that the presence of well dispersed Mo=O species over a Ni surface can be a possible active site that is related to the high coke resistance of Ni-Mo/YSZ catalysts. DFT-based calculations indicate that Ni-Mo/YSZ catalysts enhance the carbon-tolerance by increasing activation barriers for the C–H bond cleavage and C–C coupling as compared with the Ni/YSZ system. A Ni-Mo catalyst is used as an internal micro-reforming layer on top of conventional Ni-YSZ anode-supported single cells. The single cell displays a significantly improved stability with a low degradation rate.

Improving SOFC Anode Electrocatalytic Activity Using Nanoparticle Infiltration into MIEC Compositions

Mitigating activation polarization in the anode is one of the major challenges in intermediate-temperature operation of solid oxide fuel cells (SOFCs). Liquid phase infiltration of nanoscale electrocatalysts has been shown to result in significant reductions in activation polarization in SOFC anodes. In this study, we explore liquid-phase infiltration of nickel, gadolinium doped ceria (GDC), and Ni/GDC electrocatalysts into two different types of cermet anodes: one with a conventional Ni-YSZ composition, and the other with a Ni-MIEC cermet anode where the YSZ has been doped with 3 mol% TiO2 to impart electronic conductivity. The principal goal of this study is to explore the role of electronic transport in the MIEC phase in effective utilization of the infiltrated nanoscale electrocatalysts. The role of temperature, infiltration cycles and the type of electrocatalysts have been experimentally studied in symmetric cells using electrochemical impedance spectroscopy (EIS). Distribution of relaxation times (DRT) modeling has been used to elucidate the contributions of various charge transfer processes.

NiMo-ceria-zirconia-based anode for solid oxide fuel cells operating on gasoline surrogate

A multi-functional NiMo-ceria-zirconia composite was developed as an anode for a solid oxide fuel cell (SOFC) running on isooctane, a commonly used gasoline surrogate. The anode layer was fabricated on an electrolyte-supported single cell using yttria-stabilized zirconia (YSZ) as the electrolyte and La0.6Sr0.4Co0.2Fe0.8O3-δ as the cathode. Our results indicate that the single NiMo-ceria-zirconia layer possesses a dual-functionality: firstly to internally convert complex hydrocarbons into synthesis gas with a high resistance to coking and secondly to electrochemically oxidize the synthesis gas mixture for electric power generation. Compared with the conventional Ni-YSZ anode single cell, the application of the ceria-zirconia in the anode significantly suppresses carbon deposition and improves the performance stability of the single cell. Furthermore, the addition of Mo in the Ni-ceria-zirconia appears to facilitate a higher degree of sintering for the anode, which increases the electronic conductivity and maximum power density of the single cell. Consequently, at 800 °C the single cell with 5 wt.% Mo in the Ni-ceria-zirconia-based anode displayed a higher maximum power density of 212 mW cm−2 at 0.48 V and significantly enhanced performance stability than the conventional Ni-YSZ anode single cell in the isooctane/air operating mode.

Molybdenum dioxide as an alternative catalyst for direct utilization of methane in tubular solid oxide fuel cells

Direct utilization of methane in conventional tubular solid oxide fuel cells (SOFCs) with a Ni-YSZ anode support was proposed using MoO2 as a partial oxidation catalyst for methane reforming at the cell inlet. A promising stability was achieved for a continuous operation in a mixture of methane and air (1, 1.5) for >150h under a load voltage of 0.7V at 750°C. The addition of the MoO2 catalyst at the anode inlet made tubular SOFCs with the conventional Ni-YSZ anode an efficient and practically promising candidate for direct hydrocarbon utilization.