Anode-Engineered Protonic Ceramic Fuel Cell with Excellent Performance and Fuel Compatibility

Directly utilizing hydrocarbon fuels, particularly methane, is advantageous yet challenging in high-performance protonic ceramic fuel cells. In this work, this technological hurdle is well addressed by selective deposition of secondary electrocatalysts within the porous Ni-cermet anode. This novel strategy sheds light on the development of multifunctional porous structures for energy and catalysis applications.

A Durable Ruddlesden-Popper Cathode for Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) have been proved as an efficient energy converter at intermediate temperatures. To accelerate the kinetics of the proton-involved oxygen reduction reaction (p-ORR), developing efficient and durable cathodes is of great importance for improving PCFCs. In this work, a new triple-layered Ruddlesden-Popper (R-P) structure oxide, Sr₃ EuFe_2.5 Co_0.5 O_10-δ (3-SEFC_0.5 ), was developed as a potential single-phase cathode for PCFCs, showing high oxygen non-stoichiometry and desirable structural thermal stability. By employing this highly active and stable single-phase cathode, the PCFC demonstrated unprecedented low polarization resistances and exceptionally great peak power densities, which were approximately 0.030 Ω cm² and 900 mW cm^-2 measured at 700 °C, respectively. These findings not only manifest the effectiveness of optimal doping in improving the structural stability and electrocatalytic activity in the multi-layered perovskite family, but also highlight the great potential of using multi-layered R-P series oxides as highly active and durable catalysts for PCFCs.

Electrokinetic Proton Transport in Triple (H+ /O2- /e- ) Conducting Oxides as a Key Descriptor for Highly Efficient Protonic Ceramic Fuel Cells

Recently, triple (H+ /O2- /e- ) conducting oxides (TCOs) have shown tremendous potential to improve the performance of various types of energy conversion and storage applications. The systematic understanding of the TCO is limited by the difficulty of properly identifying the proton movement in the TCO. Herein, the isotope exchange diffusion profile (IEDP) method is employed via time-of-flight secondary ion mass spectrometry to evaluate kinetic properties of proton in the layered perovskite-type TCOs, PrBa0.5 Sr0.5 Co1.5 Fe0.5 O5+ δ (PBSCF).Within the strategy, the PBSCF shows two orders of magnitude higher proton tracer diffusion coefficient (D* H , 1.04 × 10-6  cm2 s-1 at 550 °C) than its oxygen tracer diffusion coefficient at even higher temperature range (D* O, 1.9 × 10-8  cm2 s-1 at 590 °C). Also, the surface exchange coefficient of a proton (k*H ) is successfully obtained in the value of 2.60 × 10-7  cm s-1 at 550 °C. In this research, an innovative way is provided to quantify the proton kinetic properties (D* H and k*H ) of TCOs being a crucial indicator for characterizing the electrochemical behavior of proton and the mechanism of electrode reactions.

Building Ruddlesden-Popper and Single Perovskite Nanocomposites: A New Strategy to Develop High-Performance Cathode for Protonic Ceramic Fuel Cells

Here a new strategy is unveiled to develop superior cathodes for protonic ceramic fuel cells (PCFCs) by the formation of Ruddlesden-Popper (RP)-single perovskite (SP) nanocomposites. Materials with the nominal compositions of LaSr_x Co_1.5 Fe_1.5 O_{10- δ} (LSCFx, x = 2.0, 2.5, 2.6, 2.7, 2.8, and 3.0) are designed specifically. RP-SP nanocomposites (x = 2.5, 2.6, 2.7, and 2.8), SP oxide (x = 2.0), and RP oxide (x = 3.0) are obtained through a facile one-pot synthesis. A synergy is created between RP and SP in the nanocomposites, resulting in more favorable oxygen reduction activity compared to pure RP and SP oxides. More importantly, such synergy effectively enhances the proton conductivity of nanocomposites, consequently significantly improving the cathodic performance of PCFCs. Specifically, the area-specific resistance of LSCF2.7 is only 40% of LSCF2.0 on BaZr_0.1 Ce_0.7 Y_0.2 O_{3- δ} (BZCY172) electrolyte at 600 °C. Additionally, such synergy brings about a reduced thermal expansion coefficient of the nanocomposite, making it better compatible with BZCY172 electrolyte. Therefore, an anode-supported PCFC with LSCF2.7 cathode and BZCY172 electrolyte brings an attractive peak power output of 391 mW cm^-2 and excellent durability at 600 °C.

Assessing Substitution Effects on Surface Chemistry by in Situ Ambient Pressure X-ray Photoelectron Spectroscopy on Perovskite Thin Films, BaCe xZr0.9- xY0.1O2.95 ( x = 0; 0.2; 0.9)

Performance of proton-solid oxide fuel cells (H⁺-SOFC) is governed by ion transport through solid/gas interfaces. Major breakthroughs are then intrinsically linked to a detailed understanding of how parameters tailoring bulk proton conductivity affect surface chemistry in situ, at an early stage. In this work, we studied proton and oxygen transport at the interface between H⁺-SOFC electrolyte BaCe _xZr_{0.9- x}Y_0.1O_2.95 ( x = 0; 0.2; 0.9) thin films and the gas (100 mTorr of H₂O and O₂) by using synchrotron-based ambient pressure X-ray photoelectron spectroscopy at operating temperature (>400 °C). We developed highly textured BaCe _xZr_{0.9- x}Y_0.1O_2.95 epitaxial thin films, which exhibit high level of in-plane proton conductivity, that is, up to 0.08 S cm^-1 at 500 °C for x = 0.9. Upon applying 100 mTorr water partial pressure above 300 °C, major changes are observed only in the O 1s and Y 3d core level spectra, with a clear Zr/Ce ratio dependency. OH^- formation is favored by Ce content while initiated near Y. Hydration is also associated with surface secondary phase growth comprising oxygen-under-coordinated yttrium and/or yttrium hydroxide. With BaCe_0.2Zr_0.7Y_0.1O_2.95, high levels of ionic conductivities and chemical stability are obtained as a result of the optimized surface reaction kinetics, with low activation energy barrier for proton transport while restraining formation of OH^-/SO₄^2- adsorb species.

High-Performance Ammonia Protonic Ceramic Fuel Cells Using a Pd Inter-Catalyst

This study reports the performance and durability of a protonic ceramic fuel cells (PCFCs) in an ammonia fuel injection environment. The low ammonia decomposition rate in PCFCs with lower operating temperatures is improved relative to that of solid oxide fuel cells by treatment with a catalyst. By treating the anode of the PCFCs with a palladium (Pd) catalyst at 500 °C under ammonia fuel injection, the performance (peak power density of 340 mW cm^-2 at 500 °C) is approximately two-fold higher than that of the bare sample not treated with Pd. Pd catalysts are deposited through an atomic layer deposition post-treatment process on the anode surface, in which nickel oxide (NiO) and BaZr_0.2 Ce_0.6 Y_0.1 Yb_0.1 O_3-δ (BZCYYb) are mixed, and Pd can penetrate the anode surface and porous interior. Impedance analysis confirmed that Pd increased the current collection and significantly reduced the polarization resistance, particularly in the low-temperature region (≈500 °C), thereby improving the performance. Furthermore, stability tests showed that superior durability is achieved compared with that of the bare sample. Based on these results, the method presented herein is expected to represent a promising solution for securing high-performance and stable PCFCs based on ammonia injection.

Electrokinetic Insights into the Triple Ionic and Electronic Conductivity of a Novel Nanocomposite Functional Material for Protonic Ceramic Fuel Cells

Triple ionic and electronic conductivity (TIEC) in cathode materials for protonic ceramic fuel cells (PCFCs) is a desirable feature that enhances the spatial expansion of active reaction sites for electrochemical oxygen reduction reaction. The realization of optimal TIEC in single-phase materials, however, is challenging. A facile route that facilitates the optimization of TIEC in PCFC cathodes is the strategic development of multiphase cathode materials. In this study, a cubic-rhombohedral TIEC nanocomposite material with the composition Ba(CeCo)_0.4 (FeZr)_0.1 O_{3- δ} (BCCFZ) is designed via self-assembly engineering. The material consists of a mixed ionic and electronic conducting phase, BaCo_{1-( x + y + z )} Ce_x Fe_y Zr_z O_{3- δ} (M-BCCFZ), and a dominant proton-conducting phase, BaCe_{1-( x + y + z )} Co_x Zr_y Fe_z O_{3- δ} (H-BCCZF). The dominant cerium-rich H-BCCFZ phase enhances the material's oxygen vacancy concentration and the proton defects formation and transport with a low enthalpy of protonation of -30 ± 9 kJ mol^-1 . The area-specific resistance of the BCCFZ symmetrical cell is 0.089 Ω cm² at 650 °C in 2.5% H₂ O-air. The peak power density of the anode-supported single cell based on BCCFZ cathode reaches 1054 mW cm^-2 at 650 °C with good operation stability spanning over 500 h at 550 °C. These promote BCCFZ as a befitting cathode material geared toward PCFC commercialization.

High-Performance Protonic Ceramic Fuel Cells with Thin-Film Yttrium-Doped Barium Cerate-Zirconate Electrolytes on Compositionally Gradient Anodes

In this study, we used a compositionally gradient anode functional layer (AFL) consisting of Ni-BaCe(0.5)Zr(0.35)Y(0.15)O(3-δ) (BCZY) with increasing BCZY contents toward the electrolyte-anode interface for high-performance protonic ceramic fuel cells. It is identified that conventional homogeneous AFLs fail to stably accommodate a thin film of BCZY electrolyte. In contrast, a dense 2 μm thick BCZY electrolyte was successfully deposited onto the proposed gradient AFL with improved adhesion. A fuel cell containing this thin electrolyte showed a promising maximum peak power density of 635 mW cm(-2) at 600 °C, with an open-circuit voltage of over 1 V. Impedance analysis confirmed that minimizing the electrolyte thickness is essential for achieving a high power output, suggesting that the anode structure is important in stably accommodating thin electrolytes.

Operation Protocols To Improve Durability of Protonic Ceramic Fuel Cells

To develop reliable and durable protonic ceramic fuel cells (PCFCs), the impacts of the operation protocols of PCFCs on the cell durability are investigated through analyses of the main degradation mechanisms. We herein propose three appropriately designed control protocols, including cathode air depletion, shunt current, and fuel cell/electrolysis cycling, to fully circumvent the operating-induced degradation of PCFCs. For this purpose, anode-supported cells, comprised of a NiO-BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3-δ anode, BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3-δ electrolyte, and NdBa_0.5Sr_0.5Co_1.5Fe_0.5O_5+δ-Nd_0.1Ce_0.9O_2-δ composite cathode, are prepared, and their long-term performances are evaluated under a galvanostatic condition of 0.5 A·cm^-2 at 650 °C. The cell voltages of the protected cells using the operation protocols to prevent performance degradation are stably maintained under the applied current density for more than 1200 h without any noticeable degradation, whereas the performance of the unprotected cell gradually decreased with time, and the decay ratio was 14.9% over 850 h. The significant performance decay of the unprotected cell is strongly associated with the cathode degradation phenomenon, which was caused by the water vapor continuously produced during the electrochemical reactions. Hence, the performance recovery of the PCFCs with the operation protocols is achieved by incrementally decreasing the cathode potential (close to a value of zero) to minimize the effect of high P_H2O and P_O2 during the PCFC operations.

Enhanced Proton Conduction with Low Oxygen Vacancy Concentration and Favorable Hydration for Protonic Ceramic Fuel Cells Cathode

Protonic ceramic fuel cells (PCFCs), as an efficient energy storage and conversion device, have great potential to solve the serious problems of energy shortage and environmental pollution. Improving the proton conductivity of the promising cathode materials is an effective solution to promote the widespread application of PCFCs at low temperatures (450-650 °C). Herein, considering the high oxygen reduction reaction (ORR) activity of BaCoO₃-based perovskite oxide and beneficial proton uptake capacity of Zn-doping, we construct BaCo_0.4Fe_0.4Zn_0.1Y_0.1O_3-δ (BCFZnY) as the PCFCs cathode, and compare it with the classic triple-conducting cathode BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ (BCFZrY). Different from the general strategy of increasing the initial oxygen vacancy concentration of cathode materials, this work unveils that enhancing the hydration of perovskite oxide with low oxygen vacancy concentration is a more effective strategy to accelerate the proton diffusion in the electrode. Therefore, the BCFZnY cathode achieved excellent proton conductivities of 8.05 × 10^-3 and 6.38 × 10^-3 S cm^-1 as obtained by hydrogen permeation measurements and peak power densities of 982 and 320 mW cm^-2 in a BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ-based anode-supported fuel cell at 600 and 450 °C, respectively.

Self-Construction of Efficient Interfaces Ensures High-Performance Direct Ammonia Protonic Ceramic Fuel Cells

Direct ammonia protonic ceramic fuel cells (PCFCs) are highly efficient energy conversion devices since ammonia as a carbon-neutral hydrogen-rich carrier shows great potential for storage and long-distance transportation when compared with hydrogen fuel. However, traditional Ni-based anodes readily suffer from severe structural destruction and dramatic deactivation after long-time exposure to ammonia. Here a Sr2 Fe1.35 Mo0.45 Cu0.2 O6-δ (SFMC) anode catalytic layer (ACL) painted onto a Ni-BaZr0.1 Ce0.7 Y0.1 Yb0.1 O3- δ (BZCYYb) anode with enhanced catalytic activity and durability toward the direct utilization of ammonia is reported. A tubular Ni-BZCYYb anode-supported cells with the SFMC ACL show excellent peak power densities of 1.77 W cm-2 in wet H2 (3% H2 O) and 1.02 W cm-2 in NH3 at 650 °C. A relatively stable operation of the cells is obtained at 650 °C for 200 h in ammonia fuel. Such achieved improvements in the activity and durability are attributed to the self-constructed interfaces with the phases of NiCu or/and NiFe for efficient NH3 decomposition, resulting in a strong NH3 adsorption strength of the SFMC, as confirmed by NH3 thermal conversion and NH3 -temperature programmed desorption. This research offers a valuable strategy of applying an internal catalytic layer for highly active and durable ammonia PCFCs.

Facile Deficiency Engineering in a Cobalt-Free Perovskite Air Electrode to Achieve Enhanced Performance for Protonic Ceramic Fuel Cells

As a crucial component responsible for the oxygen reduction reaction (ORR), cobalt-rich perovskite-type cathode materials have been extensively investigated in protonic ceramic fuel cell (PCFC). However, their widespread application at a commercial scale is considerably hindered by the high cost and inadequate stability. In response to these weaknesses, the study presents a novel cobalt-free perovskite oxide, Ba0.95La0.05(Fe0.8Zn0.2)0.95O3-δ (BLFZ0.95), with the triple-conducting (H+|O2-|e-) property as an active and robust air electrode for PCFC. The B-site deficiency state contributes significantly to the optimization of crystal and electronic structure, as well as the increase in oxygen vacancy concentration, thus in turn favoring the catalytic capacity. As a result, the as-obtained BLFZ0.95 electrode demonstrates exceptional electrochemical performance at 700 °C, representing extremely low area-specific resistance of 0.04 Ω cm2 in humid air (3 vol.% H2O), extraordinarily high peak power density of 1114 mW cm-2, and improved resistance against CO2 poisoning. Furthermore, the outstanding long-term durability is achieved without visible deterioration in both symmetrical and single cell modes. This study presents a simple but crucial case for rational design of cobalt-free perovskite cathode materials with appreciable performance via B-site deficiency regulation.

Reverse Atom Capture on Perovskite Surface Enabling Robust and Efficient Cathode for Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) hold potential for sustainable energy conversion, yet their widespread application is hindered by the sluggish kinetics and inferior stability of cathode materials. Here, a facile and efficient reverse atom capture technique is developed to manipulate the surface chemistry of PrBa0.5Sr0.5Co1.5Fe0.5O5+ δ (PBSCF) cathode for PCFCs. This method successfully captures segregated Ba and Sr cations on the PBSCF surface using W species, creating a (Ba/Sr)(Co/Fe/W)O3- δ (BSCFW)@PBSCF heterostructure. Benefiting from enhanced kinetics of proton-involved oxygen reduction reaction and strengthened chemical stability, the single cell using the optimized 2W-PBSCF cathode demonstrates an exceptional peak power density of 1.32 W cm-2 at 650 °C and maintains durable performance for 240 h. Theoretical calculations unveil that the BSCFW perovskite delivers lower oxygen vacancy formation energy, hydration energy, and proton transfer energy compared to the PBSCF perovskite. This protocol offers new insights into advanced atom capture techniques for sustainable energy infrastructures.

Realizing Simultaneous Detrimental Reactions Suppression and Multiple Benefits Generation from Nickel Doping toward Improved Protonic Ceramic Fuel Cell Performance

Anode-supported protonic ceramic fuel cells (PCFCs) are highly promising and efficient energy conversion systems. However, several challenges need to be overcome before these systems are used more widely, including the poor sintering of recently developed proton-conducting oxides and the decreased proton conductivity due to detrimental reactions between the nickel from anode and the electrolyte occurring during high-temperature co-sintering. Herein, a Ni doping strategy to increase the electrolyte sintering, suppress the detrimental phase reactions, and generate stable Ni nanoparticles for enhanced performance is proposed. A nickel-doped perovskite oxide is developed with the nominal composition of Ba(Zr_0.1 Ce_0.7 Y_0.1 Yb_0.1 )_0.95 Ni_0.05 O_{3- δ} . Acting as a sintering aid, such a small amount of nickel effectively improves the sintering of the electrolyte. Concomitantly, reactions between nickel and the Ni-doped ceramic phase are suppressed, turning detrimental phase reactions into benefits. The nickel doping further promotes the formation of Ni nanoparticles, which enhance the electrocatalytic activity of the anode toward the hydrogen oxidation reaction and improve the charge transfer across the anode-electrolyte interface. As a result, highly efficient PCFCs are developed. The innovative anode developed in this work also shows favorable activity toward ammonia decomposition, making it highly promising for use in direct ammonia fuel cells.

Surface Self-Assembly Protonation Triggering Triple-Conductive Heterostructure with Highly Enhanced Oxygen Reduction for Protonic Ceramic Fuel Cells

Triple-conducting (H⁺ /O^2- /e^- ) cathodes are a vital constituent of practical protonic ceramic fuel cells. However, seeking new candidates has remained a grand challenge on account of the limited material system. Though triple conduction can be achieved by mechanically mixing powders uniformly consisting of oxygen ion-electron and proton conductors, the catalytic activity and durability are still restricted. By leveraging this fact, a highly efficient strategy to construct a triple-conductive region through surface self-assembly protonation based on the robust double-perovskite PrBaCo_1.92 Zr_0.08 O_5+δ , is proposed. In situ exsolution of BaZrO₃ -based nanoparticles growing from the host oxide under oxidizing atmosphere by liberating Ba/Zr cations from A/B-sites readily forms proton transfer channels. The surface reconstructing heterostructures improve the structural stability, reduce the thermal expansion, and accelerate the oxygen reduction catalytic activity of such nanocomposite cathodes. This design route significantly boosts electrochemical performance with maximum peak power densities of 1453 and 992 mW cm^-2 at 700 and 650 °C, respectively, 86% higher than the parent PrBaCo₂ O_5+δ cathode, accompanied by a much improved operational durability of 140 h at 600 °C.

Single-Atom Enables Reverse Hydrogen Spillover for High-Performance Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) offer a promising avenue for sustainable energy conversion, however, their commercial potential is hindered by sluggish proton-involved oxygen reduction reaction (P-ORR) kinetics and inadequate durability of cathode materials. Here, a novel single-atom Ru anchor on BaCe0.125Fe0.875O3-δ (BCF) perovskite, synthesized by a facile and scalable solid-state approach, as a potential cathode for PCFCs is reported. Theoretical and experimental analyses demonstrate that the single-atom Ru on BCF, characterized by a unique 4-coordinate Ru-O-Fe configuration, not only induces reverse hydrogen spillover but also acts as an active site for P-ORR. The application of the optimized 2Ru-BCF (2 wt.% Ru) cathode in a single cell delivers an exceptional peak power density of 1.78 W cm-2 at 700 °C, along with excellent operational stability over 200 h. These findings provide new insights into single-atom engineering, advancing the commercial viability of PCFCs.

Tailoring an Interface Microstructure for High-Performance Reversible Protonic Ceramic Electrochemical Cells via Soft Lithography

Micropatterning is considered a promising strategy for improving the performance of electrochemical devices. However, micropatterning on ceramic is limited by its mechanically fragile properties. This paper reports a novel imprinting-assisted transfer technique to fabricate an interlayer structure in a protonic ceramic electrochemical cell with a micropatterned electrolyte. A dense proton-conducting electrolyte, BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3-δ, is micropatterned in a chevron shape with the highest aspect ratio of patterns in electrode-supported cells to the best of our knowledge, increasing surface areas of both electrode sides more than 40%. The distribution of relaxation time analysis reveals that the chevron-patterned electrolyte layer significantly increases the electrode contact areas and active electrochemical reaction sites at the vicinity of the interfaces, contributing to enhanced performances of both the fuel cell and electrolysis operations. The patterned cell demonstrates improved fuel cell performance (>45%) and enhances electrolysis cell performance (30%) at 500 °C. This novel micropatterning technique is promising for the facile production of layered electrochemical cells, further opening a new route for the performance enhancement of ceramic-based electrochemical cells.