Investigating the impact and reaction pathway of toluene on a SOFC running on syngas

The integration of solid oxide fuel cells (SOFCs) with gasification systems have theoretically been shown to have a great potential to provide highly efficient distributed generation energy systems that can be fuelled by biomass including municipal solid waste. The syngas produced from the gasification of carbonaceous material is rich in hydrogen, carbon monoxide and methane that can fuel SOFCs. However, other constituents such as tar can cause catalyst deactivation, and blockage of the diffusion pathways. This work examines the impact of increasing concentrations of toluene as a model tar in a typical syngas composition fed to a NiO-GDC/TZ3Y/8YSZ/LSM–LSM SOFC membrane electrode assembly operating at 850°C and atmospheric pressure. Results suggest that up to 20 g/Nm³ of toluene and a low fuel utilisation factor (c.a. 17%) does not negatively impact cell performance and rather acts to increase the available hydrogen by undergoing reformation. At these conditions carbon deposition does occur, detected through EDS analysis, but serves to decrease the ASR rather than degrade the cell.     

A steel slag–derived Boudouard reaction catalyst for improved performance of direct carbon solid oxide fuel cells

Solid oxide fuel cells (SOFCs) can directly utilize solid carbon as fuel by integrating with the reverse Boudouard reaction in the anode chamber. Efficiency of the Boudouard gasification of solid carbon fuel is one of the crucial factors influencing the performance of direct carbon SOFCs (DC‐SOFCs). In this paper, a novel Boudouard reaction catalyst derived from steel slag was first introduced into DC‐SOFCs for improving the electrochemical performance. The catalytic activity of the steel slag was activated using the molten alkali method to decompose the inert mineral phases of the raw material. The steel slag–derived catalyst was loaded on the activated charcoal by a wet ball milling method. This kind of catalyst can match up to the readily available solid carbon fuels in cost. Promoted by this highly active Boudouard reaction catalyst, the initial Boudouard gasification temperature of the carbon fuel decreased by 99°C, and the producing rate of carbon monoxide doubled. Furthermore, the power outputs of the fuel cells increased from 91 to 159 mW cm^?2, and the fuel utilization increased from 17.10% to 46.43% at 825°C. This study demonstrates that the steel slag–derived catalyst is a promising material for the performance improvement of DC‐SOFCs and may make a valuable contribution to their commercial application.     

Hydrazine as efficient fuel for low-temperature SOFC through ex-situ catalytic decomposition with high selectivity toward hydrogen

Hydrazine is a promising fuel for portable fuel cells because it is a liquid, it is carbon free and it has a high energy density. In this work, hydrazine was investigated as an efficient fuel for low temperature solid-oxide fuel cells (SOFCs) with a traditional nickel anode. A catalytic system with high selectivity toward hydrogen was developed using Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) as the main catalyst and potassium hydroxide as the promoter. The result of compositional analysis of the products showed that the hydrazine can be decomposed into hydrogen and nitrogen with 100% selectivity when an appropriate amount of KOH promoter is used. Acceptable power densities were achieved for a thin-film samaria-doped ceria (SDC) electrolyte cell operating on hydrazine decomposition products and hydrogen over a complete operation temperature range of 650–450 °C. In addition, a similar cell with ammonia as the fuel displayed a much lower performance.     

Self-sustained operation of a kWe-class kerosene-reforming processor for solid oxide fuel cells

In this paper, fuel-processing technologies are developed for application in residential power generation (RPG) in solid oxide fuel cells (SOFCs). Kerosene is selected as the fuel because of its high hydrogen density and because of the established infrastructure that already exists in South Korea. A kerosene fuel processor with two different reaction stages, autothermal reforming (ATR) and adsorptive desulfurization reactions, is developed for SOFC operations. ATR is suited to the reforming of liquid hydrocarbon fuels because oxygen-aided reactions can break the aromatics in the fuel and steam can suppress carbon deposition during the reforming reaction. ATR can also be implemented as a self-sustaining reactor due to the exothermicity of the reaction. The kW_e self-sustained kerosene fuel processor, including the desulfurizer, operates for about 250 h in this study. This fuel processor does not require a heat exchanger between the ATR reactor and the desulfurizer or electric equipment for heat supply and fuel or water vaporization because a suitable temperature of the ATR reformate is reached for H₂S adsorption on the ZnO catalyst beds in desulfurizer. Although the CH₄ concentration in the reformate gas of the fuel processor is higher due to the lower temperature of ATR tail gas, SOFCs can directly use CH₄ as a fuel with the addition of sufficient steam feeds (H₂O/CH₄ ≥ 1.5), in contrast to low-temperature fuel cells. The reforming efficiency of the fuel processor is about 60%, and the desulfurizer removed H₂S to a sufficient level to allow for the operation of SOFCs.     

Coal gas fuel utilization effects on electrolyte supported solide oxide fuel cell performance

Solid oxide fuel cells (SOFCs) transform the energy of the fuel instantly into electric energy with a large fuel option. Coal, which is a local energy source, is a preferred fuel despite its negative features because it is cheap and abundant. The use of coal and coal-based fuels in SOFCs has recently attracted considerable attention. In this study, performance analysis of the SOFC has been performed experimentally by using hydrogen, generator gas (contained 12% H₂), and water-gas (contained 50% H₂) in an electrolyte-supported SOFC (ES-SOFC). The numerical modelling of the fuel cell had been previously performed. In addition, the effect of inlet gas fuel flow rates on the ES- SOFC has been investigated numerically in this study. The temperature effect on the performance of ES-SOFC has been examined experimentally. It is seen that the performance of SOFCs fueled hydrogen is favorable than fueled water gas and generator gas. This is because of the higher hydrogen substance in the water gas measure against the other gas. In addition, it is seen that the increase in temperature increases the performance with positive effects on the reactions. It is also concluded that the performance of SOFC increases when inlet fuel flow rates increase.     

Recent progress in integration of reforming catalyst on metal-supported SOFC for hydrocarbon and logistic fuels

The metal-supported solid oxide fuel cell (MS-SOFC) is of current research interest in the clean energy field due to its high performance, quick start-up, thermal cycle stability, and lower raw material cost compared to the conventional cermet-based SOFC. To efficiently operate a MS-SOFC using complex hydrocarbon and logistic fuels, it is required to introduce an internal reforming catalyst within the anode metal scaffold. This review article discusses some examples of the performance of MS-SOFCs under hydrocarbon and logistic fuels with and without an additional reforming catalyst. We also discuss the performance improvement of conventional cermet-based SOFCs by adding reforming catalysts via the infiltration method. This information can be directly applied to future MS-SOFC applications. Furthermore, this review article proposes possible novel methods such as direct precursor infiltration, catalyst-anode premixing, and atomic layer deposition methods to introduce the reforming catalyst into a MS-SOFC for improving its initial electrochemical performance and long-term stability under hydrocarbon and logistics fuel.     

Hydrogen production via catalytic propane partial oxidation over Ce1-xMxNiO3-λ (M=Al,Ti and Ca) towards solid oxide fuel cell (SOFC) applications

Indirect hydrogen production routes presented extensive compatibilities for distributed solid oxide fuel cell systems. Catalyst activity directly determines hydrogen production and profoundly affects the power generation. In this work, Ce_1-xM_xNiO_3-λ (M = Al, Ti and Ca) were synthesized for hydrogen production from propane partial oxidation (POx). From the results, it indicated that the choice of catalyst compositions could directly affect the microstructure during the preparation process. Also, different Ce_1-xM_xNiO_3-λ catalysts displayed distinctive carbon tolerance performances due to the different active particle sizes and surface properties of the catalysts. In general, the synthesized Ce_1-xM_xNiO_3-λ catalysts showed higher hydrogen production than a commercial nickel cerium catalyst. From the observation of a SOFC test system powered by injecting the generated H₂ from catalytic propane POx reaction, the obtained power density of CNO–Al displayed an increase of 22.6% compared to the commercial nickel cerium catalyst. It was quite impressive that the equivalent hydrogen (160 ml/min) produced over CNO–Al and the obtained power density (482.6 mW/cm²) of SOFCs were competitive while CNO–Ca presented an excellent stability with a better carbon tolerance performance for the long-term tests. The achievements of this work might offer a novel point of view for developing low-cost catalyst towards indirect hydrogen production for SOFC.     

Sr0.92Y0.08TiO3−δ/Sm0.2Ce0.8O2−δ anode for solid oxide fuel cells running on methane

Yttria-doped strontium titanium oxide (Sr_0.92Y_0.08TiO_3−δ; SYT) was investigated as an alternative anode material for solid oxide fuel cells (SOFCs). The SYT synthesized by the Pechini method exhibits excellent phase stability during the cell fabrication processes and SOFC operation and good electrical conductivity (about 0.85 S/cm, porosity 30%) in reducing atmosphere. The performance of SYT anode is characterized by slow electrochemical reactions except for the gas-phase diffusion reactions. The cell performance with the SYT anode running on methane fuel was improved about 5 times by SDC film coating, which increased the number of reaction sites and also accelerated electrochemical reaction kinetics of the anode. In addition, the SDC-coated SYT anode cell was stably operated for 900 h with methane. These results show that the SDC-coated SYT anode can be a promising anode material for high temperature SOFCs running directly on hydrocarbon fuels.     

Hydrogen‐rich gas production from catalytic gasification of pine sawdust over Fe‐Ce/olivine catalyst

In order to improve hydrogen production and reduce tar generation during the biomass gasification, a catalyst loaded Fe‐Ce using calcined olivine as the support (Fe‐Ce/olivine catalysts) was prepared through deposition‐precipitation method. The characteristics of catalysts were determined by XRF, BET, XRD, and FTIR. Syngas yield, hydrogen yield, and tar yield were used to evaluate the catalyst activity. Meanwhile, the stability of catalysts was also studied. The results showed that the specific surface area and pore volume of olivine after calcined at high temperature were improved which was beneficial for the load of metals. α‐Fe₂O₃ and CeO₂ were the main active component of Fe‐Ce/olivine catalyst. The Fe‐Ce/olivine catalyst displayed a good performance on the catalytic gasification of pine sawdust with a syngas yield of 0.93 Nm³/kg, H₂ yield of 21.37 mol/kg, and carbon conversion rate of 55.14% at a catalytic temperature and gasification temperature of 800°C. Meanwhile, the Fe‐Ce/olivine catalyst could maintain a good stability after 150 minutes used.     

Construction of high-performance NiCe-MOF derived structured catalyst for steam reforming of biomass tar model compound

High-performance and inexpensive catalysts play a large role in effective removal of biomass tar produced during biomass gasification. In this study, raw wood, with long, through, but distorted channels and a low tortuosity, was selected as a support. A layered NiCe-metal organic framework (NiCe-MOF) was grown in-situ on the surface of raw wood microchannels by using abundant surface hydroxide groups. Then, this catalyst was carbonized at 600 °C in a N₂ atmosphere to obtain NiCe-MOF derived catalyst/wood carbon (NiCe-MDC/WC), which was selected as a structured reactor for the steam reforming of biomass tar. NiCe-MDC/WC achieved an excellent conversion rate of approximately 99% for toluene and a high catalytic stability of 48 h at low temperature of 550 °C. Moreover, NiCe-MDC/WC showed higher catalytic performance than Ni-MDC/WC (～79%), crushed-NiCe-MDC/WC (～94%), and Ni/WC (～75%) in stability tests. These excellent results were assumed to be derived from the multilevel structure obtained from wood carbon microchannels and secondary layered MOF channels, appropriate metal-support interactions, and the presence of Ce, which could improve the dispersion of active sites and mass transfer efficiency and inhibit coke formation. Thus, such Ni-based MOF-derived structured reactors are promising for tar conversion and useful syngas production.     

Ammonia‐fed solid oxide fuel cells for power generation—A review

Ammonia has been identified as a promising sustainable fuel and hydrogen source for solid oxide fuel cells (SOFC). This paper aims to provide a literature review on ammonia‐fed SOFCs. Both experimental studies and mathematical modeling investigations on NH₃‐fed SOFC are included and discussed. It is found that NH₃ is a technically feasible fuel for direct use in SOFCs and the performance of NH₃‐fed SOFC is comparable with that of the H₂ fed SOFC. Experimental study in literature also demonstrates that both oxygen ion‐conducting electrolyte (SOFC‐O) and proton‐conducting electrolyte (SOFC‐H) can be used in NH₃‐fed SOFC, as the amount of NO_x generated in a SOFC‐O is negligible. Fabricating thin film electrolyte and developing more reactive electrode materials are important to improve the performance of NH₃‐fed SOFCs. Mathematical models are useful design tools for understanding the coupled transport and reaction phenomena and for optimizing the SOFC performance. Thermodynamic and pioneering 1D electrochemical models have been developed, validated and demonstrated to be reliable by the present author. Copyright © 2009 John Wiley & Sons, Ltd.     

Direct operation of cone-shaped LT-SOFCs with methane fuel for portable application

Anode-supported cone-shaped tubular solid oxide fuel cells (SOFCs) and segmented-in-series (SIS) SOFCs stack based on gadolinia-doped ceria (GDC) electrolyte film direct utilization methane as fuel are successfully developed in this study. The single cell exhibits maximum power densities of 484 mWcm⁻² and 414 mWcm⁻² at 600 °C by using moist hydrogen and moist methane as fuel, respectively. A durability test of the single NiO-GDC/GDC/LSCF-GDC cell is performed at a constant current density of 0.4 Acm⁻² direct fueled with methane for about 140 h at 600 °C. It stabilizes with no apparent degradation during the durability test. Very little carbon is detected on the anodes, suggesting that carbon deposition is limited during cell operation. The results show that the stability and dependability of as-prepared single cell is good and it is very significant for portable application of low-temperature SOFCs (LT-SOFCs). A three-cell-stack based on the above-mentioned SOFCs is fabricated and tested by direct utilization of methane. Its typical electrochemical performance is investigated. And the stack has experienced 5 times thermal cycling test. Good thermo-mechanical properties and stability are observed and that the developed segmented-in-series LT-SOFCs stack with GDC electrolyte film is highly promising for portable application.     

Development of co-sintering process for anode-supported solid oxide fuel cells with gadolinia-doped ceria/lanthanum silicate bi-layer electrolyte

Gadolinia-doped ceria (GDC) and lanthanum silicate (LS) are expected to be promising materials for electrolytes of solid oxide fuel cells (SOFCs) because of their high ionic conductivities at intermediate temperatures. However, performance degradation of SOFCs is caused by current leakage through GDC and poor densification of LS. In the present study, LS was used as a blocking layer for preventing the current leakage of GDC electrolyte. Thermal shrinkage measurements and scanning electron microscopy (SEM) observation suggested that the addition of Bi₂O₃ in LS electrolyte (LSB) contributed to the decrease in the sintering temperature of the LS and improved densification of the GDC/LS bi-layer electrolyte. Consequently, the open-circuit voltage for the cell with GDC/LS and GDC/LSB bi-layer electrolytes increased effectively in comparison with that of the cell with GDC single-layer electrolyte. The electrical conductivity and fuel cell characteristics were compared among the cells with GDC, GDC/LS, and GDC/LSB electrolytes.     

Recent progress on solid oxide fuel cell: Lowering temperature and utilizing non-hydrogen fuels

A solid oxide fuel cell (SOFC) is a promising energy conversion device with high efficiency and low pollutant emission. The practical application of the conventional SOFCs is limited mainly because of their high operating temperature and the inconvenience brought by the H₂ fuel utilization. This work reviews the recent progress on intermediate temperature SOFCs especially with non-hydrogen fuels. Composite electrolyte consisting of a solid oxide ionic conducting phase and a molten carbonate phase exhibits sufficient ionic conductivity in the intermediate temperature range, i.e. 500–800 °C, and facilitates the simultaneous conduction of H⁺, O²⁻ and CO₃²⁻ ions. A single cell with the composite electrolyte shows a promising power density, 1700 mW cm⁻² at 650 °C with hydrogen as the fuel. The composite electrolyte has been also employed in a direct carbon fuel cell (DCFC), and the simultaneous conduction of O²⁻ and CO₃²⁻ in the electrolyte has been proposed. Recently, perovskite structured materials are found to have good resistance to coke formation as the anode of the direct hydrocarbon solid oxide fuel cell, and several carbon resistant perovskite anodes are employed in all-perovskite structured SOFCs, which exhibit excellent performance with CH₄ and methanol as the fuel.     

Gliding arc plasma reforming of toluene for on-board hydrogen production

Hydrogen is considered as a clean and promising fuel, and hydrogen production on-board has attracted widespread research attention. In this work, a gliding arc discharge (GAD) plasma reactor was utilized to reform toluene at room temperature and atmosphere pressure. The performance of hydrogen production through oxidative reforming with toluene as raw material under different input power, oxygen to carbon molecular ratio (O/C), residence time and argon addition was investigated. The optimal yields of H₂ and CO (48.6% and 44.3%) were obtained under the condition of the input power of 32 W, the O/C of 0.68, the residence time of 18.4 s and 10 vol% Ar addition. By analyses of spectrum lines and GC-MS, the plasma reforming mechanism of toluene was proposed. It is believed that N₂(B³Πg) and Ar* could increase the formation of reactive oxygen species (O⁺, O (¹D), O and so on), and N₂(B³Πg) could impact directly the reforming of toluene.     

Development of activated biochar supported Ni catalyst for enhancing toluene steam reforming

Catalytic steam reforming of tar is considered to be an attractive pathway for tar removal and H₂ production in the modern world. In this study, activation of biochar (B) from pine wood pyrolysis was performed to boost its specific surface area and pore structure. The activated biochar (AB) was used as a catalyst support with the aim to enhance the catalytic activity. The catalytic reforming performance of toluene over Ni/AB catalyst was investigated, and the catalytic behavior of Ni/AB catalysts was compared with Ni/Al₂O₃ and Ni/B. The effect of potassium hydroxide (KOH) to biochar ratio, Ni loading, reforming temperature, weight hourly space velocity and steam to carbon ratio(S/C) on the performance of Ni/AB catalysts were studied. The results showed that Ni/AB catalysts exhibited a superior catalytic activity for carbon conversion and H₂ production to Ni/B and Ni/Al₂O₃ catalysts. In addition, high carbon conversion (86.2%) and H₂ production (64.3%) can be achieved with Ni/AB catalyst under the optimal operating conditions. Furthermore, in order to improve the stability of the Ni/AB catalyst, Ce was introduced to Ni/AB catalyst. According to stability tests, the H₂ concentration of Ni-Ce/AB catalysts was still higher than 2.24 mmol/min even after 20 hours reaction.     

Use of a catalyst layer for anode-supported SOFCs running on ethanol fuel

Solid oxide fuel cells (SOFCs) operating directly on hydrocarbon fuels have attracted much attention in recent years. A two-layer structure anode running on ethanol was fabricated by tape casting and screen printing technology in this paper, the addition of a Cu–CeO₂ catalyst layer to the supported anode surface yielded much better performance in ethanol fuel. The effect that the synthesis conditions of the catalyst layer have on the performances of the composite anodes was investigated. Single cells with this anode were also fabricated, of which the maximum power density reached 566 mW cm⁻² at 800 °C operating on ethanol steam. Long-term performance of the anodes was presented by discharging as long as 80 h without carbon deposition.     

Operation of solid oxide fuel cells on glycerol fuel: A thermodynamic analysis using the Gibbs free energy minimization approach

Solid oxide fuel cells (SOFCs) are very flexible, unlike other fuel cells. In principle, SOFCs can operate on almost any fuel. Currently much effort is invested in the development of SOFCs for portable applications operating directly on liquid fuels such as methanol and ethanol rather than hydrogen. However, there are very few publications dealing with the direct use of glycerol in SOFCs for portable systems. A recently published study shows that the performance achieved for an SOFC fueled by pure glycerol is quite interesting even when there is a thick electrolyte membrane, indicating that glycerol is a promising fuel for portable applications. For this reason a thermodynamic analysis for SOFCs operating directly on glycerol fuel is performed in the present study. The Gibbs energy minimization method computes the equilibrium compositions of the anode gas mixture, carbon deposition boundaries and electromotive forces (EMFs) as a function of fuel utilization and temperature. Moreover, the minimum amounts of H₂O, CO₂ (direct internal reforming case) and air (partial oxidation case) to be added to glycerol in the feedstock to avoid carbon deposition at the open circuit voltage (OCV) are calculated. Finally, a thermodynamic analysis is performed, taking into account the experimental conditions employed in a previous study. Experimental observations concerning carbon deposition in an SOFC operating on glycerol can be explained by the theoretical analysis developed in the present study. Additionally, the effect of mixed electronic-ionic conduction of the electrolyte on carbon deposition at the anode is discussed based on the thermodynamic analysis of the C-O system.     

Exploring the role of promoters (Au,Cu and Re) in the performance of Ni–Al layered double hydroxides for water-gas shift reaction

Water-gas shift (WGS) reaction is well-known industrial process targeting hydrogen production. Designing well-performing and economically profitable WGS catalysts is the key toward production of pure hydrogen for application in fuel cell processing systems. Promotional role of Au, Cu, or Re in the WGS performance of Ni–Al formulations derived from hydrotalcite precursor was analysed on the basis of deep characterization by BET, XRD, UV–Vis, XPS, and TPR measurements of as-prepared and WGS-tested samples. Additionally, modification by ceria was examined. WGS results revealed that catalyst behaviour was strongly dependent on promoter type. The best performance exhibited gold-promoted Ni–Al layer double hydroxide modified with ceria. This system showed a superior catalytic activity as 99.7% CO conversion at 220 °C that correlated well with significantly enhanced reducibility of support. Although Au-containing CeO₂-modified Ni–Al catalyst outperformed WGS activity of Cu- and Re-promoted analogues, stability of Re-containing sample and enhanced activity of Cu-based sample after tests at different reaction conditions manifested promising results. They leave open space for future investigations addressing improved catalyst performance by tuning Re⁴⁺/Re⁷⁺ redox structures or optimizing catalyst composition.