Direct Internal Reforming Research Articles

Modeling and analysis of direct internal reforming in ethanol- fueled SOFC

Modeling and analysis of direct internal reforming in ethanol- fueled SOFC

A simple dip-coating-co-firing fabricated anode supported tubular solid oxide fuel cells for bio-ethanol carbon dioxide internal dry reforming and power generation

Direct internal dry reforming of hydrocarbon is a promising way for the growth of solid oxide fuel cells (SOFCs) due to the convenient storage and transportation of hydrocarbon fuels. Herein, NiO-YSZ (Y2O3-stabilized ZrO2) anode supported tubular SOFCs (T-SOFCs) are successfully fabricated by a simple dip-coating-co-firing method with NiFe2O4–Gd0.1Ce0.9O2-δ(NFO-GDC) internal reforming layer, and the electrochemical and carbon resistance are characterized under three different bio-ethanol carbon dioxide components (40 %, 50 %, 60 % ethanol partial pressure). The maximum power density of the T-SOFC in H2 atmosphere is 434.08 mW cm−2. With CO2–C2H5OH mixture as the fuel, the maximum power density is obtained at 50 % C2H5OH -CO2 atmosphere. This difference in performance is attributed to the varying levels of carbon dioxide affecting the dry reforming of ethanol. Distribution of relaxation times (DRT) analysis of T-SOFCs are carried out to explore the contribution of different electrode reactions. Long-term stability studies, gas chromatography measurements of exhaust gases and Raman scanning results are collected under three ethanol partial pressures to obtain the stability of single cell, catalytic reactions and carbon tolerance of fuel electrode. All experiments are designed to investigate the optimal performance of bio-ethanol carbon dioxide fueled single cells in terms of electrochemical performance and stability.

Progress in Solid Oxide Fuel Cells with Hydrocarbon Fuels

Solid oxide fuel cells (SOFCs)’ main advantage in fuel flexibility appears to be an interesting subject for further exploration. From the literature survey, direct utilisation of hydrocarbon as fuel for SOFCs has garnered attention with promising results reported. Various approaches, showcasing potential for using methane (CH4) and heavier hydrocarbons in SOFCs, have been described. The direct use of hydrocarbons can occur through either direct internal reforming or gradual internal reforming, with requisite precautionary measures to mitigate carbon formation. While the internal reforming process could proceed via steam reforming, dry reforming or partial oxidation, an exciting development in the direct use of pure hydrocarbons, seems to progress well. Further exploration aims to refine strategies, enhance efficiency and ensure the long-term stability and performance of hydrocarbon-fuelled SOFC systems. This review delves into the progress in this field, primarily over the past two decades, offering comprehensive insights. Regardless of fuel type, studies have largely concentrated on catalyst compositions, modifications and reaction conditions to achieve better conversion and selectivity. Finding suitable anode materials exhibiting excellent performance and robustness under demanding operating conditions, remains a hurdle. Alternatively, ongoing efforts are directed towards lowering working temperatures, enabling consideration of a wider range of materials with improved electrochemical performance.

Design of High Specific Power Solid Oxide Fuel Cells

The development of solid oxide fuel cells (SOFCs) has progressed from the early Electrolyte Supported Cell (ESC) to state-of-the-art Anode Supported Cell (ASC), which allows the implementation of thinner electrolyte layer (less than 10 micron) and reduction in the operating temperature (below 800°C). The various components of SOFC are constantly being optimized by many research groups to further improve the overall stack performance, including specific power, power density, thermal shock resistance, rapid start-up, and thermal cycling exposure.Precision Combustion, Inc. (PCI) has been working on an advanced electrochemical-based energy storage and power generator design for meeting aggressive specific-power and specific-energy targets required for mobile and transportation applications, such as all-electric propulsion of ground and air vehicles. The key drivers are an exceptionally power-dense solid oxide fuel cell design operating with energy-dense liquid fuels and a hybridized system architecture that maximizes component efficiencies for ultra-high system efficiency. This effort builds on PCI’s experience in developing groundbreaking SOFC generators for mobile and space applications.PCI has developed and demonstrated a novel design of fuel cells with high specific power, that also allows for direct internal reforming of methane and hydrocarbon fuels within a SOFC stack. The system consists of interconnected internal reforming Microlith® metal mesh catalysts strategically embedded within the solid oxide stack. The fuel cell configuration was optimized to reduce CTE mismatch and to improve area specific resistance. The resulting enhanced heat transfer design of the combined components offers the potential for higher overall system efficiency and system simplification as well as enables further compactness and weight reduction of the fuel cell while improving the conditions for long system life. The approach also offers the potential to operate with a wide range of input fuels (i.e., high hydrocarbons as well as various levels of CO2 and water in the fuel inlet) without forming carbon. Carbon formation within the stack system has been known to be detrimental to the performance and durability. Our approach allows for the operation of a modular, advanced SOFC stack for generating power directly from hydrocarbon fuels. Computational design, process simulation, and qualification testing were performed to validate the concept.In this presentation, the results from a breadboard SOFC stack system operation will be highlighted, including the power density, efficiency, and durability. An improvement in the performance as a result of the design advancement, which could improve the stack lifetime, will also be described. The carbon avoidance in the stack while operating with hydrocarbon fuels and with a low water requirement was confirmed. Sensitivity study of the concept to temperature, flow rate, and anode fuel composition was performed and will be highlighted. Finally, preliminary results from the fuel cell design optimization activities will be summarized.

Experimental identification of the impact of direct internal and external methane reforming on SOFC by detailed online monitoring and supporting measurements

Solid Oxide Fuel Cells (SOFCs) are able to use biogas or natural gas with its main compound methane as fuel but utilization of methane bears risks which can lead to early performance loss. Application of a suitable type of methane reforming as well as online monitoring tools and a holistic knowledge about possible degradation mechanisms can limit degradation rates. Here, we compare direct internal reforming and external methane reforming on a large planar SOFC with an active area of 80cm2 at different operating temperatures and methane flow rates. To do so, the measured temperature distribution, applied electrochemical impedance spectroscopy and its advanced tool distribution of relaxation times (DRT) as well as results from post mortem microscopic analysis are used. We observed that the ohmic resistance and high frequency peaks in the DRT spectra seem to be influenced not only by the average cell temperature but also by direct internal reforming (DIR) conditions. Furthermore, we observed that high temperature gradients induced by DIR could lead to or accelerate damages of the cells structure and the sealing. The results presented in this work are useful to control or manage safe SOFC operation with C containing fuels for real world SOFC applications.

Efficient conversion of ethanol to electricity using large-scale flat-tube solid oxide fuel cells

Conversion of renewable energy sources like bioethanol to electricity using solid oxide fuel cells (SOFCs) is promising to reduce the consumption of fossil fuels and to mitigate global warming. However, direct ethanol-fed SOFCs are susceptible to carbon deposition on Ni-based anode. In this study, the power generation from and degradation mechanism of large-scale flat-tube SOFCs by direct internal reforming of ethanol are investigated. The steam/carbon (S/C) ratio causes minor influence on the cell performance but considerably affects the long-term durability. Elevating temperature improves ethanol conversion rate and cell performance. Ethanol is efficiently reformed by the thick anode support and long anode channels, with low selectivity for CH4 and C2H4. Stable power generation with current density of 200 mA/cm2 is obtained over 300 h under S/C = 2 and 3 at 800 °C. Due to the high operating temperature and complex cell structure, the in-situ measurements of the temperature and gas compositions within the cell, related to carbon deposition, are difficult. The distributions of the gas compositions and temperature within the cell before and after the durability test are clarified by simulation. Simulation results reveal that, in addition to CH4 and C2H4, the cold zone near inlet contributes to carbon formation.

A stable chromite anode for SOFC with Ce/Ni exsolution for simultaneous electricity generation and CH4 reforming

Solid oxide fuel cells (SOFCs) operating at a high temperature can be used to generate electricity and produce syngas from hydrocarbon fuels. In this work, the in-situ decoration of CeO2 and Ni nanoparticles on the surface of chromite anode has been explored; i.e., the exsolution of CeO2 from La0.75Ce0.05Ca0.2Cr0.9Ni0.1O3 (Ce-LCN) can be achieved in the oxygenation in air to boost the exsolution of Ni0 under the fuel condition. The SOFC with a Ce-LCN anode showed higher performance and better stability under propane and H2 fuel than the one La0.8Ca0.2Cr0.9Ni0.1O3 (LCN) anode because of the formation of CeO2 and Ni0 nanoparticles. Setting in the distribution of H2 in the existing natural gas pipeline, hydrogen-injection in CH4 (20% H2 in volume in CH4) was found for the first time to efficiently improve the coking resistance of the anode because the H2 was able to boost the transfer of oxygen from the anode to the direct internal reforming. The conversion of CH4 was found to be around 85% and the selectivity for CO was close to unity. This study provides a viable solution to the design of complex perovskite SOFC to produce electricity and syngas simultaneously from CH4.

Simultaneous characterizations of segmented electrochemical characteristics and temperature distribution in the hythane-fueled direct internal reforming solid oxide fuel cell

The solid oxide fuel cell with direct internal reforming is promising for cost-effective utilization of hythane produced by blending hydrogen in natural gas. Deep understanding of the inhomogeneous distributions of physiochemical processes is essential to assist in optimization of hythane-fueled fuel cell. In this work, the effects of H2 blending ratio and steam-to-carbon ratio on local electrochemical performance and temperature of a segmented cell are comprehensively examined. Local electrochemical processes are clarified by various electrochemical impedance spectroscopy investigation approaches including analysis of differences in impedance spectra, distribution of relaxation times, and equivalent circuit model fitting. H2 blending reduces the concentration overpotential significantly while also homogenizing the reforming distribution and promoting the anodic electrochemical process in all segments. H2 blending ratio above 20 % greatly reduces the cold spots induced by endothermic reforming but results in hot spots in the gas outlet when the voltage is below 0.7 V because of high electrochemical reaction heat. Regardless of the H2 blending or steam-to-carbon ratio, a nearly thermal neutral state is observed at current density of 300 mA cm−2. These findings demonstrate the potential of boosting performance and simultaneously maintaining homogeneous temperature in the direct internal reforming solid oxide fuel cells.

Artificial neural network assisted multi-objective optimization of a methane-fed DIR-SOFC system with waste heat recovery

The main purpose of this study is to enhance the performance of solid oxide fuel cell systems. For this purpose, a mathematical model of a direct internal reforming (DIR) methane-fed solid oxide fuel cell system with waste heat recovery was designed in the engineering equation solver program. We optimised the performance of the solid oxide fuel cell using a genetic algorithm and TOPSIS technique considering exergy, power, and environmental analyzes. An ANN working with the Levenberg-Marquardt training function was designed in the MATLprogram to create the decision matrix to which the TOPSIS method will be applied. According to the power optimization, 786 kW net power was obtained from the system. In exergetic optimization, the exergy efficiency was found to be 57.6%. In environmental optimization, the environmental impact was determined as 330.6 kgCO2/MWh. According to the multi-objective optimization results, the exergy efficiency, the net power of the solid oxide fuel cell system, and the environmental impact were 504.1 kW, 40.08%, and 475.4 kgCO2/MWh.

Performance study of solid oxide fuel cell with Ni-foam indirect internal reformer: Intrinsic reforming kinetics and temperature uniformity

For solid oxide fuel cells, non-uniform temperature distribution has a large effect on the cell’s efficiency over the long-term operation. A methane steam reformer with 10 %Ni/10 %MgO/Ni foam as a catalyst was designed, and the intrinsic kinetic model of the catalyst is developed based on the Langmuir-Hinshelwood theory. An indirect internal reforming (IIR)-SOFC stack is constructed by combing the reformer and the single SOFC stack to improve the uniform temperature distribution and reduce the cell temperature gradient under various operating conditions. The electrical performance and temperature distribution of the IIR-SOFC stack and direct internal reforming (DIR)-SOFC stack are comparatively studied by experiments and numerical simulations. The results show that the two SOFC stacks have almost identical polarization curves under different temperatures, fuel–air flow rates, or steam/methane (S/C). It indicates that the IIR-SOFC stack just changes the position of methane reforming, and the amount of hydrogen and carbon monoxide produced by methane reforming is almost the same. As compared to the DIR-SOFC stack, the IIR-SOFC stack observably lowers the cell temperature uniform index, and the cell global and local temperature gradient, making the cell temperature distribution more uniform. The maximum temperature difference and the maximum temperature gradient on the IIR-SOFC anode are 35.1 % and 307 % less than on the DIR-SOFC anode under the operating condition of 800 °C, S/C = 2.5 and 0.6 V. Overall, the Ni-foam-based IIR-SOFC stack can homogenize the cell temperature distribution, and reduce the cell carbon deposition and mechanical failure.

Power generation from flat-tube solid oxide fuel cells by direct internal dry reforming of methanol: A route for simultaneous utilization of CO2 and biofuels

Dry reforming of liquid alcohols coupled with solid oxide fuel cells (SOFCs) is a promising approach for clean and efficient energy conversion. Herein, the feasibility of power generation from flat-tube SOFCs with direct internal dry reforming of methanol has been studied. The effects of CO2/MeOH ratio, temperature, and current density on cell performance and long-term durability were investigated. Higher CO2/MeOH ratios reduced the power density, but suppressed carbon deposition and enhanced long-term durability. A cell was operated stably over 500 h with a constant current density of 200 mA/cm2 under CO2/MeOH = 1 and 2 at 750 °C. In addition to stable power generation, simultaneous syngas production and reduction in CO2 emissions were achieved. Density functional theory (DFT) calculations elucidated the possible pathways for methanol dry reforming and mechanism of carbon removal. Our experimental and simulation results provide insights into the direct utilization of methanol in SOFCs using dry reforming.

Direct utilization of gaseous fuels in metal supported solid oxide fuel cells

Direct utilization and internal reforming of gaseous fuels is investigated on symmetric-architecture metal supported solid oxide fuel cells (MS-SOFCs) with thin ceramic electrolyte and scaffold backbone layers, and low cost ferritic stainless steel supports on both sides. Infiltrated Pr-oxide and Ni/samarium-doped ceria catalysts are added to the cathode and anode electrodes, respectively. Initial performance and durability is evaluated for MS-SOFCs operating with natural gas, propane, ammonia, and dimethyl ether at 700 °C. Cells for natural gas and propane utilize a novel high entropy alloy (HEA) catalyst for internal reforming with performance and degradation rates similar to H2 (0.5 W cm−2 and ∼12%/100 h). Initial testing with sulfur shows reversible degradation for levels found in natural gas and irreversible degradation for higher levels found in commercial propane. Overall, MS-SOFCs show successful fuel flexibility.

High-entropy alloy anode for direct internal steam reforming of methane in SOFC

High-entropy alloy (HEA) anode and reforming catalyst, supported on gadolinium-doped ceria (GDC), have been synthesized and evaluated for the steam reforming of methane under SOFC operating conditions using a conventional fixed-bed catalytic reactor. As-synthesized HEA catalysts were subjected to various characterization techniques including N2 adsorption/desorption analysis, SEM, XRD, TPR, TPO and TPD. The catalytic performance was evaluated in a quartz tube reactor over a temperature range of 700–800 °C, pressure of 1 atm, gas hourly space velocity (GHSV) of 45,000 h−1 and steam-to-carbon (S/C) ratio of 2. The conversion and H2 yield were calculated and compared. HEA/GDC exhibited a lower conversion rate than those of Ni/YSZ and Ni/GDC at 700 °C, but showed superior stability without any sign of carbon deposition unlike Ni base catalyst. HEA/GDC was further evaluated as an anode in a SOFC test, which showed high electrochemical stability with a comparable current density obtained on Ni electrode. The SOFC reported low and stable electrode polarization. Post-test analysis of the cell showed the absence of carbon at and within the electrode. It is suggested that HEA/GDC exhibits inherent robustness, good carbon tolerance and stable catalytic activity,` which makes it a potential anode candidate for direct utilization of hydrocarbon fuels in SOFC applications.

Solid oxide fuel cells (SOFCs) fed with biogas containing hydrogen chloride traces: Impact on direct internal reforming and electrochemical performance

This study is particularly aimed at investigating the influence of hydrogen chloride traces in biogas on direct internal reforming in solid oxide fuel cells (SOFCs). The experiments are performed with simulated biogas containing methane to carbon dioxide ratio of 3:2, the usual average proportion in biogas. To the best of our knowledge, there are no reported studies that investigated the effect of hydrogen chloride on direct internal reforming by clearly establishing the effect of reforming with outlet gas composition measurements. The experiments at SOFC operating temperature of 850 °C reveals no negative effect on reforming or cell performance, with 4, 8, and 12 ppm(v) of hydrogen chloride in biogas. At 800 °C, there is no visible performance degradation, but a negligible amount of methane (∼ 1%) is detected in the anode off gas. Both the reforming and electrochemical performance are marginally affected at 750 °C. Further, post-test analyses (FESEM-EDS, XRD) of the used SOFC reveals no damage to the cell at microstructure level or chlorine poisoning. All the experiments are performed in the context of utilizing the biogas generated from sewage treatment plants in an SOFC system. The reported level of chlorine traces in biogas generated from sewage sludge is < 10 ppm(v) and hence the limit set for experiments is at par with this value.

Multi-physics modeling of a symmetric flat-tube solid oxide fuel cell with internal methane steam reforming

Methane is regarded as one of the ideal fuels for solid oxide fuel cells (SOFCs) due to its huge reserves and transportation properties. In this study, a 3D numerical model coupling with chemical reaction, electrochemical reaction, mass transfer, charge transfer, and heat transfer is developed to understand the heat and mass transfer processes of methane steam direct internal reforming based on double-sided cathodes (DSC) SOFC. After the model verification, the parametric simulations are performed to study the effects of operating voltage, inlet temperature, and steam to carbon (S/C) ratio on the performance of a DSC. It is found that the non-uniform distribution of flow rate among channels results in the non-uniform distribution of each physical field. Increasing the inlet temperature significantly enhances the performance of DSC, however, when the temperature is above 1073 K, the concentration loss and the temperature gradient of DSC increase, which is not conducive to the long-term operation of the DSC. In addition, we revealed the effect of the S/C ratios on the heat and mass transfer process. This study provides an insight into the heat and mass transfer process of SOFC with a mixture of steam and methane and operating conditions for enhancing the performance.

Ni-Ce-ZrO2 system as anode material for direct internal reforming biogas solid oxide fuel cells

This paper is focused on the synthesis of ceria-doped Ni-ZrO2 nanocrystals (Ni-CZ) via a novel synthetic strategy based on wet impregnation and its application as anode material for solid oxide fuel cell (SOFC) directly fuelled by biogas. The electrochemical behaviour of Ni-CZ was evaluated by means of IV curves and impedance spectroscopy in H2 and simulated biogas at 750–850 °C using yttria stabilized zirconia (YSZ) electrolyte-supported cell. The cell achieved higher power density in H2 and at higher temperature. The distribution of relaxation time (DRT) analysis of impedance data was carried to determine the contribution of electrodes processes. Detailed of electrochemical analysis revealed that the cell performance limiting factor corresponds to the electrodes processes at low frequencies which are related to gas diffusion in H2 and dry reforming process and water-gas shit reaction coupled to gas diffusion in biogas. The cell showed a stable performance or even better activation in biogas under aggressive operation condition (400 mV) that could favour its degradation at 750 °C and 800 °C for 20 h and at 850 °C for 200 h. Furthermore post-tests analysis detected negligible carbon deposition on the anode surface. Although Ni-CZ could be postulated as SOFC anode material for direct biogas due to its good stability, an improvement its electrochemical perform is required.

DIR-FCEV powered by different fuels – Part I: Well-to-wheel analysis for the Brazilian and Spanish contexts

This article describes the life cycle assessment of the Direct Internal Reforming Fuel Cell Electric Vehicle (DIR-FCEV) for the Brazilian and Spanish contexts. This recently proposed vehicle technology produces hydrogen onboard via heat recovery, while the Solid Oxide Fuel Cell (SOFC) and the gas turbine provide electricity to the electric motor with high overall efficiency. The exhaust gas emission was obtained via GASEQ software and the well-to-tank data were collected through literature search. These values were entered in the GREET Model software version v1.3.0.13656 to assess the negative environmental impacts of the DIR-FCEV in terms of global warming potential (GWP) and human toxicity potential (HTP). Using 1 km distance driven by a light-duty vehicle as the functional unit, the tank-to-wheel results indicate that regardless of the fuel, the DIR-FCEV achieved better than the internal combustion engine vehicle fuelled with gasoline A in both categories. Also, the DIR-FCEV powered by biomethane, gasoline A, gasoline C (73% gasoline A and 27% ethanol, in volume basis), glycerine, and ethanol attended all future tailpipe emissions standards stipulated by United States and European Union. Biomethane and gasoline-fuelled DIR-FCEV had more commendatory environmental performance in both countries. Thus, it is expected to obtain environmental indicators to stimulate the use of biofuels synergistically with the advancement of electromobility in Brazil and Spain.

Coupling deep learning and multi-objective genetic algorithms to achieve high performance and durability of direct internal reforming solid oxide fuel cell

Direct internal reforming (DIR) operation of solid oxide fuel cell (SOFC) reduces system complexity, improves system efficiency but increases the risk of carbon deposition which can reduce the system performance and durability. In this study, a novel framework that combines a multi-physics model, deep learning, and multi-objective optimization algorithms is proposed for improving SOFC performance and minimizing carbon deposition. The sensitive operating parameters are identified by performing a global sensitivity analysis. The results of parameter analysis highlight the effects of overall temperature distribution and methane flux on carbon deposition. It is also found that the reduction of carbon deposition is accompanied by a decrease in cell performance. Besides, it is found that the coupling effects of electrochemical and chemical reactions cause a higher temperature gradient. Based on the parametric simulations, multi-objective optimization is conducted by applying a deep learning-based surrogate model as the fitness function. The optimization results are presented by the Pareto fronts under different temperature gradient constraints. The Pareto optimal solution set of operating points allows a significant reduction in carbon deposition while maintaining a high power density and a safe maximum temperature gradient, increasing cell durability. This novel approach is demonstrated to be powerful for the optimization of SOFC and other energy conversion devices.

A review on mathematical modelling of Direct Internal Reforming- Solid Oxide Fuel Cells

The Solid Oxide Fuel Cells (SOFCs) anode materials are catalytically active for Direct Internal Reforming (DIR) thus avoiding the need of external reformer. However, practical application of DIR in SOFCs requires careful system design and selection of operating conditions to avoid cell degradation due to carbon depositions and other impurities. In recent years, numerous simulation studies, besides experimental investigations, have been carried out to understand the physical and electrochemical complexities of DIR-based SOFC systems in order to develop viable designs and optimize the operating conditions before conducting costly experiments. The objective of this work is to review the present status of DIR-SOFC modeling efforts and consolidate their findings in order to highlight the unresolved problems for future research in this field. A specific focus of this review has been given to the multiscale mathematical modeling. Pre-reforming techniques, influences of the chemical and electrochemical reaction kinetics and operational variables along with future prospects of the DIR-SOFC have been also reviewed and discussed.

Power generation from a symmetric flat-tube solid oxide fuel cell using direct internal dry-reforming of methane

Direct conversion of methane to electricity in solid oxide fuel cells is challenging, especially for large-scale cells/stacks, due to coking on Ni-based anodes, which may cause an inhomogeneous temperature and/or stress distribution. In this work, we investigated for the first time direct internal dry reforming of CH 4 for power generation using a flat-tube SOFC (FT-SOFC) with symmetric double-sided cathodes with an active area of 70 cm 2 , and studied the effects of CO 2 :CH 4 ratio, temperature, and current density on the performance and durability of the cell. Our results indicate that the thick anode support and inner channels of the FT-SOFC function as an efficient micro-reactor for reforming of methane, resulting in high conversion rates of methane, and thus a durable cell operation for 500 h in CO 2 /CH 4 = 2 with a constant current density of 0.2 A cm −2 at 750 °C. Ni/YSZ catalysts granules placed in the internal fuel channels can further alleviate coking and improve the durability of cells. The unique cell configuration of FT-SOFC makes possible the direct utilization of methane for power generation. • Direct operation of flat-tube SOFC (FT-SOFC) with double-sided cathodes with methane. • Thick anode support and inner channels of FT-SOFC form an efficient microreactor. • The cell structure improved the methane conversion. • The degradation mechanism for varied CO 2 /CH 4 ratios were clarified. • Stable operation for 500 h was reached under a flow of CO 2 /CH 4 = 2 at 750 °C.