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In this work, the performance, electrochemical processes, and stability of GDC (Ce0.8Gd0.2O1.9) fuel electrode containing single cells (GDC/8YSZ/GDC/LSCF) were examined in CO2 electrolysis conditions. The current density and area specific resistance is determined for different operation conditions. The examined cells showed a higher performance compared to state‐of‐the‐art Ni−YSZ fuel electrode (Ni‐YSZ/8YSZ/GDC/LSCF) based single cells with a similar production route. Furthermore, the cells were examined by means of electrochemical impedance spectroscopy (EIS) and the recorded data were evaluated by the distribution of relaxation times (DRT) analysis. An equivalent circuit model (ECM) consisting of four time constants and a Gerischer impedance (LR−RQ1−RQ2−G−RQ4−RQ5) was established to gain further insight into the individual processes in the cells. For instance, the low–frequency process P5 referring to RQ5 is the rate‐determining step in CO2 electrolysis and is assigned to a surface reaction including the charge transfer and possibly the gas diffusion in the GDC fuel electrode. A long–term stability test was performed in CO2 electrolysis conditions at 900 °C with a constant current load of −0.5 A ⋅ cm−2 for up to 1200 h. A degradation rate of 62 mV ⋅ kh−1 was observed. By EIS analysis, a similar contribution of the ohmic and polarization resistances to the degradation was determined. The low–frequency process P5 and thus the surface reaction including the charge transfer in the GDC fuel electrode is contributing most to the increase in polarization resistance. After the long–term stability test, scanning electron microscopy (SEM) analysis was carried out and a coarsening of GDC particles in the fuel electrode was observed. [ABSTRACT FROM AUTHOR]

The conventional Ni–YSZ (yttria-stabilized zirconia) fuel electrode experiences severe degradation due to Ni- agglomeration and migration away from the electrolyte. Therefore, herein, we have considered Ni free electrodes, i.e., La0.6Sr0.4MnO3-δ (LSM)-based perovskite oxides as fuel electrodes. The LSM perovskite phase transforms into a Ruddlesden–Popper LSM (RP-LSM) phase with exsolved MnOx under reducing atmospheres. The RP-LSM is mainly interesting due to its good electrical conductivity, redox stability, and acceptable electrochemical behaviour. In this work, we synthesized the LSM powder and characterized it using several methods including X-ray diffraction (XRD), thermogravimetry analyses (TGA), four-probe conductivity, and scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDX). Finally, the electrolyte-supported single cells were fabricated and electrochemically characterized using AC and DC techniques under electrolysis conditions. In addition to pure LSM fuel electrodes, we have also investigated the electrochemical behaviour of LSM + YSZ (50:50) and LSM + GDC (50:50) composite fuel electrodes. The single cells containing LSM and LSM + GDC fuel electrodes show higher cell performance than LSM + YSZ. For instance, current densities of 1, 1.03, and 0.51 A·cm−2 at 1.5 V are obtained for LSM, LSM + GDC, and LSM + YSZ fuel electrodes containing single cells, respectively, with a 50% N2 and 50% H2O feed gas mixture. Moreover, the performance of the cell was also investigated under co-electrolysis with 50% CO2 and 50% H2O and under direct CO2 electrolysis conditions with 100% CO2 fuel gas. [ABSTRACT FROM AUTHOR]

Lanthanide nickelate Ln2NiO4+δ (Ln = La, Pr, or Nd) based mixed ionic and electronic conducting (MIEC) materials have drawn significant attention as an alternative oxygen electrode for solid oxide cells (SOCs). These nickelates show very high oxygen diffusion coefficient (D*) and surface exchange coefficient (k*) values and hence exhibit good electrocatalytic activity. Earlier reported results show that the partial substitution of Co2+ at B-site in La2Ni1−xCoxO4+δ (LNCO) leads to an enhancement in the transport and electrochemical properties of the material. Herein, we perform the substitution at A-site with Sr, i.e., La2−xSrxNi0.8Co0.2O4+δ, in order to further investigate the structural, physicochemical, and electrochemical properties. The structural characterization of the synthesized powders reveals a decrease in the lattice parameters as well as lattice volume with increasing Sr content. Furthermore, a decrease in the oxygen over stoichiometry is also observed with Sr substitution. The electrochemical measurements are performed with the symmetrical half-cells using impedance spectroscopy in the 700–900 °C temperature range. The total polarization resistance of the cell is increased with Sr substitution. The electrode reaction mechanism is also studied by recording the impedance spectra under different oxygen partial pressures. Finally, the kinetic parameters are investigated by analyzing the impedance spectra under polarization. A decrease in exchange current density (i0) is observed with increasing Sr content. [ABSTRACT FROM AUTHOR]

In the temperature range of high temperature co-electrolysis of both steam and carbon dioxide, the reverse water-gas shift reaction (RWGS) takes place. Prior studies were conducted with a narrow gas composition range to investigate the role of RWGS during co-electrolysis. The results for steam electrolysis, CO2 electrolysis, and co-electrolysis caused different conclusions regarding the role of electrochemical CO2 and H2O conversion compared to RWGS during co-electrolysis. This work aims to resolve the role of CO2 conversion as part of RWGS in co-electrolysis. The boundary is characterized by AC and DC measurements over a broad gas composition range from CO2 electrolysis towards co-electrolysis with nearly 50%eq H2O. Especially, the electrochemical CO2 reduction and CO2 conversion in the RWGS are compared to clarify their role during co-electrolysis. The results revealed that gas composition determined the predominant reaction (H2O or CO2 reduction). The cell performance of co-electrolysis in the boundary region up to 5%eq H2O was similar to the performance of CO2 electrolysis. Up to 30%eq H2O, the performance increases with H2O concentration. Here, both CO2 and H2O electrolysis occur. Above 30%eq H2O, steam electrolysis and the RWGS reaction both dominate the co-electrolysis process. [ABSTRACT FROM AUTHOR]

The article presents a study on the possible causes of degradation in Solid Oxide Fuel Cells (SOFCs) with metallic interconnects. There are two major groups of degradation phenomena in SOFCs, the internal phenomena and the external parameters. An elaboration of incorporation of volatile Cr species into the cathode and the microstructural change of the cathodic contact layers is presented.

Power-to-X concepts promise a reduction of greenhouse gas emissions simultaneously guaranteeing a safe energy supply even at high share of renewable power generation, thus becoming a cornerstone of a sustainable energy system. Power-to-syngas, that is, the electrochemical conversion of steam and carbon dioxide with the use of renewably generated electricity to syngas for the production of synfuels and high-value chemicals, offers an efficient technology to couple different energy-intense sectors, such as "traffic and transportation" and "chemical industry". Syngas produced by co-electrolysis can thus be regarded as a key-enabling step for a transition of the energy system, which offers additionally features of CO 2 -valorization and closed carbon cycles. Here, we discuss advantages and current limitations of low- and high-temperature co-electrolysis. Advances in both fundamental understanding of the basic reaction schemes and stable high-performance materials are essential to further promote co-electrolysis., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)