Area Specific Resistance Values Research Articles

Effects of Pr substitution in Y1-xPrxBaCo3ZnO7+δ (0 ≤ x ≤ 0.5) cathodes for intermediate temperature solid oxide fuel cells

In this investigation, we successfully synthesized a series of Swedenborgite-type Y1-xPrxBaCo3ZnO7+δ (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5, abbreviated as YPxBCZ) oxides by a solid-state reaction method. The results show that YPxBCZ (x = 0.0, 0.1, 0.2, and 0.3) are single-phase structures, but YP0.4BCZ and YP0.5BCZ show interesting self-assembled composite phases. After long-term phase stability testing, YP0.3BCZ showed the best thermal stability. All samples show good chemical and thermal compatibility with La0.9Sr0.1Ga0.8Mg0.2O3-δ electrolyte. The thermal expansion coefficients in the temperature range from 30 °C to 1000 °C are equal to 9.8-13.1 × 10−6 K−1, close to that of the LSGM electrolyte. It is also found that Pr doping improves high temperature conductivity of YPxBCZ. The conductivity of YP0.3BCZ, YP0.4BCZ, and YP0.5BCZ reach 15.1, 18.5, and 22.5 S cm−1 at 800 °C. In addition, the area specific resistance (ASR) value decreases as the Pr content increases (0.038, 0.033, and 0.027 Ω cm2 at 800 °C for YP0.3BCZ, YP0.4BCZ, and YP0.5BCZ), improving the catalytic activity of the material. Another interesting finding was that the ASR of samples subjected to high temperature thermal decomposition was not adversely affected by the presence of decomposition products. The maximum power densities of YP0.3BCZ, YP0.4BCZ, and YP0.5BCZ in the single cells at 800 °C were 845, 930, and 1044 mW cm2, respectively. These results indicate that YP0.3BCZ, YP0.4BCZ, and YP0.5BCZ are promising cathode materials for intermediate-temperature solid oxide fuel cell.

An efficient electrode for reversible oxygen reduction/evolution and ethylene electro-production on protonic ceramic electrochemical cells

Protonic ceramic electrochemical cells (PCECs) have demonstrated great promise for applications in the generation of electricity, and the synthesis of chemicals (for example, ethylene). However, enhancing the electrochemical reactions kinetics and stability of PCECs electrodes is one grand challenge. Here, we present a novel electrode material via a co-doping of cesium (Cs) and niobium (Nb) on PrBaCo2O6−δ with the composition of PrBa0.9Cs0.1Co1.9Nb0.1O6−δ (PBCCN), which naturally decomposes into dual phases of a double-perovskite PBCCN (DP-PBCCN, ∼92.3 wt%) and a single-perovskite Ba0.9Cs0.1Co0.95Nb0.05O3−δ (SP-BCCN, ∼7.7 wt%) under typical powder processing conditions. PBCCN exhibits a low area-specific resistance (ASR) value of 0.107 Ω cm2, an outstanding performance of 2.04 W cm−2 in fuel cell (FC) mode, a current density of −2.84 A cm−2 at 1.3 V in electrolysis cell (EC) mode, and promising reversible operational durability of 53 cycles in ∼212 h at +/− 0.5 A cm−2 and 650 °C. Cs doping generates more oxygen vacancies and accelerates the oxygen exchange kinetics, while Nb doping effectively enhances the stability, as illustrated by the analyses of X-ray photoelectron spectroscopy, and electrical conductivity relaxations. When applied as the positrode for electrochemical non-oxidative dehydrogenation of ethane (C2H6) to ethylene (C2H4) on PCECs, it displays an encouraging C2H6 conversion of 12.75% and a C2H4 selectivity of 98.4% at 1.2 V.

Ameliorating Ion-Transport Resistances in Membrane Capacitive Deionization Using Patterned Ion-Exchange Membranes and Ionomer Infiltrated Electrodes

Currently, 2 billion people live in water scarce regions and 4 billion people experience water scarcity for at least 1 month per year [1]. Besides implications to the broad masses, the U.S. Marine Corps also face enormous challenges of generating potable water during squad level field missions. Reverse osmosis is the most reliable and economical process for desalinating water, but it requires piping that can tolerate large pressures and is not conducive for portable missions. Membrane capacitive deionization (MCDI) is a modular and electrified water desalination platform that does not generate significant acoustic, thermal, or electromagnetic signatures nor does it require high pressure piping. Flow-by MCDI, which is commercialized, uses electrical energy to remove ions from water. The system architecture feature two porous electrodes covered by ion-exchange membranes – the latter material is used to prevent co-ion adsorption and greater Coulombic efficiency than the variant that does not utilize ion-exchange membranes.Our previous research improved the energy efficiency of MCDI by using IEMs with lower area-specific resistance (ASR) values and porous ionic conductors in the spacer channel that augmented solution conductivity and curtailed ohmic losses. Reducing these resistances enabled the MCDI to operate at 700 mV lower cell voltage at 2 mA cm-2 current density. This is important for shrinking the size of the MCDI unit and lowering the overall capital costs.This talk presents our recent work examining ionic charge transport resistance at patterned and non-patterned ion-exchange membrane interfaces in MCDI. Membrane surface patterning increased the interfacial area between the membrane and aqueous stream promoting greater salt removal fluxes. Soft-lithography methods were used to micropattern poly(phenylene alkylene) cation exchange membranes and anion exchange membranes with systematically varied topographies (e.g., cylindrical well and line structures that vary from 9 to 20 mm). We can reduce the MCDI cell voltage by 1 V when utilizing micropatterned ion-exchange membranes and ionomer infiltrated electrodes (operating at 2 mA cm-2 with a 2000 ppm NaCl feed). This translated to a 2.4x greater energy normalized adsorbed salt (ENAS) value - a metric used to assess the energy consumption for MCDI. Our future work examines electrode materials deposited at pattern membrane interfaces to reduce interfacial transport resistances from the membrane to the electrode. This strategy has been shown to be effective in reducing charge-transfer resistances in both proton exchange membrane (PEM) and AEM fuel cells and reducing the water dissociation kinetics resistance in bipolar membranes [2-5]. References Somini Sengupta, Weiyi Cai, A Quarter of Humanity Faces Looming Water Crises, in The New York Times. 2019: United States of America.Kole, S., et al., Bipolar membrane polarization behavior with systematically varied interfacial areas in the junction region. Journal of Materials Chemistry A, 2021. 9(4): p. 2223-2238.Breitwieser, M., et al., Tailoring the Membrane-Electrode Interface in PEM Fuel Cells: A Review and Perspective on Novel Engineering Approaches. Advanced Energy Materials, 2018. 8(4).Hee-Tak Kim, T.V.R., Ho-Jin Kweon, Microstructured Membrane Electrode Assembly for direct methanol fuel cell. Journal of The Electrochemical Society, 2007. 154(10).Tomizawa, M., et al., Heterogeneous pore-scale model analysis of micro-patterned PEMFC cathodes. Journal of Power Sources, 2023. 556. Figure 1

Physicochemical Properties of (La,Sr)CoO3 Thick Films on Fe-25Cr Steel under Exposure to SOFC Cathode Operating Conditions.

La0.6Sr0.4CoO3 (LSC) coatings with a thickness of 50-100 µm were deposited on Fe-25Cr ferritic stainless steel (DIN 50049) via screen printing. The required suspension had been prepared using fine LSC powders synthesised using EDTA gel processes. In its bulk form, the LSC consisted entirely of the rhombohedral phase with space group R-3c, and it exhibited high electrical conductivity (~144 S·cm-1). LSC-coated steel was oxidised in air at 1073 K, i.e., under conditions corresponding to SOFC cathode operation, for times of up to 144 h. The in situ electrical resistance of the steel/La0.6Sr0.4CoO3 layered system during oxidation was measured. The products formed on the samples after the oxidation reaction resulting from exposure to the corrosive medium were investigated using XRD, SEM-EDS, and TEM-SAD. The microstructural, nanostructural, phase, and chemical analysis of films was performed with a focus on the film/substrate interface. It was determined that the LSC coating interacts with the oxidised steel in the applied conditions, and a multi-layer interfacial zone is formed. Detailed TEM-SAD observations indicated the formation of a main layer consisting of SrCrO4, which was the reaction product of (La,Sr)CoO3, and the Cr2O3 scale formed on the metal surface. The formation of the SrCrO4 phase resulted in improved electrical conductivity of the investigated metal/ceramics layered composite material, as demonstrated by the low area-specific resistance values of 5 mΩ·cm2, thus making it potentially useful as a SOFC interconnect material operating at the tested temperature. In addition, the evaporation rate of chromium measured for the uncoated steel and the steel/La0.6Sr0.4CoO3 layered system likewise indicates that the coating is capable of acting as an effective barrier against the formation of volatile compounds of chromium.

Unveiling niobium pentoxide and cerium oxide-dispersed ferritic stainless steel for solid oxide fuel cells interconnects

Herein, the effect of niobium pentoxide (Nb2O5) and nano-sized cerium oxide (CeO2) on oxidation behavior and area specific resistance (ASR) of the ferritic stainless steel has been investigated for the development of robust metallic interconnects. An oxide-dispersed ferritic stainless steel alloy is fabricated using the powder metallurgy (PM) process. The morphologies of the alloy before and after oxidation are observed through Scanning Electron Microscope (SEM), Scanning Transmission Electron Microscopy (STEM) and Secondary Ion Mass Spectrometry (SIMS) analyses. Addition of Nb2O5 in the alloy formed a C14 Laves phase of (Fe, Cr)2(Nb, Si). The Laves phase and CeO2 controlled the oxidation behavior of the ferritic stainless steels, consequently reducing the oxide scale thickness and improving the ASR. An alloy with 1 wt% Nb2O5 and 3 wt% CeO2 showed an ASR value of 27.1 mΩ cm2 at 800 °C for 1000 h, which is similar to the ASR value of the commercial Fe–Cr alloy. The results of this study indicate that Nb2O5 and CeO2-dispersed ferritic stainless steel using the PM process can be more advantageous than the conventional process for manufacturing metallic interconnects with complex shapes and reducing production costs.

Current-Voltage (i-V) characteristics of electrolyte-supported (NiO-YSZ/NiO-SDC/ScSZ/LSCF-GDC/LSCF) solid oxide electrolysis cell during CO2/H2O co-electrolysis

Solid oxide electrolysis cells (SOECs) stabilize CO2 emissions by converting CO2/H2O into synfuel. Current-Voltage (i-V) characteristics of an electrolyte-supported button cell (NiO-YSZ/NiO-SDC/ScSZ/LSCF-GDC/LSCF) were measured as a function of temperature, water vapor concentration, and CO2 gas concentrations. The cell microstructure was characterized by the Field Emission Scanning Electron Microscope (FE-SEM). FE-SEM micrographs depict that the electrolyte layer is relatively dense, and porous fuel and air electrode layers are well adhered to the electrolyte. The i-V curves were obtained at a scan rate of 0.02 Vs−1 from 0.3 to 1.5 V. Electrolysis current density increases as the temperature increases. SOEC performance increases, but SOFC performance decreases with increased water vapor concentration. Electrolysis current densities decrease as the CO2 concentration increases. The i-V characteristics show only ohmic polarization under fuel-lean and fuel-rich conditions. At optimal conditions, current density values at 800 °C/1.5 V are -174, -187, and -195 mA cm−2 for 5 %H2O, 30 %CO2, and 30 %CO2/5 %H2O co-electrolysis. At 800 °C, open-circuit voltage (OCV) values for H2O, CO2, and co-electrolysis are 0.906, 0.891, and 0.885 V, respectively. The electrolysis area-specific resistances (ASRs) give information on the reduction of CO2 or H2O, forming CO or H2, respectively. At optimal conditions, ASR values are 3.43, 3.29, and 3.18 Ω cm2 for H2O, CO2, and co-electrolysis, respectively. Co-electrolysis has a lower ASR value than pure H2O and CO2 electrolysis, indicating that H2O and CO2 are involved in the electrochemical processes.

A-site cation deficient SrTa0.1Fe0.9O3-δ as a bi-functional cathode for both oxygen ion- and proton-conducting solid oxide fuel cells

In order to accelerate the widespread application of solid oxide fuel cells (SOFCs), especially proton-conducing solid oxide fuel cells (PCFCs), it is crucial to develop a cathode material with high activity for the oxygen reduction reaction (ORR), excellent long-term stability and CO2 tolerance. Herein, an A-site deficient cobalt-free (Co-free) perovskite oxide Sr0.95Ta0.1Fe0.9O3-δ (S0.95TF) is prepared by introducing cation deficiencies into SrTa0.1Fe0.9O3-δ (STF), and it proves to be a highly active cathode. The increased oxygen vacancies, the decreased thermal expansion coefficient (TEC) value and improved CO2 tolerance, efficiently enhance electrochemical performance and durability during long-term stability testing. As a result, the area specific resistance (ASR) values of S0.95TF at 600 °C are only 0.095 and 0.42 Ω cm2 with the Sm0.2Ce0.8O1.9 (SDC) and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) electrolytes, respectively. In addition, both of the single cells with S0.95TF cathodes, based on different electrolytes, can function stably for 200 h without obvious performance decrease. These results clearly demonstrate that S0.95TF is a highly promising candidate for both oxygen ion-conducting SOFCs and PCFCs.

Synthesis and properties of Sr doped Pr2NiO4 cathode material for intermediate temperature solid oxide fuel cells

A series of cathode materials of Pr2-xSrxNiO4 (x = 0, 0.3, 0.5, 0.7, 1, 1.5) are synthesized by the EDTA-citric acid route. The results show that the Pr1.7Sr0.3NiO4, Pr1.5Sr0.5NiO4, Pr1.3Sr0.7NiO4 and PrSrNiO4 exhibit excellent structural stability and carbon dioxide resistance, and also exhibit good chemical compatibility and thermal matching with the SDC electrolyte. It is also found that the Sr doping is beneficial in improving the high temperature conductivity of Pr2-xSrxNiO4. At 800 °C, the electrical conductivity of Pr1.5Sr0.5NiO4 and Pr1.3Sr0.7NiO4 reaches 185 S cm−1 and 317 S cm−1, respectively. In addition, the area-specific resistance (ASR) value increases significantly with Sr doping, which reduces the catalytic activity of the material. Acceptable ASR values are obtained for Pr1.5Sr0.5NiO4 and Pr1.3Sr0.7NiO4, with ASR values of 0.079 Ω cm2 and 0.082 Ω cm2 at 800 °C, respectively. Additionally, the most interesting result is the ASR value obtained after high-temperature thermal decomposition of Pr2NiO4, where Pr2NiO4* (decomposed) has the lowest ASR value of only 0.027 Ω cm2 at 800 °C, showing the best catalytic activity. The maximum power densities of Pr2-xSrxNiO4 (x = 0.5 and 0.7) and Pr2NiO4* are found to be 515, 430, and 548 mW cm−2 at 800 °C, respectively. These results show that when the Sr doping amount is less than 1.5, the stability of the Pr2-xSrxNiO4 cathode material can be effectively improved, but its catalytic performance is partially sacrificed.

Optimizing Bilayer Electrolyte Thickness Ratios for High-Performing Low-Temperature Solid Oxide Fuel Cells

Abstract Bilayer electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs) offer the potential for higher power density by lowering the ohmic area specific resistance (ASR) and increasing the open circuit voltage (OCV) of mixed ionic/electronic conducting (MIEC) type electrolyte (e.g., GDC). However, optimizing the bilayer electrolyte thickness ratio is essential to achieve high power densities at low-temperatures (650-500℃). Herein we provide a systematic study of GDC/YCSB bilayer thickness ratios on anode-supported LT-SOFCs. In all cases the bilayer maximum power density (MPD) is higher than single-layer GDC based cells with reduced ohmic ASR values. Specifically, a high MPD of ~1 W/cm2 at 650℃ was achieved on a GDC(20 μm)/YCSB(12 μm) bilayer electrolyte based SOFC, which is 62% higher than single-layer GDC based SOFC (0.64 W/cm2) operating on humidified H2 as fuel. Such enhancement is due to the 9.3% improvement in OCV and 36% reduction in ohmic ASR values with the addition of the YCSB layer. The reduction in ohmic ASR of the bilayer electrolyte SOFCs is due to an increase of GDC electrical conductivity caused by the lower pO2 at the YCSB/GDC interface which must be considered in optimizing the thickness ratio of the bilayer electrolyte for achieving higher power density LT-SOFCs.

Evaluation of selected Fe–Cr steels under single- and dual-atmosphere conditions for intermediate-temperature solid oxide fuel cell interconnect applications

For Intermediate-Temperature SOFC, the lower operating temperature allows for a broader range of steel grades to be used as interconnects. This work compares the oxidation performances of six Cr2O3-forming steels and one Al2O3-forming steel, under single- and dual-atmosphere conditions.Single-atmosphere exposures in combination with Cr(VI) evaporation measurements were carried out at 600 °C. Except for AISI 430 all the Cr2O3-forming steels showed protective behaviour with similar Cr(VI) evaporation values and low area specific resistance (ASR) values. Kanthal EF101 showed the lowest level of Cr(VI) vaporisation but substantially higher ASR values.Dual-atmosphere exposures were carried out at 600 °C in Ar-5%H2–3%H2O//air-3%H2O. All Cr2O3-forming steels suffered various degrees of breakaway corrosion. Therefore, operation under dual-atmosphere conditions is likely the life-time-limiting failure mode.

Comparative Analysis of LiCo0.6Sr0.4O2 Cathode Electrochemical Performance in Oxide- and Proton-Conducting Intermediate-Temperature Solid Fuel Oxide Cells

Solid fuel oxide cells (SOFCs) are made up of three main parts: anode, electrolyte, and cathode. The main challenge in SOFCs is their high operating temperature, which can reach 1000 °C and lead to cell degradation issues. To address this, the utilization of lithium-based materials is suggested for the cathode component, facilitating intermediate-temperature SOFC operation within the temperature range of 500 to 800 °C. Previous studies have demonstrated the potential of producing high-quality lithium-based cathode ink using a triple-roll mill (TRM). By employing the fabrication parameters recommended in these studies, the lithium-based cathode (LCSO) was tested in different working environments, specifically the oxide-conducting SOFC and proton-conducting SOFC. The LCSO inks were screen-printed on SDC for oxide-conducting SOFC and BCZY for proton-conducting SOFC electrolyte before the analysis. Electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) are used to characterize the electrochemical performance and morphology of the LCSO cathode. Based on the results, the LCSO cathode is found to respond well in oxide-conducting SOFC environment with an area-specific resistance (ASR) value of 0.75 ohms-cm2 compared to proton-conducting SOFC which shows an ASR value higher by 11.45 ohms-cm2.

Electrochemical performance of Pr0.6Sr0.4Fe0.8Co0.2O3−δ as potential cathode material for IT-SOFC

Solid oxide fuel cells (SOFCs) are renowned for being effective energy sources that have potential to influence how energy is developed in future. SOFCs operate at low temperatures provides different benefits for widespread commercialization. In the present study a perovskite material Pr0.6Sr0.4Fe0.8Co0.2O3−δ (PSFCo) was investigated as cathode for SOFC in intermediate temperature range. Glycine nitrate process was used for the preparation of the samples. PSFCo exhibited cubic structure having small particle size (100–200 nm). The electrical conductivity of the PSFCo was measured as function of temperature up to 850 ℃. The sample displayed maximum electrical conductivity of 370 Scm−1 at around 550–600 ℃. The polarization behavior of PSFCo was calculated by means of AC impedance with Sm0.8Ce0.2O2 (SDC) as electrolyte. The value of area specific resistance (ASR) was calculated as 0.146 Ωcm2 at 800 ℃ and 0.248 Ωcm2 at 700 ℃.

Effects of Mn concentration on durability of Fe-Cr ferritic steels dispersed with La2O3 for solid oxide fuel cell interconnects

This study investigates the effect of Mn concentration in La2O3-dispersed ferritic steel on the oxidation behavior, area-specific resistance (ASR), and chromium volatilization for solid oxide fuel cell (SOFC) interconnects. The results show that increasing Mn concentrations lead to a gradual increase in the oxidation rate of the alloy samples. The alloy with 0.3 wt% Mn primarily forms Cr2O3 during the initial oxidation stage, whereas the alloys containing more than 1.0 wt% Mn promote the growth of (Mn,Cr)3O4, leading to an accelerated oxidation rate. The ASR value exhibits a decreasing trend initially, followed by an increasing trend, as the Mn concentration in the alloy increases from 0.3 to 2.0 wt%. The alloy with 1.0 wt% Mn shows the lowest ASR value of 12.2 mΩ cm2 after 1000 h. The alloys demonstrate a tendency to reduce chromium volatilization as the Mn concentration increases, which can be attributed to the growth of (Mn,Cr)3O4 at the topmost layer of the oxide. The study suggests that controlling the Mn concentration in the Fe-Cr alloys can help in reducing the ASR values and Cr volatilization, making the ferritic steel alloy with 1.0 wt% Mn an effective choice for SOFC interconnects.

Pathway to high performance, low temperature thin-film solid oxide cells grown on porous anodised aluminium oxide

Reversible solid oxide cells (rSOCs) present a promising solution to future energy challenges through the efficient conversion between electrical and chemical energy. To date, the benefits of rSOC technology have been off-limits to portable power and electrolysis applications due to the excessive polarisation resistance of the oxygen electrode at low temperatures, characterised by high area specific resistance (ASR) values below 500 °C. In this work we demonstrate growth of symmetric and complete rSOC structures based on state-of-the-art vertically aligned nanocomposite (VAN) films grown by pulsed laser deposition (PLD) on porous Pt-coated anodised aluminium oxide (AAO) substrates. The symmetric rSOC structures give the first demonstration of an rSOC oxygen electrode with ASR below 0.1 Ωcm2 at temperatures less than 450 °C. This is achieved through oxygen vacancy tuning by annealing, as confirmed by Time-of-Flight Elastic Recoil Detection Analysis (ToF-ERDA) and Rutherford Backscattering Spectrometry (RBS) measurements. Thus, the present work describes a promising route towards future high-performance rSOC devices for portable power applications.

Nickel-doped NdBa0.5Sr0.5Co1.5Fe0.5O5+δ oxygen electrode material for high performance reversible protonic ceramic cells

To enhance the electrocatalytic activity in the oxygen reduction and the evolution reactions of air electrode materials, we fabricate a double perovskite structured NdBa0.5Sr0.5Co1.5Fe0.5-xNixO5+δ with triple-conducting properties for reversible protonic ceramic cells (RPCCs). In particular, Ni doping into B-site (of ABO3 perovskite structure) is used to tailor the surface properties and bulk diffusion of NdBa0.5Sr0.5Co1.5Fe0.5O5+δ perovskites. Among the various amounts of dopants, doping with 5 mol% Ni significantly increases the activity of oxygen electrodes in moist air, including the conductivity of protons and oxygen-ions. The area specific resistance (ASR) values of the NdBa0.5Sr0.5Co1.5Fe0.45Ni0.05O5+δ (NBSCFN5) electrode in the BaZr0.1Ce0.7Y0.1Yb0.1O3-δ electrolyte are 0.70 Ω·cm2 at 650 ℃. The electrical conductivity of NBSCFN5 is 423–714 S·cm−1 at the RPCCs operating temperature (500–700 ℃), which is significantly higher than that of the conventional perovskite air electrode materials. Furthermore, the ASR of the NBSCFN5 symmetrical cell decreases considerably from 9.02 to 6.86 Ω·cm2 in dry air to pH2O = 0.6 atm at 550 ℃, implying its excellent proton conduction. This suggests that NBSCFN5 is a promising air electrode material for next-generation high-performance RPCCs at lower temperatures.

(Digital Presentation) (La0.7-xNdx )Sr0.3Co1-YFeyO3- δ (x = 0.35, y = 0.2) a Novel Perovskite Type Air Electrode Material for Protonic Conducting Solid Oxide Cell (H-SOC)

Proton conducting solid oxide cell (H-SOC) is a highly efficient energy conversion device converting electrical energy into hydrogen by splitting water using solid oxide proton conductor at intermediate temperature range (500-700 0C) [1]. To enhance electrochemical performances in terms of efficient hydrogen generation, robust and durable air electrode materials are required to facilitate faster water oxidation and oxygen reduction reaction, which are the key steps for both electrolyser and fuel cell at a lower temperature [2-3]. In the present study, we have developed ‘La’ and ‘Nd’ A-site co-doped strontium cobaltite and cobalt ferrite: La0.35Nd0.35Sr0.3Co0.8Fe0.2O3-δ(LNSCF) a perovskite type cathode material exhibiting higher electrical and electrochemical performances. The electrical and O2- ion conductivity of the material shows metallic nature, and the highest conductivity values are 973 S cm-1 and 0.318 S cm-1 respectively at 400 oC. The higher value of electrical and ionic conductivity is attributed to highly efficient Co2+ to Co3+ and Fe3+ to Fe4+ transition. Electrochemical impedance spectroscopy analysis of the symmetrical cell (LNSCF/Zirconium and Yttrium doped Barium Cerate (BZCY)/LNSCF) revealed the value of Area Specific Resistance (ASR) to be 0.14, 0.47 and 3.06 Ω cm2 at 800,700 and 600 oC respectively. When operated in H-SOFC mode with humidified hydrogen as fuel and Air (3%H2O) as oxidant, the LNSCF based single cell: Ni-BZCY/BZCY (385m)/ LNSCF+BZCY achieves a maximum current density of 522, 383, and 231mA/cm2 at 800, 700, and 600 oC, respectively at 0.002 V. Whereas, in H-SOEC mode a maximum current density of -1380, -862 and -517 mA/cm2 are obtained at 800, 700, and 600 oC, respectively at 2.5 V. The contribution of different ions (O2- and H2+) and electrons (e-) in the electrochemical performances are evaluated using ion-blocking cells. The figure (1) below represents the Current Density versus Voltage (i-V) characteristic attributes for both H-SOFC and H-SOEC.

Micropatterned Ion-Exchange Membranes for Membrane Capacitive Deionization

US Marine missions require technologies that produce potable water from various water sources that include both seawater and ground water. Reverse osmosis (RO) is the most wide-spread and economical process for desalinating water from seawater. However, it is only cost-competitive and practical when deployed in large, centralized production facilities and is not conducive for marine squad units. Membrane capacitive deionization (MCDI) is an alternative water desalination platform that is enticing to military missions as it does not require high pressure piping and it does not generate significant acoustic, thermal, or electromagnetic signals. MCDI removes ions from the liquid solution using electrical energy, and the commercialized variant, flow-by MCDI, feature two porous electrodes covered by ion-exchange membranes(1). During deionization, the positively biased electrode has an anion exchange membrane (AEM) in front of it while the negatively biased electrode contains a cation exchange membrane (CEM) in front of it.Our previous research improved the energy efficiency of MCDI by using ion-exchange membranes with lower area-specific resistance (ASR) values(2) and porous ionic conductors in the spacer channel that augment solution conductivity and curtail ohmic losses(3). Reducing these resistances enabled the MCDI to operate at higher current density – which is important for shrinking the size of the MCDI unit and lowering the overall capital costs.This talk highlights our recent work examining ionic charge transport resistance at the membrane-electrode interface in MCDI. We studied the impact of this resistance on MCDI performance metrics (salt removal and energy normalized adsorbed salt (ENAS)) by systematically changing the interfacial area of the ion-exchange membrane-electrode interface via patterning of the ion-exchange membrane surfaces using soft-lithography. This strategy has been shown to be effective in reducing charge-transfer resistances in both proton exchange membrane (PEM)(4) and AEM(5) fuel cells and reducing the water dissociation kinetics resistance in bipolar membranes(6). Micropatterned AEMs and CEMs based upon poly(arylene ether) and all-carbon poly(arylene) backbones(7) were fabricated with periodic line and cylinder topographies and lateral feature sizes that vary from 2 to 20 μm. The patterned membranes were coated with graphitic carbon electrodes. It is posited that smaller lateral feature sizes, which gives rise to larger interfacial area values, reduces interfacial resistance values in MCDI and larger ENAS values. Keywords: Desalination, Membrane capacitive deionization, Ion exchange membranes, Soft lithography, Energy normalized adsorbed salt, Membrane electrode assembly References S. Porada, L. Zhang and J. E. Dykstra, Desalination, 488, 114383 (2020).V. M. Palakkal, J. E. Rubio, Y. J. Lin and C. G. Arges, ACS Sustainable Chemistry & Engineering, 6, 13778 (2018).V. M. Palakkal, M. L. Jordan, D. Bhattacharya, Y. J. Lin and C. G. Arges, Journal of The Electrochemical Society, 168, 033503 (2021).Y. Jeon, D. J. Kim, J. K. Koh, Y. Ji, J. H. Kim and Y.-G. Shul, Scientific Reports, 5, 16394 (2015).S. Jang, M. Her, S. Kim, J.-H. Jang, J. E. Chae, J. Choi, M. Choi, S. M. Kim, H.-J. Kim, Y.-H. Cho, Y.-E. Sung and S. J. Yoo, ACS Applied Materials & Interfaces, 11, 34805 (2019).S. Kole, G. Venugopalan, D. Bhattacharya, L. Zhang, J. Cheng, B. Pivovar and C. G. Arges, Journal of Materials Chemistry A, 9, 2223 (2021).W.-H. Lee, Y. S. Kim and C. Bae, ACS Macro Letters, 4, 814 (2015).

Optimizing Bilayer Electrolyte Thickness Ratios for High Performing Low-Temperature Solid Oxide Fuel Cells

Over the last several years, significant developments have been made in bilayer electrolytes (e.g. GDC(Ce0.9Gd0.1O2-δ)/ESB((Er0.20Bi0.80O1.5)) suitable for low-temperature operating solid oxide fuel cells (SOFCs). Such bilayer electrolytes offer the potential for developing high performing LT-SOFCs by lowering the ohmic area specific resistance (ASR), and by improving the open circuit voltage (OCV) of mixed ionic/electronic conducting (MIEC) type electrolyte (e.g., GDC). However, optimizing the thickness ratio of the bilayer electrolyte is essential to achieve high power densities at low-temperatures (650-500 ℃). Here, we made a systematic study by varying the thickness ratios between GDC and YCSB((Bi0.75Y0.25)1.86Ce0.14O3±δ) bilayer electrolytes on an anode-supported LT-SOFCs, in all cases, the maximum power density (MPD) of the bilayer electrolyte cells is higher than pristine GDC based cells with reduced ohmic ASR values. Specifically, a high MPD of ~1 W/cm2 at 650 ℃ was achieved on a GDC(20μm) / YCSB(12μm) bilayer electrolyte based SOFC, which is 62% higher than pristine GDC based SOFC (0.64 W/cm2) operating on humidified H2 as fuel. Such enhancement is due to the 9.3% improvement in OCV (from 0.791 to 0.865 V) and a considerable 36% reduction in ohmic ASR values (from 0.094 to 0.069 Ω.cm2). Such reduction in ohmic ASR of the GDC/YCSB bilayer electrolyte SOFCs is due to the increase of GDC electrical conductivity as a result of lower pO2 at the interface of YCSB and GDC, and hence, must be considered in optimizing the thickness ratio of the bilayer electrolyte for achieving higher power density SOFCs. Figure 1

Thermal plasma synthesis of (La,Sr)CoO3-(La,Sr)2CoO4 composite cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC)

(La,Sr)CoO3 and (La,Sr)2CoO4 dual phase powders were synthesized via thermal plasma to be used as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC). This covered pure (La,Sr)CoO3 as well as the composites where the fraction of (La,Sr)2CoO4 was gradually increased reaching the mid-composition. Powders, all synthesized in the same condition, were extremely small in size, especially at mid-composition where they were close to 30 nm in size. Area specific resistance (ASR) determined from the symmetric cell imply improved cathodic performance at the mid-composition. Taking ASR = 0.15 Ω∗cm2 as benchmark, it was found that the (La,Sr)CoO3: (La,Sr)2CoO4 = 0.53:0.47 cathode may be used at temperatures close 750 °C. Measurements taken from several runs however imply that the cathode performance was not stable and ASR values increases with cycling. This was attributed to the powder form of the cathode which would be expected to coarsen rapidly due to accelerated surface diffusion.

Optimizing Bilayer Electrolyte Thickness Ratios for High Performing Low-Temperature Solid Oxide Fuel Cells

Over the last several years, significant developments have been made in bilayer electrolytes (e.g. GDC(Ce0.9Gd0.1O2-δ)/ESB((Er0.20Bi0.80O1.5)) suitable for low-temperature operating solid oxide fuel cells (SOFCs). Such bilayer electrolytes offer the potential for developing high performing LT-SOFCs by lowering the ohmic area specific resistance (ASR), and by improving the open circuit voltage (OCV) of mixed ionic/electronic conducting (MIEC) type electrolyte (e.g., GDC). However, optimizing the thickness ratio of the bilayer electrolyte is essential to achieve high power densities at low-temperatures (650-500 ℃). Here, we made a systematic study by varying the thickness ratios between GDC and YCSB((Bi0.75Y0.25)1.86Ce0.14O3±δ) bilayer electrolytes on an anode-supported LT-SOFCs, in all cases, the maximum power density (MPD) of the bilayer electrolyte cells is higher than pristine GDC based cells with reduced ohmic ASR values. Specifically, a high MPD of ~1 W/cm2 at 650 ℃ was achieved on a GDC(20μm) / YCSB(12μm) bilayer electrolyte based SOFC.