Protonic Ceramic Electrochemical Cells Research Articles

Exploring the structural uniformity and integrity of protonic ceramic thin film electrolyte using wet powder spraying

Thin protonic ceramic electrolyte contributes to lower ohmic resistance and enhances electrochemical performance of protonic ceramic electrochemical cells. However, manufacturing of large-scale thin electrolyte remains a challenge. Wet powder spraying is an attractive technique to deposit <10 μm thin electrolyte when advanced atomizing techniques and optimized spraying process are integrated. Here ultrasonic atomization is integrated in the wet powder spray technique to reduce the thickness of electrolyte. Moreover, a parametric study is conducted to optimize the wet powder spray process to deposit uniform and crack-free electrolyte film. It is illustrated that tuning of solid loading rates and spray passes can affect the morphology of the as-sprayed electrolyte film, enabling the structural compactness of the sintered electrolyte layer. To maintain chemical stability of the electrolyte layer during sintering, effect of sintering temperature is further investigated to produce a physically thin, structurally dense, and chemically homogeneous electrolyte layer. The protonic ceramic electrochemical cells fabricated with optimized spraying and sintering parameters demonstrate excellent performance under both fuel cell and electrolysis modes. In addition, the cells exhibit remarkable structural integrity during redox and long-term stability tests. • A wet powder spraying technique was integrated into the manufacturing of protonic ceramic electrochemical cells. • Solid loading rates, spray passes, and sintering temperatures were explored and optimized. • PCECs with a 7-μm thick BZCYYb electrolyte were successfully fabricated and demonstrated good structural uniformity and electrochemcial performance.

Electrochemically Engineered, Highly Energy-Efficient Conversion of Ethane to Ethylene and Hydrogen below 550 °C in a Protonic Ceramic Electrochemical Cell

Ethylene is one of the largest building blocks in the petrochemical industry, mainly produced by steam cracking of ethane derived from naphtha or shale gas at high temperatures (>800 °C). Despite its technical maturity and economic competitiveness, the thermal steam cracking of ethane is highly energy-intensive. Herein, an electrochemically engineered direct conversion process of ethane to produce hydrogen and ethylene using a planar protonic ceramic membrane reactor with a bi-functional three-dimensional catalytic electrode is reported, with a single-pass ethane conversion of 40% and ethylene yield of 26.7% at 550 °C. Compared with the industrial ethane steam cracking, this method saves process energy input by 45.1% and improves process energy efficiency by 50.6%, based on comprehensive process simulation using Aspen Plus software. Further, steam electrolysis treatment under the solid oxide electrolysis cell mode can regenerate the system’s catalytic performance and significantly alleviate catalytic degradation by 74%, demonstrating high techno-economic viability.

Enhanced Electrochemical Performance of a Ba0.5Sr0.5Co0.7Fe0.2Ni0.1O3−δ–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ Composite Oxygen Electrode for Protonic Ceramic Electrochemical Cells

The performance of protonic ceramic electrochemical cells (PCECs) is largely restricted by the slow oxygen reactions on the oxygen electrode. Herein, an active composite oxygen electrode Ba0.5Sr0.5Co0.7Fe0.2Ni0.1O3−δ–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BSCFN–BZCYYb) with various mass ratios (6:4, 7:3, 8:2, and 9:1) is electrochemically investigated on fuel electrode-supported PCECs. BSCFN powder, with rich oxygen vacancies, shows a good chemical compatibility with BZCYYb electrolyte, as confirmed by the analyses of thermal gravimetric analysis and X-ray diffraction patterns. It is indicated that composite electrode with a ratio of 8:2 shows the best performance. For example, a peak power density (Pmax) of 1.14 W cm–2, an electrode polarization resistance (Rp) of 0.062 Ω cm2, and a reasonable durability test of 24 h at −0.5A cm–2 are delivered at 750 °C for the fuel cells with BSCFN–BZCYYb electrode with the ratio of 8:2. In addition, a stable operation (∼50 h) of cell with BSCFN–BZCYYb electrode (8:2 mass ratio) in dual modes of electrolysis and fuel cell (2 h for each mode) at ±0.5 A cm–2 is obtained, demonstrating a good reversibility.

Oxides with Mixed Protonic and Electronic Conductivity

Oxides with mixed protonic and p-type electronic conductivity (and typically containing also mobile oxygen vacancies) are important functional materials, e.g., for oxygen electrodes in protonic ceramic electrochemical cells or for permeation membranes. Owing to the presence of three carriers, their defect chemical behavior is complex. Deviations from ideal behavior (defect interactions) have to be taken into account, which are related to the partially covalent character of the transition metal–oxygen bonds. Compared to acceptor-doped Ba(Zr,Ce)O3− z electrolytes, perovskites with redox-active transition-metal cations typically show smaller degrees of hydration. Trends in the proton uptake of (Ba,Sr,La)(Fe,Co,Y,Zn)O3−δ perovskites are analyzed and correlated to structural features (local lattice distortions) and electronic properties (the position of oxygen states on an absolute energy scale). The proton mobility in such mixed-conducting perovskites is estimated. Specific aspects of the application of protonic and electronic mixed-conducting oxides in protonic ceramic electrochemical cells are discussed, and an overview of recent materials and device developments is given.

High Pressure Operation of Reversible Protonic Ceramic Electrochemical Cells

We present our development of proton-conducting ceramics for high-temperature water splitting (HTWS) and hydrogen production at elevated pressure. One of the challenges of intermittent renewable energy production from solar and wind is the mismatch between generation and demand. This decoupled production and consumption of energy has motivated extensive research in electrochemical energy storage. Depending on the application and timescale, a variety of reversible electrochemical cells are needed to address the energy storage needs of intermittent renewable energy sources. For long-term energy storage and electrical-to-chemical energy conversion, high-temperature solid-oxide electrolyzers are attractive. In this work we present some of the advantages and recent developments of electrolyzers based on protonic-ceramic materials. Protonic-ceramic electrolyzers (PCECs) have shown an encouraging performance trajectory in recent years. PCECs can deliver a pure-H2 product stream, simplifying downstream separations. Higher-pressure PCEC operation (~ 10 bar) has been demonstrated, but is at an early stage. In this presentation, we highlight a unique installation that permits the study of these systems in a variety of configurations under high-pressure conditions.Reversible protonic ceramic electrochemical cells (RePCEC) are attracting attention due to their potential low cost, energy flexibility and high proton conductivity at intermediate temperatures (300 – 700 ºC). Previous studies focus either on protonic ceramic fuel cells (PCFCs) for power generation or protonic ceramic electrolysis cells (PCECs) for dry hydrogen production. Electronic leakage through the protonic-ceramic electrolyte presents a concern; high Faradaic efficiency has been demonstrated, but has also seen wide variance across studies. Low electrode activity can also reduce Faradaic efficiency, especially at higher current densities and driving voltages. Additionally, although Hydrogen is well known for its excellent characteristics as a fuel, its low density represents a challenge since it must be compressed to high pressures for storage and transportation.In this context, high-pressure operation of RePCECs is presented as key technology to address the challenges described. Higher total pressure operation should lead to higher efficiencies by decreasing the electron hole concentration in the electrolyte, thereby diminishing the electron leakage problem. High pressure can also boost electrode activity, enabling higher currents at lower driving voltages. From a cost perspective, high-pressure electrolysis reduces downstream compression needs. Operating at pressure is potentially even more important for electrofuels, where green hydrogen is transformed into higher-value chemicals; these chemistries often require high temperatures and pressures to achieve meaningful production rates. Ammonia serves as an example; the second-most-produced global chemical that contributes nearly 1.5% of global annual CO2 emissions.In this work, we present our progress on high-pressure operation of RePCECs. The electrochemical performance of protonic-ceramic electrolyzer stacks is characterized at 550 ºC and pressures up to 12 bar. The figure shows assembly of a unit-cell stack; the protonic-ceramic membrane-electrode assembly (MEA) is bonded to a composite ceramic frame and assembled into a sealed cell stack with metallic interconnects, current collectors, sealing gaskets, and end plates. The stack is placed in a preloaded spring-based mechanical-compression system. This assembly is sealed within a stainless-steel vessel; the operating pressure of the reactants is balanced by the surrounding gas within the vessel, minimizing pressure differentials between the stack and its surroundings. The cross-cell pressure differential between the fuel and the air-steam electrodes brings the risk of cell fracture. Downstream electronic back-pressure regulators serve to maintain stable pressures throughout.The vessel, fuel side, and air side of the installation all have independently regulated flows at their respective inlets and a common regulated pressure at their outlets. Additional systems are in place to introduce steam, execute electrochemical characterizations, and monitor outlet flow rates. Furthermore, an in-line/in-situ mass spec and gas chromatograph provide continuous gas composition measurements.All of the integrated tools in the high-pressure installation are used to study hydrogen production in electrolysis mode, electricity production in fuel-cell mode, and chemical production using catalyst beds at the electrochemical reactor outlet. This powerful combination is very useful for optimizing the performance of electrodes and electrolytes at high pressure conditions and giving us new insight into the application of protonic-ceramic materials. Figure 1

Design and Modeling of Proton-Conducting Bilayer Electrolytes Using a Nernst-Planck-Poisson Formulation

Proton-conducting oxides have attracted much attention in recent years due to their good ion conductivity at intermediate temperatures (500-700°C), as opposed to conventional oxide ion-conducting oxides that require high temperatures (usually, >900°C). Lowering the operating temperature of reversible protonic ceramic electrochemical cells (RePCECs) is desirable as it reduces material, heating, and insulation costs, while also increasing the operating life of the cell. Nevertheless, along with the desired proton conductivity, typical proton-conducting solid electrolytes also allow the transport of other charged defects like oxygen-vacancies, electrons, and electron holes. The presence of these other defects, especially the electron holes, causes leakage current that significantly reduces the cell’s electrical efficiency. Therefore, an electrolyte capable of reducing leakage current is necessary. Unfortunately, there is usually a trade-off between high ionic conductivity and low hole conduction. For example, while lanthanum tungstate (LWO) has a low electron conductivity and is capable of suppressing hole conduction below 800°C, its proton conductivity is lower than that of commonly used perovskite materials like yttria-doped barium cerate (BCY) or yttria-doped barium zirconate (BZY). Nonetheless, previous studies showed that LWO67 can act as a leakage current-blocking layer when deposited on a BZY82 base electrolyte and the estimated leakage current was almost 200 times lower than that of a BZY82 single layer electrolyte under open-circuit conditions. This suggests that under certain operating conditions, bilayer electrolytes can achieve better performance when compared to their corresponding single-layer electrolytes. Therefore, in this study, we design proton-conducting bilayer electrolytes by investigating the incorporation and transport of charged defects using a steady-state Nernst-Planck-Poisson (NPP) model.The main goals of this work are twofold. Firstly, to find the combination of electrolytes that better suppresses leakage current. For this purpose, we calculate the defect concentration, flux, and electrostatic profiles inside common materials like BCY, BZY, BZCYYb, BZCY, LWO, and different combinations of bilayer electrolytes to better understand how the addition of a leakage current-blocking layer affects proton conduction and overall efficiency. We consider three mobile defects when solving the NPP equation, protons (OHO •), oxygen vacancies (vO ••), and electron holes that are treated as small polarons localized at oxygen sites (OO •). Afterward, the I-V curve and relevant theoretical efficiency are predicted within and A cm-2 (fuel cell and electrolyzer operation) at 500, 600 and 700°C, in order to identify the most promising one. Secondly, to design a cell by finding the optimal thickness of the better performing bilayer electrolyte that maximizes efficiency.

An Efficient Bifunctional Air Electrode for Reversible Protonic Ceramic Electrochemical Cells

AbstractOne of the main bottlenecks that limit the performance of reversible protonic ceramic electrochemical cells (R‐PCECs) is the sluggish kinetics of the oxygen reduction and evolution reactions (ORR and OER). Here, the significantly enhanced ORR and OER kinetics and stability of a conventional La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) air electrode by an efficient catalyst coating of barium cobaltite (BCO) is reported. The polarization resistance of a BCO‐coated LSCF air electrode at 600 °C is 0.16 Ω cm2, about 30% of that of the bare LSCF air electrode under the same conditions. Further, an R‐PCEC with the BCO‐coated LSCF air electrode shows exceptional performance in both fuel cell (peak power density of 1.16 W cm−2 at 600 °C) and electrolysis (current density of 1.80 A cm−2 at 600 °C at 1.3 V) modes. The performance enhancement is attributed mainly to the facilitated rate of oxygen surface exchange.

Composition Optimization of Triple Conducting PrNixCo1-XO3-δ Oxygen Electrodes for Protonic Ceramic Electrochemical Cells

Using protonic ceramic electrochemical cells (PCECs) to produce hydrogen is a promising approach to achieve the renewable energy storage, and development of critical materials is the key step to facilitate fast hydrogen production rate. Particularly, the sluggish electrode kinetic at reduced temperatures (400~600 °C) and chemical stability under realistic high steam concentration raises concern. We have recently reported a triple conducting oxide of PrNi0.5Co0.5O3-δ perovskite as an oxygen electrode in PCECs, which exhibits superior electrochemical performance in both fuel cell and electrolysis modes, and potential increased stability due to the absence of alkaline elements such as Ba and Sr in the composition. In this work, the continuous composition optimization of PrNixCo1-xO3-δ (x=0.1, 0.3, 0.5, 0.7, and 0.9) oxides is carried out to find the dependence of Ni/Co ratio on the catalytic activity towards oxygen reduction and water splitting reactions. The isotope water temperature-programmed desorption and thermogravimetric analysis is used to study the water uptake capability for understanding the proton concentration variation as function of doping level. The Fourier-transform infrared spectroscopy (FTIR) is also utilized to observe relative intensity change of the hydroxyl band on electrode surface to further explain the possible species evolution in the relevant reaction modes. This work provides a representative approach on composition optimization for oxygen electrode candidate down selection.

Performance of Pr2(Ni,Cu)O4+δ electrodes in protonic ceramic electrochemical cells with unseparated and separated gas spaces

The Ln 2 NiO 4+δ -based layered phases have attracted much attention as components for high-performance protonic ceramic fuel cells (PCFCs) and electrolysis cells (PCECs) enabling energy conversion with good efficiency and low pollution. The present paper aims at rationally engineering the Cu-doped Pr 2 NiO 4+δ materials and analysing their electrode behaviour for reversible protonic ceramic cells operating in both PCFC and PCEC modes. Complex oxides of Pr 2 Ni 1– x Cu x O 4+δ ( x = 0, 0.1, 0.2 and 0.3) were synthesised using the citrate-nitrate method. The obtained materials were characterised considering their crystalline structures, as well as thermal, thermomechanical and electrotransport properties. A special interest was focused on the quality of an electrode/electrolyte interface governing the electrochemical performance of the cells fabricated. It is shown that a copper doping of x = 0.2 has a positive impact on the thermomechanical compatibility of the Ba(Ce,Zr)O 3 -based electrolytes, providing a better adhesion to these electrolytes at low-temperature sintering and resulting in a decrease of the polarisation resistance of the air electrodes. A reversible protonic ceramic cell demonstrates a power density of ~340 mW cm –2 and a hydrogen output flux of ~3.8 ml cm −2 min −1 at 750 °C. The presented results propose modernised alkaline-earth-element-free and cobalt-free electrodes that can be successfully used in the electrochemical cells based on the-state-of-the-art proton-conducting electrolytes. • Pr 2 Ni 1– x Cu x O 4+ δ phases (where x = 0, 0.1, 0.2 and 0.3) were successfully prepared • Links between composition, defect structure and properties were elucidated • Pr 2 Ni 0.8 Cu 0.2 O 4+ δ (PNC0.2) shows the best thermomechanical characteristics • PNC0.2 exhibits also the improved electrochemical properties • PNC0.2 is a promising oxygen electrode candidate for SOFCs, SOECs or rSOCs.

An Active and Robust Air Electrode for Reversible Protonic Ceramic Electrochemical Cells

Reversible protonic ceramic electrochemical cells (R-PCECs) are a promising option for efficient and low-cost generation of electricity and hydrogen. Commercialization of R-PCECs, however, hinges o...

Exploring the impact of sintering additives on the densification and conductivity of BaCe0.3Zr0.55Y0.15O3-δ electrolyte for protonic ceramic fuel cells

Ceramic proton conducting BaCeO3-BaZrO3 materials have received great interest as potential electrolyte candidates for intermediate temperature protonic ceramic fuel cells. In the current work, the impact of sintering additives ZnO, NiO and CuO on densification, microstructure and electrochemical properties of the state-of-the-art electrolyte composition BaCe0.3Zr0.55Y0.15O3-δ (BCZY35) is appraised. Highly dense (> 95%) BCZY35 electrolyte pellets are obtained at the temperature of 1400 °C by use of the sintering additives, whereas only ~86% relative density is achieved for the pristine material at this temperature. The BCZY35 composition is shown to offer high chemical stability against a pure CO2 environment, as confirmed by thermogravimetric analysis. The electrical conductivity of BCZY35 with and without sintering additives is studied as a function of temperature in humid N2, O2 and H2 by A.C. impedance spectroscopy. In general, slightly lowered total conductivities are observed for all sintering additive specimens than the pristine BCZY35 material. The bulk conductivity is shown to be significantly impaired by the addition of sintering additives, in all cases, while specific grain boundary conductivity is either relatively unaffected, NiO, CuO, or improved, ZnO. This interesting feature is analysed further by application of a space-charge model, highlighting the additive containing compositions to offer lower Schottky barrier heights than the base BCZY35 phase and with this factor being most significant for the ZnO-additive. The activation energy for total and bulk conductivities is found to be in the range of 0.4–0.6 eV under humid conditions in the temperature range 400–600 °C, while slightly higher Ea values ~0.72–0.77 eV are observed for the grain boundary conductivity. The total conductivity of BCZY35 reaches the value of ~3.69 × 10-3 S cm−1 at 500 °C in humid nitrogen and hydrogen, where protons are expected to be the majority charge carriers. The results show the BCZY35 electrolyte composition to be promising to use in intermediate temperature protonic ceramic electrochemical cell applications, with the peak sintering additive being that of ZnO.

Recent advances in layered Ln2NiO4+δnickelates: fundamentals and prospects of their applications in protonic ceramic fuel and electrolysis cells

The review represents a comprehensive and critical analysis of the state-of-the-art knowledge on layered Ruddlesden–Popper nickelates as promising electrodes for protonic ceramic electrochemical cells.

A straight, open and macro-porous fuel electrode-supported protonic ceramic electrochemical cell

A straight, open and macro-porous Ni–BaZr0.1Ce0.7Y0.1Yb0.1O3 fuel electrode-supported protonic ceramic electrochemical cell has been fabricated by a modified phase-inversion method.

Advanced Manufacturing of Intermediate-Temperature Protonic Ceramic Electrochemical Cells

Proton conducting oxide (i.e., protonic ceramic) has been thought of as an ideal solid electrolyte for energy conversion and storage applications since Iwahara et al. reported the perovskite-type protonic ceramics represented by doped barium/strontium cerates and zirconates in the 1980s. Proton, as the charge carrier in protonic ceramics, possesses a much lower transport activation energy than oxide-ion, which has rendered protonic ceramics for extensive intermediate-temperature (IT, 400-700°C) electrochemical devices such as protonic ceramic fuel cells (PCFCs), reversible protonic ceramic fuel cells, and protonic ceramic membrane reactors.

Highly Efficient and Durable Materials for Protonic Ceramic Electrochemical Cells Operated at 400~600 ○c

Protonic ceramic electrochemical cells (PCECs) is an emerging and attractive approach to store intermittent renewable energies which can be converted back to electricity in reversible operation, aiming to achieve the energy conversion and storage in an electrochemical manner. Economically competitive PCEC systems have distinct advantages over conventional oxygen-ion conducting counterpart (O-SOC), but further materials innovation is still needed to improve unit-cell performance and durability at reduced operating temperature (400~600○C), enhance system lifetime and reduce cost. To achieve efficient electrochemical hydrogen and power production with stable operation, highly robust and durable oxygen electrode is urgently desired to facilitate water oxidation and oxygen reduction reactions simultaneously, which are the critical technical barriers for both electrolysis and fuel cell operation at reduced temperatures. The recent efforts have been focused on developing new triple conducting electrode with perovskite perovskite structure for high-performance and stable PCECs. The systematic material characterizations are carried out to evaluate the feasibility of activity, stability and interface compatibility, such as Fourier-transform infrared spectroscopy, high-temperature X-ray diffraction, hydrogen permeation and first-principal computation. The catalytic activity towards electrochemical reactions is demonstrated in various electrochemical performance evaluations at 400~600○C. The long-term durability of the PCEC is examined to show the high resistance against transient current density change in reversible operation and high steam concentration.

Improved Mechanical Reliability for Protonic Ceramic Electrochemical Cell Using Alumina Dispersed Electrode Support

The protonic ceramic electrochemical cell (PCEC) is increasingly attractive in energy conversion technologies like high temperature steam electrolysis and protonic solid oxide fuel cell. The mechanical durability and robustness of single PCEC, which is critical for technology scale-up and commercialization, is intrinsically lower than the conventional YSZ based oxygen ion conducting cells. In this research, we aim to increase the mechanical reliability of BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) based PCEC by dispersing alumina into the NiO-BZCYYb electrode support. The influences of alumina dispersion on chemical stability, mechanical properties like bending strength (room and high temperature), residual stress, and electrical conductivity of the PCECs with (NiO–BZCYYb)1−x(Al2O3)x (x = 0.1–5 wt%) anode support are measured and analyzed in both oxidized and reduced conditions.

Energy to Molecules and Materials (E2M2): Intermediate Temperature Electrosynthesis of Intermediates, Fuels and Chemicals Using Protonic Ceramic Electrochemical Cells (PCECs)

Energy and chemical industry showed increasing interest in energy to molecules and materials (E2M2) due to the widely available distributed feedstock and energy input (renewable and/or nuclear energy associated electricity and excess heat). These factors offer new opportunities to those technologies with smaller scale, modularized/distributed, and driven by an integrated system of renewable and other energy sources that can show promise for increased productivity with decreased energy, capital, and operating costs. Intermediate temperature electrosynthesis through solid oxide cells is a promising strategy because of the following advatanges: (1) it can control the product selectivity by changing the operating potentials and temperatures, (2) it can be operated at ambient pressure, (3) it has high production rate and low overpotential, and (4) it can be easily integrated with power and heat from nuclear energy and renewables. Despite of these promising features, this technology still faces many challenges that include but not limited to immature process, relatively low catalyst activity, and unproven operation durability. At Idaho National Laboratory, we have made significant achievements on electrosynthesis of intermediates, fuels and chemicals using natural gas, steam, carbon dioxide and nitrogen through protonic ceramic membrane reactors. The research outcomes have the potential to establish a globally competitive U.S. industry for converting the Nation’s abundant supply of feedstock into conversion-ready intermediates and/or high demand fuels and chemicals.

(Invited) Interpreting Electrochemical Impedance Spectra with Physical Models of Mixed-Conducting Protonic Ceramic Electrochemical Cells

As Mogensen and colleagues demonstrated effectively for YSZ-based electrochemical cells [1,2], thoughtful implementation and interpretation of electrochemical impedance spectroscopy (EIS) can evaluate performance aspects of high-temperature electrochemical materials and devices, including fuel cells and electrolyzers. Impedance spectra measurements are typically interpreted with equivalent-circuit models, using variants of resistor-capacitor-inductor networks. Indirect inferences can be drawn between equivalent-circuit elements and physical processes and properties (e.g., charge-transfer rates, porous-media transport, charge-defect mobility, etc.). In addition to and support of measurements, detailed physical models of high-temperature electrochemical materials and devices, based upon deriving and solving dynamic conservation equations of the relevant fluid, thermal, and electrochemical processes, can produce impedance spectra. Such models link critical material properties and rate parameters, which can be measured or estimated independently, to EIS and thereby assist in evaluation of design and operational alternatives of electrochemical systems.As in experiments, impedance spectra from a physical model are derived by imposing a small harmonic-current actuation and recording the harmonic response of voltage (and possibly other observables such as temperature). By repeating this over a wide range of perturbation frequencies, the complex impedance is constructed from magnitude differences and phase shifts between the actuations and responses. Deriving impedances from physical models requires that the computational algorithm represent transient responses accurately. In principle, physical models can be understood in the context of locally linearized state-space representations. The rate of change of the electrochemical state (in terms of ion and species concentrations, electrostatic potentials, temperatures, etc...) is a linearized function of the state itself and the transient “actuation” (generally a sinusoidal current). The locally linear relationships in a state-space models are represented in terms of Jacobian matrices, which can be evaluated using numerical differentiation of the physical model. Although matrix evaluation may be a difficult and tedious task for an electrochemical system, the evaluation is always possible and producing the complex electrochemical impedance spectra involves inverting the Jacobian matrix. Oftentimes, the Jacobian may be large due to discretization of the physical model and/or poorly conditioned due to a wide range of time-constants of the governing processes. Nevertheless, evaluation of the full impedance spectra is computationally very efficient and thus with the physical model derived EIS, direct relationships can be evaluated between physical properties and the impedance spectra. Calibration of model-derived impedance spectra with measured spectra provides a valuable tool for assessing otherwise difficult, if not impossible, physical parameters to isolate from experimental measurements in high-temperature electrochemical cells.This paper illustrates the power of using dynamic physical models to formulate impedance spectra as a means for interpreting high-temperature electrochemical processes measured experimentally in protonic-ceramic symmetric-cells as reported by Pers, et al. [3]. This system (Fig. 1) was chosen because the present investigators have independently developed a physical model for BCZYYb (BaCe0·7Zr0·1Y0.1Yb0.1O3−δ) and Ni-BCZY composite electrodes [4] to interpret the performance of this system. Unlike the more well understood YSZ system, the BCZYYb and Ni/BCZY electrochemical cell presents unique modeling challenges due to the multiple ion conduction in BCZYYb and BCZY – notably protons and oxide vacancies as illustrated in Figure 1. The physical model incorporating ambipolar diffusion of the multiple ions in the electrolyte and cermet electrodes has been resolved and reported by Zhu and Kee [5]. The physical model predicts accurately the experimentally measured EIS as illustrated in Figure 1 The present study utilizes these models to develop equivalent-circuit models to evaluate the measured and the physically modeled impedance of the high-temperature proton-conducting electrochemical cells based on BCZYYb electrolytes. The results show the power of models to provide new insights in understanding alternative interpretations of the EIS for these promising materials for next-generation fuel cells and electrolyzers. The physical models provide direct relationships between impedance features and physical properties that can assist quantifying equivalent-circuit elements and physical behaviors. Such quantitative insights may accelerate design and development of electrochemical material systems for fuel cell and electrolysis units.

Author Correction: Highly efficient reversible protonic ceramic electrochemical cells for power generation and fuel production

Author Correction: Highly efficient reversible protonic ceramic electrochemical cells for power generation and fuel production

Barium-doped nickelates Nd2–xBaxNiO4+δ as promising electrode materials for protonic ceramic electrochemical cells

One of the main directions for the attainment of high-performance solid oxide electrochemical cells, including those based on proton-conducting electrolytes, consists in the rational engineering of functional materials. Herein, we examine the use of Nd2–xBaxNiO4+δ (NBNx, 0 ≤ x ≤ 0.4) materials as potential oxygen electrodes for protonic ceramic fuel cells (PCFCs) based on conventional Ba(Ce,Zr)O3-electrolytes. A Ba-doping strategy is proposed for Nd2NiO4+δ for reducing chemical interdiffusion of barium-ions from electrolyte to electrode during long-term operation. It is experimentally confirmed that a moderate Ba-content is beneficial in terms of reducing the quantity of impurity phases formed at the NBNx/Ba(Ce,Zr)O3 interface during deliberately-imposed extreme temperature conditions (1250 °C for 20 h). In addition, materials with x = 0.1 and 0.2 exhibit the highest electrical conductivity with no adverse effects on their thermomechanical properties. Thus, when characterising symmetrical cells in wet air conditions, NBN0.1 and NBN0.2 electrodes demonstrates lower polarisation resistances (down to 1.7 Ω cm2 at 700 °C) compared with NBN0, NBN0.3 and NBN0.4 electrodes. Based on these findings, the Ba-doping of nickelates can be recommended as a promising modification for the design of electrodes having good performance and chemical compatibility.