Bilayer Electrolyte Research Articles

Targeted Solutions to Improve the Overall Performance of Hydride‐Based All‐Solid‐Batteries

AbstractAll‐solid‐state lithium batteries using solid electrolytes hold promise for enhancing energy density. However, some electrolytes with high ionic conductivity are declared unusable because they failed to show compatible with the anode, cathode or even worse, both. Herein, it simultaneously introduced doping and interfacial tuning to prepare fast ion conductor LiBH4‐MgO‐MgI2, which can achieve an ionic conductivity of 1.45 × 10−4 S cm−1 at 50 °C. This electrolyte has the usable ionic conductivity near room temperature, but faces the most extreme challenge of instability at both the lithium anode and high‐voltage cathode. Targeted solution strategies is proposed to return this electrolyte to serviceability. The physical isolation and lithium alloy is employed to solve the lithium anode issue, while the bilayer electrolyte design is applied to the high voltage cathode issue. The LiCoO2|Li3InCl6|LiBH4‐MgO‐MgI2|C|Li and LiCoO2|Li3InCl6|LiBH4‐MgO‐MgI2|LiAl, cycled upon 25 cycles at 0.1 C, achieving reversible capacities of 70 and 90 mAh g−1, respectively. With the targeted solutions for ionic conductivity, anode and cathode compatibility, it will pave the way for commercial application for hydride electrolytes.

Mechanical Milling – Induced Microstructure Changes in Argyrodite LPSCl Solid‐State Electrolyte Critically Affect Electrochemical Stability

AbstractMicrostructure of argyrodite solid‐state electrolyte (SSE) critically affects lithium metal electrodeposition/dissolution. While the stability of unmodified SSE is mediocre, once optimized state‐of‐the‐art electrochemical performance is achieved (symmetric cells, full cells with NMC811) without secondary interlayers or functionalized current collectors. Planetary mechanical milling in wet media (m‐xylene) is employed to alter commercial Li6PS5Cl (LPSCl) powder. Quantitative stereology demonstrates how milling progressively refines grain and pore size/distribution in the SSE compact, increases its density, and geometrically smoothens the SSE‐Li interface. Mechanical indentation demonstrates that these changes lead to reduced site‐to‐site variation in the compact's hardness. Milled microstructures promote uniform early‐stage electrodeposition on foil collectors and stabilize solid electrolyte interphase (SEI) reactivity. Analysis of half‐cells with bilayer electrolytes demonstrates the importance of microstructure directly contacting current collector, with interface roughness due to pore and grain size distribution being key. For the first time, short‐circuiting Li metal dendrite is directly identified, employing 1.5 mm diameter “mini” symmetrical cell and cryogenic focused ion beam (cryo‐FIB) electron microscopy. The branching sheet‐like dendrite traverses intergranularly, filling the interparticle voids and forming an SEI around it. Mesoscale modeling reveals the relationship between Li‐SSE interface morphology and the onset of electrochemical instability, based on underlying reaction current distribution.

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.

Reversible characterization of power generation and steam electrolysis for protonic ceramic cells with bi-layer electrolyte of BaZr0.8Yb0.2O3-δ and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ

This work presents the reversible operation between fuel cell and steam electrolysis modes in a protonic ceramic cell (PCC) with a bi-layer electrolyte structure composed of BaZr0.8Yb0.2O3-δ and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ. PCC using the bi-layer electrolyte demonstrated a slightly less leakage current and an improved performance than other samples using only BaZr0.8Yb0.2O3-δ electrolyte. In the fuel cell mode, the cell exhibited the maximum power density of 0.61 W cm−2 at 600 °C. Meanwhile, in steam electrolysis mode at 600 °C, the cell showed a current density of 0.94 A cm−2 and a Faraday efficiency 46% when operating in thermoneutral voltage. However, when evaluated in steam electrolysis mode at 600 °C with a current density of 0.6 A cm−2 for 250 h, it was confirmed that the air electrode had deteriorated, causing a decrease in Faraday efficiency from 46% to 25% after 250 h of operation, indicating a degradation in the efficacy of leak current mitigation during extended operating conditions. After 250 h operating a distribution of relaxation times analysis revealed a characteristic peak at low frequencies that could be associated with variation in the ionic transference number of the electrolyte after long-term operation.

Improved bi-layer electrolytes of solid oxide cells: the role of a Sm0.2Ce0.8O2−δ diffusion barrier layer

This study demonstrates integration of YSZ/SDC bi-layer electrolyte in Ni–YSZ FESCs via single-step 1250 °C co-sintering, resulting in scalable cell production and enhanced performance with twice the interdiffusion conductivity of YSZ/GDC.

Bilayer electrolyte design toward high-voltage durable solid-state lithium metal batteries

To obtain higher energy density, the choice of LiCoO2 (LCO) with extraordinary theoretical volumetric energy density as the cathode has absolute advantages, and more discharge capacity can be obtained by increasing the cut-off voltage.

Halide-sulfide bilayer electrolytes for LiFePO4-based all-solid-state batteries

In pursuit of cost-effectiveness and stability of batteries, halide-sulfide bilayer electrolyte is designed for LFP-based ASSLBs, aiming to achieve favorable interfacial compatibilities with both the LFP cathode and Li-In alloy anode.

Design of cost-effective and highly efficient systems for protonic ceramic fuel cells based on techno-economic analysis

Theoretically, protonic ceramic fuel cells (PCFCs) are considered to achieve higher energy conversion efficiencies than conventional solid oxide fuel cells. However, doped barium-based perovskite oxide, a typical electrolyte material, has a significant leakage current derived from hole conduction. Therefore, it is still unclear whether the actual performance of whole PCFC systems can reach the expected high efficiency. In this study, two strategies to suppress the leakage current, namely, low-temperature operation and a bilayer electrolyte cell using a high-ion and low-hole conductor, were discussed. The effects of these approaches on production costs and system efficiency were investigated from an economic perspective for social implementation. Moreover, the following technological options were discussed to comprehensively investigate the effects of cell, manufacturing process, and system designs on the system efficiencies and system costs; (1) cell design: examining a high-performance electrode; (2) module production process design: examining the annual production rate, co-sintering of electrode and electrolyte layers, and fabrication of an electrolyte layer with vapor-phase deposition; and (3) system design: examining a methane-fueled system, a multi-stage PCFC operation, a membrane for hydrogen separation, and lower oxygen utilization. Here, we focused on a residential 5 kW alternating current (AC) class system. Consequently, system efficiency and module production cost were calculated as 57 % based on the lower heating value (LHV) in a direct current (DC) and 4,650 USD/system adopting a monolayer electrolyte cell using BaZr0.8Y0.2O3-δ (BZY20) at 600 °C, assuming hydrogen as fuel under the annual production rate of 50 k/year. However, it was suggested that the system efficiency could be improved to 63 % in case of a lower temperature operation at 550 °C and 69 % adopting a bilayer electrolyte cell at 600 °C. Furthermore, technological options resulted in a system efficiency of 71 % and a production cost of 4,480 USD/system in the case of the bilayer cell, assuming a high-performance cathode when fabricated using the co-sintering method. Finally, the electricity cost was calculated to investigate the system lifetime and fuel cost requirements to achieve the present baseload electricity cost. From an economic and performance perspectives, this study could contribute to the widespread use of PCFC devices by exploring new technological options.

Impact of Stack Temperature on Solid Oxide Electrolysis System Operation for Lunar Production of Hydrogen and Oxygen Propellants

Solid oxide electrolysis (SOEC) systems have the potential to produce hydrogen and oxygen propellant from lunar ice found in the permanently shadowed cream on the moon. Because SOEC systems electrolyze steam instead of liquid water as in more conventional alkaline and proton-exchange membrane electrolysis systems, they require lower stack voltages for thermal-neutral operation (about 1.29 V/cell vs. 1.48 V/cell for liquid-fed cells) and thus can have lower stack specific energy as defined by stack power requirements per kg of hydrogen produced. However, at a system level, power requirements in a remote lunar setting for vaporizing the steam and flowing it through the stack increase system-level power demands such that the advantages of the SOEC system are reduced due to the balance of plant loads contributing as much as 20 to 25% of the system energy at 800 deg. C. Our team at Mines collaborated with our partners at OxEon Energy to demonstrate an SOEC system with a stack operating temperature of 800 deg. C that demonstrated an overall system-level specific energy just below 50 kWh electric per kg of hydrogen. That study and a supporting model validation study provided a basis for showing the viability for high-temperature SOEC to be scaled-up for lunar production of hydrogen and oxygen propellant for propulsion. The current study builds on that previous work by exploring the impact of SOEC stack temperature on both the stack and balance of plant power requirements. This study explores the trade-offs between reduced balance of plant parasitics and increased stack mass with lower SOEC operating temperatures and explores the advantages of higher conducting mixed-ionic-electronic conducting electrolytes with electron blocking layers to increase current densities at lower temperatures.This study was performed using stack and balance of plant models that have been calibrated in the lab-scale demonstration of an SOEC system with an electrically driven steam generator, a scroll-compressor for driving the steam flow, and cathode and anode exhaust recuperators for heat recovery to the stack inlet steam flow. The system also includes H2 drying from the SOEC cathode exhaust by heat exchange with the incoming water stream. The current study looks updates the previous model by replacing the compressor with a higher pressure steam generator and an expansion valve that allows the operation of the system without the parasitic loads of a compressor. In the current study, three different electrolytes traditional yttrium-stabilized zirconia (YSZ), higher conductivity scandium-stabilized zirconia (ScSZ), and mixed ionic-electronic conducting gadolinium-doped ceria (GDC) with a YSZ blocking layer. The GDC bilayer electrolyte cells have the highest conductivity and allow for reasonable hydrogen production at operating temperatures below 700 deg. C. The results show that the lower operating temperatures enabled by the GDC bilayer electrolyte and by the ScSZ electrolytes not only reduce the system mass with smaller heat exchangers and thermal insulation, but also lower requirements for steam generation by enabling more heat recovery in the steam generator. The impact of stack operating temperatures on the feasibility of scaling up a lunar-deployed SOEC system to produce more than 1 kg/h are presented to further emphasize the feasibility of SOEC systems as part of a lunar propellant production facility.

Si-Drive European Project: Developing Crosslinked Polymer and Composite Membrane Electrolytes for Lithium-Based Batteries

Currently the main application of lithium ion batteries is in portable electronics, but new emerging applications such as electric cars require lower cost, improved cycle life, sustainability, safety and energy density.The ambition of Si-DRIVE European project is proposing next-generation batteries for electric cars built in Europe, designed to ensure recycling above 50%. Si-Drive battery will contain a Silicon anode, which has a high specific capacity, and a high voltage cathode without cobalt to reduce the cost and improve sustainability.As an alternative to conventional organic solvents, ionic liquids have been widely investigated over the years, due to their excellent properties in terms of safety and stability.The 1st generation of electrolytes for Si-Drive includes selected ionic liquids with high ionic conductivity and wide electrochemical stability. The 2nd generation of electrolytes combines the ionic liquids and the precursors of the polymer matrix in the formulation, in order to obtain crosslinked self-standing flexible films. The addition of ceramic super lithium ion conductors to obtain composite polymer electrolytes is also envisaged to improve the electrochemical stability window of the electrolyte.Here we present several different polymer electrolytes and semi interpenetrating polymer networks encompassing ionic liquids and ceramic materials having ionic conductivity > 10 mS/cm at 20 °C, which can be in situ-deposited and crosslinked on top of the electrodes, and combined to form bi-layered electrolyte membranes to tune the compatibility with the electrode materials. The cycling performance with different positive and negative electrodes at ambient temperature is also demonstrated. Acknowledgements: The Si-DRIVE project has received funding from the European Union’s Horizon 2020 Research&Innovation programme, under Grant Agreement 814464. References J.-Y. Hwang, S.-T. Myung, Y.-K. Sun, Chem. Soc. Rev. 46, 3529-3614 (2017)M. Falco, C. Simari, C. Ferrara, J.R. Nair, G. Meligrana, F. Bella, I. Nicotera, P. Mustarelli, M. Winter, C. Gerbaldi, Langmuir 35, 8210-8219 (2019)M. Falco, L. Castro, J.R. Nair, F. Bella, F. Bardé, G. Meligrana, C. Gerbaldi, ACS Appl. Energy Mater. 2, 1600-1607 (2019)M. Falco et al., Electrochem. Commun. 118 106807 (2020)S. Saffirio, M. Falco, G.B. Appetecchi, F. Smeacetto, C. Gerbaldi, Journal of the European Ceramic Society, 42(3), 1023-1032 (2022).

Design and Fabrication of Protonic Ceramic Fuel Cells Based on BaZr0.8Y0.2O3−δ |BaZr0.1Ce0.7Y0.1Yb0.1O3−δ Bilayer Electrolyte

Reducing electronic leakage is important for improving the performance of protonic ceramic fuel cells (PCFCs) because it can considerably decrease power efficiency. In this work, we explore the efficacy of bilayer electrolytes using BaZr0.8Y0.2O3−δ (BZY) and BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) as the anode and cathode-side electrolytes, respectively. Theoretical calculations were used to guide the design and experimental fabrication of highly efficient cells. Computational results showed that higher efficiencies were achieved when a thin BZY layer was applied to a thicker BZCYYb layer. This configuration served as a barrier, effectively preventing electronic leakage. Subsequently, a BZY|BZCYYb cell was fabricated and tested using I-V and electrochemical impedance measurements. The results were compared with those of single-layer BZY and BZCYYb cells. The bilayer electrolyte exhibited higher open-circuit voltages, suggesting a reduction in the leakage current. Moreover, the bilayer cell exhibited the lowest ohmic resistance and highest power density. Thus, BZY|BZCYYb bilayer electrolytes can potentially improve the performance and efficiency of PCFCs.

Lowering the Temperature of Solid Oxide Electrochemical Cells Using Triple-Doped Bismuth Oxides.

Despite the great potential of solid oxide electrochemical cells (SOCs) as highly efficient energy conversion devices, the undesirable high operating temperature limits their wider applicability. Herein, a novel approach to developing high-performance low-temperature SOCs (LT-SOCs) is presented through the use of an Er, Y, and Zr triple-doped bismuth oxide (EYZB). This study demonstrates that EYZB exhibits > 147 times higher ionic conductivity of 0.44 S cm-1 at 600 °C compared to commercial Y-stabilized zirconia electrolyte with excellent stability over 1000h. By rationally incorporating EYZB in composite electrodes and bilayer electrolytes, the zirconia-based electrolyte LT-SOC achieves the unprecedentedly high performance of 3.45 and 2.02W cm-2 in the fuel cell mode and 2.08 and 0.95 A cm-2 in the electrolysis cell mode at 700 °C and 600 °C, respectively. Further, a distinctive microstructural feature of EYZB that largely extends triple phase boundary at the interface is revealed through digital twinning. This work provides insights for developing high-performance LT-SOCs.

Constructing bilayer heterogeneous organogel electrolytes of Lewis acidic/basic polymers to suppress self-discharge of supercapacitors

Flexible supercapacitors with fast charging rate, long cyclic lifetime and high power density, but often suffer from their rapid self-discharge process, which remains a big challenge for their widely commercial application. Here, we for the first time report a bilayer heterogeneous organogel electrolyte (BHOE) consisting of a layer of Lewis acidic polymer (LAP) and a layer of Lewis basic polymer (LBP), to develop high-performance flexible supercapacitors with slow self-discharge process. The existing strong coordination interaction between the charged LAP (or LBP) and its counter anions (or cations) can effectively restrict the diffusion of ions accumulated on/in the electrodes into or throughout the bilayer electrolyte, which endowed the charged BHOE-based supercapacitor with slow self-discharge time (9.7 h) from its open-circuit voltage to the half, more than ten times longer than those (0.9 h) of devices based homogeneous LAP or LBP electrolytes. Furthermore, the BHOE-based supercapacitor possessed high capacitance retention up to 95 % after thousands of folding cycles, suggesting excellent mechanical flexibility. This study provides a novel strategy to build high-performance flexible supercapacitors with slow self-discharge, which is great meaningful for their practical application in the near future.

Insights into strontium zirconate-induced interface pressures in solid oxide electrolysis cells

Modeling the oxygen partial pressure at the interfaces of solid oxide electrolysis cells is essential to understand their degradation. Here we present a bilayer electrolyte equivalent circuit model that does not assume continuity of the oxygen chemical potential at the electrolyte interface, in line with experimental results. We use the model to assess the assumption that strontium zirconate growth is responsible for oxygen electrode interface pressure increases and delamination. We find that 5% Y-doped strontium zirconate does not drive fracture for accumulations up to 250 nm except at 800°C and 1.6V. With a low electronic conductivity, 5% La-doped strontium zirconate shows a region of stability where increased thickness actually stabilizes the interface pressure. We also highlight the importance of modeling interface stability with the proper electronic conductivity. Finally, we present interface stability requirements and contextualize the strontium zirconate composition results in terms of interface stabilization strategies.

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

Bilayer Cell Model and System Design of Highly Efficient Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) are promising devices for highly efficient next-generation fuel cell systems. PCFCs provide several benefits. Water formation at the cathode can improve fuel utilization. Also, lowering operation temperature using proton-conducting solid electrolyte membranes will enable a long lifetime and low system costs. On the other hand, ionic and electronic transport properties, i.e., proton, oxide ion, hole, and electron conductions, in PCFCs induce leakage current in electrolyte membranes and decrease energy conversion efficiency. Therefore, controlling the transport properties and designing cell structures to prevent them are important issues for developing highly efficient PCFCs. In this study, a comprehensive design approach was conducted from a bilayer cell to a PCFC system.It has been reported that bilayer electrolytes can improve the interface between cathode and electrolyte and also prevent nickel diffusion (1). Additionally, it has been reported that bilayer electrolytes can suppress leakage current by using a hole blocking layer (2, 3). Therefore, the use of bilayer electrolytes can help improve the efficiency and performance of PCFCs. In this study, a bilayer PCFC consisting of BaZr0.8Y0.2O3−δ (BZY) and BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) was modeled by considering the transport properties of each electrolyte. The main objective of the modeling was to determine the best cell design and operating conditions that maximize PCFC efficiency. Calculations were done by solving the set of integral equations described by Choudhury and Patterson (4) but extended for bilayer electrolytes (3) to obtain the cell potential, and the total and proton current densities.It was found that higher efficiencies were obtained when using a thin layer of BZY with a thicker layer of BZCYYb. The calculations suggest that the thin BZY layer acts as an electron-blocking layer. For example, leakage currents of less than 5% can be achieved by using a BZY(1 µm)|BZCYYb (19 µm). It was also found that the PCFC efficiency increased with decreasing temperature. Thus, higher efficiencies were obtained at 500°C than at 600°C.In addition, the energy conversion efficiency of a 5kW(DC)-class PCFC system was evaluated. In this study, the fuel in an anode was assumed to be hydrogen obtained by steam reforming of methane. Gas compositions in the streams of the PCFC system were calculated based on thermodynamic equilibrium at atmospheric pressure. The operating temperature of PCFC module was set as 500°C-600°C, and the external current density was assumed to be 300 mA/cm2. Here, the leakage current ratio was defined as a percentage of the leakage current to the total ion current density. The system efficiency was defined as an extracted power of the PCFC to the combustion heat of methane (25°C, LHV).The results are described as a standard case of 600°C as follows. A system efficiency of 69.5％ (LHV, DC) was attainable, assuming the cell voltage of 0.85 V, leakage current ratio of 1%, and fuel utilization of 94.2％. In this case, the steam-to-carbon ratio (S/C) was 2.5. In addition, a system efficiency of over 70％ (LHV, DC) was obtained under the cell voltage of 0.9 V, leakage current ratio of less than 5%, and fuel utilization of over 90％. Based on the above results, a cell design with bilayer electrolyte was discussed considering electrode/electrolyte materials and physical properties (e.g., transport number and conductivity). Acknowledgments This work was supported by a project, (JPNP20003), commissioned by the New Energy and Industrial Technology Development Organization (NEDO) and JSPS KAKENHI JP21H04938 and JP21J14251.

(Digital Presentation) GDC/YSZ Bilayer Electrolyte Fabrication by In-situ Hydrothermal Growth

GDC (gadolinia-doped ceria) can be used as barrier layer between the high-performance LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ) cathode and YSZ (8% mol yttria stabilized zirconia) electrolyte, to prevent chemical incompatibility and elements diffusion. However, the GDC layer is difficult to achieve as high density as the YSZ electrolyte, especially under low sintering temperatures. While, increase sintering temperature over ~1200 ℃ could induce the formation of (Ce,Zr)O2 solid solution.In this work, we report a highly dense bilayer GDC/YSZ electrolyte prepared at low sintering temperature. Specifically, the as-sintered anode supported SOFC half-cell with already-dense YSZ electrolyte was immersed in solution of Gd(NO3)3·6H2O and Ce(NO3)3·6H2O, followed by a hydrothermal treatment at 180 ℃ (accounts for steam pressure of ~1 MPa) for 36 h. This yielded a dense GDC layer growth on YSZ electrolyte with thickness of ~200 nm. Then, the cells were sintered at 1100, 1150 and 1200 ℃, respectively. Afterwards, the hydrothermal treatment was repeated once, to grow an additional GDC layer. This post-grown GDC was then co-sintered with the screen printed LSCF cathode at 1075 ℃.Results show that, the GDC/YSZ bilayer electrolyte is successfully fabricated under low sintering temperature below 1200 ℃, with overall GDC layer as thick as ~540 nm and ultra-high density as the YSZ electrolyte. The single cell with 1200 ℃ sintered GDC, named as GDC-1200, shows the best output performance, i.e. maximum power density of ~0.96 W/cm2 at 780 ℃. Moreover, the cell runs stably at 720 ℃ for 300 hours, showing decent durability.Fig. 1 (a) j-V-P curves of bilayer electrolyte SOFCs with varied GDC sintering temperature; (b) operation voltage versus time for GDC-1200 cell under constant current mode; (c) SEM images and (d) EDS mapping of single cell (GDC-1200) fracture Figure 1

Durable and High-Performance Thin-Film BHYb-Coated BZCYYb Bilayer Electrolytes for Proton-Conducting Reversible Solid Oxide Cells.

Proton-conducting reversible solid oxide cells are a promising technology for efficient conversion between electricity and chemical fuels, making them well-suited for the deployment of renewable energies and load leveling. However, state-of-the-art proton conductors are limited by an inherent trade-off between conductivity and stability. The bilayer electrolyte design bypasses this limitation by combining a highly conductive electrolyte backbone (e.g., BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb1711)) with a highly stable protection layer (e.g., BaHf0.8Yb0.2O3-δ (BHYb82)). Here, a BHYb82-BZCYYb1711 bilayer electrolyte is developed, which dramatically enhances the chemical stability while maintaining high electrochemical performance. The dense and epitaxial BHYb82 protection layer effectively protects the BZCYYb1711 from degradation in contaminating atmospheres such as high concentrations of steam and CO2. When exposed to CO2 (3% H2O), the bilayer cell degrades at a rate of 0.4 to 1.1%/1000 h, which is much lower than the unmodified cells at 5.1 to 7.0%. The optimized BHYb82 thin-film coating adds negligible resistance to the BZCYYb1711 electrolyte while providing a greatly enhanced chemical stability. Bilayer-based single cells demonstrated state-of-the-art electrochemical performance, with a high peak power density of 1.22 W cm-2 in the fuel cell mode and -1.86 A cm-2 at 1.3 V in the electrolysis mode at 600 °C, while demonstrating excellent long-term stability.

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.

Bilayer Cell Model and System Design of Highly Efficient Protonic Ceramic Fuel Cells

A highly efficient power generation system was designed by minimizing leakage current in protonic ceramic fuel cells (PCFCs) using bilayer electrolytes. The best electrolyte designs are achieved by optimizing the cell efficiency based on the transport properties of electrolyte materials assuming hydrogen as fuel. In parallel, the effect of the electrodes on the overall cell performance was also considered. Additionally, a PCFC system was modeled using the designed cells. Two PCFC systems were investigated. One based on hydrogen as a fuel, and another based on methane as fuel. It was found that a bilayer electrolyte consisting of BaZr0.8Y0.2O3−δ (BZY) with a thin layer of lanthanum tungstate (La28-xW4+xO54+3x/2v2-3x/2) is the most effective at reducing leakage current at 600°C. For this cell, a system efficiency of 69% (LHV, DC) and 65% (LHV, AC) were obtained under the cell voltage of 0.93 V, with a leakage current ratio of less than 1%, and fuel utilization of 95% when using hydrogen as fuel. On the other hand, when methane was used as fuel, the efficiency increased up to 78% (LHV, DC) and 74% (LHV, AC).