Dong Ding

Protonic ceramic electrochemical cells (PCECs) are emerging as promising technologies for efficient energy conversion and hydrogen production because they operate at intermediate temperatures with improved efficiency and durability compared with conventional solid oxide electrochemical cells. However, the long-term reliability and commercialization of PCEC stacks remain strongly limited by the performance of sealants, which are required to maintain gas tightness, electrical insulation, and mechanical integrity under harsh thermal and chemical environments. Among various sealing approaches, glass–ceramic sealants are considered the most practical and scalable due to their excellent wettability, chemical tunability, and strong interfacial adhesion. This review provides a comprehensive overview of recent advances in glass–ceramic sealants for intermediate-temperature protonic ceramic electrochemical systems. The fundamental design principles of sealant compositions are first discussed, followed by recent developments in deposition methods, sintering strategies, surface treatments, and degradation monitoring techniques. Particular attention is given to the unique challenges associated with PCEC operating conditions, including hydrothermal degradation, interfacial reactions with barium-containing electrolytes, and thermal mismatch. Finally, future opportunities involving sustainable materials, multiscale modeling, additive manufacturing, and artificial intelligence-assisted sealant optimization are highlighted.

Protonic ceramic electrochemical cells (PCECs) are promising platforms for efficient energy conversion, hydrogen production, and high-value chemical synthesis at intermediate temperatures. However, large-scale deployment of PCECs remains constrained by the poor sinterability, high fabrication cost, and long processing time associated with state-of-the-art proton-conducting ceramic (PCC) electrolytes. Here, we report a time-efficient, ball-milling-free solid-state reaction approach using nano-sized precursor particles (n-SSR) to synthesize Ba (Zr,Ce,Y,Yb)O _{3− δ} proton-conducting electrolytes with enhanced manufacturability and performance. Compared with the conventional solid-state reaction route using micro-sized precursors ( μ -SSR), the n-SSR process largely shortens powder fabrication time by eliminating ball-milling process while producing fine electrolyte particles (200–600 nm) with superior sintering activity. As a result, PCECs fabricated with n-SSR electrolytes exhibit lower densification temperature and markedly improved electrochemical performance, delivering a 32% higher peak power density in fuel cell mode and a 40% higher electrolysis current density at 600 °C, primarily due to reduced ohmic resistance. Long-term stability exceeding 500 h without measurable degradation is demonstrated. Importantly, a techno-economic analysis reveals that the n-SSR process reduces total electrolyte fabrication costs by 25%–29% by minimizing comminution, calcination time, and processing complexity. Large-area (5 cm × 5 cm) single-cell fabrication further validates the scalability of this approach. These results establish n-SSR as a practical and generalizable manufacturing strategy for high-performance PCCs, addressing a key bottleneck for the large-scale deployment of protonic ceramic energy technologies.

High‐temperature electrochemical oxide devices are promising for many applications. These devices are known to be prone to degradation, yet the mechanisms remain poorly understood. In this perspective, we summarize the techniques most used to study degradation in metal oxide electrochemical devices, examining the advantages, challenges, and limitations of each. Although charge transfer processes, structural evolution, and compositional variation underlying degradation are widely studied, surface chemistry is often neglected. Surface chemical processes evolve with temperature, gas composition, and electrochemical bias with possible intermediary degradation steps that go unseen in ex situ analyses. Direct observation is necessary to understand these pathways. Operando diffuse reflectance infrared fourier transform (DRIFT) spectroscopy is well‐suited for this task. DRIFT spectroscopy offers high surface sensitivity, chemical specificity, and compatibility with elevated temperatures and reactive gas compositions. We discuss recent advances of operando DRIFT spectroscopy for metal oxide electrochemical systems, including the development of a novel high‐temperature spectro‐electrochemical chamber and emerging disposable reactors designed for poisoning studies. Finally, we outline strategies for coupling DRIFT spectroscopy with complementary analytical techniques. By enabling chemically resolved operando insights, DRIFT spectroscopy can advance the mechanistic understanding of degradation and inform smart design of durable metal oxide electrochemical devices.

High‐temperature electrochemical oxide devices are promising for many applications. These devices are known to be prone to degradation, yet the mechanisms remain poorly understood. In this perspective, we summarize the techniques most used to study degradation in metal oxide electrochemical devices, examining the advantages, challenges, and limitations of each. Although charge transfer processes, structural evolution, and compositional variation underlying degradation are widely studied, surface chemistry is often neglected. Surface chemical processes evolve with temperature, gas composition, and electrochemical bias with possible intermediary degradation steps that go unseen in ex situ analyses. Direct observation is necessary to understand these pathways. Operando diffuse reflectance infrared fourier transform (DRIFT) spectroscopy is well‐suited for this task. DRIFT spectroscopy offers high surface sensitivity, chemical specificity, and compatibility with elevated temperatures and reactive gas compositions. We discuss recent advances of operando DRIFT spectroscopy for metal oxide electrochemical systems, including the development of a novel high‐temperature spectro‐electrochemical chamber and emerging disposable reactors designed for poisoning studies. Finally, we outline strategies for coupling DRIFT spectroscopy with complementary analytical techniques. By enabling chemically resolved operando insights, DRIFT spectroscopy can advance the mechanistic understanding of degradation and inform smart design of durable metal oxide electrochemical devices.

Protonic solid oxide electrolysis cells (P-SOECs) have emerged as a promising technology for efficient hydrogen production, primarily due to their low activation energy for proton conduction, which enables high water-splitting performance at intermediate temperatures. Central to the functionality and efficiency of P-SOECs are proton-conducting ceramic electrolytes, which play a decisive role in determining overall cell performance. Significant research efforts have been devoted to the development and optimization of high-performance protonic ceramics for use as electrolyte materials. Among the leading candidates are perovskite-based compounds such as Ba(Ce,Zr)O₃, doped with elements like Yttrium or Ytterbium. These materials have shown promise in balancing ionic transport, chemical resilience, and compatibility with high-temperature fabrication techniques. Nevertheless, concerns remain regarding the long-term stability of these materials, particularly following repeated thermal treatments during cell fabrication. High-temperature sintering, while essential for achieving desired densification and microstructural characteristics, can introduce challenges such as oversintering, nickel diffusion, and phase instability. In this study, we investigate how processing parameters influence the structural integrity of electrolyte materials and the electrochemical performance of P-SOECs, aiming to provide insights into optimizing manufacturing strategies for enhanced cell durability and efficiency.

Protonic ceramic cells (PCCs) are a promising technology for power generation, energy storage, and value-added chemical synthesis at intermediate temperatures (300–600 °C). While recent advances in materials development have significantly improved device performance, mechanistic understanding of the underlying proton-related processes remains very limited. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), a rapid and cost-effective technique for probing vibrational fingerprints, has proven to be a powerful surface-sensitive tool for examining structural and functional characteristics. In this work, we explore a high-temperature operando DRIFTS approach developed at Idaho National Laboratory (INL) to investigate hydration behavior and proton-exchange kinetics in protonic electrolytes. Preliminary kinetic analysis highlights the capability of DRIFTS to gain direct insight into hydration and proton-related processes under realistic conditions. These insights advance our understanding of proton exchange phenomena and provide guidance for the rational design of next-generation PCC materials.

Protonic solid oxide electrolysis cells (P-SOECs) have emerged as a promising technology for efficient hydrogen production, primarily due to their low activation energy for proton conduction, which enables high water-splitting performance at intermediate temperatures. Central to the functionality and efficiency of P-SOECs are proton-conducting ceramic electrolytes, which play a decisive role in determining overall cell performance. Significant research efforts have been devoted to the development and optimization of high-performance protonic ceramics for use as electrolyte materials. Among the leading candidates are perovskite-based compounds such as Ba(Ce,Zr)O₃, doped with elements like Yttrium or Ytterbium. These materials have shown promise in balancing ionic transport, chemical resilience, and compatibility with high-temperature fabrication techniques. Nevertheless, concerns remain regarding the long-term stability of these materials, particularly following repeated thermal treatments during cell fabrication. High-temperature sintering, while essential for achieving desired densification and microstructural characteristics, can introduce challenges such as oversintering, nickel diffusion, and phase instability. In this study, we investigate how processing parameters influence the structural integrity of electrolyte materials and the electrochemical performance of P-SOECs, aiming to provide insights into optimizing manufacturing strategies for enhanced cell durability and efficiency.

Intermediate-temperature solid oxide electrochemical cells (IT-SOECs, operating at 400–600°C) offer a practical compromise by enabling the use of more cost-effective catalysts and materials for cell components while mitigating rapid degradation to optimize reaction kinetics. However, these cells impose stringent demands on electrode and cell materials. In this temperature regime, heterogeneous functional materials—particularly nano-engineered composites—hold significant promise. These materials can be effectively integrated into real devices through advanced manufacturing technologies, maintaining both high catalytic activity and durability.

Electrochemical utilization of CO₂ into carbon monoxide (CO) via high-temperature CO₂ electrolysis based on solid oxide electrolysis cells (SOECs) can provide oxygen source for in-situ oxidative coupling of methane (OCM) into value added chemicals such as ethylene. However, this technology still faces significant obstacles, particularly in designing CO₂ electrodes that are both highly active and durable for SOECs. Here we present an innovative samarium-doped dual-phase perovskite material, Sm_xCa_1-xFe_0.8Ni_0.2O_3-δ (SmCFN, where x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0), designed as a fuel electrode for pure CO₂-SOEC, exhibiting outstanding electrochemical performance. Of all the compositions evaluated, Sm_0.4Ca_0.6Fe_0.8Ni_0.2O_3-δ (x = 0.4) showed the lowest polarization resistance of 0.23 Ω cm² at 800 °C under open-circuit voltage conditions. Utilizing Sm_0.4CFN as the fuel electrode in a single cell with an LSGM electrolyte and an LSCF air electrode resulted in a remarkable electrolysis current density of 1.54 A cm² at 1.5 V and 800 °C. The impact of samarium A-site doping on the structural and electrochemical properties of the material is systematically analyzed. The exceptional electrocatalytic performance of Sm_0.4CFN is attributed to the additional oxygen vacancies generated by the Ca₂Fe₂O₅ phase in combination with the ABO₃-type perovskite phases, creating synergistic active sites for CO₂ adsorption and reaction.

Proton-conducting solid oxide electrolysis cells (p-SOECs) represent a transformative approach to high-temperature hydrogen production, operating efficiently at temperatures below 600 °C while offering enhanced ionic conductivity and product purity. At Idaho National Laboratory (INL), recent research has focused on scaling p-SOEC technology from button-cells to single-cell and short stack configurations, with an emphasis on improving electrochemical performance and long-term performance. This presentation will detail the progressive development of large-area p-SOECs, optimized for robust performance under standard operating conditions. Scaling up p-SOECs typically introduces challenges such as reduced performance and stability, stemming from manufacturing defects (e.g., pin poles, cracks, low electrolyte density, and warping) and engineering complexities (e.g., current collection and distribution, steam supply and utilization, sealing integrity, and thermal management).We will present results from button cells up to 25 cm² and 100 cm² single-unit cells (SUCs), highlighting key manufacturing and engineering strategies implemented to these issues and enhance scalability. Additionally, we will share insights from INL’s SUC and short-stack test stands designs, including improved steam generation and delivery systems, thermal management approaches and real-time hydrogen production quantification for faradaic efficiency measurements. These developments support the scale-up of p-SOEC technology and highlights its potential for efficient hydrogen generation. This work contributes to the broader effort to establish high-temperature electrolysis as a basis of hydrogen infrastructure, bridging fundamental materials science with real-world energy applications.