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The development of new electrocatalysts for the oxygen evolution reaction (OER) is fundamental for water-splitting devices. In this work, a novel composite based on Ca3Co4O9 (C349) and Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF) was synthesized and characterized using XRD with Rietveld refinement, SEM, EDX, and FTIR. The electrochemical properties were evaluated in a KOH alkaline medium. The composite exhibited exceptional OER electrocatalytic activity, showing an overpotential of 389 mV at 10 mA cm−2, which is lower than the pristine BSCF and C349 samples. Tafel slope of 77 mV dec−1 and double-layer capacitance (Cdl) of 4.37 mF were obtained, indicating an ECSA of 109.25 cm2. The composite also demonstrated a high turnover frequency (TOF) of 1.9 × 10−3 mol O2 s−1, underscoring its superior catalytic efficiency. Impedance spectroscopy revealed that the C349 and BSCF samples exhibited greater limitations in charge transfer compared to the composite. These results highlight the composite's potential as a highly effective OER electrocatalyst, leveraging the synergistic effects of C349 and BSCF. [ABSTRACT FROM AUTHOR]

Summary: In this article, the electrode performance of the misfit‐layered calcium cobaltite (C349), as cathode for solid oxide fuel and anode for solid oxide electrolysis cell (SOEC), is analysed by electrochemical impedance spectroscopy using a 3‐probe cell configuration. The addition of Ce0.8Gd0.2O2−δ (CGO20) as a composite electrode phase significantly boosts the electrochemical processes, decreasing the polarisation resistance (Rp) by approximately half an order of magnitude over the studied temperature range (550°C‐700°C). Electrical measurements under cathodic and anodic polarisation indicate that the C349/CGO20 composite is a promising oxygen electrode for reversible solid oxide cells with enhanced performance when operated as a SOEC anode. Short‐term stability testing of 50 h, under anodic polarisation at 700°C, demonstrates a stable current density with no observable microstructure delamination after measurements, being promising to avoid common degradation issues during SOEC operation. [ABSTRACT FROM AUTHOR]

Previously sintered (1500 °C, 4 h) dense pellets of Ce 0.9 Gd 0.1 O 1.95 (GDC) were covered and heat treated with eutectic mixtures of Na 2 CO 3 and Li 2 CO 3 (NLC), and their electrical performance was assessed against pure GDC and chemically synthesized GDC + NLC. Microstructural analysis of NLC impregnated samples confirmed slight migration of the molten phase to the interior of the GDC pellets via grain boundaries, resulting in a significant improvement of the grain boundary conductivity, increasing with duration of heat treatment (0.5–2 h) and temperature (600–800 °C range). The observed total conductivity exceeded in almost 20% the corresponding values obtained for standard GDC samples. Cells tested before and after direct current polarization (0.5 V, 500 °C) showed the same electrical performance, discarding the possibility of parallel contributions of salt ions to the total conductivity. Grain boundary engineering using salt infiltration is an effective tool to improve the electrical performance of ceramic electrolytes. [ABSTRACT FROM AUTHOR]

Samples of Gd-doped ceria (GDC, Ce 0.9 Gd 0.1 O 1.95) with eutectic mixtures of Na 2 CO 3 and Li 2 CO 3 (NLC), or K 2 CO 3 , Na 2 CO 3 and Li 2 CO 3 (KNLC) as sintering aids (5 mol%) were studied against pure GDC and cobalt doped GDC. The former electrolytes reached densifications in excess of 95% when sintered at 1100 °C, values comparable to pure GDC sintered at 1500 °C, and more than 20% higher than for GDC sintered at 1100 °C. X-ray diffraction powder patterns showed only typical GDC peaks without any noticeable lattice modification and microstructural analysis suggested a homogeneous distribution of residual amounts of sintering aids. The electrical properties of all materials were studied by impedance spectroscopy in air from 200 to 750 °C. Materials with NLC and KNLC showed a total ionic conductivity matching pure GDC at 600 °C. Hebb-Wagner polarization measurements, used to assess the impact of sintering aids on the n and p-type electronic conductivity of GDC (600–750 °C) showed that NLC and KNLC additions lower the p-type conductivity of GDC while Co additions have the opposite effect. The efficacy of alkali metal salts to produce ceria-based electrolytes with competitive ionic and electronic transport properties is exposed. K, Na and Li carbonates sintering aids lower σ p with respect to GDC or Co-doped GDC. Image 1 • High densification of GDC at low temperature (96% at 1100 °C/4 h). • Microstructures similar to pure GDC sintered at 1500 °C/4 h. • Lower p-type conductivity in GDC with alkali metal carbonates. • Handling of sets of discrete Hebb-Wagner polarization data. [ABSTRACT FROM AUTHOR]

Abstract Nano-sized composite La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF)-Ce 0.8 Sm 0.2 O 1.9 (SDC) powder was synthesised by one-step microwave self-assisted combustion synthesis and characterized by X-ray diffraction and transmission electron microscopy. Electrochemical performance of composite LSCF-SDC cathode in contact with Ce 0.8 Gd 0.2 O 1.9 (GDC) solid electrolyte under steady state polarisation was studied employing electrochemical impedance spectroscopy in 3-electrode cell configuration. The evolution of elementary steps of oxygen reduction reaction was analysed under cathodic polarisation in potentiostatic mode (up to −0.8 V) in the temperature range 650–750 °C. The composite LSCF-SDC cathode prepared by one-step microwave combustion route demonstrated a lower overall polarisation resistance when compared to literature reports of similar cathodes produced by other synthesis routes. [ABSTRACT FROM AUTHOR]

NiO-Ce 0.9 Gd 0.1 O 1.95 (NiO-CGO) composite powders produced by a one-step chemical route were assessed as precursors of fuel cell anode cermets. Porous NiO-CGO composites were prepared by uniaxial pressing followed by firing at 1400 °C for 4 h. Ni-CGO cermets were subsequently obtained by reduction in 10 vol% H 2  + 90 vol% N 2 at 750 °C. Similar materials obtained by conventional mechanical mixing of commercial powders were also prepared and tested. The structure and particle size of the calcined material were investigated by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). The electrical properties of all materials were duly studied by impedance spectroscopy (NiO-CGO) (in air and several N 2  + O 2 gas mixtures) or dc conductivity (Ni-CGO). The total and relative magnitude of impedance arcs observed in the low temperature impedance spectra can be used to obtain significant insight on microstructural characteristics, due to a variable role of NiO when shifting from a well percolated electronic conducting pathway to a dispersed ion-blocking phase. The confirmed superior conductivity of one-step materials was interpreted as a consequence of the presence of a network of well-connected and homogeneously distributed NiO(/Ni) grains, as shown by SEM. [ABSTRACT FROM AUTHOR]

A new composite cathode for solid oxide fuel cells based on Ca 3 Co 4 O 9 (C349) and PrO x was synthesized using a novel solution blow spinning (SBS) process. It is demonstrated that the presence of PrO x in this cathode permits a remarkable decrease in total polarisation resistance, by ∼15 times, mainly due to improvements in charge transfer and surface exchange processes. [ABSTRACT FROM AUTHOR]

In this study, composite powders synthesized by a novel one-step sol-gel method were used to obtain Ni-CGO anodes, while anodes of the same composition prepared from commercial powders were used as reference. The anodes performance was studied by impedance spectroscopy and dc polarization in the temperature range of 650-750 °C in flowing humidified 10% H2+90% N2 gas mixtures, using a three-electrode configuration cell, with clear advantage for the novel one-step route. One-step anodes fired at 1450 °C showed an area specific resistance of 0.15 Ω cm² under open circuit conditions and an anodic overpotential of 91 mV at 750 °C for a current density of 322 mA/cm², which are amongst the best results mentioned in the literature. The enhanced electrochemical performance of one-step anodes is mainly attributed to unique microstructural features, namely small grain size (submicrometer scale even after firing at 1450 °C) and homogeneous phase distribution, which is expected to extend the triple-phase boundary length. [ABSTRACT FROM AUTHOR]

La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) powders were synthesized by a combination of citrate and hydrothermal methods. The thermal decomposition behavior of the as-prepared powder was carried out by simultaneous thermogravimetry–differential thermal analysis. The calcined powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size distribution (PSD). Screen-printed LSCF/CGO/LSCF symmetrical cells were sintered between 1150 and 1200°C and studied by impedance spectroscopy in order to assess the cathode kinetics for the oxygen reduction reaction. Rietveld refinement of XRD data showed the formation of a single perovskite LSCF phase with crystallite size of 53nm at 900°C. The best area specific resistance (ASR) value, measured in static air, was found to be 0.34Ωcm2 at 750°C, demonstrating that the novel citrate–hydrothermal method is an effective way to prepare cathode materials for SOFC. Cathode performance can be further enhanced by additional surface modification through impregnation with Pr-containing solution, reaching 0.17Ωcm2 at 750°C. Furthermore, the activation energy of the PrO x -impregnated cathode is 83.4kJ/mol, i.e., much lower than 123.8kJ/mol, the best value determined for PrO x -free cathodes. [ABSTRACT FROM AUTHOR]

Abstract: A comparative microstructural study between Ni–Ce0.9Gd0.1O1.95 (Ni–CGO) anodes obtained from NiO–CGO nanocomposite powders prepared by in situ one-step synthesis and by mechanical mixture (two-step synthesis) of NiO and CGO powders is reported. The open porosity and microstructure of sintered and reduced pellets were investigated as a function of the citric acid content used as pore forming agent. Nanosized crystallites for the one-step and two-step routes were around 18nm and 24nm against 16nm and 37nm, for CGO and NiO, respectively. Overall results show that both routes provided suitable microstructures either for anode-support, or for functional anodes for solid oxide fuel cells (SOFCs), with more versatile characteristics in the case of the one-step route. The electrical characterization of selected NiO–CGO samples, carried out between 90 and 260°C by impedance spectroscopy, confirms electrical percolation of both phases in the composites. However, based on combined microstructural and impedance data, it seems clear that the one-step processing route is the best approach to make SOFC anodes with improved performance. [Copyright &y& Elsevier]

Understanding the processes of different cathode materials is part of the journey toward the development of intermediate-temperature solid oxide fuel cells. In this work, the one-dimensional Ca 3 Co 2 O 6 (C326) electrode and its composite with Ce 0.9 Gd 0.1 O 2- δ (CGO) are systematically investigated as a function of sintering temperature using a symmetrical cell test. For both batches of samples, the optimum sintering temperature is 1000 °C. Interpretation of the impedance spectra reveals that this optimization is associated with improvements in the processes of surface diffusion and interfacial charge transfer due to the higher effective reaction area for ionic transfer at the electrode/electrolyte interface and better connectivity between the electrode grains. The temperature dependence of the individual processes indicates that the addition of CGO significantly improves the steps of dissociative oxygen adsorption and diffusion, which should occur first on its surface, with the charge transfer of oxygen species at the CGO/C326 boundary being the rate-limiting step. • Single-phase Ca 3 Co 2 O 6 (C326) and composite C326/CGO electrodes are proposed for SOFCs. • The lowest polarization resistance was optimized at the sintering temperature of 1000 °C. • The oxygen reduction reaction mechanism of both electrodes is outlined. • C326-based cathodes are limited by oxygen surface diffusion and charge transfer. • CGO phase accelerates the dissociative adsorption of O 2 and subsequent diffusion. [ABSTRACT FROM AUTHOR]

PSFC (Pr 0.5 Sr 0.5 Fe 1−x Cu x O 3−δ ) is a new perovskite-type oxide that has gained considerable attention as cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs), due to its high mixed ionic-electronic conductivity below 800 °C. In this work, PSFC (Pr 0.5 Sr 0.5 Fe 1−x Cu x O 3−δ , x = 0.2 and 0.4) powders were synthesized by the citrate method and structurally characterized by X-ray diffractometry. Screen-printed cathodes were sintered at 1050 °C and electrochemically characterized by impedance spectroscopy at 600–800 °C in pure oxygen. The area specific resistances (ASR) of the Pr 0.5 Sr 0.5 Fe 0.8 Cu 0.2 O 3−δ material are shown to be competitive with typical values reported for cobalt-based cathodes in the measured temperature range, while, importantly, offering a significantly lower activation energy, 0.62 eV. The thermal expansion coefficients of these Co-free cathodes are in the range of 13–15 × 10 −6 °C −1 , in a temperature range 200–650 °C, demonstrating a good thermal compatibility with gadolinia doped ceria (CGO) electrolytes. [ABSTRACT FROM AUTHOR]

Mullite-glass composites were obtained by solid-state reactive sintering of kaolinite clay and kaolin waste mixtures with waste additions up to 100 wt%. The structural and microstructural analysis of starting powders and sintered samples were evaluated by X-ray diffractometry (XRD) and field-emission scanning electron microscopy (FESEM). The mechanical properties were evaluated by measuring the flexural strength of sintered bodies. Electrical properties of the composites were assessed by impedance spectroscopy (at 30 °C and from 400 to 700 °C) in air. A viscous flux mechanism resulting from the glassy phase filled up the open porosity and increased the mechanical strength. Electrical conductivity, dielectric constant and dielectric loss were strongly dependent on the microstructural features, namely glassy phase and porosity. The activation energies (0.89–0.99 eV) for electrical conduction were lower than typical literature values of mullite-based materials. The results indicated that the herein synthesized mullite-glass composites with up to 53.6 wt% mullite are promising low-cost materials for electronics-related applications. • Mullite-glass composites from kaolin waste-based formulations. • Effect of microstructure on properties of mullite-glass composites. • Electrical and dielectric properties by impedance spectroscopy. • Low-cost material for electronics-related applications. [ABSTRACT FROM AUTHOR]

Abstract We report the effect of PrO x addition on the oxygen reduction reaction (ORR) mechanism of a [Ca 2 CoO 3-δ ] q [CoO 2 ] SOFC cathode (also known as Ca 3 Co 4 O 9-δ , C349) obtained by solid-state synthesis of a stoichiometric mixture of mollusk shell powder (a natural source of calcium carbonate) and cobalt oxide. Symmetrical cells of screen-printed pristine C349 and PrO x -infiltrated C349 compositions are analyzed by electrochemical impedance spectroscopy (EIS) as a function of oxygen partial pressure (pO 2 = 1-10−2 atm) in the temperature range 600–800 °C. The results show a decrease in total polarization resistance (R p) of ∼8 times by the addition of PrO x to the C349 phase in pure oxygen at 700 °C. This improvement is shown to be mainly due to a large decrease (∼13 times) in the charge-transfer processes occurring at the surface of electrode, which dominate the total polarization resistance. The polarization resistance of the PrO x -impregnated C349 cathode is also demonstrated to be very competitive in comparison to typical Ca-cobaltite-based cathodes. Graphical abstract Image 1 Highlights • [Ca 2 CoO 3-δ ] q [CoO 2 ] (C349) cathode by the mollusk solid-state synthesis route. • Effects of PrO x addition on the oxygen reduction reaction (ORR) mechanism. • Impedance spectroscopy as a function of the oxygen partial pressure and temperature. • Surface exchange limitations are improved by ∼ 13 times over that of pristine C349. [ABSTRACT FROM AUTHOR]

Abstract NiO-Ce 0.9 Gd 0.1 O 1.95 (NiO-GDC) composites (30, 40 and 50 wt% NiO) were obtained by a " one-step " synthesis method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses were applied to the calcined compositions, revealing powders in the nanometer range. NiO-GDC composites were sintered at 1450–1550 °C and the respective Ni-GDC cermets were produced in a 10%H 2 -N 2 atmosphere at 800 °C. A factorial design tool allowed to establish a regression equation that correlates the effects of Ni content and sintering temperature on the porosity of Ni-GDC cermets. Impedance spectroscopy was used to analyse the electrical properties of the solid oxide composites in air (at 500–650 °C) and of the Ni-GDC cermets in 10%H 2 -N 2 (at 650 °C). The impedance analysis in reducing conditions revealed an improved in the electrical properties for the Ni-GDC cermet derived from the composite with 50 wt% NiO and sintered at 1450 °C. The electrical resistivity values are among the best ones reported for Ni-based cermets produced by different conditions. Graphical abstract fx1 Highlights • Ni-GDC cermets derived from one-step synthesised powders. • Porosity as a function of NiO content and sintering temperature. • Impedance spectroscopy in oxidizing and reducing atmospheres. • Optimized electrical resistivity of 0.43 ohm.cm at 650 °C in 10%H 2 -N 2. [ABSTRACT FROM AUTHOR]

Abstract Pure phase misfit Ca-cobaltite powder, [Ca 2 CoO 3−δ ] q [CoO 2 ] (C349), was successfully synthesised by the proteic sol-gel synthesis route and characterised by X-ray diffraction. The electrochemical performance of the C349 cathode screen-printed onto Ce 0.9 Gd 0.1 O 1.95 (GDC) solid electrolyte was studied employing electrochemical impedance spectroscopy in 3-electrode cell configuration. Cathodic polarisation was evaluated in potentiostatic mode in the temperature range 550–700 °C. The C349 cathode prepared by proteic sol-gel synthesis route demonstrates lower polarisation resistances than similar misfit Ca-cobaltite compositions reported in the literature, produced by different synthetic approaches. A highly competitive performance of the formed C349 cathode is also highlighted upon comparison to typical SOFC cathodes under applied DC bias. Graphical abstract Image 1 Highlights • Phase pure Ca 3 Co 4 O 9 (C349) cathode is produced by proteic sol gel synthesis. • The cathodic polarisation of C349 under applied DC bias is reported. • Rate limiting steps for oxygen reduction reaction in C349 cathodes are clarified. • Variation of diffusion and surface exchange processes under DC bias is clarified. [ABSTRACT FROM AUTHOR]

A new CeO 2 -Co 3 O 4 nanocomposite was obtained from Metal-Organic frameworks (MOFS). The morphological investigation confirms homogeneous distribution of phases in the composite. The electrocatalytic properties for OER were investigated in alkaline medium and an overpotential of 366 mV was observed, similar to or higher than other CeO 2 -based materials. [Display omitted] Although water splitting is an efficient method to synthesize H 2 , the development of new electrocatalysts is required to improve the economic viability of this process. In this way, the search for new methodologies to obtain new high-performance electrocatalysts based on Earth-abundant metals has gained urgent attention over the past decade. Thus, this work reports the synthesis of a new CeO 2 /Co 3 O 4 nanocomposite obtained using Metal-Organic Frameworks (MOFs) as a sacrificial mold, applied as electrocatalyst for Oxygen Evolution Reaction (OER). CeO 2 /Co 3 O 4 was obtained from the MOF-Ce@ZIF-67 composite (MOF-Ce = cerium succinate, ZIF-67 = Zeolitic-Imidazolate Framework-67) using calcination at 350 °C in air. The electrocatalyst was characterized by X-ray diffraction (XRD), confirming the crystalline phases and average crystallite size of 31 nm. The FT-IR spectrum indicates the main M−O vibration modes of cobaltite and ceria. UV–VIS results show charge transfer and d-d bands related to cobalt and cerium ions. SEM images reveal irregular morphology; however, a homogeneous elemental distribution was observed in the EDS maps. The electrocatalytic performance of the CeO 2 /Co 3 O 4 for the OER was investigated by cyclic voltammetry, linear scanning voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy, in an aqueous basic solution (KOH 1.0 mol/L). The electrochemical tests show an excellent overpotential of 366 mV (at J = 10 mA cm−2) and chemical stability until 15 h. The Tafel slope was 92.6 mV dec-1 and the double layer capacitance was found to be 3.19 mF. These results show similar or superior electrocatalytic performance compared to other ceria-based materials in the literature. [ABSTRACT FROM AUTHOR]

Misfit Ca-cobaltites of nominal composition Ca 3 Co 4 O 9-δ (C349) have attracted great attention as Solid Oxide Fuel Cell (SOFC) cathode material. The present work reports, for the first time, the solid-state synthesis of C349 powders from a mixture of cobalt oxide and mollusk shells, a natural source of calcium carbonate. The synthesized material was studied by X-ray diffraction, with Rietveld refinement of the XRD data, and Transmission Electron Microscopy (TEM). Screen-printed C349 porous electrodes were fired on both sides of dense gadolinia-doped ceria ceramics and electrochemically characterized by impedance spectroscopy at 700–800 °C in air. The measured area specific resistance (ASR of 1.47 Ω cm 2 at 800 °C in air) is in line with literature data for similar cathodes prepared by other synthetic routes. [ABSTRACT FROM AUTHOR]

CuO-Ce 0.9 Gd 0.1 O 1.95 (CuO-CGO) nanocomposite powders obtained by in situ one-step synthesis were used to prepare Cu-CGO cermet anodes for solid oxide fuel cells (SOFCs). The effects of the CuO content (varying from 40 to 60 wt.%) on the lattice parameter and crystallite size of CuO and CGO phases were investigated by X-ray diffraction (XRD) with Rietveld refinement of the XRD data. CuO-CGO composites were screen-printed on both faces of ceria-based substrates, fired at 1150 °C, reduced to Cu-CGO cermets, and electrochemically characterized by impedance spectroscopy in hydrogen and synthetic biogas atmospheres. One-step Cu-CGO anodes with 40 wt.% CuO showed area specific resistances of 0.15 Ω.cm 2 (in hydrogen) and 2.30 Ω.cm 2 (in biogas) at 800 °C. The anode performance is deteriorated by increasing the CuO content to 60 wt.%. [ABSTRACT FROM AUTHOR]

The present work reports the synthesis, structure and electrochemical assessment of Cu-doped calcium cobaltites as cathode materials for solid oxide fuel cells (SOFCs). Powders of composition Ca 3−x Cu x Co 4 O 9−δ (0 ≤ x ≤ 0.2) were obtained by a proteic sol-gel method which uses gelatin as polymerizing agent. As-prepared materials were calcined at 900 °C for 1 h and characterized by X-ray diffraction, with Rietveld refinement of the diffraction data, and scanning electron microscopy. Screen-printed porous electrodes fired (at 950 °C for 2 h) on both faces of ceria based electrolytes were electrochemically characterized by impedance spectroscopy between 600 and 800 °C in air atmosphere. The results indicated the attainment of Ca 3−x Cu x Co 4 O 9−δ solid solutions with monoclinic misfit layered structure and around 2 vol% Co 3 O 4 as a secondary phase. Micro-plates like powders had irregular shape and average diameter near 2 μm. The area specific resistance (ASR) is in line with literature data for cathodes of similar compositions prepared by other synthetic routes. ASR was optimized for the composition Ca 2.99 Cu 0.01 Co 4 O 9−δ , achieving 0.84 Ω cm 2 at 800 °C in air. [ABSTRACT FROM AUTHOR]

Nanocomposite powders are interesting electrocatalysts for efficient water splitting in alkaline medium. In this work, Mo–Ag nanocomposites were prepared by high energy ball milling of (NH 4) 6 Mo 7 O 24.4H 2 O and AgNO 3 precursors, with subsequent reduction in hydrogen atmosphere. High energy ball milling formed spheres composed of needle-like structures of different sizes. The particle size decreases with increasing the milling time from 20 h to 40 h, with the same trend observed for crystallite sizes. The electrochemical performance for the oxygen evolution reaction (OER) is assessed using linear sweep (LSV) and cyclic (CV) voltammetry, electrochemical impedance spectroscopy (EIS), and chronopotentiometry (CP). The values of overpotential, Tafel slope, double layer capacitance (C DL) and turnover frequency (TOF) of samples milled for 20 h and 40 h are determined to be 350 and 330 mV vs. RHE, 84 and 75 mV dec−1, 5.4 and 6.2 mF cm−2, 3.84 × 10−3 and 6.98 × 10−3 mol O 2 s−1, respectively, which suggests an improved electrocatalytic activity for the sample milled for 40 h. The increased surface area dramatically boosts the electrochemical processes with adsorbed species. Chronopotentiometry measurements for 15 h reveal that electrodes exhibit acceptable short-term electrochemical stability. The overall results suggest that Mo–Ag nanocomposites are promising materials for the oxygen evolution reaction, being among the best Mo-based electrocatalysts reported in the literature. [Display omitted] • Mo–Ag nanocomposite prepared by High Energy Ball Milling followed by H 2 reduction. • The nanocomposites exhibited overpotential below 360 mV and excellent short term electrochemical stability for the OER. • The excellent electrochemical properties of Mo–Ag are due to their needle-like structures. • Mo_Ag_40 h shows low overpotential of 330 mV vs RHE at J = 10 mA cm−2. [ABSTRACT FROM AUTHOR]

• Effect of composition on the polarisation resistance of BCO/CGO electrodes. • 50 vol% CGO-50 vol% BCO shows the lowest polarisation resistance. • The improvement relies on an increased triple-phase boundary (TPB) length. [Display omitted] Solid oxide electrochemical cells are promising devices for energy conversion and chemical synthesis. In this respect, one of the main challenges to improving cell performance is the decrease in the polarisation resistance (R p) of the oxygen electrodes. Here, the electrochemical properties of composite electrodes of Ba 2 Co 9 O 14 /Ce 0.8 Gd 0.2 O 2- δ (BCO/CGO) are investigated by electrochemical impedance spectroscopy at 600–800 °C. The composite with 50 vol% CGO exhibits the lowest polarisation resistance, 0.3 Ω cm² at 600 °C in O 2. The comparatively superior performance results from an increased triple-phase boundary (TPB) length due to the increased percolation of both phases. This successful result presents a high-performing oxygen electrode for solid oxide electrochemical systems. [ABSTRACT FROM AUTHOR]