Fuel Cell Mode Research Articles

Clean Conversion of Aqueous Ammonia Using a Solid Oxide Cell

Ammonia (NH3) is present as an impurity in coke oven gas (COG), which is a by-product of coke-making processes required for the manufacture of steel. Due to its highly corrosive and toxic nature, ammonia is removed from COG by water scrubbing processes generating a highly problematic aqueous waste stream containing ammonia (19 vol%), hydrogen sulphide (4 vol%), carbon dioxide (14 vol%) and tars. At Tata Steel Port Talbot (South Wales, UK) alone, approximately 44,000 m3 of COG and 264 kg of ammonia are produced every hour. This is currently disposed of via incineration, contributing to air pollutant emissions and wasting a valuable and useful resource.It is well known that solid oxide fuel cells (SOFCs) can convert ammonia gas to electrical power and heat when operating in fuel cell mode [1-3]. In this work, conversion of a liquid aqueous ammonium hydroxide solution (35%) using a commercially available anode-supported button cell was investigated in fuel cell and electrolysis mode. This mixture served as a basic initial simulation of the waste ammonia streams produced from coke-making processes. The electrical performance of the cell was characterised using I-V curves and electrochemical impedance spectroscopy, and the output gases of the cell were measured in real-time using quadrupole mass spectrometry (QMS).The QMS data show the ammonia decomposed to nitrogen and hydrogen at the open circuit voltage (OCV). In fuel cell mode, the cell utilised hydrogen to produce electrical power. I-V curves were measured showing the effect of the ammonium hydroxide solution on cell efficiency compared with deionised water (see figure). Increasing the deionised water flow rate decreased the OCV considerably and substantially increased the concentration losses; under a 20/80 vol% H2/H2O mixture, the cell produced 50-80% of the current yielded under pure H2. With the ammonium hydroxide solution, OCV and concentration losses were affected much less as the flow rate of the mixture was increased, indicating conversion of ammonia into electrical power with high efficiency. The I-V curves and electrochemical impedance spectra indicated very low activation losses.In electrolysis mode, the presence of ammonium hydroxide decreased performance and this was attributed to the decreased presence of H2O, which the I-V curves (see figure b) and impedance spectra show increased the activation and concentration losses. However, the QMS data have demonstrated that electrolysis of H2/NH4OH mixtures increases the H2 production by a factor of approx. 2.3 and yields a gas mixture composed of approx. 87 vol% H2 balanced in N2, with no NO x production observed.

Development of a 10/40kW-Class Reversible Solid Oxide Cell System at Forschungszentrum Jülich

The Forschungszentrum Jülich GmbH has successfully developed a 5/15 kW-class reversible Solid Oxide Cell (rSOC) system in recent years, promising a high system efficiency in fuel cell and electrolysis mode [1]. The core element of the system is the well-known Integrated Module developed, which has been adapted from fuel cell to the rSOC operation. This Module consisted of four 10-layer sub stacks, in which each layer had an active cell area of 320 cm². It also contained fuel and air heat exchangers, arranged on top and underneath the stacks, to bring the incoming gases to the operating temperature. In addition, three electrically operated heating plates were implemented to heat up the system at the beginning of the operation and to adjust the stack temperature during the endothermic electrolysis operation. Other components necessary for the system operation such as the evaporator, blowers, condenser and control system are attached near the Integrated Module in a compact and suitable manner. This system was extensively examined after its completion. A maximum power of 5.3 kWDC at a current density of 0.5 A cm-2 and a fuel utilization of 97.3% could be achieved in fuel cell mode. Under these conditions, an electrical efficiency of 62.7% (LHV, DC) was reached. Furthermore, a maximum electrical input power of - 14.3 kWDC could be achieved in electrolysis mode with a current density of -0.89 A cm-2 at a steam conversion rate of 85%. An electrical efficiency of 70% (LHV, DC) was measured for this operating point. In the further course of the tests, the switching between the operating modes was investigated and optimized. The change from fuel cell to electrolysis mode took approximately 13 minutes limited by steam generation and the opposite direction took less than 3 minutes [2]. In the fuel cell mode, a maximum system fuel utilization of more than 99% was achieved through the use of an off-gas recirculation. Such a high utilization could be realized because the steam content has been removed from the recirculated gas stream by condensation before feeding back to the stack inlet. Furthermore, the system behavior during load variation was examined. With this system design, a minimum part load of 0.1 A cm-2 in the fuel cell and - 0.05 A cm-2 in the electrolysis mode could be demonstrated [3]. Based on these experiences, a new rSOC system with a power of 10 kW in fuel cell and 40 kW electrolysis mode will be constructed. For this purpose, the stacks used and the supporting components have to be adapted. In addition, the efficiency in the electrolysis mode will be increased by using a more effective steam generation process. The new developed system as well as its test results will be presented at the conference for the first time.[1] M. Frank, R. Deja, R. Peters, L. Blum, D. Stolten, Applied Energy, 217 (2018) 101-112.[2] R. Peters, M. Frank, W. Tiedemann, I. Hoven, R. Deja, V.N. Nguyen, L. Blum, D. Stolten, ECS Transactions, 91 (2019) 2495-2506.[3] R. Peters, M. Frank, W. Tiedemann, I. Hoven, R. Deja, N. Kruse, Q. Fang, L. Blum, R. Peters, Journal of the Electrochemical Society, (2021).

Development Progress at Hexis SOC Activities

HEXIS is developing and manufacturing SOFC-based micro-CHP systems for houses and / or small companies. While being a subsidiary of the Viessmann Group (until 06/2020) the company has been mostly focusing on the new generations of highly efficient (>95 % LHV) fuel cell modules – these modules are running in small quantities at customer sites - meanwhile, Hexis belongs to the h2e group and has expanded its technical activities.This paper will present the long-term experiences on long-term and cyclic testing of fuel cell modules in lab tests as well as results on robustness and performance in the field. It was observed that degradation rates as low as approx. 0.3 % / kh, i.e. 13 mΩ cm² / kh on the short-stack level for over 50,000 h can be reached. These stacks have been analyzed with electrochemical impedance spectroscopy (EIS) at regular intervals, which can provide valuable insights in understanding fundamental degradation mechanisms for long term operation of SOFC stacks.Moreover, the paper will include highlights of new developments since the new era for Hexis as an important part in the h2e group has started. These new developments are improvements on cell and stack level as well as new applications for the Hexis technology in general. Finally, the paper will outline some of the future challenges in Hexis’ development activities.

Stack Optimization and Testing for its Integration in a rSOC-Based Renewable Energy Storage System

This work aims at developing an innovative solution for storing renewable energies, so-called “Smart Energy Hub” (SEH) developed by Sylfen, based on reversible Solid Oxide Cell (rSOC) technology. It is able to operate either in electrolysis (SOEC) mode storing excess electricity to produce hydrogen, or when energy needs exceed local production, in SOFC (solid oxide fuel cell) mode producing electricity (and heat) from hydrogen or any other hydrogenated fuel. Particularly this paper focuses on stack development and optimization, partly performed through the REFLEX project supported by European commission funding.To achieve the project’s objectives, in terms of efficiency and increase of system power density, as well as multi-stack operation, optimizing CEA stack is necessary to upgrade a stack originally designed for SOEC research purposes, to a stack reversibly operated, but also integrated as a part of module. This paper presents results of stack optimisations and integration of cells developed within the REFLEX project.First, a reduction in cell thickness of ~20 % led to adapting the stack manufacturing process parameters. Some tests, here presented, demonstrate that the stack performances were not affected by this change.Then, significant effort was devoted to air distribution at the Single Repeat Unit (SRU) scale to minimize pressure drop, undesirable for both global system efficiency and mechanical resistance of stack sealing. At the SRU scale, air path adjustment reduced the pressure drop by a factor 2; at stack scale, the performances obtained in i-V curves demonstrated reactants distributions were unchanged.Optimized cells (so called G2) developed in the frame of REFLEX project were then integrated in a short stack (5 cells vs. 25 full size) to be compared to short stack comprising regular cells produced by Elcogen. Both stacks were tested in terms of durability over more than 1000 hours at 700°C. A first period of about 800 h of operation was conducted alternating from SOFC to SOEC mode by steps of ≈100 h. During this first part, the stack was supplied by 50/50 H2O/H2 at total flow rate of 12.0 NmL/min/cm² on fuel side and air (clean and dry) on oxygen side. Stack performances were checked at each change of operating mode through i-V curves recorded at 800, 750 and 700°C.For the reference cell, durability tests were operated galvanostatic at 0.36 A/cm² in fuel cell mode and -0.51 A/cm² in electrolysis mode. The fuel utilization (FU) was respectively 42% in SOFC, and Steam Conversion (SC) 59% in SOEC. For the optimized cell, tests were carried out at 0.35 A/cm² (FU=41%), and -0.58 A/cm² (SC=67%). A second stage of more than 250h of operation consisted to alternate daily from SOEC to SOFC by cycles of respectively 8h and 16h. Finally, degradation was evaluated and despite the increase in SOEC current density during G2 cell testing, degradation rate was very similar for both cells in SOEC as well as in SOFC mode.A full size (25-cells) stack made of G2 cells was manufactured integrating the fluidic optimizations but also manifold and an electrical insulation necessary to operate stacks serially connected electrically within the REFLEX modules produced by Sylfen. The change of scale was validated by obtaining similar i-V curves recorded for 5-cells and 25-cells stacks.REFLEX Smart Energy Hub will be operated in ENVIPARK Torino using three modules comprising of four stacks each. Stack production has to be as uniform as possible and consequently, manufacturing process has to be optimized. Dispersion in performance, that results of cell production and stack manufacturing process is checked at final stage by i-V curves recording before delivery. Uniformity in production (in terms of tightness, reactant distribution and so initial electrochemical performance) is found to be satisfactory, the dispersion of median cell stack voltage over the stack production is less than the voltage dispersion observed between the whole cells at stack level.For near future needs in rSOC system, an increase of stack power density is required to both reduce the CAPEX and increase system energy efficiency. In that frame cells produced by Elcogen has an active cell area that was extended from 100 to 196 cm² and tested at stack levels of 5 and 25 cells, respectively. Enlarged stack performances are measured via i-V curves and compared to reference 100 cm² cells stacks. As difference in median cell voltage is less than 10 mV up to a current density of -1.25 V/cm² (80% SC), this paper shows that, from a mechanical and fluidic point of view, the enlarged cell were successfully integrated in full-scale stack. Figure 1

Leveling Transient and Spatial Gradients in Planar Solid Oxide Cells Using Spatially Varied Microstructures: A Numerical Study

Sharp spatial and transient gradients of overpotential, current density, gas species and temperature within planar solid oxide cells (SOCs) can lead to increased degradation rates, decreased active area utilization and high thermal stresses. Such issues will lead to decreased cell efficiency and functional lifetime while increasing the risk of sudden cell failure due to cracking or delamination. Spatial gradients occur in part due to the interconnect geometry. Commonly, the electrochemical reaction rate within SOC electrodes is disproportionately higher near the inlet regions of the fuel or steam channels and decreases towards the outlets as the concentrations of fuel or steam decreases for fuel cell and electrolysis modes, respectively. Transient gradients occur on short time scales due to rapid fluctuations in loading during ramp up or ramp down and for reversible operation when the current direction is reversed. It might be possible to greatly reduce both transient and spatial gradients by controlling the reaction rate distribution within SOC electrodes through the strategic manipulation of the electrode active layer microstructures. Advances in additive manufacturing techniques now facilitate the design of engineered electrodes with precisely controlled microstructure properties such as pore size, porosity and volume ratios of active layer materials (i.e. Ni or YSZ). The purpose of the present study is to explore the impact and possible benefits of applying functionally graded or regionally altered microstructural properties in the active layer of planar SOCs using a previously developed transient 3D multiphysics performance model of commercial sized planar SOCs. Percolation theory is used to estimate properties such as triple phase boundary (TPB) density and tortuosities from the applied variations of particle sizes, volume fractions and pore former properties as shown in Figure 1(a). It is shown that indeed both spatial and transient gradients can be significantly decreased by engineering gradients in composition and microstructure. For example, under the extreme conditions of ramping up from 0 to 0.75 A/cm2 current density and 75% H2 utilization in fuel cell mode, the multiphysics performance model predicts a nearly 300K temperature increase in approximately 100s for the baseline case as shown in Figure 1(d). Applying linear gradients of porosity and Ni/YSZ ratios such that TPB density increases from the fuel inlet to outlet significantly decreases this temperature gradient by 25-100K. However, there may be a tradeoff in terms of overall performance with decreasing steady state cell voltage corresponding with decreased temperature gradients. This is partly associated with the decreased temperature itself as the reaction kinetics are assumed to increase with increasing temperature resulting in decreased overpotential at the TPBs. Additional impacts of these and other functionally graded microstructures include decreased current density gradients and more uniform oxygen reduction in the oxygen electrode compared to the baseline case. Results indicate that functionally graded electrode microstructures could be designed based on the desired operating conditions to reduce degradation and thermal stresses within cell and stack assemblies. Such electrode designs have the potential to significantly reduce cell failure rate and increase cell lifetime particularly in transient loading and/or high current density applications. Figure 1

Load Cycling Tests of Reversible Solid Oxide Cells – Effects of Current Density, Steam Content, and Utilization

This work aims at developing an innovative renewable energy storage solution, based on reversible Solid Oxide Cell (rSOC) technology. That is to say, one system optimized to operate either in electrolysis mode (SOEC) for steam electrolysis to store excess electricity and to produce H2, or in fuel cell mode (SOFC) when energy needs exceed local production, to produce electricity and heat again from H2. In this work rSOC tests were conducted at single cell, in order respectively to finely understand performance and degradation mechanisms and to perform tests in representative conditions; and single cell rSOC test are finally compared to stack test results.Single cell rSOC tests were conducted to investigate the effect of current density, inlet steam content and degree of steam utilization both upon galvanostatic SOFC and SOEC testing, and upon load cycling operation. Cells having high initial electrochemical performance from Elcogen were used for these studies (1). Via four different long-term tests, we have investigated degradation at 700°C during constant galvanostatic SOFC (250 h) and SOEC (250 h) conditions followed by load cycling operation (up to 1000 h) in cycles of 16 h SOFC and 8 h SOEC. The applied current densities were either severe (0.6 A/cm2 in SOFC and -1.2 A/cm2 in SOEC) or moderate (0.4 A/cm2 and -0.6 A/cm2); applying different inlet gas composition ie. p(H2O)/p(H2) of 90/10 in SOEC and dry H2 in SOFC, or applying p(H2O)/p(H2) of 50/50 for both modes. Furthermore, two different steam and H2 utilization degrees of 80% and 40% were used. Figure 1 depicts examples of recorded cell voltage curves over time for two examples of the long-term rSOC testing where the inlet gas compositions were varied between p(H2O)/p(H2) of 50/50 for one test and p(H2O)/p(H2) of 90/10 and dry H2 for the other test.The electrochemical durability was assessed recording voltage over time and via electrochemical impedance spectroscopy (EIS). The characterization of the cells was supplemented by post-mortem scanning electron microscopy studies.Key findings include: 1) The cells degraded to a significantly larger degree in SOEC mode than in SOFC mode during the initial galvanostatic testing sequences. 2) At the given conditions and applying a current density of -1.2 A/cm2, the cells operate at a cell voltage above thermoneutral potential during the constant SOEC operation while this is not the case for the low-current density tests applying an electrolysis current of -0.6 A/cm2. 3) Load cycling does not increase the rate of degradation; rather the cell voltage stabilized for parts of the load cycling test sequences. 4) The major contribution to the resistance increase during long-term operation can be attributed to the fuel electrode and for the test, having the highest fuel electrode resistance increase (high current density test) a ~60% increase of the ohmic resistance was also observed during SOEC testing. 5) For the harshest tested (high current density) cells, Ni migration have been observed in parts of the fuel electrodes. 6) Nano-scaled detachment between Ni and YSZ particles were observed in several locations in several cells together with non-percolating Ni particles ie. where Ni-Ni connection has been lost; and a general trend was that the higher the fuel electrode overpotential during testing, the more pronounced was the effect of Ni-network changes upon microscopy post-mortem analysis in line with previous studies (2). 7) Inclusions of silica-containing impurities were found in the Ni/YSZ fuel electrodes as also observed in previous work (3, 4).Based on the single cell tests the recommendation for stack and system operation will, at 700 °C be, to operate in the current density regime of 0.4 A/cm2 and -0.6 A/cm2 rather than 0.6 A/cm2 and -1.2 A/cm2 to ensure long-term durability. Single cell test results were supplemented and trends confirmed by long-term rSOC test on 5-cell stacks at similar conditions. Figure 1: Cell voltage curves over time for two long-term rSOC test at 700°C. Inlet gas compositions of p(H2O)/p(H2):50/50 (blue curve) for one test and p(H2O)/p(H2):90/10 and dry H2 for the other test (red curve). Current densities of 0.4 A/cm2 and -0.6 A/cm2, respectively and a H2O (SOEC) and H2 (SOFC), utilization of 40%. References A. Ploner, A. Hauch, S. Pylypko, S. D. Iorio, G. Cubizolles, J. Mougin, in ECS Transactions (2019), vol. 91, pp. 2517–2526.A. Hauch, K. Brodersen, M. Chen, M. B. Mogensen, Solid State Ionics. 293, 27–36 (2016).A. Hauch, S. H. Jensen, J. B. Bilde-Sørensen, M. Mogensen, J. Electrochem. Soc. 154 (2007), doi:10.1149/1.2733861.M. Riedel, M. P. Heddrich, K. A. Friedrich, Fuel Cells. 20, 592–607 (2020). Figure 1

Modeling of Reversible Solid Oxide Cell Stacks with an Open-Source Library

Fuel cells are potential contenders of the traditional internal combustion engines, with relative high efficiency and low/no emission of pollution and greenhouse gases. Electrolyzers convert electricity into chemical energy, e.g. hydrogen, and in case of high-temperature electrolyzers in syngas, e.g. hydrogen and carbon-monoxide, etc. A reversible solid oxide cell (rSOC) is able to operate in both modes. This represents a promising electrochemical device for future applications. Comprehensive experimental investigations on rSOCs are typically expensive and time-consuming. These may be conveniently augmented by numerical models to improve and optimize and enable the provision of more rapid prototypes. These models usually consider some or all of the underlying physical processes, e.g. heat and mass transfer (including thermal radiation), structural analysis, etc. They range from zero-dimensional (0-D) and 1-D models in system-level models1, 2 to coupled 3-D models in cell/stack-level applications.3–5 Stack/system level models are attracting more and more attention due to their practical applications to commercial/industrial designs. In this work, a steady-state, 3-D, non-isothermal, and homogenized stack model has been developed from an extension of previous studies4–6 and implemented into the open-source library, OpenFOAM.7 It addresses all major physical processes, including fluid flow, heat and mass transfer (including thermal radiation), and electrochemical reactions. The model strategy applies a multi-region approach to consider every unit-cell as different sub-regions, namely, cathode, anode, electrolyte, and interconnect. Inter region heat and mass transfer is prescribed during the calculations. The micro-structures within the subregions are treated using volume-averaging method, in which case, the flow distribution can be easily described by replacing the viscous losses with a drag or friction term in the governing momentum equation(s). This greatly decreases the computational effort,6 and predicts quite similar results to those from experimental measurements.5 In the present work a surface-to-surface (S2S) model, also referred to as a viewFactor model, is utilized to simulate the external thermal radiations. Internal radiation is neglected due to its relative unimportance.Figure 1: Comparisons of temperature variations between experimental measurements and simulations, i = 0.5 A cm−2 . The present model is applied to investigate the performance of an in-house designed rSOC stack, the key component of a 5/15kW-class rSOC system.8 A 1-D simulation is also performed with a previous developed Simulink model.1 The stack consists of four 10-layer sub-stacks with an active cell area per layer of 320 cm2. It operates in both fuel cell and electrolysis modes, in a temperature range of 600 – 800 ◦C. To reduce heat losses to adjacent components and ambient environment, it is surrounded by insulating plates. More details can be found in the recent publication.8 As shown by Figure 1, temperature variations are compared between experimental measurements and numerical predictions, at a mean current density of 0.5 A cm-2 . In fuel cell mode, the cell voltages are 0.818 V, 0.821 V, and 0.824 V, for the experiment, Simulink, and stack model, respectively. In the electrolysis mode, the values are 1.240 V, 1.234 V, and 1.260 V, respectively. These results indicate fairly good agreement between the predictions and experiments. It can be found that the stack model predicts smaller temperature deviations than is seen in the experiments and the Simulink predictions. However, the former consumes approximately 1 hour for every run, while the later costs only several minutes. In future work, thermal stresses, which play important roles in design optimization, will be considered. Considering the 3-D nature of the stress distribution, the coupling between present model and a structural analysis program/solver would be a promising topic.

B-Site Sc Doping of La0.6Ca0.4Fe0.8Ni0.2O3- d as an Electrode for Solid Oxide Cells

Reversible solid oxide electrochemical cell (RSOC) is a competitive option which has attracted increasing focus on alleviating some environmental problems and energy crisis with the capability of reversibly operating in solid oxide fuel cell (SOFC) mode and solid oxide electrolysis cell (SOEC) mode [1].Solid oxide cells (SOCs) have received increasingly attention due to their high efficiency and broad applications. However, electrodes with rapid hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR), oxygen evolution reaction (OER) and sufficient durability play a key role in solid oxide cells. A multifunctional perovskite oxide La0.6Ca0.4Fe0.8Ni0.2O3-δ (LCFN) has been investigated as an electrode for SSOCs in our previous work. The results confirm that LCFN shows excellent ORR, OER, CO2-RR and HOR catalytic activity [2-3]. However, the investigation of LCFN for SOCs has been hindered due to the lack of stability. Herein, a novel perovskite La0.6Ca0.4Fe0.7Sc0.1Ni0.2O3-δ (LCFSN) is investigated as an electrode of SOCs. Its structural stability has been improved under H2 atmosphere. The polarization resistance (Rp) of the electrode LCFSN is only 0.147 Ω cm2 at 800 °C under air. The single cell Ni-YSZ/YSZ/GDC/LCFSN displays a peak power density of 1.36 W/cm2 in fuel cell mode and a low Rp value of 0.131 Ω cm2. Most importantly, the cell exhibits admirable durability of 130 h without apparent degradation. All these results suggest that LCFSN is a promising candidate electrode for SOCs.

Post-Operational Characterization of a Long-Term Operated Solid Oxide Fuel Cell Stack

A two layer solid oxide cell stack based on anode-supported cells was operated galvanostatically at 0.5 A / cm² and 700°C for nearly 100,000 h in fuel cell mode. The overall degradation rate during the operation was approx. 0.5 %1000 h but the stack shows different degradation rates over different time periods. In contrast to our typical stack material choice this stack was mainly assembled with another type of metal: ITM from Plansee SE, Austria instead of Crofer22APU. Crofer 22 APU was merely used for a 200 µm thick foils inserted in the manifold areas at the gas in- and outlet of the cells. After controlled shut-down, the stack was post-test analyzed. After leakage test by pressure drop method, part of the stack was embedded as a whole and part was dissected plane-by-plane. All stack components, the cell, the metallic interconnects, frames and the glass-ceramic sealing were afterwards characterized by means of SEM, TEM and wet chemical analysis. Some analysis were made on whole stack parts including the top and bottom plates and some were performed on dissected individual parts.In summary, most of the components look optically quite good despite the 11 years operation. The measured gas-tightness at room temperature was below the threshold of 1 % gas loss on the fuel side but in an acceptable range regarding the air side. The microstructure of the glass-ceramic sealant showed a high crystallization state of the material with moderate porosity. The triple phase boundary to the furnace atmosphere had a thin layer of barium chromate indicating an early crystallization equilibrium achieved after short terms not being effected by the long-term exposition afterwards. An antiquated application method was used for the sealant resulting in an infiltration of the protective layer up to 100µm depth by the excess glass-ceramic squeezing out of the joining gap. Regarding the interfacial reactions to the YSZ electrolyte, zirconium containing silicate needles are formed as a thin layer. The reaction zone to the steel ITM is very similar to the phenomena observed for Crofer22APU: a chromium manganese spinel layer is dissolved by the glass during joining process resulting in an interfacial layer of 1-2 µm thickness.The interconnect steel ITM formed a thin protective chromia surface scale. The relatively high contents of chromium (ca. 25%) and molybdenum (ca. 3%) in the steel resulted in extensive s-phase formation in the large areas of the interconnect. Gas distributing steel foils of 200 µm thickness made from Crofer 22 APU showed only in some locations nodules of Fe-rich oxide. Substantial parts of these foils formed a protective surface oxide scale consisting of an outer Mn, Cr- spinel layer on top of an inner chromia scale. Interdiffusion phenomena were observed at the spot-welded joints between nickel contact wires and steel components. Ni diffusion from the wire into the ITM interconnect and Crofer 22 APU foils resulted in local transformation of ferritic into austenite structure. On the other hand diffusion of Cr from the interconnect into the Ni-wires resulted in minor Cr-oxide formation on the surfaces of the Ni wires.The cell itself and the air-side contacting reveal no obvious macroscopic changes like delamination, cracking etc. A closer look into the cell shows the formation of an interface zone between the LSCF cathode and the GDC barrier layer. This zone looks fragmented and being composed of various tiny crystals which in turn can be traced back to LSCF and GDC. But in many areas additionally Cr as foreign element could be detected. This Cr is also present in the first micrometers of the GDC barrier layer forming also tiny crystals on the inner surface of pores within the GDC. In the fuel electrode, composed of Ni and 8YSZ, also very small foreign phases containing Mn and Al were found. The amount is very low as the ITM contains only traces of Mn. But an enrichment in Ni in the fuel electrode could be detected. This is opposite to the effect in electrolysis mode were a Ni depletion takes place.To sum up the cell-related findings: i) an enrichment in Nickel in the fuel electrode has been observed in this stack for the first time; ii) a foreign phase composed of Mn-Al-(O) is present in the fuel electrode; iii) the LSCF cathode is, closed to the barrier layer, fragmented and chemically disintegrated; iv) the GDC barrier is also fragmented at the border towards the cathode and lastly v) an interaction between Cr and GDC has been observed also for the first time.

Development and Demonstration of a Decentralised Hydrogen rSOC System

The quality of life and economic prosperity of the population depends to a large extent on a secure and sustainable electricity supply. In order to ensure this for generations to come, a comprehensive integration of renewable, decentralized electrical energy sources is necessary. Such developments are already evident in the world's largest markets. Inevitably, electricity production is increasingly being distributed over larger areas and energy supply systems are tending towards decentralization. Traditional role distributions, such as centralized feed-in and load adjustment by large power plants and decentralized demand, are being replaced by decentralized feeders at all grid levels and prosumers. Security of supply can only be achieved by balancing fluctuating output and demand. Therefore, in order to achieve the EU's 2050 climate targets, in addition to flexibility on the consumer side and sector coupling strategies, increased balancing options in the form of storage systems are required. Currently available storage technologies such as pumped storage power plants, etc. can be considered as complementary solutions. In Europe, their capacities are limited by almost exhausted utilization potentials. Since the fluctuating generation profiles also contain a significant seasonal component, long-term storage solutions are essential. In order to offer appropriate long-term storage services, the additional use of gaseous energy carriers enabled by PtG (Power-to-Gas) technologies is the only alternative.Currently, however, PtG storage technologies are still in the development and demonstration phase, so that further research is required primarily at the system but also at the component level. Another major issue is the commercial viability related to full-load operating hours and installation cost of PtG technologies, if the operation is only given when surplus electricity is available. Fuel cell technologies like reversible solid oxide cell systems (rSOC) that combine both electrolysis and electricity generation in one unit offer great potentials to address these issues.Within the Austrian funded R&D project FIRST (Fully Integrated Reversible Solid oxide cell system) a compact, reversible, high-temperature solid oxide (rSOC) system with a rated power of 15 kWel in SOEC operation and a rated power of 5 kWel in SOFC operation is being developed and demonstrated.In order to realize a compact and thus economically operable system, the Balance of Plant (BoP) components are being optimized for both SOEC and SOFC operation compared to two separate units. In addition, the stand alone system targets a fast switching between gas and electricity production and enables intelligent linking with electricity, gas and heat grids.The reversible solid oxide cell (rSOC) demonstrator shall be capable to produce H2 with > 70 % efficiency, or electricity with > 50% efficiency, in a simplified system with low operating costs. Flexible operation by rapidly switching between electrolysis and fuel cell modes within minutes to enable optimal use of electricity from fluctuating energy sources such as wind and solar. Load forecasting models are applied to respond in advance to changes in demand or yield, bringing new system control strategies to bear.The project aims to test the usability of the technology beyond test bed operation under real operating conditions as a long-term application. Therefore, the results will be relevant to industrial stakeholders as well as utilities.Within this work the status of the FIRST project will be presented including results from the simulative investigation and optimization within a dynamic model.

Principle Demonstration of Fuel Cell System with CO2 Capture

Recently, the desire of decarbonization is increasing on the part of the general public worldwide as many companies take part in RE100 initiative. Tokyo Gas Co., Ltd. declared to reduce 10 million tons carbon dioxide emission by 2030 in “Compass 2030” which is company vision of Tokyo Gas group in November 27th, 2019. We drive CO2 net-zero including emission from customer and lead the transition to a decarbonized society. To achieve CO2 net-zero, we will take two actions. The first one is expansion of use of renewable energy. Second is development of decarbonization technologies for gaseous energy, which include effective use of natural gas, use of carbon capture, utilization and storage (CCUS).Fuel cell system is expected to use natural gas effectively. In Japan, residential fuel cell system has already installed extensively since the first model was sold in 2009. Tokyo Gas have also studied fuel cell technologies for over three decades. These days, we developed and reported mono generation system which had AC-power generation efficiency of over 65.0%LHV and output of 5kW. In this system, anode lines of solid oxide fuel cell (SOFC) stacks are connected in series. A fuel regenerator is placed between two-stage SOFC stacks, which remove H2O from the anode off-gas of first-stage SOFC stack. Then, the regenerated anode off-gas is used as a fuel of the second-stage SOFC stack. Hence, this system can be operated at high total fuel utilization (Uf) value of over 90% and enable each SOFC stack to be operated at safe Uf condition for each, simultaneously. We could make easy flow system by using condenser as fuel regenerator.This system can reduce much CO2 than existing power resource because of its higher efficiency, but still exhausts some amount of CO2 gas. To achieve decarbonized society, further reduction of CO2 emission for fuel cell system will be required. Therefore, we focused on CO2 separation membrane as a fuel regenerator which has high selectivity for both H2O and CO2. In previous work, we performed DC-power generation of 75.5%LHV by connecting membrane module as the fuel regenerator of the two-stage SOFC system. CO2 recovery rate from membrane reached to about 40%. To improve the CO2 recovery rate, we invent the new system as figure 1. The new system recycles regenerated anode off-gas which was removed H2O and CO2 by CO2 separation membrane. The membrane has high selectivity of H2O and CO2. In addition, a separation at the membrane was driven on the differential pressure by decompressing without sweep gas. As a result, high concentration of CO2 was recovered. In ideal situation, the new system will be operated under Uf of 100% and recovered CO2 of 100%. In this study, we demonstrated this system as shown in figure 1. Membrane was put in fuel cell module. It was operated at a total Uf of 97.1%, and power generation efficiency reached DC 77.3%LHV at power output of 5.65 kW under the thermal self-sustainable condition without the electric heater. Assuming the efficiencies of the auxiliary machines and the power conditioner to be respectively 94% and 95%, the estimated AC-power generation efficiency of the hot module was 69.0%LHV and CO2 emission factor reached to 294 g-CO2/kWh. At the same time, CO2 recovery rate was 85%. We achieved high efficiency and low in this system. In the future, we have to discuss about the use of recovery CO2. Figure 1

Electrochemical Reduction of H2O and CO2 Using Anode Supported SDC Cells

Solid oxide electrolysis cells (SOECs) have emerged as an attractive approach for electrochemical reduction of CO2 and/or H2O to high energy molecules, such as CO and/or H2, and demonstrated high faradic efficiency (good selectivity), high energy efficiency (low cell voltage), and high operating current density (high productivity). Conventionally SOECs based on YSZ as electrolyte material operate approximately 800oC in order to achieve a practical cell performance and to mitigate carbon deposition. However, high operating temperature leads to high cost and fast degradation of the SOEC system. Meanwhile, it becomes impossible to produce chemical fuels, such as methane, from the co-electrolysis of CO2 and H2O through in situ methanation.In this contribution, we studied electrochemical reduction of H2O and CO2 at reduced temperatures using anode supported SDC cells, with Ni-SDC anode and SSC cathode of effective area of 2 cm2, and the SDC electrolyte about 10-15 um in thickness. We found that the SDC cell performance (Cell#1) under electrochemical reduction of H2O reaches 0.5 A/cm2 at 1.15 V at 500oC with inlet gas composition of 50% H2O + 50% H2, at a flow rate of 100 ml/min/cm2. We repeated electrochemical reduction of H2O test using another SDC cell (Cell#2), and also conducted electrochemical reduction of CO2 at reduced temperatures. It was noticed that the cell performance under electrochemical reduction of H2O showed slightly better than, but quite similar to, that under CO2 reduction. The SDC cell (Cell#2) performance under electrochemical reduction of CO2 showed 0.5 A/cm2 at 1.17 V at 500oC with inlet gas composition of 80% CO2 + 20% H2, at a flow rate of 10 ml/min. This cell also showed no degradation during a short term (72hr) stability test under the CO2 reduction condition.Interestingly, under the tested conditions, SDC cells showed much better performance under the electrolysis cell (EC) mode than under the fuel cell (FC) mode. For example, at 500 oC, with 100mlpm H2-100mlpm H2O, the cell OCV is about 0.844V, the cell only reached 0.25A/cm2 at 0.4V under the FC mode, while under the EC mode it reached 1.26V at 1 A/cm2, which is approximately 4 times higher with the same polarization value of the cell voltage in comparison to the FC mode. The cause for the difference are investigated.

High Pressure Operation of Reversible Protonic Ceramic Electrochemical Cells

We present our development of proton-conducting ceramics for high-temperature water splitting (HTWS) and hydrogen production at elevated pressure. One of the challenges of intermittent renewable energy production from solar and wind is the mismatch between generation and demand. This decoupled production and consumption of energy has motivated extensive research in electrochemical energy storage. Depending on the application and timescale, a variety of reversible electrochemical cells are needed to address the energy storage needs of intermittent renewable energy sources. For long-term energy storage and electrical-to-chemical energy conversion, high-temperature solid-oxide electrolyzers are attractive. In this work we present some of the advantages and recent developments of electrolyzers based on protonic-ceramic materials. Protonic-ceramic electrolyzers (PCECs) have shown an encouraging performance trajectory in recent years. PCECs can deliver a pure-H2 product stream, simplifying downstream separations. Higher-pressure PCEC operation (~ 10 bar) has been demonstrated, but is at an early stage. In this presentation, we highlight a unique installation that permits the study of these systems in a variety of configurations under high-pressure conditions.Reversible protonic ceramic electrochemical cells (RePCEC) are attracting attention due to their potential low cost, energy flexibility and high proton conductivity at intermediate temperatures (300 – 700 ºC). Previous studies focus either on protonic ceramic fuel cells (PCFCs) for power generation or protonic ceramic electrolysis cells (PCECs) for dry hydrogen production. Electronic leakage through the protonic-ceramic electrolyte presents a concern; high Faradaic efficiency has been demonstrated, but has also seen wide variance across studies. Low electrode activity can also reduce Faradaic efficiency, especially at higher current densities and driving voltages. Additionally, although Hydrogen is well known for its excellent characteristics as a fuel, its low density represents a challenge since it must be compressed to high pressures for storage and transportation.In this context, high-pressure operation of RePCECs is presented as key technology to address the challenges described. Higher total pressure operation should lead to higher efficiencies by decreasing the electron hole concentration in the electrolyte, thereby diminishing the electron leakage problem. High pressure can also boost electrode activity, enabling higher currents at lower driving voltages. From a cost perspective, high-pressure electrolysis reduces downstream compression needs. Operating at pressure is potentially even more important for electrofuels, where green hydrogen is transformed into higher-value chemicals; these chemistries often require high temperatures and pressures to achieve meaningful production rates. Ammonia serves as an example; the second-most-produced global chemical that contributes nearly 1.5% of global annual CO2 emissions.In this work, we present our progress on high-pressure operation of RePCECs. The electrochemical performance of protonic-ceramic electrolyzer stacks is characterized at 550 ºC and pressures up to 12 bar. The figure shows assembly of a unit-cell stack; the protonic-ceramic membrane-electrode assembly (MEA) is bonded to a composite ceramic frame and assembled into a sealed cell stack with metallic interconnects, current collectors, sealing gaskets, and end plates. The stack is placed in a preloaded spring-based mechanical-compression system. This assembly is sealed within a stainless-steel vessel; the operating pressure of the reactants is balanced by the surrounding gas within the vessel, minimizing pressure differentials between the stack and its surroundings. The cross-cell pressure differential between the fuel and the air-steam electrodes brings the risk of cell fracture. Downstream electronic back-pressure regulators serve to maintain stable pressures throughout.The vessel, fuel side, and air side of the installation all have independently regulated flows at their respective inlets and a common regulated pressure at their outlets. Additional systems are in place to introduce steam, execute electrochemical characterizations, and monitor outlet flow rates. Furthermore, an in-line/in-situ mass spec and gas chromatograph provide continuous gas composition measurements.All of the integrated tools in the high-pressure installation are used to study hydrogen production in electrolysis mode, electricity production in fuel-cell mode, and chemical production using catalyst beds at the electrochemical reactor outlet. This powerful combination is very useful for optimizing the performance of electrodes and electrolytes at high pressure conditions and giving us new insight into the application of protonic-ceramic materials. Figure 1

Local Characterization of a Solid Oxide Cell Operated in Fuel Cell and Electrolysis Mode Using Lock-in Thermography

Operando characterization of SOCs generally relies on current–voltage measurements that provide the spatially averaged electrochemical response of the SOC. However, these methods do not fully capture the spatial distribution of the operating conditions (e.g., gas composition, current density). Local information on the operating conditions can be gained by using operando optical characterization methods. In this work, the spatial distribution of the electro-thermal response of an SOC with a 15 cm2 active area operated in fuel cell and electrolysis mode was investigated using lock-in thermography. Lock-in thermography consists of stimulating the solid oxide cell with a sinusoidal current perturbation and analyzing the local thermal response using Fourier transforms. A camera with a silicon-based sensor was used to record the transient temperature field on the oxygen electrode (i.e., the cathode in fuel cell operation) via a specifically designed optical access. The field of view of each pixel was approximately 0.03 mm x 0.03 mm. The Fourier transform generates a compact data set that can be conveniently represented by a phase and amplitude or a real and imaginary image. Using a real–imaginary representation provided a better thermal response contrast than an amplitude–phase representation. The local thermal response was found to be dependent on the direct current bias and the frequency of the current perturbation. The thermal response of the SOC was laterally and longitudinally inhomogeneous, thereby demonstrating the capability of active thermography to characterize the local behavior of an SOC in operando. Lock-in thermography is thus a promising method for defining regions of interest for post-mortem analysis using electron microscopy and helping to link highly localized post-test analysis with spatially averaged operando characterization methods.

Enhanced Gas Diffusion in Reversible Solid Oxide Cell Fabricated by Phase-Inversion Tape Casting

Electrochemical characteristics of a hydrogen-electrode-supported solid oxide cell (SOC) fabricated by phase-inversion tape casting are experimentally evaluated in both fuel cell (FC) and electrolysis cell (EC) operations. Particular focus is on the effect of the microchannels formed in the hydrogen electrode on the gas diffusion performance in the electrode. Current-voltage and impedance characteristics are measured and compared with those obtained from an SOC fabricated by conventional tape casting technique. The activation resistance is found to be almost identical between the tested cells because both cells are fabricated with a spin-coated functional layer in the hydrogen electrode. On the other hand, the concentration resistance is significantly decreased in the cell fabricated by the phase-inversion tape casting because the microchannels in the hydrogen electrode enhances the gas diffusion performance. This is more remarkable when the cells are operated in diluted fuel composition and with higher current densities. The asymmetric behavior is observed in the current-voltage characteristics of the cells, meaning that the overpotentials in the FC and EC modes are not the same at the same FC and EC currents. The overpotential is found to be always larger in EC mode, however, the extent of asymmetry is reduced in the cell fabricated by the phase-inversion tape casting. This is mainly because the microchannels in the hydrogen electrode reduces the gas diffusion resistance associated with the steam transport in EC mode. Microstructure of the fabricated cells is also analyzed in micro- and nano-scale to quantify the structure of the microchannels formed in the hydrogen-electrode. The microchannels are initiated below the immersed surface during the phase-inversion process, and then grow towards the bottom of the layer. The average diameter of the microchannels increases, whereas its number density decreases. Also, the total porosity in the phase-inversion electrode is found to be almost the same as that in the conventional cell.

Redox-Cycling – A Tool for Artificial Electrochemical Aging of Solid Oxide Cells

Solid Oxide Cells (SOC) have an important role and hold great promise with their diverse and versatile portfolio in the energy application sector, ensuring opportunities for integration of renewable energy sources into the overall energy system. However, the spectrum of applications still meets some general barriers, summarized as durability and costs. The initial performance degrades over their lifetime due to the effect of use (electrochemical ageing), of time (calendar ageing), of different permanent and/or accidental stress conditions - thermal, current load, mechanical, poisoning etc. Considering the expected useful commercial maintenance-free lifetime of up to 80 000 hours for stationary applications, the performance of durability tests looks quite unrealistic, which opens the niche for introduction of accelerated stress tests.In respect to the fuel electrode, the main degradation mechanism during operation in both fuel cell and electrolysis mode is the reduction of the triple phase boundary points and of the Ni/gas specific surface area caused by microstructural changes in the Ni network due to Ni migration and coarsening. The migration over long distances can bring to Ni depletion near the electrolyte interface. Similar processes of Ni coarsening and migration can occur faster during oxidation of Ni caused by incidental change in the operation conditions (leakage, fuel starvation). Thus, artificial redox cycling can be applied for accelerated degradation testing. However, the oxidation/reduction cycles should mimic the normal aging.The most common experimental approach for evaluation of the redox cycling effect on the degradation is the oxidation in a furnace at high temperature for at least one hour, followed by post mortem analysis. However, this approach introduces severe oxidation conditions, even full oxidation of the Ni network, which does not represent the most common electrochemical and calendar aging.The aim of this work is to develop a procedure for accelerated stress tests by artificial aging of the anode via redox cycling. It is performed before the operation of the cell thus eliminating the influence of the degradation mechanisms coming from other components. The proposed procedure ensures reproducible and fine-tuned level of oxidation based on in situ impedance monitoring of the Ni network reduction/oxidation. A two-step algorithm is developed and approbated. Step 1. Performance of redox cycling on anode sample with in situ impedance monitoring of the Ni network reduction/oxidation. The anode sample (pellet with thickness 250 µm and diameter 20 mm) is placed between two Pt meshes. In the initial state (YSZ/NiO) the impedance of the anode has capacitive behavior with resistance about 20 kΩ which after reduction transforms into inductive one with resistance about 40 mΩ corresponding to the electronic conductivity of the produced Ni network (Fig. 1). In the same way the oxidation can be registered. Its level may vary from small oxidation depth (for instance two times increase of the resistance, i.e. from 40 mΩ to about 70-80 mΩ as it is presented in Fig. 1) to big oxidation (above 10 kΩ).For the performance of Step 2 small level of oxidation was chosen, as shown in Fig. 1, which prevents from potential irreversible damages. Thus, the redox cycling of single anode serves for definition of the experimental redox cycling conditions. The deepness of degradation is regulated by the number of cycles. Step 2. Performance of redox cycling on full cell. In this configuration the oxidation of the anode Ni network cannot be monitored, but the conditions are already defined in Step 1 which guarantees reproducible identical redox cycles. The impedance measurements ensure monitoring of the total cell behavior during redox cycling. The procedure is applied for fuel cell mode, but it is also valid for electrolyzer mode. The results are shown in Fig. 2 where the impedance diagrams after the initial reduction and after the 8th redox cycle are compared. Although there is a decrease of the ohmic resistance which is usually observed during the first 1000 hours of standard operation mainly due to improved contacts, the polarization resistance after the 8th cycle is about 14% higher. This behavior is similar to that observed for standard testing for at least 600 hours. The 8 cycles are performed for 16 working hours which confirms the accelerated aging produced by the developed algorithm. Acknowledgements: The research leading to these results received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 825027. The experiments were performed with equipment supported by the Bulgarian Ministry of Education and Science under the National Roadmap for Research Infrastructure 2017-2023 “Energy storage and hydrogen energetics (ESHER)”, approved by DCM No 354/29.08.2017. Figure 1

Solid Oxide Cell Technology for Supply, Recovery, and Storage Energy

Fuel Cell Energy, Inc. (FCE) is advancing the current state of Solid Oxide Fuel Cell (SOFC) technology towards commercial deployment for efficient and nonpolluting generation of electric power from natural gas and biomass derived fuels. Additionally, FCE is utilizing the same solid oxide cell and stack technology in electrolysis of steam for production of hydrogen from renewable sources and other electric power sources, such as nuclear power plants during the curtailment periods. Additionally, FCE’s SOFC technology has shown to be a viable technology for storage of energy by cyclic charge and discharge operation.FCE’s SOFC technology is based on anode supported thin electrolyte planar cell platform chosen for its higher power density at reduced operating temperature (700-800°C). Traditional materials, such as Ni/YSZ anodes, YSZ electrolytes and perovskite cathodes have been utilized in a basic cell structure. Research and development focus has been placed on developing better electrochemical functional areas at both cathode/electrolyte and anode/electrolyte interfaces. This was achieved through material advancements, microstructure optimization, and manufacturing process integration.The solid oxide stack is comprised of planar solid oxide fuel cells with glass ceramic seals and sheet metal, bipolar plate interconnects; and has a mix of internal and external gas manifolds. Each cell is a 0.30 mm thick annular (donut shaped), cell with 81 cm2 active area made in a process consisting of tape casting, screen printing, and firing cell components. The full height stack consists of 350 repeat units and a set of non-repeat parts. A repeat unit includes one ceramic cell, inner and outer seals, and a metallic interconnect which incorporates flow fields for both fuel and oxidant. Non-repeat parts include the end plates, manifolds, and compression components. The stack is capable of producing 7kW power when fueled with natural gas, biogas, hydrogen, or other fuels. The same stack is capable of operating at higher power density in electrolysis mode, producing 25 kg/day hydrogen with 36 kW power input.FCE’s SOFC system design philosophy is based on using factory-assembled stack building blocks, which in turn may be used to fabricate larger multi-stack modules for applications in centralized natural gas and coal fueled power plants. An attractive pathway to deployment of SOFC systems is through near-term market opportunities in natural gas fueled distributed generation (DG) applications. FCE is planning to take the advantage of the scalability, modularity, and fuel flexibility of the SOFC technology to transition the technology from small (sub-MW) systems to megawatt class power plants for distributed generation, and ultimately (through aggregation of fuel cell modules) to large stationary power plants for base-load utility applications using coal and/or natural gas fuel.FCE has recently designed, fabricated, and tested a 200kW natural gas fueled packaged system. This autonomous unit is an outdoor rated power system with capabilities for both grid-connection as well as island operation.Electricity storage is a growing need given the increasing penetration of intermittent renewable sources of solar and wind. Traditional battery storage technology uses rare materials that could pose sourcing challenges and depletion with widespread adoption. Hydrogen based energy storage is the only practical way to store the GWh of energy that will need to be stored to enable significant penetration of intermittent renewable energy on the electricity grid. Another advantage of hydrogen based energy storage is that once hydrogen is stored it can be used to make power, or exported for another use such as vehicle fueling or industrial uses.

A biogas-solar based hybrid off-grid power plant with multiple storages for United States commercial buildings

In this paper, a hybrid renewable power plant with a storage system is designed. The benefits of sizing and energy management are assessed for a commercial building under eight different climatic conditions in the United States. In the considered system, photovoltaic panels are coupled to a unitized regenerative solid oxide fuel cell. The use of biogas to feed unitized regenerative solid oxide fuel cell is investigated, employing a detailed electrochemical model of electrolyzer and fuel cell modes. A battery pack is included in the plant as a secondary storage system, together with a diesel engine operating in backup mode.Four scenarios where biogas amount is varied together with the initial state of charge of the battery were evaluated. Results demonstrate that the power plant can operate with 100 % renewable procurement if the digester produces from 6000 to 9500 stdm3/y and the battery is completely charged at the beginning of the year. By reducing the biogas availability or starting with a low state of charge, the use of the diesel generator is inevitable.The study confirms that the proposed hybrid renewable power plant is technically feasible and can be considered a reliable and clean energy source in other areas and buildings.

Enhanced Electrochemical Performance of the Fe-Based Layered Perovskite Oxygen Electrode for Reversible Solid Oxide Cells

Reversible solid oxide cells (RSOCs) present a conceivable potential for addressing energy storage and conversion issues through realizing efficient cycles between fuels and electricity based on the reversible operation of the fuel cell (FC) mode and electrolysis cell (EC) mode. Reliable electrode materials with high electrochemical catalytic activity and sufficient durability are imperatively desired to stretch the talents of RSOCs. Herein, oxygen vacancy engineering is successfully implemented on the Fe-based layered perovskite by introducing Zr4+, which is demonstrated to greatly improve the pristine intrinsic performance, and a novel efficient and durable oxygen electrode material is synthesized. The substitution of Zr at the Fe site of PrBaFe2O5+δ (PBF) enables enlarging the lattice free volume and generating more oxygen vacancies. Simultaneously, the target material delivers more rapid oxygen surface exchange coefficients and bulk diffusion coefficients. The performance of both the FC mode and EC mode is greatly enhanced, exhibiting an FC peak power density (PPD) of 1.26 W cm-2 and an electrolysis current density of 2.21 A cm-2 of single button cells at 700 °C, respectively. The reversible operation is carried out for 70 h under representative conditions, that is, in air and 50% H2O + 50% H2 fuel. Eventually, the optimized material (PBFZr), mixed with Gd0.1Ce0.9O2, is applied as the composite oxygen electrode for the reversible tubular cell and presents excellent performance, achieving 4W and 5.8 A at 750 °C and the corresponding PPDs of 140 and 200 mW cm-2 at 700 and 750 °C, respectively. The enhanced performance verifies that PBFZr is a promising oxygen electrode material for the tubular RSOCs.

Numerical investigation of effects of different flow channel configurations on the 100 cm2 PEM fuel cell performance under different operating conditions

The supply of species gases and removal of liquid water in a PEM fuel cell are performed through gas flow channels. Therefore, optimising the flow channel configurations is critical for maximising performance of fuel cells. In this paper, the ANSYS PEM Fuel Cell Module is used to simulate a PEM fuel cell with an active area of 100 cm2 and four different flow channel configurations: single-channel serpentine, two-channel serpentine, three-channel serpentine, and parallel channel with headers under two set of different operating conditions. Under both sets of operating conditions, the simulation results indicated that 3-channel serpentine configuration has the best performance due to uniform distribution of species gases over the catalyst layer. It was concluded from the simulation results that the pressure-drop along the 3-channel serpentine configuration is less compared to other serpentine channel configurations, which will require less power for the blowing in of the species gases. The results obtained from simulation under more optimal operating conditions (set 2) used by Hwang’s URFC, predicted increase in the performance of all the four channel configurations compared to the set 1 operating conditions due to higher cell temperature and stichometry of inlet gases. Under set 2 operating conditions, the values of pressure drop across all the channel configurations have increased substantially due to higher flow rates of inlet gases.