Protonic Ceramic Electrochemical Cells Research Articles

Transport properties of highly dense proton-conducting BaSn1−xInxO3−δ ceramics

Doped barium stannate belongs to the perovskite-structured complex oxides with proton transport capability. Such objects are of high interest in terms of their application in various protonic ceramic electrochemical cells. In the present work, In-doped barium stannate (BaSn1−xInxO3−δ, 0 ≤ x ≤ 0.4) materials were prepared and thoroughly characterized by structural, microstructural, and electrochemical techniques. The single-phase and high-dense ceramic materials were prepared by the conventional solid-state synthesis route over the entire doping range investigated. The chemical composition of these materials was found to be in close agreement with the nominal values, indicating no evaporation of Ba-, Sn-, or In-containing phases during sintering. The high-temperature electrochemical analysis showed that the ionic conductivity of BaSn1−xInxO3−δ gradually increases with increasing the In-content without reaching a concentration maximum, even for high dopant concentrations. The relatively high activation energy values indicate that this ionic conductivity is determined by oxygen-ionic transport, which, however, becomes predominantly protonic at reduced temperatures. The determination of bulk and grain boundary transport showed that both were improved with the In-doping. The possible reasons for these observations were discussed in detail in this work. Therefore, the obtained data are important for discovering the transport properties of stannates and their potential applications.

Highly efficient La/Ni co-doped strontium titanate catalyst for co-production of propylene and hydrogen from propane in protonic ceramic electrochemical cells

A highly efficient La/Ni co-doped strontium titanate (LSNT) perovskite catalyst is developed and integrated in a protonic ceramic electrochemical cell for co-production of propylene and high-purity hydrogen from commercial propane feedstock. Propane conversion and hydrogen production rate can be effectively enhanced under an applied current due to the electrochemical promotion effect and/or shifted reaction equilibrium induced by rapid separation of hydrogen product. Water vapor in the feed gas could significantly improve the catalyst stability by suppressing the coke formation. The propane conversion could reach up to 53% at 600 °C under a current density of 90 mA cm−2. The LSNT catalyst also shows excellent tolerance for the sulfur contaminant in commercial propane gas. The excellent performance of the LSNT catalyst is attributed to the highly active and selective Ni species at the interface with the perovskite substrate, which are formed in situ via reduction-induced exsolution under reaction conditions.

Interface Engineering to Operate Reversible Protonic Ceramic Electrochemical Cells Below 500 °C

AbstractThe low‐temperature (<500 °C) operation of reversible protonic ceramic electrochemical cells (PCECs) is desirable in achieving efficient and sustainable electricity generation, as well as green hydrogen production. However, significant interfacial resistance, which contributes to both ohmic and polarization resistance, remains a hurdle in lowering the operating temperature. In this study, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) and BaZr0.4Ce0.4Y0.1Yb0.1O3‐δ (BZCYYb) mono‐grain composite interlayers are introduced, which significantly extend the electrode/electrolyte interface and increase the concentration of vertically aligned oxygen vacancies along the heterointerface. This unique design achieves the lowest ohmic and polarization resistances among previously reported values in solid electrolyte‐based electrochemical cells. As a result, the PCEC can operate at extremely low temperature of 350 °C with an exceptional peak power density of 0.50 W cm−2 in fuel cell mode and current density of 0.25 A cm−2 at 1.3 V in electrolysis cell mode. Furthermore, it demonstrates high energy conversion efficiency and excellent stability under static and dynamic operating conditions.

Regulation of Ni/Co Ratio and Gas Transport in High‐Order Ruddlesden–Popper Perovskite Air Electrodes for Protonic Ceramic Electrochemical Cells

AbstractThe delicate design of efficient air electrodes is conducive to improving the reaction kinetics and operational durability of protonic ceramic electrochemical cells (PCECs) at intermediate‐low temperatures. Here, a series of high‐order Ruddlesden–Popper (RP) perovskite electrodes are developed via the regulation of Ni/Co ratio and porosity for efficient charge/gas transfer. As verified by structural analysis and electrochemical characterizations, the electrode with a composition of Pr4Ni1.8Co1.2O10‐δ (PNCO64) shows the most matchable thermal expansion behavior with electrolytes, and highest electrical conductivity, and best catalytic activity toward oxygen reduction/evolution reactions. The Ni/Co ratio of 6:4 can induce the formation of an optimized amount of Pr6O11 in PNCO64, which is likely the pivotal source of the improved catalytic activity. When implemented on PCECs, the PNCO64 electrodes with the addition of 5% graphite pore‐former achieve a remarkable peak power density (1.18 W cm−2) and a high current density of 2.08 A cm−2 at 1.3 V at 600 °C. Excellent durability in fuel cell mode (≈85 h) and electrolysis mode (≈92 h) is also accomplished in PCECs at 600 °C.

A Novel High‐Entropy Perovskite Electrolyte with Improved Proton Conductivity and Stability for Reversible Protonic Ceramic Electrochemical Cells (Adv. Funct. Mater. 17/2024)

A Novel High‐Entropy Perovskite Electrolyte with Improved Proton Conductivity and Stability for Reversible Protonic Ceramic Electrochemical Cells (Adv. Funct. Mater. 17/2024)

On the Role of Bimetal‐Doped BaCoO3−𝛿 Perovskites as Highly Active Oxygen Electrodes of Protonic Ceramic Electrochemical Cells (Adv. Energy Mater. 14/2024)

On the Role of Bimetal‐Doped BaCoO_3−𝛿 Perovskites as Highly Active Oxygen Electrodes of Protonic Ceramic Electrochemical Cells (Adv. Energy Mater. 14/2024)

PrBaFe2O6-δ-based composites as promising electrode materials for protonic ceramic electrochemical cells

PrBaFe2O6–δ (PBF) is considered as a promising material for mixed ionic-electronic conductors used in high-temperature applications. In the present work, PBF was used as a basis for two chemical modification approaches, including doping with cobalt, nickel and copper, as well as composite design with the addition of a BaCe0.8Sm0.2O3–δ phase. The single-phase and composite materials were successfully prepared and characterized in terms of their functional properties. The two approaches were found to synergistically affect the functional properties of PBF, allowing a trade-off between thermomechanical and transport properties to be achieved. As a result, the prepared 70 wt% PrBaFe1.9M0.1O6–δ (M = Co, Ni, Cu) + 30 wt% BaCe0.8Sm0.2O3–δ composites exhibit acceptable electrochemical activity in the intermediate-temperature range. The best electrochemical activity was found for the sample with M = Cu, whose polarization resistance at 700 °C reaches 1.7 Ω cm2. Therefore, the designed PBF-based composites can be considered as promising electrode materials for solid oxide fuel cell applications.

An active bifunctional Pd-doped double perovskite air electrode for reversible protonic ceramic electrochemical cells

Reversible protonic ceramic electrochemical cells (R-PCECs) have a good application prospect as the energy conversion and storage devices. The electrode surface kinetics (i.e., oxygen reduction reaction (ORR) and water oxidation reaction (WOR)) are major technical obstacles to developing the R-PCECs. Here, we report a phase-pure Pd-doped double perovskite with a PrBa0.8Ca0.2Co1.95Pd0.05O5+δ (PBCCPd) formula. The PBCCPd air electrode displays a polarization resistance (Rp) of 0.056 Ω cm2 in the BZCYYb-based symmetrical cell at 700 °C, and also performs a peak power density (PPD) of 2.08 W cm−2 using the fuel cell mode, and a current density of -4.42 A cm−2 at 1.3 V using the electrolysis cell mode at 700 °C. Moreover, R-PCECs with PBCCPd air electrodes show excellent stability in fuel and electrolysis cells, and cycling modes with reasonable Faradaic efficiency. It is shown that Pd doping can effectively increase the oxygen vacancy, improve the oxygen surface exchange, bulk diffusion capabilities, and electrocatalytic activity and stability in the air electrode of R-RCECs, indicated by the X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectra (EIS), electrical conductivity relaxation (ECR), and distribution of relaxation time (DRT).

Phase engineering of a donor-doped air electrode for reversible protonic ceramic electrochemical cells

Reversible protonic ceramic electrochemical cells (R-PCECs) demonstrate great feasibility for efficient energy storage and conversion. One critical challenge for the development of R-PCECs is the design of novel air electrodes with the characteristics of high catalytic activity and acceptable durability. Here, we report a donor doping of Hf into the B-site of a cobalt-based double perovskite with a nominal formula of PrBa0.8Ca0.2Co1.9Hf0.1O5+δ (PBCCHf0.1), which is naturally reconfigured to a double perovskite PrBa0.8-xCa0.2Co1.9Hf0.1-xO5+δ (PBCCHf0.1-x) backbone and nano-sized BaHfO3 (BHO) on the surface of PBCCHf0.1−x. The air electrode demonstrates enhanced catalytic activity and durability (a stable polarization resistance of 0.269 ​Ω ​cm2 for ∼100 ​h at 600 ​°C), due likely to the fast surface exchange process and bulk diffusion process. When employed as an air electrode of R-PCECs, a cell with PBCCHf0.1 air electrode demonstrates encouraging performances in modes of the fuel cell (FC) and electrolysis (EL) at 600 ​°C: a peak power density of 0.998 ​W ​cm−2 and a current density of −1.613 ​A ​cm−2 ​at 1.3 ​V (with acceptable Faradaic efficiencies). More importantly, the single-cell with PBCCHf0.1 air electrode demonstrates good cycling stability, switching back and forth from FC mode to EL mode ±0.5 ​A ​cm−2 for 200 ​h and 50 cycles.

An efficient and robust Co-free BaFeO3-based oxygen electrode for protonic ceramic electrochemical cells

Protonic ceramic electrochemical cells (PCECs) are promising devices for sustainable energy conversion and storage with high efficiency and low cost. However, the application of PCECs is limited by the scarcity of oxygen electrode materials with excellent oxygen reduction/evolution reaction (ORR/OER) activity and robust durability. In this investigation, perovskite oxide with specific non-stoichiometric ratios, namely Ba0.9Sr0.05La0.05Fe0.8Zn0.1Y0.1O3 (BSLFZY) are synthesized using a sol-gel method, and electrochemically evaluated as oxygen electrodes for PCECs. The structural and chemical stability of the synthesized material is explored and analyzed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterizations. Surface catalytic activity is assessed using X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), and oxygen temperature-programmed desorption techniques (O2-TPD). Additionally, the electronic conductivity results demonstrate the suitability of BSLFZY for application in PCECs. The electrochemical performance of the material is estimated using a homemade Ni-BZCYYb/BZCYYb cell with a BSLFZY oxygen electrode. Electrochemical impedance spectra within a specific temperature range are analyzed using the distribution of relaxation times (DRT) method. The results offer valuable insights into the underlying reasons for long-term electrochemical performance degradation in fuel cell (FC) mode. These results present the potential of BSLFZY for practical applications in PCECs, highlighting its excellent electrochemical performance and durability.

Ba-doped Pr2NiO4+δ electrodes for proton-conducting electrochemical cells. Part 3: Electrochemical applications

Layered nickelates, Ln2NiO4+δ, are promising electrode materials for many electrochemical applications, including solid oxide fuel cells and electrolysis cells. Although Ln2NiO4+δ has been extensively modified by various doping strategies to tune its functional properties, the partial substitution of Ln3+ with Ba2+ remains among the least studied routes. At the same time, such substitution is found to be favorable when Ln2NiO4+δ materials are used for protonic ceramic electrochemical cells based on Ba-containing proton-conducting electrolytes (i.e., BaCeO3, BaZrO3, Ba(Ce,Zr)O3). In this work, which is the third part of a systematic study, Pr2–xBaxNiO4+δ materials are used as electrodes for a proton ceramic fuel cell and as oxygen permeable membranes. The oxygen permeation experiments confirm that the compositions with x = 0.2 and 0.3 prevail over x = 0 and 0.1 in terms of their oxygen-ionic conductivity, while the electrochemical cell characterizations confirm the high electrochemical activity of the Pr1.8Ba0.2NiO4+δ electrode in both fuel-cell- and electrolysis-cell modes. Our research thus confirms that a Ba-doping strategy is highly promising for designing new Ln2NiO4+δ-based phases, simultaneously offering good chemical and thermal compatibility with state-of-the-art proton-conducting electrolytes and high electrochemical performance.

On the Role of Bimetal‐Doped BaCoO3−𝛿 Perovskites as Highly Active Oxygen Electrodes of Protonic Ceramic Electrochemical Cells

AbstractProtonic ceramic electrochemical cells (PCECs) hold great promise as an energy conversion and storage technology at lower temperatures (400–650 °C). However, the sluggish reaction kinetics at the oxygen electrode hinder the electrochemical activity of PCECs. Herein, a series of bifunctional oxygen electrodes based on bimetal‐doped BaCoO3‐𝛿 (BCO) are reported. Doping hampers hexagonal perovskite formation and transforms BCO into cubic perovskite, improving water uptake and hydration abilities. Density functional theory calculations highlight the effects of phase transformation on the proton transport properties of oxygen electrodes. Notably, PCECs incorporating the bimetal‐doped electrodes exhibit maximum power densities of 3.15 W cm−2 (650 °C) and 2.25 W cm−2 (600 °C) in fuel cell mode, as well as a current density of 4.21 A cm−2 at 1.3 V (650 °C) in electrolysis cell mode, setting record‐high values. The findings provide insights into the rational design of bifunctional oxygen electrodes for high‐performance PCECs.

Engineering the heterogeneous catalyst of protonic ceramic electrochemical cells for CO2/H2O co-electrolysis

Protonic ceramic electrochemical cells (PCECs) are highly promising electrochemical devices for CO2/H2O co-electrolysis reactions.

Sn-doped cobalt containing perovskite as the air electrode for highly active and durable reversible protonic ceramic electrochemical cells

Sn-doped cobalt containing perovskite as the air electrode for highly active and durable reversible protonic ceramic electrochemical cells

Phase segregation of a composite air electrode unlocks the high performance of reversible protonic ceramic electrochemical cells

One breakthrough in developing highly efficient air electrodes for reversible protonic ceramic electrochemical cells (R-PCECs) is optimizing the sluggish oxygen reduction and water oxidation reactions. Here, we present a novel...

High Performance Protonic Ceramic Electrochemical Cells Operating at

Protonic ceramic electrochemical cells (PCECs) can operate in both fuel cell and steam electrolysis modes for efficient power generation and green hydrogen production. Thanks to the low activation energy of proton conduction, PCECs are uniquely capable of operating at temperatures below 600°C. Although some intriguing demonstrations of intermediate-temperature (500-600°C) PCECs (IT-PCECs) have been made in the last decade, the operating temperature of PCECs is still too high to revolutionize ceramic electrochemical cell technology, which is ascribed to the high ohmic resistance and positive electrode polarization resistance. It has been also recognized the electrode polarization resistance dominates the total resistance at <500°C. These challenges suggest both the electrolyte and positive electrode should be redesigned to lower the PCEC operating temperature.In this work, we present two main approaches to reducing electrolyte ohmic resistance, electrolyte-positive electrode contact resistance, and electrode polarization resistance, which enables PCECs operation at <500°C. First, by using the ultrasonic spray coating system to coat the electrolyte layer on a negative electrode substrate with low Ba-deficiency, a bamboo-structured, ultrathin, and chemically homogeneous electrolyte can be fabricated. Second, a newly in-situ formed composite positive electrode was developed, which enhances the interfacial bonding between the positive electrode and electrolyte, further reducing ASRo , while improving both bulk oxygen-ion diffusion coefficient and surface oxygen exchange coefficientat <500°C.The newly developed LT-PCECs attain outstanding power densities in fuel cell mode (as high as 0.77 W cm-2 at 450°C), and exceptional current densities in electrolysis mode (over -1.28 A cm-2 at 1.4 V and 450°C). Furthermore, reducing the temperature does not sacrifice the fuel flexibility of these ceramic fuel cells. We demonstrated that the PCECs can directly utilize ammonia and methane for power generation at <500°C. Exceptional durability has been also demonstrated in both fuel cell and electrolysis modes at <500°C.These results further emphasize that through the PCEC scalable manufacturing processes and novel positive electrode materials presented here, PCECs can be employed for power generation and H2 production at <500°C, thereby transforming the architectures and removing previous operational constraints of ceramic electrochemical cells for scaled operation. PCECs can therefore be considered as one part of the growing hydrogen economy, while leveraging the existing fossil fuel infrastructure and achieving higher energy efficiency and lower CO2 emissions.

(High-Temperature Energy, Materials, & Processes Division J. B. Wagner, Jr. Young Investigator Award) Protonic Ceramic Electrochemical Cells for Power Generation, Hydrogen Production, and Chemicals Synthesis

Protonic ceramic electrochemical cells (PCECs) show great promise for power generation, renewable hydrogen production, and sustainable chemical synthesis. Our laboratory at Kansas State University has made significant progress in designing PCEC materials, fabricating PCEC devices, and characterizing PCECs for various applications. In this presentation, I will first introduce our novel PCEC materials and fabrication processes, which have enabled reduced operating temperatures, enhanced performance, and improved durability. Then, I will discuss the research and development of three primary applications of PCECs by our group: power generation in fuel cell mode, green hydrogen production in electrolysis mode, and the synthesis of high-value chemicals using abundant feedstocks.

Approaches to Reduce the Operating Temperature of Protonic Ceramic Electrochemical Cells to

Protonic ceramic electrochemical cells (PCECs) have been developed as a promising technology for efficient power generation and hydrogen production via steam electrolysis. However, the current operating temperature range of 450-600°C still limits their widespread application and adoption in ceramic electrochemical cell technology. To address this issue, lowering the operating temperature range to 250-450°C has been proposed, which would expand the range of materials for building PCEC systems and reduce their cost. In this presentation, I will discuss our group's series of approaches to redesign PCECs. These approaches include using readily fabricated single-grain thick, chemically homogeneous, and robust electrolytes, as well as newly developed positive electrode materials. Our innovations have simultaneously reduced the electrolyte ohmic resistance, electrolyte-positive electrode contact resistance, and electrode polarization resistance, while also improving durability. As a result, we have set several new records of using PCECs for both power generation and renewable hydrogen production.

Oxygen Electrode Surface Constructing for Reversible Protonic Ceramic Electrochemical Cells

Reversible protonic ceramic electrochemical cells (R-PCECs) have great potential for energy conversion and storage at low-intermediate temperatures (400-700oC), which could enable the conversion of H2O into H2 in electrolysis (EL) mode, and inversely the production of electricity in fuel cell (FC) mode. However, the sluggish kinetics of oxygen reduction/evolution reaction (ORR/OER) at reduced temperatures, as well as undesired surface segregation and structural deterioration, have impeded the development of R-PCECs devices. In this presentation, we introduce a double-perovskite type oxygen electrode that has been optimized for enhanced reaction activity and surface stability using an efficient fluorite catalyst coating. Specifically, the oxygen electrode, PrBaCo2O5+δ (PBC), has been infiltrated with an active and durable shell, Pr0.1Ce0.9O2+δ (PCO). The obtained results show that PCO-PBC possess elevated oxygen vacancy concentration which would improve the surface exchange process, facilitate ion diffusion, and provide multiple active reaction sites, while simultaneously preventing Ba segregation during operation. Therefore, the fuel-electrode-supported single cell with a PCO-PBC oxygen electrode achieves high performance and a negligible degradation in EL and FC dual modes for 25 cycles and 100 h at 650 oC with 3vol.% H2O.

Functional properties of La1–xBaxFeO3–δ as symmetrical electrodes for protonic ceramic electrochemical cells

Functional properties of La1–xBaxFeO3–δ as symmetrical electrodes for protonic ceramic electrochemical cells