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.

Internal dry reforming (IDR) of methane for biogas-fed solid oxide fuel cell (SOFC) applications has been experimentally investigated on planar Ni-GDC (cermet anode) electrolyte-supported cells. This study focuses on the effect of CO₂ concentration, current density, operating temperature, and residence time on internal methane dry reforming. A single cell is fed with different CH₄/CO₂ mixture ratios between 0.6 and 1.5. Extra CO₂ recovered from carbon capture plants can be utilized here as a reforming agent. The I-V characterization curves are recorded at different operating conditions in order to determine the best electrochemical performance while the power production is maximized, and carbon deposition is suppressed. The outlet gas from the anode is analyzed by a micro gas chromatograph to investigate methane conversion inside the anode fuel channel and to understand its influence on the cell performance. Relatively long-term experiments have been performed for all gas mixtures at 850°C under a current density of 2000 A m⁻². The results indicate that when the cell is fed with biogas with an equimolar amount of CH₄ and CO₂, carbon deposition is prevented, and maximum power density is obtained.

The influence of operation temperature, inlet gas composition, current density and the anode thickness on the methane steam reforming reaction over nickel yttria-stabilized zirconia anodes was experimentally studied in solid oxide fuel cells. The experimental results were analyzed using data fitting in Power-Law and Langmuir–Hinshelwood kinetic models. Similar trends of dependence of methane and steam partial pressures were observed in both models. The methane reaction order is positive. Negative influence of steam partial pressure on the methane steam reforming reaction rate are found. The electrochemical reaction and anode thickness affect the reforming kinetics parameters. The anodes thickness shows particular influences on the steam reaction order, and the activation energy when a current is produced. The model evaluation suggests that the two models are comparable and the extra parameters within the Langmuir–Hinshelwood kinetic model are contributing to the lower mean absolute percentage error and higher coefficient of determination R².

This study investigates the feasibility of electricity production in a solid oxide fuel cell using methane recovered from groundwater as the fuel. Methane must be removed from groundwater for the production of drinking water to, amongst others, avoid bacterial regrowth. Instead of releasing methane to the atmosphere or converting it to carbon dioxide by flaring, methane can also be recovered by vacuum stripping and served as a fuel. However, the electrical efficiency of currently used combustion-based technologies fuelled with methane-rich gas is limited to 35% due to the low heating value of the recovered gas (70 mol. % methane) and power derating due to the presence of carbon dioxide (25 mol.%). We propose to use a solid oxide fuel cell to use the methane-rich gas as fuel. Solid Oxide Fuel Cells are fuel-flexible and potentially attain higher electrical efficiencies up to 60%. To this end, specific gas processing, including cleaning and methane reforming, is required to allow for durable operation in a solid oxide fuel cell. We assessed whether electricity could be generated by a solid oxide fuel cell using methane recovered from a full-scale drinking water treatment plant as a fuel. The groundwater had a methane concentration of 45 mg∙L^-1, and the recovered gas by vacuum towers contained 70 mol% methane. We used a gas cleaning reactor with impregnated activated carbon to remove hydrogen sulfide traces from the methane-rich gas. Thermodynamic calculations showed that additional steam is required to achieve a high methane reforming. The added steam and the carbon dioxide content in the recovered gas simultaneously contribute to the methane reforming to prevent carbon deposition. The measured open circuit potential corresponded with the theoretical Nernst voltage, implying high methane reforming in the solid oxide fuel cell. The achieved power density of the cell fuelled with the methane-rich gas (mixed with steam) was 27% less than the hydrogen-fuelled cell. Ultimately, 51.2% of the power demand of the plant can be covered by replacing the gas engine in a drinking water treatment with a 915 kW solid oxide fuel cell system fuelled by the methane recovered from the groundwater, while the greenhouse gas emission can be reduced by 17.6%.

Internal dry reforming of methane is envisaged as a possibility to reduce on capital and operation costs of biogas fuelled solid oxide fuel cells (SOFCs) system by using the CO₂ present in the biogas. Due to envisaged internal dry reforming, the requirement for biogas upgrading becomes obsolete, thereby simplifying the system complexity and increasing its technology readiness level. However, impurities prevailing in biogas such as H₂S have been reported in literature as one of the parameters which affect the internal reforming process in SOFCs. This research has been carried out to investigate the effects of H₂S on internal dry reforming of methane on nickel-scandia-stabilised zirconia (Ni-ScSZ) electrolyte supported SOFCs. Results showed that at 800°C and a CH₄:CO₂ ratio of 2:3, H₂S at concentrations as low as 0.125 ppm affects both the catalytic and electric performance of a SOFC. At 0.125 ppm H₂S concentration, the CH₄ reforming process is affected and it is reduced from over 95% to below 10% in 10 h. Therefore, future biogas SOFC cost reduction seems to become a trade-off between biogas upgrading for CO₂ removal and biogas cleaning of impurities to facilitate efficient internal dry reforming.

Energy and exergy performance of ammonia fuelled solid oxide fuel cell (SOFC) integrated system in wastewater treatment plants (WWTPs) is evaluated in this study. Ammonia can be recovered through a struvite precipitation process in the form of an ammonia-water mixture (with 14 mol.% ammonia) and used as a carbon-free fuel. A series of experiments has been conducted for SOFC single cell to evaluate the performance with different ammonia-water mixture ratios. An ammonia-SOFC system was modeled in Cycle Tempo for detailed thermodynamic analysis. The heat from the electrochemical reaction in the SOFC and catalytic combustion in an afterburner is used in the struvite decomposition process. However, the generated heat is not sufficient to meet the heat demand of the struvite decomposition reactor. To improve the sustainability of the system in terms of heat demand, the system can be integrated into a heat pump assisted distillation tower, meanwhile, the ammonia concentration of the fuel stream increases. Increasing the ammonia concentration to 90 mol.% increases the energy and exergy efficiencies of the SOFC system. The net energy efficiency of the integrated system with a heat pump assisted distillation tower is 39%, based on the LHV of the ammonia-water mixture.

Anaerobic Digestion (AD) is used worldwide for treating organic waste and wastewater. Biogas produced can be converted using conventional energy conversion devices to provide energy efficient, integrated waste solutions. Typically, the electrical conversion-efficiency of these devices is 30–40% and is lowered due to biogas utilization instead of high pure refined natural gas. The Solid Oxide Fuel Cell (SOFC) as an alternative device offers high (50–60%) electrical efficiency with low emissions (CO2, NOx) and high temperature residual heat. The high quality residual heat from SOFCs could be used to improve biogas production through thermal pre-treatment of the substrate for anaerobic digestion. This work discusses the advantages and challenges of integrated AD-SOFC systems against the most recent scientific and practical developments in the AD and SOFC domain. First, the biogas production process and its influence on the composition and level of contaminants in biogas are explained. Subsequently, the potential of various biogas cleaning techniques is discussed in order to remove contaminants that threaten stable and long-term SOFC operation. Since SOFCs utilize H2 and/or CO as fuel, possibilities for internal and external reforming are explained in detail. Special attention is given to biogas dry reforming in which CO2 naturally present in the biogas is utilized effectively in the reforming process. A detailed discussion on the choice of SOFC materials is presented, with a focus on biogas internal reforming. Various integrated SOFC system models with multiple configurations are also reviewed indicating the overall efficiencies. Some biogas SOFC pilot-plants are described and discussed to conclude with the techno-economic aspects of biogas SOFC systems.