Open Circuit Voltage Conditions Research Articles

Copper recovery with electricity generation using reduced graphene oxide/ polyaniline cathode electrode in microbial fuel cell

This research studied the amount of Cu recovery using a two-chamber microbial fuel cell (MFC). The effect of initial Cu concentration in the cathode and also different cathode materials including carbon cloth (CC), carbon cloth modified with reduced graphene oxide (CC/rGO), and carbon cloth modified with reduced graphene oxide and polyaniline (CC/rGO/PANI) was examined. Analysis of the statistical results showed the CC/rGO/PANI electrode compared to the other two electrodes significantly better performance (p-value <0.05), and amount of Cu recovery at 100 mg/L was significantly higher than at 500 mg/L (p-value <0.001). The highest voltage obtained in the open circuit voltage (OCV) condition was 561 mV. The CC/rGO/PANI electrode achieved a Cu recovery rate of 99.3 %, a maximum output voltage of 647 mV, and a maximum power density of 981 mW/m³ after 120 h at an initial Cu concentration of 500 mg/L. Based on regression efficient for kinetic Cu recovery was examined and result showed the first-order rate (R2 = 0.98) has more accurate prediction and explanation of the reaction.

Effect of current density and operating temperature on degradation of protonic ceramic fuel cells containing BaZr0.8Yb0.2O3-δ electrolyte during long-term operation

Barium zirconate doped with 20 mol% Yb (BaZr0.8Yb0.2O3-δ, BZYb20) is one of the most promising candidates for use as an electrolyte material in protonic ceramic fuel cells (PCFCs) due to its high proton conductivity and high chemical stability under CO2-containing fuel conditions. The long-term durabilities of PCFCs prepared using the BZYb20 electrolyte were evaluated as a function of the current density at 500 and 600 °C over a period of 1000 h. At 600 °C, the internal resistance of the cell increased even under open circuit voltage (OCV) condition. Comparing the voltage lowering rates at a current density of 0.172 A cm−2 based on the current density–voltage curves recorded during the durability tests, rates of 3.0, 5.3, and 9.0%/1000 h were achieved at the OCV, 0.047, and 0.172 A cm−2, respectively. A small amount of Ni elements diffused into the electrolyte from the anode to the cathode side, resulting in the formation of cumulus cloud shapes that corresponded to Ni element segregation at the grain boundaries in the electrolyte layer after long-term durability testing at 0.172 A cm−2. At current densities of 0.047–0.048 A cm−2, the voltage lowering rate at 500 °C was higher than that at 600 °C, with values of 6.0 and 2.6%/1000 h being recorded, respectively. This effect may be due to the higher resistance of the cell at 500 °C compared to that at 600 °C.

Effects of voltage stress conditions on degradation of iridium-based catalysts occurring during high-frequency operation of PEM water electrolysis

Proton exchange membrane water electrolysis (PEMWE) is needed to store renewable energy in the form of hydrogen. To improve the performance of PEMWE, elucidating the degradation mechanism of iridium (Ir)-based catalysts used for oxygen evolution reaction (OER) that is a rate-determining step is important. To date, it is known that one important reason for that is undesirable change in crystal structure of Ir. To further evaluate its degradation mechanism, in this study, effects of operating voltage conditions on crystal structure of Ir are investigated because the voltage conditions can accelerate changes in crystal structure of Ir. Especially how Ir was changed into an unfavorable metallic form was analyzed. PEMWE single cells under conditions of (i) a constant voltage of 1.9 V, (ii) a voltage cycle of 1.7–1.9 V, then a constant voltage of 1.9 V, and (iii) an applied voltage cycle with open circuit voltage (OCV). In the OCV condition, the crystalline structure of Ir was irreversibly transformed into a metallic form. This transformation induced lower OER activity than other crystalline states of Ir, followed by lower performance of PEMWE single cells. These findings help to establish baseline protocols for the stable operation of PEMWEs using Ir-based catalysts.

Optimization of Realistic Accelerated Stress Tests for PEM Fuel Cells Using Standardized Automotive Driving Cycles

Proton exchange membrane (PEM) fuel cells have so far not achieved the targeted lifetime necessary to be an economical alternative for automotive applications. This is mainly caused by their high degradation rates. To better understand the degradation mechanisms, the use of accelerated stress tests (ASTs) at the component level is widespread. However, it is still a challenge to transfer their results to real-world applications.To address this problem, the approach of this work is to derive load profiles from standardized driving cycles for passenger cars. In combination with a fuel cell system model that is used to define the operating conditions of the media, such as temperature or pressure, a test procedure is obtained that results in a realistic degradation of the fuel cell. The proposed test procedure exposes the PEM fuel cell (PEMFC) to the most important degradation conditions in mobile applications. Dynamic operation is responsible for deterioration processes within the PEMFC and is the underlying cause of typical hygrothermal and voltage cycling events. Such cycling also occurs during start-stop operations, causing severe damage to the PEMFC catalysts. In addition, idling conditions may prompt open-circuit voltage (OCV) conditions in the PEMFC, resulting in dissolution of the Pt catalyst and subsequent chemical degradation of the PEM. Additionally, high load operation may also lead to catalyst degradation. Finally, the inertia of the auxiliary components, such as the humidifier, during load changes causes not ideal conditions, such as relative humidity changes, resulting in further mechanical stress on the membrane.Due to the targeted PEMFC lifetime of up to 8,000 hours for automotive applications [1], realistic degradation test procedures have a very long test duration, making them particularly challenging and costly to conduct. To overcome this hurdle, the load profile of the proposed test procedure is shortened by using an in-house developed optimization algorithm. For this purpose, four operation modes are defined as degradation-accelerating: voltage cycling, relative humidity (RH) cycling, OCV/idling, and high load operation. Based on state-of-the-art AST procedures, a sub-algorithm is developed for each operating mode. Such sub-algorithms are capable of identifying all occurrences within a given test procedure that may lead to accelerated fuel cell degradation. For each sub-algorithm, the degradation parameters (namely upper and lower potential limits for voltage cycling, membrane tensile stress for RH cycling, fluoride emission rate for OCV/idling, and voltage degradation rate for high load) are specified by the user. This allows the comparison of different fuel cells in terms of their resistance to conventional degradation mechanisms.The developed algorithm can be used to optimize various driving cycles such as the worldwide harmonized light vehicles test cycle (WLTC) for various mobile applications. All cycle events identified as accelerating degradation are connected with a point connector function based on the fuel cell polarization curve. This ensures moderate voltage steps between the identified phases and thus prevents the algorithm from inducing further degradation of the fuel cell.The optimization algorithm obtained can reduce the test duration by up to 40%. The method can be repeated frequently during AST operation by repeatedly measuring the polarization curve to consider the continuous degradation in the test procedure. Decreasing fuel cell performance leads to more severe voltage drops during load changes and thus an increase of degradation-accelerating phases over the test period. Furthermore, start-stop ASTs developed by Bisello et al. [2] are also included due to their strong contribution to fuel cell degradation in automotive applications.Finally, the optimized cycles are analyzed using two simulation tools to evaluate the degradation. The first tool by Ao et al. [3] uses the electrochemical surface area (ECSA) to quantify the proceeding degradation during cycle operation. A characteristic voltage and the voltage change rate are extracted from the driving cycle. For both values, the resulting decrease in ECSA is modeled and aging is defined as the ECSA loss rate. The second tool by Pei et al. [4] examines the driving cycle according to the four degradation-inducing conditions and combines them with experimentally determined degradation rates. Both tools allow an analysis of the degradation derivative between the initial and optimized test procedures. By adjusting the degradation rate for the different degradation mechanisms, the AST procedure is improved in terms of its representativeness for real-world applications.

Physical-chemical processes at Mo-doped ceria-yttria stabilized zirconia (YSZ) anodes in solid oxide fuel cells using syngas derived by the distribution of relaxation times method

The use of environment-friendly carbonaceous fuels (such as, biomass and synthetic fuels) to produce electricity using solid oxide fuel cells (SOFCs) has emerged as a promising alternative to the use of high-purity hydrogen, which remains as a difficult to produce and store gas. Much effort has been put in the development of SOFC anodes highly active and stable for the use of carbonaceous fuels, such as ceria-based materials, but only recently research has focused on the comprehensive analysis of the interfacial physical-chemical processes affecting their performance.This work presents an in-depth analysis of the interfacial processes occurring at a Mo-doped ceria-yttria stabilized zirconia (YSZ) cermet anode in a SOFC using humidified syngas as fuel. To this end, electrochemical impedance spectroscopy (EIS) data is generated and analysed by the distribution of relaxation times (DRT) method. In addition, gas chromatography analysis of the internal reforming products generated under open circuit voltage (OCV) conditions and post-mortem analysis of the electrode materials after polarization are discussed in support of the DRT results.It is observed that the presence of carbon monoxide (CO) in fuel, as compared to pure hydrogen, influences the anodic charge transfer processes not only due to promotion of the water-gas-shift reaction at the anode two-phase (fuel | electrode) and three-phase (fuel | electrode | electrolyte) interfaces, but also because of its direct electrooxidation at the anode three-phase interfaces. The electrooxidation of carbon monoxide presents a slightly higher activation energy than the electrooxidation of hydrogen (ca. 1.86 and 1.21 eV, respectively), which explains the slower kinetics of SOFCs when using syngas as fuel. Additionally, other oxidation processes of CO at the anode interfaces (such as, the Boudouard reaction) promote the formation of carbon deposits lacking ordered structure, which are more reactive than graphitic structures formed at Ni-YSZ anodes but still can negatively influence the electrochemical kinetics.

Real-time Thermal Energy Harvesting from Solar Radiation in Malaysia at Low-Temperature Difference

.Malaysia is located in a tropical climate with an abundance of solar radiation. Due to the low albedo of roofing material, around 20 % to 90 % of heat is absorbed from solar radiation. Thus, it is possible to harvest thermal energy from solar radiation using TEG, which promotes the diversity of renewable energy sources in Malaysia. Previous research evaluates the potential of thermal energy harvesting of the TEG open circuit voltage and unipolar condition. Thereby, this research focuses on designing and developing a thermal energy harvesting system (TEHS) for harvesting thermal energy at low-temperature differences from solar radiation. The TEHS can harvest thermal energy in bipolar conditions, different voltage levels, TEG input voltage fluctuations, and rapid weather-changing conditions during real-time field tests. Parallel with series balance TEG array configuration obtained impedance matching at 125 Ω. The field test method was conducted for 105 days. The maximum mean efficiency obtained is 94.33 %, with an output power range between 0.46 mW and 66.10 mW. The promising finding indicates that the developed TEHS is robust and capable of operating at optimum power transfer at uncontrollable solar radiation and weather conditions. In addition, the potential of the power generated evaluation is to be used as a power supply to several sensor nodes.

Lead-chelating hole-transport layers for efficient and stable perovskite minimodules

The defective bottom interfaces of perovskites and hole-transport layers (HTLs) limit the performance of p-i-n structure perovskite solar cells. We report that the addition of lead chelation molecules into HTLs can strongly interact with lead(II) ion (Pb2+), resulting in a reduced amorphous region in perovskites near HTLs and a passivated perovskite bottom surface. The minimodule with an aperture area of 26.9 square centimeters has a power conversion efficiency (PCE) of 21.8% (stabilized at 21.1%) that is certified by the National Renewable Energy Laboratory (NREL), which corresponds to a minimal small-cell efficiency of 24.6% (stabilized 24.1%) throughout the module area. Small-area cells and large-area minimodules with lead chelation molecules in HTLs had a light soaking stability of 3010 and 2130 hours, respectively, at an efficiency loss of 10% from the initial value under 1-sun illumination and open-circuit voltage conditions.

Initial Evolution of Passivation Layers in Non-Aqueous Aluminium Batteries

Aluminium batteries (AlBs) have gathered considerable attention, primarily due to the high capacity, the low cost, the large abundance in the Earth’s crust, and the recyclability of the Al metal anode. However, several hurdles must be surpassed to make AlBs a feasible energy storage technology and two of them are interconnected; the presence of an ionic and electronically insulating native oxide layer on the Al metal anode that calls for special non-aqueous, most often ionic liquid based acidic electrolytes, to enable reversible plating and stripping of Al. We here find the passivation layer initially formed in contact with an ionic liquid electrolyte (ILE) to have a porous and very complex nature, i.e. an outer inorganic/organic layer and an inner oxide-rich layer. Furthermore, it grows under open circuit voltage conditions by simultaneous dissolution and re-deposition of dissolved products, while during galvanostatic cycling this is exacerbated by an electrochemical etching that causes pitting corrosion of the Al metal itself. All of this leads to unstable interfaces being formed and the co-existence of several species at the Al metal anode surface, of which a proper understanding and mitigation are crucial to make AlBs a reality.

Chemical stability and functionality of Al2O3 artificial solid electrolyte interphases on alkali metals under open circuit voltage conditions

We studied chemical stability of atomic layer deposition-grown Al2O3 artificial solid electrolyte interphases (SEIs) on lithium and sodium upon contact with liquid electrolyte by electrochemical impedance spectroscopy (EIS) and in the case of Li also by x-ray photoelectron spectroscopy. Both methods show that the formed Al2O3 is porous for all nominal thicknesses, and that the natural SEI grows in its pores and cracks. EIS shows that the porosity of the SEI on Na is higher than the one observed on Li, in particular at higher nominal thicknesses of Al2O3. The observed values of activation energies related to the transport through the SEI indicate either a denser natural SEI in the pores of Al2O3 and/or considerable space charge effect between Al2O3 and the SEI phase.

Open-circuit and short-circuit loss management in wide-gap perovskite p-i-n solar cells

In this work, we couple theoretical and experimental approaches to understand and reduce the losses of wide bandgap Br-rich perovskite pin devices at open-circuit voltage (VOC) and short-circuit current (JSC) conditions. A mismatch between the internal quasi-Fermi level splitting (QFLS) and the external VOC is detrimental for these devices. We demonstrate that modifying the perovskite top-surface with guanidinium-Br and imidazolium-Br forms a low-dimensional perovskite phase at the n-interface, suppressing the QFLS-VOC mismatch, and boosting the VOC. Concurrently, the use of an ionic interlayer or a self-assembled monolayer at the p-interface reduces the inferred field screening induced by mobile ions at JSC, promoting charge extraction and raising the JSC. The combination of the n- and p-type optimizations allows us to approach the thermodynamic potential of the perovskite absorber layer, resulting in 1 cm2 devices with performance parameters of VOCs up to 1.29 V, fill factors above 80% and JSCs up to 17 mA/cm2, in addition to a thermal stability T80 lifetime of more than 3500 h at 85 °C.

Accurate, Fast and Power Efficient PV Emulator Based on Hybrid Passive and Active Circuits

A photovoltaic emulator (PVE) has been proposed based on a physical equivalent photovoltaic cell model. It has fast dynamic performance that is compatible with a real PV system. The PV emulator can analyze and assess PV systems, including maximum power point tracking (MPPT). It is power efficient at the maximum power point. However, it has higher power loss at an open-circuit voltage (OCV). This paper, therefore, presents a hybrid solution using a switching circuit (SC) paralleled with the diode string (DS) to minimize the power loss. The SC consists of a two-switch non-inverting buck-boost dc/dc converter. The DS operates with a low power loss region, i.e., the current source region (CSR) of the I-V curve, in which the SC switches in to replace the DS in the voltage source region (VSR) to minimize power loss of the DS while maintaining the emulator’s circuit operation. The SC handles only a fraction of the rated emulator power and has a much narrower control bandwidth than a pure switching converter-based solution. Experimental results show that in the worst-case scenario, i.e., OCV condition, the efficiency and temperature of the PVE based on DS alone configuration reach 2.8% and 94.2 °C, respectively, as compared to 85.98% and 26.5 °C for the proposed hybrid solution. Under the 30% to 60% insolation change test, the suggested PV emulator lags the actual PV panel by only 3.2 ms, compared to 120 ms lagging for a commercial emulator. Furthermore, the control strategy is implemented to handle the trade-off between thermal and dynamic performances of the proposed solution.

Effect of current density on membrane degradation under the combined chemical and mechanical stress test in the PEMFCs

This study elucidates the effects of current density on membrane degradation under combined mechanical and chemical stress tests. Relative humidity (RH) cycling tests using hydrogen gas and air are conducted on a polymer electrolyte membrane fuel cell based membrane NRE211 at the open circuit voltage (OCV), 0.05 and 0.3 Acm−2 conditions. The different current density conditions result in different in-plane membrane stresses and H2O2 formation rates during the test. After every 200 RH cycles, membrane integrity is assessed via the hydrogen crossover rate and OCV. Furthermore, catalytic combustion is analyzed during OCV measurement using a thermal imaging method employing high-transmittance glass at the cathode side. The membrane failed after 1600, 1800, and 2200 RH cycles under the OCV condition, 0.05 of 0.3 Acm−2, respectively. The vigorous membrane degradation under OCV conditions can be attributed to higher mechanical stress and H2O2 formation rate. Hotspots created owing to the combustion between the crossover hydrogen and air were successfully captured, with a maximum temperature rise ranging from 15 to 16 °C compared with a given cell temperature of 80 °C. Moreover, a post-mortem analysis (SEM imaging) revealed the presence of pinholes, through-membrane cracks, and membrane thinning at the hotspot locations.

The Possibility of Intermediate–Temperature (120 oC)–Operated Polymer Electrolyte Fuel Cells

The technical possibility and possible issues of an intermediate–temperature–operated polymer electrolyte fuel cell (@120 °C, IT–PEFC) was investigated toward the launching of new fuel cell heavy–duty vehicles. Commercial perfluorosulfonic acid membrane (PSFA, NRE212) and a commercial Pt catalyst supported on carbon (Pt/C: TEC10E50E, TKK) were selected to clarify the possible issues in the fuel cells. The higher oxygen back–pressures, over 200 kPa(abs.), allowed us to obtain higher power densities than those for cells operated at 80 °C (Fig. 1), because the water vapor pressure at 120 °C exceeded 100 kPa(abs.) above 50% RH. The mass activity at 0.85 V increased monotonically with increasing back–pressure above the water vapor pressure of 160 kPa(abs.) at 120 °C, 80% RH. The open circuit voltage (OCV) exceeded 1.0 V for back–pressures above 200 kPa(abs) at the Pt loadings on the cathode catalyst layer above 0.20 mgPt cm–2 (Fig. 2), which would relate with the hydrogen crossover in the PFSA membrane. The mass activity (@0.85 V) decreased moderately with decreasing cathodic Pt loading amount at each back–pressures (Fig. 3), indicating that the limitation of Pt mass activity in the lower Pt loading cathode catalyst layers occurred at 120oC, 80 %RH. The load cycle durability test (0.60V-1.0 V, 6 sec.) of the Pt catalyst supported on carbon at 120 °C at low humidity (20% RH) was higher than that at 120 °C at high humidity (80% RH) and 80 °C at 80% RH (Fig. 4), indicating that effect of Ostwald ripening would mitigate. The degradation of PFSA membrane accelerated at open circuit voltage condition by increasing operating temperature despite of the operation under the high humidity condition of 80% RH. We propose that the further improvement of both the gas transport properties in gas diffusion layers and the durability of the PFSA membrane to realize the IT–PEFC operation. Acknowledgment This work was partially supported by funds for the project “Electrolytes, Catalysts and Catalyst layers with Extraordinary Efficiency, power and Durability for PEFCs-2040 (ECCEED’40) from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. Reference K. Kakinuma, H. Taniguchi, T. Asakawa, T. Miyao, M. Uchida, Y. Aoki, T. Akiyama, A. Masuda, N. Sato, A. Iiyama J. Electrochem. Soc. 169, 044522 (2022). Figure 1

Visualization of Combustion in Polymer-Electrolyte-Membrane Fuel Cell - Mechanism on Abrupt Change from Moderate to Accidental Scale-

This study is focused on elucidating the catalytic combustion phenomenon in proton-exchange membrane fuel cells. A visualization cell and an infrared (IR) camera are used to capture the thermal behavior under combined chemical and mechanical accelerated stress conditions in situ. A 3.4 cm2 catalyst coated membrane (CCM) embedded in the cell is subjected to a relative humidity (RH) cycling test at atmospheric pressure and a cell temperature of 80 °C under open-circuit voltage (OCV) conditions. The temperature distribution on the gas diffusion layer surface at the cathode is captured using a high-transmittance glass window (ZnS window). Continuous IR imaging revealed a hot spot at ca. 500 RH cycles, suggesting the existence of a pinhole in the degraded CCM and the occurrence of catalytic combustion there. The occurrence of the hot spot coincides with the time at which the electrochemical indicators detect membrane failure, i.e., hydrogen crossover rate, OCV. Furthermore, the post mortem analysis revealed a 105-micrometer diameter pinhole, the position of which matched that of the hotspot. An accidental combustion during the durability test could cause the formation of a pinhole. This pinhole is responsible for the rapid increase in the hydrogen crossover rate as well as the significant decrease in the OCV at 500 RH cycles until the end of the durability test. Figure 1

A-site deficiency in La0.5Ca0.5MnO3-δ cathode allows high performance for proton-conducting solid oxide fuel cells

The A-site deficiency strategy is proposed for the ABO3 perovskite structure La0.5Ca0.5MnO3-δ (LCM), which provides higher performance as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs). The A-site deficiency can happen at the La site or the Ca site, and either can enhance the oxygen vacancy content and the oxygen reduction reaction (ORR) ability compared with the traditional LCM. Comparatively, the performance improvement for the La-site defective material is more profound, resulting in to a high cell performance of 1265 mW cm−2 at 700 °C, the largest ever reported for single-phase Mn-based cathode cells. The analysis for the cell resistances reveals that the A-site deficiency can promote the cathode reaction, leading to smaller cathode polarization resistances. The La-site deficient cathode shows the smallest polarization resistances under both the open circuit voltage (OCV) condition and loading. Furthermore, the A-site defective materials possess excellent chemical stability against CO2 and H2O, making them attractive cathode candidates for high-performance H-SOFCs.

Investigation of in-situ catalytic combustion in polymer-electrolyte-membrane fuel cell during combined chemical and mechanical stress test

This study is focused on elucidating the catalytic combustion phenomenon in proton-exchange-membrane fuel cells. A visualization cell and an infrared (IR) camera are used to capture the thermal behavior under combined chemical and mechanical accelerated stress conditions in situ. Catalyst coated membrane (CCM) embedded in the cell is subjected to a relative humidity (RH) cycling test under open-circuit voltage (OCV) conditions at atmospheric pressure and at a cell temperature of 80 °C. The temperature distribution on the gas diffusion layer surface at the cathode is captured through a high-transmittance glass window (ZnS window). Continuous IR imaging revealed a hot spot at ca. 500 RH cycles, suggesting the existence of a pinhole in the degraded CCM and the occurrence of catalytic combustion there. The occurrence of the hot spot coincides with the time at which the electrochemical indicators detect membrane failure, i.e., hydrogen crossover rate, OCV. Furthermore, a post mortem analysis revealed a 105-μm diameter pinhole, the position of which matched that of the hot spot. This pinhole is responsible for the rapid increase in the hydrogen crossover rate as well as the significant decrease in the OCV at 500 RH cycles until the end of the durability test.

Ethylene and power cogeneration from proton ceramic fuel cells (PCFC): A thermo-electrochemical modelling study

Ethylene is a vital chemical worldwide but its production is very energy-intensive with high CO2 emissions. C2H6-fueled proton ceramic fuel cells (PCFCs) are promising electrochemical processes for cogeneration of ethylene and electric power with high performance and low emission. Herein, a tubular thermos-electrochemical model is established to investigate the characteristics of C2H6-fueled PCFC. Parametric studies are performed to examine the effects of operating voltage, inlet fuel flow rate, and inlet temperature on PCFC cogeneration performance. PCFC under open-circuit voltage (OCV) condition at 700 °C, the ethane conversion and ethylene selectivity are 15.69% and 99.47%, respectively. The ethylene production is enhanced by the electrochemical reaction. At 0.4 V and 700 °C, the conversion of ethane is increased to 32.59% and the PCFC can deliver a peak power density of 146.12 mW cm−2. Increasing the inlet temperature significantly improves the cogeneration performance of PCFC but also increases the temperature gradient in the cell. In addition, H2 depletion in the anode results in local electrochemical performance degradation. The results demonstrate the enhanced ethylene production by electrochemical processes and the operating and structural parameters can be optimized in the subsequent study to further improve ethylene production.

LaBa0.8Ca0.2Co2O5+δ cathode with superior CO2 resistance and high oxygen reduction activity for intermediate-temperature solid oxide fuel cells

The development of highly efficient cathode materials with durable performance and high resistance toward environmental impurity is crucial for realizing the practical applications of intermediate temperature - solid oxide fuel cells (SOFCs). Since CO2 as the oxidation product of hydrocarbons is unavoidable in the surrounding air atmosphere for SOFCs operating on hydrocarbon fuels, CO2 tolerance of the air electrode is a big concern. Herein, LaBa0.8Ca0.2Co2O5+δ (LBCC) double perovskite is proposed as a promising cathode with superior CO2 tolerance and favourable oxygen reduction activity. It shows a relatively low area specific resistance of 0.128 Ω cm2 at 600 °C in a CO2-free synthetic air atmosphere, tested based on a symmetrical cell configuration (LBCC | Gd0.2Ce0.8O1.9 | LBCC). In addition, under open-circuit voltage condition, it can run stably for more than 120 h in the air containing 1% CO2 (1% CO2, 21% O2 and 78% N2) at 650 °C. More attractively, the LBCC shows high reversibility in performance by removing CO2 from air. An anode-supported single SOFC with thin film doped ceria electrolyte (∼25 μm) and LBCC cathode shows a favourable peak power density of 1063 mW cm−2 at 700 °C by using ambient air as the cathode atmosphere and hydrogen as the fuel.

Impedance-based Solid Oxide Fuel Cell testing as scalable and reliable Quality Control tool for cell and batch manufacturing: first findings

Testing is a necessary step in the manufacturing process of Solid Oxide Fuel Cells (SOFC) to assess the performance of the produced cells before on-field deployment. In this work, the implementation of Electrochemical Impedance Spectroscopy (EIS) and subsequent data elaboration via Equivalent Circuit Modelling (ECM) is evaluated as a viable experimental framework for characterization and Quality Control (QC) of cells or cell batches, complemented to standard polarization-based methods. By performing a statistical analysis of the ECM parameters (representative of each physico-chemical process) the cell and batch operational parameters can be determined and compared. The validity of the proposed methodology is assessed using a wide experimental dataset of a significant number of SOFC samples (20 cells from 3 batches – two of which identical and the third with an intentional modification in the manufacturing process in order to validate the proposed methodology) tested in identical conditions. Results show that the impedance-based method provide detailed information in terms of impedance breakdown (anode gas diffusion process resulting the main criticality), as well as confirming the preliminary results obtained from the polarization approach (Batch#2 showing the lowest total performance and highest uniformity). Highly reproducible intra-batch distributions of the ECM parameters encourage the applicability of such methodology for QC purposes, even with few data collected only in Open Circuit Voltage (OCV) conditions. A relevant deviation of charge transfer and diffusion resistances in Batch#3 respect to other batches is observed (not visible from the polarization curves), which is reconducted to the modified anode functional layer, opening potential applications of the proposed methodology to assess the impact of targeted modifications of manufacturing methods on specific cell electrochemical performances.

Assessing the degradation pattern and mechanism of membranes in polymer electrolyte membrane fuel cells using open-circuit voltage hold and humidity cycle test protocols

As the degradation of polymer electrolyte membranes (PEMs) shows catastrophic failures with pinholes and cracks, studies on PEM degradation are essential to improve the reliability and lifetime of polymer electrolyte membrane fuel cell (PEMFC) membrane electrode assemblies (MEAs). However, the investigation of the degradation patterns and understanding of the degradation mechanisms of PEMs are still very limited at the PEMFC MEA level. Herein, open-circuit voltage (OCV) hold (chemical degradation) and humidity cycle test (mechanical degradation) protocols are applied to assess the durability of membrane components of PEMFC MEAs. OCV hold test is conducted at low relative humidity (30%) and OCV condition for 540 h. Humidity cycle test (5000 cycles) is carried out under repeating low (0%) and high (150%) relative humidities. We investigate degradation patterns and mechanisms of PEMs for MEAs after OCV hold and humidity cycle tests using various electrochemical and physicochemical analyses tools. The present study, by providing fundamental understanding of major degradation mechanisms, generates scientific information regarding design tools for the fabrication of highly durable PEMs. Additionally, this study, through accelerated degradation tests, can provide baseline information regarding the durability and lifetime of PEMs by statistically analyzing the deterioration pattern of MEAs.