Effect of Ni diffusion into BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte during high temperature co-sintering in anode-supported solid oxide fuel cells

Diffusion behavior of Ni during high temperature co-sintering was quantitatively investigated for anode-supported solid oxide fuel cells (SOFCs) that had BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3?δ (BZCYYb) proton-conducting electrolyte and NiO-BZCYYb anode. Although diffused Ni in such SOFCs effectively acts as a sintering aid to densify the BZCYYb electrolyte layer, it often negatively affects the electrolyte conductivity. In the present study, field emission electron probe microanalysis (with wavelength dispersive X-ray spectroscopy) clearly revealed that Ni diffused into the BZCYYb electrolyte layer, and that the amount of diffused Ni increased with increasing co-sintering temperature. In particular, relatively high Ni concentration within the electrolyte layer was observed near the electrolyte/anode interface, e.g., approximately 1.5 and 2.8 wt% at co-sintering temperature of 1300 and 1400 °C, respectively. Electrochemical measurements showed that, compared with the lower co-sintering temperatures (1300–1350 °C), the highest co-sintering temperature (1400 °C) led to the highest ohmic resistance because of lower electrolyte conductivity. These results suggest that high co-sintering temperature causes excessive Ni diffusion into the BZCYYb electrolyte layer, thus degrading the intrinsic electrolyte conductivity and consequently degrading the SOFC performance.     

Hybrid additive manufacturing of the modified electrolyte-electrode surface of planar solid oxide fuel cells

Digital Control of the surface patterning of functional layers of solid oxide fuel cells (SOFCs), via the inkjet printing technique, offers better efficiency in performance. A combination of inkjet printing and tape casting in a single machine system defines as hybrid additive manufacturing, facilitates printing complex structures. Also, implementing this idea removes the blocking of the print head nozzle orifice issue. In this paper, a highly dispersed and long-term stable colloidal zirconia-based suspension, with optimal printability characteristics, is designed to be prepared in approximately three hours to fabricate the macro patterned structure of the SOFC electrolyte. Hybrid Additive Manufacturing is successfully employed to make a symmetric cathode side cell with a modified electrolyte-electrode surface to reduce the electron resistivity.     

A review study on software-based modeling of hydrogen-fueled solid oxide fuel cells

Among various types of energy conversion systems, hydrogen-fueled solid oxide fuel cells (SOFCs) have been acknowledged as one of the most promising technologies, thanks to the high energy density and numerous environmental and technical benefits they offer. The current study aims to provide a comprehensive review on numerical software-based modeling of these systems. The work is motivated by the increasing demand in utilization of software packages for investigating the multi-physiochemical phenomena occurring within the cell. The available software packages are introduced with the different applications being outlined. Novelty of each work as well as the corresponding drawbacks are represented through a critical approach. In the end, innovative designs and models, existing gaps in the literature, careful considerations for developing the numerical models, and recommendations for achieving further improvements in the field are provided.     

Effect of hetero-structured nano-particulate coating on the oxygen surface exchange properties of La0.6Sr0.4Co0.2Fe0.8O3-δ

In this study, dense La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) electrodes decorated with the novel hetero-structured ceramic oxide mixture in four different ratios of Ce_0.8Gd_0.2O_2-δ (GDC) and La₂Mo₂O₉ (LMO). The time-dependent conductivity transients were acquire using electrical conductivity relaxation (ECR) technique at a chosen conditions of temperature in the range of 650–850 °C and instantaneous pO₂ step change between 0.2 and 0.8. Fitting of time-dependent conductivity to the appropriate non-equilibrium solutions of Fick's diffusion equation has yielded the chemical diffusion coefficient, D_chem, and oxygen surface exchange coefficient, k_chem. As expected, the D_chem of the coated samples remained invariant, whilst the k_chem is found to vary with the change in GDC-LMO coating mixture ratio. Substantial increase of a factor of 10 in the surface exchange coefficient is noticed for the LSCF coated with a 1:0.75 mixing ratio as compared to bare sample at 850 °C. The enhancement in k_chem is attributed to the optimal triple-phase boundary (TPB) regions which promotes oxygen surface exchange kinetics. Thus, coating of selective ratio of hetero-structured oxide in a form of nano-particulate layer over the LSCF surface is considered to be a promising candidate for solid oxide fuel cell (SOFC) cathode.     

Fuel cells hybrid systems for resilient microgrids

Nowadays, resilient grids meet growing interest for their capability of let survive critical load even in case of power fault coming from grid disturbance and disasters.In particular, telecommunications infrastructures (point-to-point and cell infrastructure) have distributed systems (RBS, DCs) equipped with storage devices used to guarantee continuous operation of the supplied equipment. Since high value services are provided to a wide set of customers, unexpected service unavailability is source of economic losses.This embedded UPS function, despite avoiding service interruption and contract penalties to the service providers, requires batteries whose unused capacity could be fruitfully exploited to provide the grid with valuable and paid energy services (frequency regulation - power and/or energy regulation in time slots - peak smoothing).For this reason, the supply systems of such plants, beside the internal energy storage devices, had better to have redundancy of energy sources (e.g. electrical grid and natural gas network) and tailored power flows control strategies to optimize the equipment utilization and costs, even in the case of external energy shortage.In this work, a combined approach with Fuel Cell (FC) and Fuzzy Logic (FL) is investigated to determine a good compromise between equipment installation, control logic, and availability of the service (downtime probability), even accounting for weather forecast, energy price and storage system exploitation (depth of discharge).For the implemented case studies of the simulation, a landline station located in Italy is analyzed by simulating different functions and power equipment to assess the benefits achievable the presented approach.     

Gadolinia-doped ceria mixed with alkali carbonates for SOFC applications: II – An electrochemical insight

Composite materials based on gadolinia-doped ceria (GDC) and alkali carbonates (Li₂CO₃-K₂CO₃ or Li₂CO₃-Na₂CO₃) are potential electrolytes for low temperature solid oxide fuel cell applications (LTSOFC). This paper completes a first one dedicated to the thermal, structural and morphological study of such compounds; it is fully focussed on their electrical/electrochemical properties in different conditions, temperature, composition and gaseous atmosphere (oxidative or reductive). The influence of the gaseous composition on the Arrhenius conductivity plots is evidenced, in particular under hydrogen atmosphere. Finally, electrical conductivity determined by impedance spectroscopy is presented as a function of time to highlight the stability of such composites over 6000 h. First results on single cells showed performance at 600 °C of 60 mW cm⁻².     

Effect of hydrogen sulfide inclusion in syngas feed on the electrocatalytic activity of LST-YDC composite anodes for high temperature SOFC applications

The performance of La_0.4Sr_0.6TiO_3±δ-Y_0.2Ce_0.8O_2−δ (LST-YDC) composite anodes in solid oxide fuel cells significantly improved when 0.5% H₂S was present in syngas (40% H₂, 60% CO) or hydrogen. However, electrochemical impedance spectroscopy measurements at OCV showed that polarization resistance of the cell increased when the concentration of H₂S exceeded 0.5%. Gas chromatographic and mass spectrometric analyses revealed that the rate of electrochemical oxidation of all fuel components improved when H₂S was present in the fuel. Electrochemical stability tests performed under potentiostatic conditions showed that there was no power degradation caused by the presence of H₂S in different feeds, and that there was power enhancement when 0.5% H₂S was present.     

Systematic analysis of biomass derived fuels for fuel cells

As the demand for energy continuously increases, alternatives to fossil resources must be found to both prevent fossil source depletion and decrease overall environmental impact. One solution is increasing contributions from renewable, biological feedstock, and from wastes. This paper presents an analysis of the current methods of biomass conversion, to extract biofuels and biologically produced gases to then be used in fuel cells. Pathways for converting biomass feedstock into fuel cell fuels selected here were anaerobic digestion, metabolic processing, fermentation, gasification, and supercritical water gasification, which were compared to natural gas and fossil hydrogen reference cases. These thermochemical and biological conversion pathways can also make use of residues from agriculture, forestry, or some household and industry wastes, producing hydrogen and hydrogen-rich gases. Solid oxide fuel cells were also found to be the preferred technology for such bio-derived fuel gases, due to their wide range of fuel options, wide scalability from single kW to multi 100 kW, and high efficiency.     

Safe heating-up of a full scale SOFC system using 3D multiphysics modelling optimisation

Heating-up strategies of full scale solid oxide fuel cell (SOFC) systems still affect the safe operation of the system and incorporation of the technology into the global energy sector. To ensure rapid start-up times whilst retaining the structural reliability of the SOFC system components, requires a safe heating-up operation. To master a controlled heating-up stage, detailed understanding of the component interaction and multiphysics within a fuel cell system is required. State of the art dynamic fuel cell system modelling comprises sub-models of the assembly, or is based on empirical nature. However, invaluable information of the multiphysics inside the system is lost. Therefore, it is of paramount importance to understand and improve the knowledge of the detailed processes, occurring within the interacting components. The effect of integrating different electrical heater cartridges at different locations has been thoroughly investigated to optimise the heating-up of the system. The study utilises a previously developed and experimentally validated full scale three dimensional planar type SOFC system model to mitigate experimental costs and shed light on the details, occurring within the system. A comparison to a simplified variant of the model has been added to shed light on its effect on the results.     

Personal power using metal-supported solid oxide fuel cells operated in a camping stove flame

A complete stand-alone product prototype providing combined cooking and power is fabricated by retrofitting a commercial camping stove with a stack of metal-supported solid oxide fuel cells (MS-SOFCs) delivering power to microelectronic LED driver and voltage boost circuits. The 5-cell stack produces 2.7 W (156 mW cm^?2) while cooking on the stove, and is demonstrated to produce LED lighting and mobile phone charging while operating outdoors. Cooking efficiency is minimally impacted by the presence of the MS-SOFCs. It is found that vertical orientation of the cells is critical to maintain separation of fuel and air when a pot is placed on the stove.