Siloxane, a common contaminant present in biogas, is known for adverse effects on cogeneration prime movers. In this study, the siloxane deposition products and mechanism in the solid oxide fuel cell nickel-yttria stabilized zirconia (Ni-YSZ) anode are investigated analytically and experimentally. An SOFC with Ni-YSZ anode and pure Ni/YSZ pellets were exposed to a simulated biogas-reformate fuel with octamethylcyclotetrasiloxane (D4) contamination at 750 °C. The electrochemical characterization results show that the SOFCs performance degradation caused by D4 contamination is irreversible. Morphology and XRD results illustrate that silicon and carbon deposition can both be detected in the anode and pellets. Graphite, SiC and SiO ₂ are all possible products based on the results of XRD test. According to the formation of graphite and SiC, the new mechanism suggests that carbon is also an essential factor in siloxane contamination of Ni-YSZ anodes besides silicon, which can be explained by the catalytic and electrochemical analysis.

Siloxanes, as a type of impurity in biogas, can poison the Ni-YSZ anode of SOFCs. However, the influence of individual components of the anode, such as Ni, ZrO ₂ , and Y ₂ O ₃ , on the siloxane deposition process has not been investigated extensively. In this study, Ni, ZrO ₂ , and Y ₂ O ₃ pellets were exposed to H ₂ + N ₂ + H ₂ O + D4 (octamethylcyclotetrasiloxane, 2.5 ppm _v ) and H ₂ + N ₂ + D4 (2.5 ppm _v siloxane) gas mixtures at 750 °C to investigate their affinity and tolerance for siloxane degradation. Surface morphology analysis and electrochemical analysis including electrochemical impedance spectroscopy (EIS), related distribution of relaxation times (DRT) analysis and equivalent circuit modeling with complex nonlinear least square (CNLS) fitting were conducted. A microstructure parameter—tortuosity factor to porosity ratio τ / ε calculated by diffusion polarization resistance was utilized for siloxane deposition evaluation. After comparing pellets surface morphology changes before and after experiments and τ / ε change following the contamination, Ni is considered as a major factor in siloxane deposition reactions in Ni-YSZ anode.

Renewable natural gas derived from biogas presents a viable pathway for decarbonizing natural gas systems. Wastewater treatment plants equipped with anaerobic digesters often flare or utilize biogas for heat and electricity generation, missing the potential of renewable natural gas. This study investigates the techno-economic feasibility and emission impact of a renewable natural gas system at a small wastewater treatment plant in the Southwestern United States. Due to a lack of existing data on biogas composition and contaminants from plants originating within the United States, samples were tested seasonally for a year, and gas components are reported in this analysis. Using hourly biogas production data, the analysis incorporates costs and renewable fuel credits at 2022 market prices and the cost to remove the biogas contaminants. The results show a 15-year net present value of USD 16.3 million, with a payback period of three years, surpassing the economic performance of combined heat and power systems previously assessed for the same facility. Additionally, renewable natural gas systems achieve a 22% reduction in site emissions compared to combined heat and power systems. These findings highlight renewable natural gas as a profitable and environmentally superior alternative for biogas utilization in small-scale wastewater treatment plants, contingent on access to renewable fuel credits.

The geometry of the electrode/electrolyte interface is critical to solid oxide fuel cell (SOFC) performance. Adding 3D microstructures on electrode/electrolyte interface may enhance the performance of SOFCs potentially. In this study, the pillar shape yttria-stabilized zirconia (YSZ) 3D microstructures with ~ 60 m to 90 m diameter were fabricated by 3D inkjet printing on the interface of electrolyte and cathode to increase the TPB area and enhance the connection between the dense YSZ electrolyte and mixed YSZ ionic conductor. Scanning Electron Microscopy (SEM) is utilized to assess the morphology and microstructure of the YSZ interface. To investigate the influence of the modified interface on the performance of the SOFC, electrochemical performance testing and characterization are conducted for the SOFCs with/without the modified YSZ layer. SOFCs performance is investigated with a different number of printed interfacial layers fabricated with the 3D inkjet printer.

In this study, the degradation of the solid-oxide fuel cell (SOFC) nickel-yttria stabilized zirconia anode under decamethyltetra-siloxane (L4) contamination is examined. A model is developed for the polarization losses based on the charge transfer coefficient, α, and diffusion layer thickness, į, and fitted to the experimental data to understand how the siloxane degrades the SOFC performance with time. Ohmic losses are dominant in the anode due to much higher anode thickness (380 µm) compared to electrolyte thickness (13 µm). Activation losses vary with α, which decreases from 0.31 to 0.25. Mass transport losses vary with both į and α, with įincreasing from 28 µm to 45 µm. The results of the model indicate that the total polarization losses increase for each subsequent time interval, with a total increase of approximately 45% from 0 to 180 min. Activation losses dominate the polarization losses initially but decrease in their total contribution while mass transport losses increase.

Ethylene epoxidation is an important reaction to form ethylene oxide (EO), which is a precursor to many other critical chemicals. This study links short-term EO production to the effects on the microstructure of Ag/yttria-stabilized zirconia cells with and without an electrochemically promoted catalyst (EPOC). Nano scale features called striations were observed using a Scanning Electron Microscope (SEM) on the silver under all reaction conditions tested. While appearing in both cases, the striations for the EPOC case are finer in size (~150 to 250 nm) compared to the no current case (~400 to 500 nm). These features did not appear when epoxidation conditions were not present. Striation formation was further linked to the epoxidation reaction through electrochemical impedance spectroscopy (EIS) and gas chromatography (GC). Ethylene conversion to EO declines over the course of hours as striations form, indicating that striations have a negative influence on the reaction. Striation formation further effected the electrochemical performance of the cells, resulting in the low frequency depressions observed in EIS to shrink in both cases after 10 hours of epoxidation.